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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #117738
Title: RESIDUAL PHOSPHORUS DISTRIBUTION AND SORPTION IN STARTER FERTILIZER BANDS APPLIED IN NO-TILL CULTURE

Author
item STECKER, JOHN - UNIV OF MO
item BROWN, JAMES - UNIV OF MO
item Kitchen, Newell

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Tillage practices on farmland, such as plowing and discing, mix the soil and the nutrients it contains. Many farmers, however, have adopted no-till practices to reduce erosion, essentially eliminating soil mixing. A critical step in good crop-nutrient management is obtaining a representa- tive sample of soil in the field. This soil sample, once analyzed in the laboratory, is the basis for fertilizer recommendations. Getting a representative sample for immobile nutrients has been complicated by banding of fertilizers within no-till practices. Previous research has shown that residual fertilizer bands in no-till can result in large short- range (within 1-30 in) variation in soil-test results. Therefore, getting a good representative soil sample to determine fertilizer recommendations is almost impossible in no-till fields when using current soil sampling procedures. This research was conducted to characterize the distribution of banded phosphorus (P) over time in order to develop soil sampling strategies that accurately reflect availability to crops. Over an 18-month period on 3 different soils, we found that residual P levels in band- affected soil were 5 to 30 times greater than in the unaffected soil and that the high levels remained within 3 in of the point of application. By cross-sectional sampling, the band area was found to be between 3 and 10 square inches. The results of this study will benefit farmers and crop consultants by helping them understand the degree of error introduced in soil sample results when the short-range variability created by P fertilizer bands is not considered. The results will also be used to develop improved soil sampling strategies when P fertilizer is banded in no-till cropping systems.

Technical Abstract: When fertilizer phosphorous (P) is banded in no-till culture, soil P distribution remains heterogeneous for months to years. The objective of this research was to quantify the spatial and temporal distribution of banded P in order to assist in assessment of P availability. In three field studies, starter fertilizer bands of 10 and 20 kg P ha**-1 were marked with monofilament line. Soils included a Mexico silty clay loam (Mollic Endoaqualf), a Putnam silty clay loam (Vertic Albaqualf), and a Dockery silt loam (Aquic Udifluvent). After digging a small pit within the band row, cross-sectional P distribution of the band was determined by taking 1.27 by 1.27-cm square samples out of the pit side wall on a grid around the band. Bands were sampled at 6, 12, and 18 months following banding. Soil P was determined with a Bray-1 test. Band affected soil was defined as having a P concentration 1.5 times higher than adjacent non-band daffected soil. Band P concentrations decreased logarithmically from band centers. Band dimensions tended to be the largest at the 12 month sampling. Phosphorus did not redistribute greatly from the initial band over the 18 months. Averaged over sites and sampling dates, band dimensions varied horizontally from 5 to 8 cm and vertically from 5 to 12 cm. The cross-sectional area of bands at 12 months ranged from 18 to 52 cm**2 and 26 to 63 cm**2 for the 10 and 20 kg P ha**-1, respectively. From P sorption curves, soil from the band centers resulted in solution P concentrations that would exceed a plant's potential maximum rate of uptake. Soil sampling procedures for accurate fertilizer P recommendations in no-till systems need to account for this stratification of soil nutrients.