Nutrient Placement and Movement Under Zero-Till Conditions

Illinois Fertilizer Conference Proceedings
January 29-31, 1996

Main Index 1996 Index Search

Nutrient Placement and Movement Under Zero-Till Conditions

Lyle Paul¹

spacer

Introduction

As grain producers change their tillage and planting operations to include more reduced tillage or to using no tillage prior to planting, there is less opportunity for mixing nutrients into the soil. Some advocates of zero-till have said that the benefits of zero-till are increased if the soil is left undisturbed for a period of time (several years). They feel that the benefit to not disturbing the soil is greater than any negative effect from not mixing the fertilizer into the soil. There has been concerns expressed by others that occasionally fertilizer needs to be mixed into the soil to get maximum yields.

The objectives of this study were to determine:

The changes of soil pH, P₁, and K soil test under zero-till cropping system.
If mixing of soil nutrients into the soil profile is necessary
If stratification of nutrients occurs and if so, is it detrimental to crop yields.
To include a final report at the conclusion of the study.

Methods and Materials

This study is a randomized complete block design with four replications with corn and soybean crops being planted each year in a corn-soybean rotation. The initial treatments that were to add enough lime to raise the pH to 6.5, add 1/3 the amount of lime to raise the pH to 6.5 or add no lime. The fertilizer treatments were to add nothing, add phosphorus to raise the soil P₁, test to 50 and potassium to raise the soil K test to 300 and then add maintenance fertilizer or to no more fertilizer after the original application. One-half of the plots were disked and plowed after liming and fertilization and other one-half were untilled. In succeeding years all plots have been no-tilled.

These plots were established on Flanagan silt loam and Drummer silty clay loam. The average initial soil test levels are pH-5.6, P₁,-39, and K-225. Previously this field has been in a corn and soybean rotation with minimal fertilizer added for a period of years.

To make the needed pH changes, powdered limestone that would pass through a 200 mesh screen was applied to the individual plots according to the experimental plan and to the average of the four initial incremental soil tests of the individual plots. Fertilizers in the forms of 0-46-0 and 0-0-60 were also applied to the individual plots according to the plan design and soil test. After fertilizer application in the spring of 1991 the plots selected for incorporated fertilizer were disked once and moldboard plowed. After plowing, the incorporated plots were disked twice and field cultivated once before planting. After planting the only additional disturbance to any plots was a row cultivation in 1991. The entire study area was row cultivated using a zero-till cultivator. The only other soil disturbance has been the annual shallow incorporation of 28% UAN as the nitrogen source for the corn crop except in 1995 when anhydrous ammonia was used.

After the original incorporation of fertilizer, the additional amounts needed for the maintenance fertilizer has been applied as dry material to the surface of the field. The only incorporation of this material was that which would occur with the planting operations and the mixing the might occur when spraying and harvest would was done.

Due to the wet conditions in the spring of 1995, the crops were planted later than planned. The corn in the study area was planted on May 31, 1995. The variety used was DeKalb Genetics DK 591 planted at 33,000 seeds per acre in 30 inch rows. Nitrogen was applied on June 23 at 180# of nitrogen per acre. The nitrogen was in the form of anhydrous ammonia sidedressed at a depth of about 6-7" inches using a knife applicator with the knives on thirty inch centers.

The soybean crop was planted on June 6,1995. The variety was DeKalb Genetics variety CX232. The beans were planted with a John Deere No-till drill in seven & one-half inch rows at a seeding rate of 180,000 seeds per acre.

Roundup and 2,4-D were applied to all of the study area prior to planting. Preemergence herbicides were used in both crops. There were also postemergence herbicides applied in the soybean crop. With the uneven rainfall patterns, less than adequate weed control was achieved.

Incremental soil tests were pulled in the falls of 1994 following harvest. The changes from the original soil tests at each of the increments are reported in tables 2, 3, 4, and 5. Table 6 shows the samples as if they were taken as a normal soil test.

Results and Discussion

Yields in 1995 (Table 1) in the corn have been adversely affected by the lack of effective weed control. The late planting dates for both corn and soybean crops affected yields. The corn yields showed a response to the fertilizer and lime applications, but not to lime applications alone. Over the length of the study, the soybean crop has responded little to the original incorporation of fertilizer. The corn has responded to the original incorporation of fertilizer for the period of study. With the corn there was a better response to the lower level of lime than with the full rate. The soybean crop responded to the higher levels of lime.

Conclusions

The following conclusions can be drawn from this study.

Do not apply the full rate of lime that is needed to raise the pH to 6.5 from 5.6 unless it is incorporated, and even then it may be beneficial to incorporate the lime over a two year period.
The growing crop will mine and move nutrients from deeper levels of the soil into the plants and unto the surface as the plant residue decays.
Farmers will not be able to avoid nutrient stratification under no-till operations.
Incorporation of lime and fertilizer initially applied to a soil will slow the mining or nutrient movement from lower levels, but it will not stop it under no-till farming.
The soils at the Northern Illinois Agronomy Research Center may not build and hold higher soil tests without continued fertilizer application.
There is not a large benefit to the initial nutrient incorporation on an annual basis, but over the four years of the study, without tillage in that year, the average yield increase in corn is 11 bushels per acre per year due to the fertilizer incorporation. The increase for soybean is a little less than a bushel per acre per year.
Based on the annual yield increases, it would appear that the initial incorporation of fertilizer is beneficial and would pay for the tillage operation that is necessary to achieve that.