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CDFA Inspection Services Division


Corn Fertilization Guidelines

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Nitrogen
(N)

 

Corn Nitrogen Nutrition

Deficiency Symptoms

Nitrogen deficiency symptoms on younger plants include pale, yellowish appearance and spindly stalks [N77]. In older plants, the leaf tips turn yellow (chlorosis). The yellowing progresses towards the base of the leaves along the midrib, while the leaf margins may remain green. When N deficiency persists, the leaf tips die and dry (necrosis). Older leaves are affected first because N is mobile in the plants and can be translocated from older to younger leaves when N supply is insufficient [N77].

Picture of N
                deficient corn leaf Pale yellow chlorosis at the leaf tip advancing down the leaf along the mid-rib in a V-shaped pattern (photo provided by the International Plant Nutrition Institute).

Phosphorus
(P2O5)

 

Corn Phosphorus Nutrition

Deficiency Symptoms

Phosphorus deficient plants are dark green with reddish purple tips and leaf margins [P35]. Growth is slow and plants remain shorter when P deficiency persists. As P is mobile in plants, deficiency symptoms are first seen on older leaves. In soil, however, P is immobile. For this reason, P deficiency is most common in young plants which have not yet established an extensive root system. Cold weather, extreme soil moisture or root damage by insects, herbicides or farm machinery can aggravate P deficiency symptoms [P35].

Picture of P
                deficient corn plantsPhosphorus deficient corn with purple leaf tips and margins (photo provided by the International Plant Nutrition Institute).

Potassium
(K2O)

 

Corn Potassium Nutrition

Deficiency Symptoms

Potassium deficiency is characterized by yellow tips and margins of lower leaves (chlorosis) with the midribs remaining green [K43]. Starting at the tips, leaf tissue turns brown and dies (necrosis). The yellow leaf margins of K deficient plants contrast with N deficiency where the middle of the leaf blade turns yellow and the margins remain green.

Potassium is mobile in the plant and can be translocated from older to younger leaves. However, when K deficiency persists, younger leaves will also show symptoms. Stalks of K deficient plants are weaker, which can result in lodging late in the season [K43].

Picture of K
                deficient corn leafPotassium deficient leaf showing marginal chlorosis and necrosis starting from the leaf tip (photo provided by the International Plant Nutrition Institute).

Affected Areas

Potassium deficiencies on corn have only been found in a few areas of the state. Kent Brittan [K2] recommended applying K with the starter in the Clarksburg area. In addition, some soils on the east side of the San Joaquin Valley tend to fix K which may result in K deficient corn plants [K29] (see K Fixation in the San Joaquin Valley).

Soil Tests

Soil Nitrate Test

Nitrogen is predominantly taken up by corn in the form of ammonium and nitrate. Most soil tests only measure nitrate-N because the ammonium concentration is generally very low in aerated soils. Soil nitrate tests measure the plant available N at the time of sampling. The nitrate level depends on a number of factors related to soil properties, weather and crop management (see Factors Affecting Soil Nitrate Concentrations in Spring). The test is field-specific and needs to be carried out every year. Due to the variability of nitrate in the soil, care must be taken that the sample is representative for the field (see Sampling for Soil Nitrate Determination).

Soil samples for nitrate analysis should be taken before the first N application of the season. Depending on the fertilization program, soil samples are therefore either collected prior to the pre-plant N application (this test is generally called pre-plant nitrate test; PPNT), or before the first side-dress N application (pre-sidedress nitrate test; PSNT).

Pre-Plant Nitrate Test (PPNT)

The PPNT is a valuable tool to adjust pre-plant N applications. Samples should be taken to a depth of at least 2 feet [N20].

The PPNT measures the N carried over from the previous crop, plus N released from soil organic matter, crop residues, and manure applications [N17, N25]. Heavy irrigation rates between soil sampling and the time of high N uptake by corn plants may leach nitrate below the root zone, making it unavailable for the plants. In this case, the PPNT overestimates the available soil N [N25]. Therefore, the PPNT and high pre-plant N applications are only an efficient fertilization strategy when leaching during the early stages of corn growth is minimal. Furthermore, the PPNT does not include N mineralized between soil sampling and the time of high uptake. Therefore, when most N is sidedressed, the pre-sidedress nitrate test is the better option.

Pre-Sidedress Nitrate Test (PSNT)

The PSNT provides a measure of the soil N available to the crop prior to sidedressing and can be used to determine the need for sidedress N [N1, N25]. As the sample is taken just prior to the period of high N uptake rates, the PSNT more accurately determines available residual N than the PPNT.

A soil sample is taken from the top foot of the profile when the corn plants are 6-12 inches tall, corresponding to the 4- to 6-leaf stage [N48].

Plant Analyses

Plant Analyses

Plant analyses can be useful in diagnosing nutrient limitations before deficiency symptoms become visible, and in determining whether current fertility programs are adequate [N26]. Plant tissue nutrient concentrations are somewhat variable. Yield and plant tissue concentrations from previous years, as well as nitrogen and irrigation water budgets help with the interpretation of the results.

Leaf N Concentrations

The nutrient concentration in plants changes over time and varies between plant parts. In order to be able to interpret the results correctly, care must be taken to sample the correct plant parts at a specific growth stage (see Table) [N36]. For instructions on how to take a representative sample see Plant Tissue Sampling.

Plant tissue analysis guidelines for corn [N19]. Corn Tissue
                      Analysis

When N concentrations are below the sufficiency range, yield may be decreased even in the absence of deficiency symptoms. Concentrations above the sufficiency range may indicate excess N availability.

Leaf Greenness

The N status of corn plants is reflected in the leaf color, with a light green color indicating low N availability while a dark green color is typical for N sufficient plants. The leaf greenness of corn plants can be determined using a hand-held device, such as the SPAD Chlorophyll Meter, or a canopy reflectance meter.

Leaf chlorophyll readings should be averaged from 20 to 30 plants. Before tassels appear, readings are taken from the most recent leaf with a fully visible collar. The values are more consistent when the reading is taken at approximately the same position on the leaf blade [N25].

Leaf greenness readings can be used for real-time N management decisions [N64]. Currently, no functions relating absolute leaf greenness readings at a specific growth stage with N fertilizer requirements are available for California. However, relative values can be used to assess the N status of a field. The relative leaf greenness (often referred to as N sufficiency index), is the average leaf greenness of the field relative to the average leaf greenness of a well fertilized strip within the same field with identical management and variety. Studies found that N fertilization is required to prevent yield loss when the relative leaf greenness drops below 90 to 96% of the well fertilized strip [N64].

Corn Stalk Nitrate

To review and evaluate the N fertilization program and to make adjustments for the following years, a stalk nitrate test at corn maturity can be performed [N10, N11].

Samples can be taken just before silage harvest when the milk line is one-fourth of the way down the kernel and through about 3 weeks after black layer formation. During this period, the nitrate concentration in the lower part of the stalk remains relatively stable [N27]. A 8-inch long section of the stalk is cut, with the lower cut being about 6 inches above the soil surface. Leaves are removed from the stalk [N11]. Ten to 20 samples are taken from a field. The samples are immediately submitted to a laboratory for nitrate-N analysis [N11, N67].

Binford and coworkers [N11] reported an optimal range of 700 to 2000 ppm nitrate-N. This range has been confirmed in a number of large field studies and is used by the extension service in several states [N6, N33, N39, N41, N53, N60, N67]. Optimal stalk nitrate-N concentrations in fields where manure was fall applied are generally higher, possibly because a larger proportion of the manure N becomes available later in the season. This N often cannot offset the potential yield loss from early or midseason N deficiency [N39]. Oregon State University Extension Service recommends an optimal range of 3,500 to 5,500 ppm nitrate-N [N34].

Preplant N

Preplant Nitrogen

Application Rate

Little recent data about optimal N application rates for corn production in California exist. Brittan [N14] recommended total application rates of 200 to 275 lbs N/acre on mineral soils, depending on plant population and previous crop. This is in line with a trial carried out at Davis, where an average grain yield of 225 bu/acre (6.3 tons/acre) was produced with 200 lbs N/acre [N3]. Doubling the N rate had no effect on yield or grain protein content.

Pre-plant N fertilization rates should be adjusted by the nitrate-N present in the soil profile in early spring (see Soil Analyses). One ppm of nitrate-N in the top 2 feet of the profile corresponds to 7-8 lbs/acre (3.5-4 lbs/acre per foot of soil). During the growing season more N will be made available by N mineralizing soil microorganisms, with the amount of N mineralized depending among other factors on soil organic matter content and recent applications of organic material. No University of California recommendations exist for application rates based on pre-plant soil nitrate levels.

Colorado State University Extension recommends reducing the suggested N rate by 8 lbs/ac for each ppm nitrate-N in the soil for a 2-foot sampling depth [N20]. University of Nebraska Extension recommends adjusting the pre-plant N application rate based on residual nitrate (PPNT, 0-4 ft), yield goal, and soil organic matter content (see Table).

University of Nebraska Extension N fertilizer recommendations (lbs/ac) based on expected yield with adjustments for pre-plant soil nitrate-N and soil organic matter [N68]. These values have not been tested in California. Corn PPNT

How much of the pre-plant nitrate is crop available depends to a large part on the irrigation management between the time of sampling and the period of high N uptake. High irrigation water applications may leach the nitrate below the root zone making it unavailable to the crop. Therefore, pre-plant N applications are only efficient when leaching during the early stages of corn growth is minimal.

Mode of Application

Anhydrous ammonium and aqua ammonia must be injected 6 to 8 inches deep in loamy soils and 8-10 inches deep in sandy soils to avoid losses of gaseous ammonia [N13, N25, N70, N72, N73].

Urea and UAN solution should be incorporated to reduce ammonia volatilization losses, especially in no-till corn [N5, N25, N30, N63].

Injecting UAN solution in a band below the surface has been found to be more efficient than broadcasting and incorporating it [N47]. However, the band should not be placed directly under the corn row, because the release of ammonia can injure roots and substantially lower yield [N25].

Fertilizer Type

Common N fertilizers are anhydrous ammonia, aqua ammonia, urea, UAN (sometimes referred to as UN32) and ammonium sulfate [N73, N76].

If properly applied, the various mineral N fertilizers are equally effective. Choice therefore can be based on the cost per unit of N and the fertilization plan [N5, N57, N69].

Under leaching conditions, losses from fertilizers containing nitrate and fertilizers that are nitrified quickly may be high, reducing the amount of N available for corn uptake [N4]. Anhydrous ammonia is the slowest of all N fertilizer forms to be converted to nitrate, reducing the risk of leaching directly after the application [N76].

Time of Application

Pre-plant N should be applied close to planting. The longer the time between application and crop uptake, the higher the risk of N losses through leaching or denitrification. Leaching may be caused by rainfall or high irrigation water application rates. For these reasons, fall applications are generally less effective than spring applications [N24, N76].

Starter N

Starter Nitrogen

A fertility program where starter N is combined with sidedress N applications gives growers more flexibility adjusting the N rate to the growth conditions than a program that relies on a single pre-plant application.

Starter fertilizer provides seedlings with a readily accessible nutrient source that supports early growth [N78]. In general, starter fertilizers promote early growth and may have a positive effect on corn yield [N42, N50, N78]. The N applied with the starter should cover the crops’ needs until the first sidedress application.

Application Rate

Corn fertilization guidelines in a number of states recommend applying between 10 and 60 lbs N/acre with the starter [N1, N14, N20, N21, N29, N34, N44, N49, N76].

In a study carried out with silage corn in the Modesto area, the total N in the aboveground biomass was below 40 lbs/acre one month after planting [N31]. Therefore, with careful irrigation management, a starter application rate of 40 lbs/acre together with the residual soil nitrate supplies enough N to the corn plants during the first month of growth.

The maximum amount of starter N that can be applied depends on fertilizer placement and the composition of the material (see Mode of Application).

Mode of Application

Starter fertilizer is traditionally applied in a band 2 inches to the side and 2 inches below the seed to reduce the risk of salt damage [N52, N58, N59]. Even when applied at this distance to the seed, the N plus K2O applied should not exceed 70-80 lbs/acre [N1, N5, N7].

The application of fertilizer in direct contact with the seeds (popup placement) may damage seedlings, especially in sandy soil and when the fertilizer has a high ammonium or K concentration [N61]. The maximum rate of N and K2O applied should not exceed 10-15 lbs/acre in medium and fine textured soils. Cooperative extension in some states even recommends limiting the amount of N and K2O applied to 8 lbs/acre [N76]. Seed placement is not recommended in sandy or dry soils [N58].

Fertilizer Type

Early studies have shown that P uptake and root growth can be increased by using starter fertilizers that contain P and N [N22, N51]. Monoammonium phosphate (MAP, 11-52-0) and ammonium polyphosphate (10-34-0) are popular starter fertilizers [N5, N40].

Urea, UAN solutions and diammonium phosphate (DAP, 18-46-0) produce free ammonia, which can severely damage seedling roots [N2, N52]. These fertilizers should only be used at low rates and when the material is placed at least two inches away from the seed [N5]. However, in some cases free ammonia from DAP bands has been found to diffuse 3 inches or more away from the band [N2].

Sidedress N

Sidedress Nitrogen

Sidedressing can help minimize N losses because N is applied close to the time of crop uptake reducing its residence time in the soil. In addition, the application rate can be adjusted based on the residual nitrate-N [N1, N25, N76]. A number of studies in other states found that adjusting sidedress N rates based on the pre-sidedress nitrate test (PSNT) produced the same yield as higher pre-plant N applications [N32, N66, N71, N79].

Application Rate

When losses are minimized, corn needs about 1-1.25 lbs N/bushel of grain, which corresponds to approximately 6-7.2 lbs N/ ton of silage corn [N1, N5, N23, N25, N62, N68].

Therefore, for a grain yield of 180 bu/acre (5 tons/acre) or a silage corn yield of 30 tons/acre the plants require between 180 and 216 lbs N/acre. This includes fertilizer N and soil derived N. No official University of California sidedress N application rates based on the pre-sidedress nitrate test (PSNT) exist. Cooperative Extension guidelines in a number of states recommend reducing the fertilizer N rate when the PSNT value is higher than 10 ppm. When the PSNT exceeds 25-30 ppm, it is generally recommended applying no sidedress N [N12, N15, N38]. The adjustments made for PSNT values between these two thresholds differ. The table gives the range of common recommendations found used in different states. However, these recommendations have not been tested in California.

Range of recommended total N application rates (sidedress N plus starter N) based on expected yield and PSNT values from different states. These values have not been tested in California. Corn PSNT

Based on recommendations from DE [N75], IN, KS [N15], PA [N5], TE [N65], OR [N49], WA and ID [N16].

Further adjustments may be necessary for nitrate-N in the irrigation water, manure applications in the past years as well as for legumes in the crop rotation [N20, N29, N43, N75].

Mode of Application

Banding is generally the most efficient method of applying sidedress N [N5] because corn roots generally do not reach the middle of the rows until the corn plant has eight fully emerged leaves. Therefore, during approximately the first six weeks after planting, nutrients applied in a band close to the corn row are more likely to be available for plant uptake than nutrients broadcast over the entire soil surface [N1]. Furthermore, sidedress broadcasting of granular fertilizer may cause leaf burn [N17]. Leaf injury and yield reduction have been found to be more pronounced with UAN and ammonium nitrate than with urea [N54]. However, up to 90 lbs N/acre as UAN or urea may be applied at the 4- to 5-leaf stage or up to 60 lbs/acre at the 8-leaf stage without reducing yields [N17].

Urea containing fertilizers should be incorporated into the soil to prevent ammonia losses [N5, N17, N54]. Ammonia volatilization is promoted by crop residue cover on the soil surface, absence of rainfall following the application, high temperatures, and high soil pH [N17]. Nitrogen broadcast on fields with a residue cover may be subject to immobilization by the soil microorganisms that decompose the residue [N1].

Sub-surface bands should be placed 8-15 inches away from the plants to reduce the amount of root pruning and injury from ammonia [N5, N25].

In furrow irrigation systems, N should only be applied with the irrigation water when a tailwater recovery and reuse system is in place [N20].

Fertilizer Type

The safest source of N for sidedressing is UAN (UN32) solution [N14]. Under the cool and humid climatic conditions prevalent in Quebec, Canada, UAN was found to be more efficient N fertilizer than aqueous ammonia and calcium ammonium nitrate when banded into the soil at sidedress [N28]. However, under California conditions, nitrification is generally fast, so that the difference between the materials is small.

However, when the plants are already deficient, nitrate and urea are preferred over ammonium, because the former two are more mobile in the soil and move readily into the root zone with the first irrigation following the fertilizer application [N21].

Time of Application

Corn plants take up little N until they reach the 6-leave stage. Between the 6-leave stage (V6) and the milk stage (R3), however, N uptake rates are high [N37]. In a study carried out with silage corn in the Modesto area, maximum N uptake rates reached 4.5 lbs/acre per day [N31]. Daily N uptake rates may even reach 8 lbs/acre [N37]. When corn reaches the tasseling stage, it has generally taken up more that 60% of the total N [N18, N31, N37].

Sidedress N should therefore be applied between the 3- to 4-leaf stage and tasseling [N20, N21, N25, N54]. The optimal timing of the first sidedress N application depends on the available soil N and the amount of starter N applied. Nitrogen fertilization after silking is generally only beneficial, when the plants are clearly deficient [N9, N34, N68]. Nitrogen fertilizer applications at milk stage (R3) may increase yield in extremely deficient plants, but may actually decrease yield when corn is only slightly deficient [N9].

Foliar N

Foliar Nitrogen

The amount of N that can be absorbed through the leaves is relatively small [N45] and studies generally did not find a yield effect due to foliar N applications.

For example, the foliar application of 6 and 12 lbs N/acre as urea in 15 gallons per acre at the V6 and V12 stages had no effect on yield [N46]. Foliar urea sprays of 18 lbs urea-N/acre (1.92% urea in solution) applied either at early silking stage or four weeks later had no consistent effect on silage corn yield neither, even though the urea was absorbed by the corn plants [N35, N74]. However, the second spray tended to increase protein yield [N35]. Below and coworkers [N8] did not find a yield effect of foliar urea applications before and at various times after silking either. However, the risk of lodging tended to be increased.

High N concentrations in the foliar solutions may damage the leaves [N55, N56]. Urea was found to cause less leaf damage than potassium nitrate, ammonium polyphosphate, ammonium sulfate or urea phosphate [N55].

Soil Test

Soil Analysis

Soil Sampling

Soil samples are generally taken in fall or spring (see Soil Test Sampling for sampling instructions). Samples are taken from the top foot of the profile [P31], which is the main rooting zone. Studies found 65-85% of the roots of irrigated corn in the top foot of the soil profile and 80-94% in the upper two feet [P14, P20]. However, corn roots may reach to a depth of 6 feet [P20, P26].

In California, the available soil P is generally determined by extracting the soil samples with a sodium bicarbonate solution (Olsen-P test).

Interpretation of Test Results

Based on earlier studies summarized by Reisenauer and coworkers [P31], corn grown in soils with Olsen-P values greater than 12 ppm is unlikely to respond to P applications, while a response is likely with Olsen-P values below 6 ppm (see Table). The intermediate level between 6 and 12 ppm is comparable to optimal Olsen-P values from other states, where the lower limit of this range is generally between 5 and 8 ppm, and the upper limit between 11 and 15 ppm [P4, P7, P30, P32].

The optimal soil P test value may vary depending on site- and production-specific factors [P19, P36]. Combining soil tests with plant analyses and P budgets helps identifying sites where a yield response to P fertilization is likely.

Interpretation of P and K soil test levels in the top foot of the soil profile [P31].
Corn Soil Test

1) ppm Olsen-P
2) ppm ammonium acetate extractable K

Soil Test Based Application Rates

When Olsen-P values are between 6 and 12 ppm, P fertilizer is applied to prevent yield losses at responsive sites and to maintain soil P availability in the optimal range. This can be achieved by applying the amount of P removed with the harvested grains. Literature values for the amount of P2O5 removed with harvested grains ranges from 0.344 to 0.44 lb/bu (6.2 to 7.9 g/kg) [P12]. With a yield of 180 bu/acre (5 tons/acre), between 60 and 80 lbs P2O5/acre are removed with the grains. The amount of P removed with silage corn may range from 60 to 100 lbs P2O5/acre [P36]. However, the economically optimal P rate may be lower, depending on site specific condition. Contact your local farm advisor for more information.

For Olsen-P values below 6 ppm, the application rate may be increased, while no or only a small starter P application is needed when the Olsen-P values exceed 12 ppm. Regular soil and plant analyses indicate whether the P fertilization program is adequate. On the long term, the Olsen-P values should reach and remain in the optimal range of 6 to 12 ppm.

In acidic and alkaline soils, P availability is greatly reduced. Under these conditions, soil P availability is better increased by adjusting the soil pH, rather than by applying large amounts of P fertilizer.


Plant Analysis

Plant Analysis

The nutrient concentration in plants changes over time and varies between plant parts. In order to be able to interpret the results correctly, care must be taken to sample the correct plant parts at a specific growth stage (see Table) [P14]. For instructions on how to take a representative tissue sample see Plant Tissue Sampling.

Plant tissue nutrient concentrations are somewhat variable. Yield and plant tissue concentrations from previous years, as well as P budgets help with the interpretation of the results.

Plant tissue analysis guidelines for corn [P6]. Corn Tissue Analysis

When P concentrations are below the sufficiency range, yield may be decreased even in the absence of deficiency symptoms. Concentrations above the sufficiency range may indicate excess P availability.

The sufficiency ranges for P in the table are very similar to those used by the University of Wisconsin Extension [P5]. In contrast, for irrigated corn in Nebraska Rehm and coworkers [P29] reported critical values for early season samples of 0.22% for silage corn and 0.26% for grain corn, which are significantly lower than the values in the table. In the same study, the critical value for ear leaves at silking was found to be 0.22-0.23%, which is at the lower end of the range reported in the table [P29].

The results of leaf analyses may be known too late to correct P deficiency in the same season. However, they provide valuable information for managing P in the following season.

Preplant P

Preplant Phosphorus

Application Rate

Application rates should be based on soil test results (see Soil Test). With intermediate soil P test values of 6-12 ppm Olsen-P, replacing the amount of P removed with the harvested crops ensures that P availability remains in the optimal range over the years. Between 60 and 80 lbs P2O5/acre are removed from the field when the grains are harvested and 60-100 lbs P2O5/acre with silage corn [P12, P36]. However, the economically optimal P rate may be lower, depending on site-specific condition. Contact your local farm advisor for more information. When soil P test values are below 6 ppm, higher application rates may be required, while P application rates may be reduced or skipped when soil P test values are above 12 ppm (see Soil P Test).

Mode of Application

Pre-plant applied P can be broadcast and incorporated or applied in a band. However, broadcast applied P has been found to be less effective than band-applied P, especially in fields with a low P availability [P27].

Broadcast applied P should be incorporated because P is immobile in the soil and does not leach into the major root zone with rain or irrigation water. Incorporating P into the soil also reduces the risk of losses through runoff [P33].

Fertilizer Type

A number of granular and liquid P fertilizers are available. Fact sheets of the most common fertilizers can be found on the web site of the International Plant Nutrition Institute.

In general, polyphosphate and orthophosphate fertilizers are equally effective [P8, P21], even though polyphosphate fertilizers have been found to promote root growth more than orthophosphate in some soils [P34].

For fall or early spring applications, superphosphate should be preferred over blends containing ammonium or other forms of N, because once the ammonium is nitrified, the nitrate is prone to leaching by winter rains or irrigation water (see pre-plant N).

Time of Application

When smaller application rates are required, all the P may be applied as a starter. When larger quantities are needed, it may be more practical to apply a small amount as a starter and broadcast and incorporate the rest pre-plant. A combination of broadcasting and band-applied starter has been found to be most efficient for corn grown in soil with low soil P test values [P27].

Preplant P applications can be made in the fall or spring [P17]. Phosphorus is immobile in the soil and does not leach. However, P may be removed with surface runoff, especially when not incorporated into the soil [P33].

When only low rates are required, P fertilizer can be applied in alternate years [P30].

Starter P

Starter Phosphorus

Generally, P supply is most limiting early in the season, when the soil is cooler and the root system of the crop is still small. For this reason, P fertilization during the growing season has been found to be less effective than pre-plant or starter applications [P13, P28].

Application Rate

For high-yielding corn, 40-60 lbs P2O5/acre may be applied in a band at planting [P30]. When the recommended annual application rate exceeds this amount, the difference between the total and starter can be applied pre-plant [P21].

When blends containing ammonium and K are used, the maximum application rate is determined by these two nutrients, because high concentrations of N and K2O in the root zone may damage the roots of the seedlings (see starter N).

Mode of Application

Starter fertilizer is traditionally applied in a band 2 inches to the side and 2 inches below the seed to prevent salt damage [P23, P27, P28]. The proper distance to the seed is especially important for starter fertilizers that contain N and K, because salt damage is generally caused by these two nutrients and not by P [P23].

Applying starter fertilizer in a band has generally been found to be the most efficient way to supply P to corn. Compared to a broadcast application, P fertilizer applied in a band is restricted to a smaller volume of soil, which reduces interaction with soil particles so that more P remains available for a longer period of time [P27]. The increase in P use efficiency is generally highest in soils with low soil P test values, when only a small quantity of P is applied, or when soil temperatures are low [P27].

Fertilizer Type

Early studies have shown that P uptake and root growth can be increased by starter fertilizers that contain P and N [P9, P22].

Monoammonium phosphate (MAP, 11-52-0) and ammonium polyphosphate (10-34-0) are popular starter fertilizers [P2, P16]. In contrast, diammonium phosphate (DAP, 18-46-0) should be used with caution because it produces free ammonia, which can severely damage seedling roots [P1, P23].

Sidedress P

Sidedress Phosphorus

Generally, P supply is most limiting early in the season, when the soil is cooler and the root system of the crop is still small. For this reason, P fertilization during the growing season has been found to be less effective than pre-plant or starter applications [P13, P28].

Foliar P

Foliar Phosphorus

Results from studies investigating the effect of foliar P and K applications on corn performance have been inconsistent. In a study carried out in Oklahoma, the application of up to 7.1 lbs P/acre in the form of potassium dihydrogen phosphate (KH2PO4) at the tasseling stage increased grain yield in some of the experiments [P10]. Early applications were less effective mainly because of the small leaf area. However, foliar fertilization at the 4-5-leaf stage was found to increase N and P uptake, but not K uptake [P11]. In contrast, the application of a foliar N-P-K-S fertilizer containing 3.3 lbs/acre of each, P and K had no effect on yield when applied either before or after silking [P3].

These results suggest that foliar fertilization may partially compensate for insufficient root uptake of nutrients required for grain filling. However, the amount of P that plants can take up through the leaves is relatively small. Therefore, foliar fertilization can only complement but not substitute soil applications [P10, P18].

A comparison of different fertilizers revealed that potassium dihydrogen phosphate (KH2PO4) and ammonium polyphosphate (11.9% N, 17.1% P) cause less leaf damage per unit P applied than urea phosphate and dipostassium hydrogen phosphate (K2HPO4) [P24, P25].

Soil Test

Soil Analysis

Soil Sampling

Soil samples are generally taken in fall or spring (see Soil Test Sampling for sampling instructions). Samples are taken from the top foot of the profile [K38], which is the main rooting zone. Studies found 65-85% of the roots of irrigated corn in the top foot of the soil profile and 80-94% in the upper two feet [K17, K22]. However, corn roots may reach to a depth of 6 feet [K22, K26].

Plant available K is determined by extracting the soil samples with an ammonium acetate solution [K38].

Interpretation of Test Results

Based on earlier studies summarized by Reisenauer and coworkers [K38], corn grown in soils with soil test K values greater than 80 ppm is unlikely to respond to K applications, while a response is likely with soil test K values below 50 ppm (see Table).

Interpretation of P and K soil test levels in the top foot of the soil profile [P31].
Corn Soil Test

1) ppm Olsen-P
2) ppm ammonium acetate extractable K

The optimum or medium soil test K levels used in other states tend to be higher, with the lower limit ranging from 60 to 100 ppm and the upper limit from 100 to 150 ppm [K3, K5, K7, K10, K19, K37, K41, K42].

However, in a study carried out in Iowa on 28 fields of which 18 had acetate extractable K levels between 80 and 150 ppm in the top 6 inches of the soil, Mallarino and Higashi [K20] only found a significant yield response to K fertilizer at one site. Combining soil tests with plant analyses and K budgets helps identifying sites where a yield response to K fertilization may be likely.

Soil Test Based Application Rates

When soil test K values are between 50 and 80 ppm, applying the amount of K removed at harvest ensures that the K availability remains in the optimal range over the years. Literature values for the amount of K2O removed with harvested grains ranges from 0.2 to 0.3 lb/bu (3.6 to 5.2 g/kg) [K14]. With a yield of 180 bu/acre (5 tons/acre), between 37 and 52 lbs K2O/acre are removed with the grains. Potassium removal with silage ranges from 280 to 365 lbs K2O/acre [K44]. However, the economically optimal K rate may be lower, depending on site-specific condition. Contact your local farm advisor for more information.

For soil test K values below 50 ppm, the application rate may be increased, relative to crop removal, especially for grain corn because the total K uptake of the plant far exceeds the K removed with the grains. In contrast, when soil test values are higher than 80 ppm, K application rates may be reduced or skipped. Regular soil and plant analyses indicate whether the K fertilization program is adequate. On the long term, the soil test K values should reach and remain in the optimal range of 50 to 80 ppm.

Plant Analysis

Plant Analysis

The nutrient concentration in plants changes over time and varies between plant parts. In order to be able to interpret the results correctly, care must be taken to sample the correct plant parts at a specific growth stage (see Table) [K15]. For instructions on how to take a representative tissue sample see Plant Tissue Sampling. Plant tissue nutrient concentrations are somewhat variable. Yield and plant tissue concentrations from previous years, as well as K budgets help with the interpretation of the results.

When K concentrations are below the sufficiency range, yield may be decreased even in the absence of deficiency symptoms. Concentrations above the sufficiency range may indicate excess K availability.

Plant tissue analysis guidelines for corn [K4]. Corn Tissue Analysis

Recommended K concentrations in other states are comparable to those listed in the table with the exception that upper limits of the sufficiency range at silking of up to 3.5% are being used [K6, K32, K39, K40].

Preplant K

Preplant Potassium

Application Rate

Grain corn trials carried out in Nebraska showed that soil test K levels can be maintained with annual applications of 30 lbs K/acre (37 lbs K2O/acre). The average grain yield in these studies ranged from 150 to 155 bu/acre (4.2-4.3 tons/acre) [K34, K35, K36]. This application rate roughly corresponds to the amount of K removed with the harvested grains. With a yield of 180 bu/acre (5 tons/acre), between 37 and 52 lbs K2O/acre are removed with the grains.

Corn stalk and leaves contain a lot of K. When the whole plant is harvested for silage, between 280 to 365 lbs K2O/acre may be removed [K44]. However, the economically optimal K rate may be lower, depending on site-specific condition. Contact your local farm advisor for more information.

Mode of Application

Band application has been found to be more effective than broadcast application, especially in soils with a low K availability [K28]. If K is broadcast, the fertilizer is best incorporated to increase its availability to plant roots.

Fertilizer Type

Potassium chloride (KCl), potassium sulfate (K2SO4), and potassium magnesium sulfate (K2SO4, 2Mg SO4) are common K fertilizers. They all contain readily available K. The choice may therefore be made based on price and whether the application of chloride, sulfate or magnesium is beneficial.

Unlike some other crops, corn is not very susceptible to high concentrations of chloride [K11, K27]. In contrast, chloride in KCl may suppress corn stalk rot [K12]. Fact sheets of the most common fertilizers can be found on the web site of the International Plant Nutrition Institute.

Time of Application

In most soils, K is not leached and can be applied in fall or spring. However, leaching of K may occur in sandy soils with a low soil organic matter content, due to the low cation exchange capacity. In these soils, spring K applications, close to the time it is needed by the plants, are more efficient [K18].

For K deficient soils, the recommended rates should be applied annually [K42]. When only low rates are required, K fertilizer can be applied in alternate years [K37].

Starter K

Starter Potassium

Application Rate

Applying potassium with the starter fertilizer generally has no effect on corn development and yield [K21]. However, Brittan [K2] recommended using a starter blend containing K in the Clarksburg area. Trials have shown that 20-40 lbs K2O/acre banded is sufficient in most cases [K2].

Heckman and Kamprath [K13] compared a band application 2 inches to the side and 2 inches below the seed with an incorporated broadcast application in a sandy soil with low K test values. Banding 56 lbs K2O/acre reduced early K uptake, presumably due to the high salt concentration but had no effect on grain yield.

Mode of Application

Starter fertilizer is traditionally applied in a band 2 inches to the side and 2 inches below the seed to prevent salt damage [K23, K30, K31]. Even when applied at the proper distance, the total amount of N plus K2O should not exceed 70-80 lbs/acre [K16, K42].

The application of fluid fertilizer in direct contact with the seed (popup placement) may damage seedlings, especially in sandy soil and when the fertilizer has a high ammonium or K concentration [K33]. The maximum rate of N and K2O applied should therefore not exceed 10-15 lbs/acre in medium and fine textured soils. Cooperative extension in some states even recommends limiting the amount of N and K2O applied to 8 lbs/acre [K42]. Seed placement is not recommended in sandy or dry soils [K30].

Sidedress K

Sidedress Potassium

Potassium is generally applied pre-plant to corn. Smaller quantities can also be included with the starter. Little research has been done to study the effect of sidedress K on corn.

Foliar K

Foliar Potassium

Foliar K applications have in general little effect on corn yield. In a study carried out in Oklahoma, the application of up to 9 lbs K/acre in the form of potassium dihydrogen phosphate (KH2PO4) at the tasseling stage increased grain yield in some of the experiments [K8]. Early applications were less effective mainly because of the small leaf area. However, other studies found that foliar fertilization at the 4-5-leaf stage or around silking had no effect on yield [K1, K9].

K2HPO4 has been found to induce leaf damage at much lower K concentrations than other K containing foliar fertilizers, such as KNO3, KH2PO4, K2SO4 [K25]. Leaf damage is most severe under water stress [K24].

Acknowledgments

Guidelines and Webpage Design:

  • Daniel Geisseler, Ph.D.; Post Doctoral Scientist; Department of Land, Air and Water Resources, University of California, Davis

Reviewers:

  • Carol Frate; Farm advisor; University of California Cooperative Extension Tulare County
  • William R. Horwath, Ph.D.; Professor of Soil Biogeochemistry and James G. Boswell Endowed Chair in Soil Science; Department of Land, Air and Water Resources, University of California, Davis

Support:

  • Asif Maan, Ph.D.; Branch Chief Feed, Fertilizer, and Livestock Drugs Regulatory Services, California Department of Food and Agriculture
  • Amrith Gunasekara, Ph.D.; Science Advisor to the Secretary; California Department of Food and Agriculture
  • Erika Lewis; Fertilizer Reserach and Education Program, California Department of Food and Agriculture

Last Update: January, 2014

Additional Information:

  1. Grain Corn Nitrogen Uptake and Partitioning
  2. Silage Corn Nitrogen Uptake and Partitioning
  3. Corn Production in California
    (Historic Background, Production Statistics)
  4. FREP Database

References:


TOP OF PAGE

Nitrogen

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  3. Arjal, R.D., Prato, J.D., Peterson, M.L., 1978. Response of corn to fertilizer, plant population, and planting date. California Agriculture 32(3), 14-15.
  4. Ball-Coelho, B.R., Roy, R.C., 1999. Enhanced ammonium sources to reduce nitrate leaching. Nutrient Cycling in Agroecosystems 54, 73–80.
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  7. Beegle, D.B., Roth, G.W, Lingenfelter, D.D., 2003. Starter fertilizer. Penn State Extension. Agronomy Facts 51.
  8. Below, F.E., Lambert, R.J., Hageman, R.H., 1984. Foliar applications of nutrients on maize. I. Yield and N content of grain and stover. Agronomy Journal 76, 773-777.
  9. Binder, D.L., Sander, D.H., Walters, D.T., 2000. Maize response to time of nitrogen application as affected by level of nitrogen deficiency. Agronomy Journal 92, 1228–1236.
  10. Binford, G.D., Blackmer, A.M., El-Hout, N.M., 1990. Tissue test for excess nitrogen during corn production. Agronomy Journal 82, 124-129.
  11. Binford, G.D., Blackmer, A.M., Meese, E.G., 1992. Optimal concentrations of nitrate in cornstalks at maturity. Agronomy Journal 84, 881-887.
  12. Blackmer, A.M., Voss, R.D., Mallarino, A.P., 1997. Nitrogen fertilizer recommendations for corn in Iowa. Iowa State University Extension.
  13. Blue, W.G., Eno, C.F., 1954. Distribution and retention of anhydrous ammonia in sandy soils. Soil Science Society of America Proceedings 18, 420-424.
  14. Brittan, K., 2004. 2003 Yolo/Solano/Sacramento field corn production. University of California Cooperative Extension.
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  18. Ciampitti, I.A., Camberato, J.J., Murrell, S.T., Vyn, T.J., 2013. Maize nutrient accumulation and partitioning in response to plant density and nitrogen rate: I. Macronutrients. Agronomy Journal 105, 783–795.
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  34. Hansen, D., Binford, G., Sims, T., 2004. End-of-season corn stalk nitrate testing to optimize nitrogen management. University of Delaware Cooperative Extension.
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  36. Ippersiel, D., Alli, I., MacKenzie, A.F., Mehuys G.R., 1989. Nitrogen distribution, yield, and quality of silage corn after foliar nitrogen fertilization. Agronomy Journal 81, 783-786.
  37. Jones Jr., J.B., 1998. Field sampling procedures for conducting a plant analysis. In: Kalra, Y.P. (Ed.). Handbook of Reference Methods for Plant Analysis. CRC Press, Boca Raton. pp. 25-35.
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  40. Kyveryga, P.M., Blackmer, T.M., 2012. On-farm evaluations to calibrate tools for estimating late-season nitrogen status of corn. Agronomy Journal 104, 1284–1294.
  41. Larson, E., Oldham, L., 2008. Corn fertilization. Mississippi State University Extension Service. Information Sheet 864.

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  43. Lawrence, J., Ketterings, Q., Godwin, G., Czymmek, K., Renuka, R., 2012. Corn stalk nitrate test (CSNT). Cornell University Cooperative Extension. Agronomy Fact Sheet 31.
  44. Lehrsch, G.A., Sojka, R.E., Westermann, D.T., 2000. Nitrogen placement, row spacing, and furrow irrigation water positioning effects on corn yield. Agronomy Journal 92, 1266–1275.
  45. Leikam, D.F., Lamond, R.E., Mengel, D.B., 2003. Soil test interpretations and fertilizer recommendations. Kansas State University.
  46. Leikam, D., Mengel, D., 2007. Nutrient management. In: Kansas State University (Ed). Corn Production Handbook.
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  48. Ma, B.L., Li, M., Dwyer, L.M., Stewart, G., 2004. Effect of in-season application methods of fertilizer nitrogen on grain yield and nitrogen use efficiency in maize. Canadian Journal of Soil Science 84, 169–176.
  49. Maddux, L.D., Raczkowski, C.W., Kissel, D.E., Barnes, P.L., 1991. Broadcast and subsurface-banded urea nitrogen in urea ammonium nitrate applied to corn. Soil Science Society of America Journal 55, 264-267.
  50. Magdoff, F.R., Ross, D., Amadon, J., 1984. A soil test for nitrogen availability to corn. Soil Science Society of America Journal 48, 1301-1304.
  51. Marx, E.S., Christensen, N.W., Hart, J., Gangwer, M., Cogger, C.G., Bary, A.I., 1997. The pre-sidedress soil nitrate test (PSNT) for Western Oregon and Western Washington. Oregon State University Extension Service. Nutrient Management Guide.
  52. Mascagni Jr., H.J., Boquet, D.J., 1996. Starter fertilizer and planting date effects on corn rotated with cotton. Agronomy Journal 88, 975-982.
  53. Miller, M.H., Ohlrogge, A.J., 1958. Principles of nutrient uptake from fertilizer bands 1. Effect of placement of nitrogen fertilizer on the uptake of band-placed phosphorus at different soil phosphorus levels. Agronomy Journal 50, 95-97.
  54. Mortvedt, J.J., 1976. Band fertilizer placement – How much and how close? Fertilizer Solutions 20, 90-96.
  55. Murdock, L.W., Schwab, G.J., 2004. Corn stalk nitrate test. University of Kentucky Cooperative Extension.
  56. Nelson, K.A., Scharf, P.C., Stevens, W.E., Burdick, B.A., 2011. Rescue nitrogen applications for corn. Soil Science Society of America Journal 75, 143-151.
  57. Neumann, P.M., 1979. Rapid evaluation of foliar fertilizer-induced damage: N, P, K, S on corn. Agronomy Journal 71, 598-602.
  58. Neumann, P.M., Ehrenreich, Y., Golab, Z., 1981. Foliar fertilizer damage to corn leaves: Relation to cuticular penetration. Agronomy Journal 73, 979-982.
  59. Power, J.F., Alessi, J., Reichman, G.A., Grimes, D.L., 1972. Effect of nitrogen source on corn and bromegrass production, soil pH, and inorganic soil nitrogen. Agronomy Journal 64, 341-344.
  60. Randall, G.W., Hoeft, R.G., 1988. Placement methods for improved efficiency of P and K fertilizers: A review. Journal of Production Agriculture 1, 70-78.
  61. Rehm, G.W., 1986. Effect of phosphorus placement on early growth, yield and phosphorus absorption by irrigated corn. Journal of Fertilizer Issues, 3(1), 12-17.
  62. Rehm, G., 2005. The basal stalk nitrate test for corn. Minnesota Crop eNews.

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  64. Rehm, G.W., Lamb, J.A., 2009. Corn response to fluid fertilizers placed near the seed at planting. Soil Science Society of America Journal 73, 1427-1434.
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  66. Roberts, R.K., Howard, D.D., Gerloff, D.C., Johnson, L.A., 1995. Economic analysis of nitrogen sources and placement methods in no-tillage corn. Journal of Production Agriculture 8, 575-580.
  67. Samborski, S.M., Tremblay N., Fallon E., 2009. Strategies to make use of plant sensors-based diagnostic information for nitrogen recommendations. Agronomy Journal 101, 800-816.
  68. Savoy, H.J., 2009. The pre-sidedress nitrate-N soil test (PSNT) for nitrogen management in corn production systems of Tennessee. The University of Tennessee Agricultural Extension Service.
  69. Scharf, P.C., 2001. Soil and plant tests to predict optimum nitrogen rates for corn. Journal of Plant Nutrition 24, 805-826.
  70. Shapiro, C.A., DeLoughery, R.L., 2001. The corn stalk nitrate test. University of Nebraska Extension. Publication NF01-491.
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  74. Spellman, D.E., Rongni, A., Westfall, D.G., Waskom, R.M., Soltanpour, P.N., 1996. Pre-sidedress nitrate soil testing to manage nitrogen fertility in irrigated corn in a semi-arid environment. Communications in Soil Science and Plant Analysis 27, 561-574.
  75. Stanley, F.A., Smith, G.E., 1956. Effect of soil moisture and depth of application on retention of anhydrous ammonia. Soil Science Society of America Proceedings 20, 557-561.
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  78. University of Delaware, 2003. Grain Corn.
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  81. Wiese, R.A., 1978. Starter program requires less fertilizer. Fertilizer Solutions 22 (Jan-Feb), 101-103.
  82. Zebarth, B.J., Paul, J.W., Younie, M., Bittman, S., 2001. Fertilizer nitrogen recommendations for silage corn in high-fertility environment based on pre-sidedress soil nitrate test. Communications in Soil Science and Plant Analysis 32, 2721-2739.
TOP OF PAGE

Phosphorus

  1. Allred, S.E., Ohlrogge, A.J., 1964. Principles of nutrient uptake from fertilizer bands. VI. Germination and emergence of corn as affected by ammonia and ammonium phosphate. Agronomy Journal 56, 309-313.
  2. Beegle, D.B., Durst, P.T., 2003. Nitrogen fertilization of corn. Penn State Extension. Agronomy Facts 12.
  3. Below, F.E., Lambert, R.J., Hageman, R.H., 1984. Foliar applications of nutrients on maize. I. Yield and N content of grain and stover. Agronomy Journal 76, 773-777.
  4. Brown, B., Hart, J., Horneck, D., Moore, A., 2010. Nutrient management for field corn silage and grain in the Inland Pacific Northwest. Pacific Northwest Extension. Publication PNW 615.
  5. Bundy, L.G., 1998. Corn fertilization. University of Wisconsin Cooperative Extension. Publication A3340.
  6. California Plant Health Association, 2002. Western Fertilizer Handbook 9th edition. Interstate Publishers, Inc.
  7. Davis, J.G., Westfall, D.G., 2009. Fertilizing corn. Colorado State University Extension. Fact Sheet No. 0.538.
  8. Dick, R.P., Tabatabai, M.A., 1987. Polyphosphates as sources of phosphorus for plants. Fertilizer Research 12, 107-118.
  9. Duncan, W.G., Ohlrogge, A.J., 1958. Principles of nutrient uptake from fertilizer bands. II. Root development in the band. Agronomy Journal 50, 605-608.
  10. Girma, K., Martin, K.L., Freeman, K.W., Mosali, J., Teal, R.K., Raun, W.R., Moges, S.M., Arnall, D.B., 2007. Determination of optimum rate and growth stage for foliar-applied phosphorus in corn. Communications in Soil Science and Plant Analysis 38, 1137-1154.
  11. Giskin, M., Efron, Y., 1986. Planting date and foliar fertilization of corn grown for silage and grain under limited moisture. Agronomy Journal 78, 426-429.
  12. Heckman, J.R., Sims, J.T., Beegle, D.B., Coale, F.J., Herbert, S.J., Bruulsema, T.W., Bamka, W.J., 2003. Nutrient removal by corn grain harvest. Agronomy Journal 95, 587–591.
  13. Hergert, G.W., Reuss, J.O., 1976. Sprinkler application of phosphorus and zinc fertilizers. Agronomy Journal 68, 5-8.
  14. Jones Jr., J.B., 1998. Field sampling procedures for conducting a plant analysis. In: Kalra, Y.P. (Ed.). Handbook of Reference Methods for Plant Analysis. CRC Press, Boca Raton. pp. 25-35.
  15. Laboski, C.A.M., Dowdy, R.H., Allmaras, R.R., Lamb, J.A., 1998. Soil strength and water content influences on corn root distribution in a sandy soil. Plant and Soil 203, 239–247.
  16. Larson, E., Oldham, L., 2008. Corn fertilization. Mississippi State University Extension Service. Information Sheet 864.
  17. Leikam, D., Mengel, D., 2007. Nutrient management. In: Kansas State University (Ed). Corn Production Handbook.
  18. Ling, F., Silberbush, M., 2002. Response of maize to foliar vs. soil application of nitrogen–phosphorus–potassium fertilizers. Journal of Plant Nutrition 25, 2333-2342.
  19. Mallarino, A.P., Blackmer, A.M., 1992. Comparison of methods for determining critical concentrations of soil test phosphorus for corn. Agronomy Journal 84, 850-856.
  20. Mayaki, W.C., Stone, L.R., Teare, I.D., 1976. Irrigated and nonirrigated soybean, corn, and grain sorghum root systems. Agronomy Journal 68, 532-534.

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  22. Mengel, D., Ruiz-Diaz, D., 2012. Starter fertilizer rates and placement for corn. Kansas State University Extension. Agronomy e-Updates 338, 1-4.
  23. Miller, M.H., Ohlrogge, A.J., 1958. Principles of nutrient uptake from fertilizer bands 1. Effect of placement of nitrogen fertilizer on the uptake of band-placed phosphorus at different soil phosphorus levels. Agronomy Journal 50, 95-97.
  24. Mortvedt, J.J., 1976. Band fertilizer placement – How much and how close? Fertilizer Solutions 20, 90-96.
  25. Neumann, P.M., 1979. Rapid evaluation of foliar fertilizer-induced damage: N, P, K, S on corn. Agronomy Journal 71, 598-602.
  26. Neumann, P.M., Ehrenreich, Y., Golab, Z., 1981. Foliar fertilizer damage to corn leaves: Relation to cuticular penetration. Agronomy Journal 73, 979-982.
  27. Newell, R.L., Wilhelm, W.W., 1987. Conservation tillage and irrigation effects on corn root development. Agronomy Journal 79, 160-165.
  28. Randall, G.W., Hoeft, R.G., 1988. Placement methods for improved efficiency of P and K fertilizers: A review. Journal of Production Agriculture 1, 70-78.
  29. Rehm, G.W., 1986. Effect of phosphorus placement on early growth, yield and phosphorus absorption by irrigated corn. Journal of Fertilizer Issues 3(1), 12-17.
  30. Rehm, G.W., Sorensen, R.C., Wiese, R.A., 1983. Application of phosphorus, potassium, and zinc to corn grown for grain or silage: Nutrient concentration and uptake. Soil Science Society of America Journal 47, 697-700.
  31. Rehm, G., Randall, G., Lamb, J., Eliason, R., 2006. Fertilizing corn in Minnesota. University of Minnesota Extension Service.
  32. Reisenauer, H.M., Quick, J., Voss, R.E., Brown, A.L., 1976. Chemical soil tests for soil fertility evaluation. In: Reisenauer, H.M. (Ed.). Soil and Plant-Tissue Testing in California. University of California, Division of Agricultural Sciences, Bulletin 1879. pp. 39-41.
  33. Shapiro, C.A., Ferguson, R.B., Hergert, G.W., Wortmann, C.S., Walters, D.T., 2008. Fertilizer suggestions for corn. University of Nebraska Extension. Publication EC 117.
  34. Tarkalson, D.D., Mikkelsen, R.L., 2004. Runoff phosphorus losses as related to phosphorus source, application method, and application rate on a Piedmont soil. Journal of Environmental Quality 33:1424–1430.
  35. Torres-Dorante, L.O., Claassen, N., Steingrobe, B., Olfs, H.W., 2006. Fertilizer-use efficiency of different inorganic polyphosphate sources: effects on soil P availability and plant P acquisition during early growth of corn. Journal of Plant Nutrition and Soil Science 169, 509–515.
  36. Voss, R.D., 1993. Corn. In: Bennett, W.F. (Ed.). Nutrient Deficiencies and Toxicities in Crop Plants. APS Press, St. Paul, MN. pp. 11-14.
  37. Wortmann, C.S., Dobermann, A.R., Ferguson, R.B., Hergert, G.W., Shapiro, C.A., Tarkalson, D.D., Walters, D.T., 2009. High-yielding corn response to applied phosphorus, potassium, and sulfur in Nebraska. Agronomy Journal 101:546–555.
TOP OF PAGE

Potassium

  1. Below, F.E., Lambert, R.J., Hageman, R.H., 1984. Foliar applications of nutrients on maize. I. Yield and N content of grain and stover. Agronomy Journal 76, 773-777.
  2. Brittan, K., 2004. 2003 Yolo/Solano/Sacramento field corn production. University of California Cooperative Extension.
  3. Brown, B., Hart, J., Horneck, D., Moore, A., 2010. Nutrient management for field corn silage and grain in the Inland Pacific Northwest. Pacific Northwest Extension. Publication PNW 615.
  4. California Plant Health Association, 2002. Western Fertilizer Handbook 9th edition. Interstate Publishers, Inc.
  5. Davis, J.G., Westfall, D.G., 2009. Fertilizing corn. Colorado State University Extension. Fact Sheet No. 0.538.
  6. Doerge, T.A., Roth, R.L., Gardner, B.R., 1991. Nitrogen fertilizer management in Arizona. University of Arizona.
  7. Gardner, E.H., Hall., L.F., Pumphrey, F.V., 2000. Field corn - Eastern Oregon, east of Cascades. Oregon State University Extension Service. Fertilizer Guide.
  8. Girma, K., Martin, K.L., Freeman, K.W., Mosali, J., Teal, R.K., Raun, W.R., Moges, S.M., Arnall, D.B., 2007. Determination of optimum rate and growth stage for foliar-applied phosphorus in corn. Communications in Soil Science and Plant Analysis 38, 1137-1154.
  9. Giskin, M., Efron, Y., 1986. Planting date and foliar fertilization of corn grown for silage and grain under limited moisture. Agronomy Journal 78, 426-429.
  10. Hart, J., Sullivan, D., Gamroth, M., Downing, T., Peters, A., 2009. Silage corn (Western Oregon). Oregon State University Extension Service. Nutrient Management Guide.
  11. Heckman, J.R., 1995. Corn responses to chloride in maximum yield research. Agronomy Journal 87, 415-419.
  12. Heckman J.R., 1998. Corn stalk rot suppression and grain yield response to chloride. Journal of Plant Nutrition 21, 149-155.
  13. Heckman, J.R., Kamprath, E.J., 1992. Potassium accumulation and corn yield related to potassium fertilizer rate and placement. Soil Science Society of America Journal 56, 141-148.
  14. Heckman, J.R., Sims, J.T., Beegle, D.B., Coale, F.J., Herbert, S.J., Bruulsema, T.W., Bamka, W.J., 2003. Nutrient removal by corn grain harvest. Agronomy Journal 95, 587–591.
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