Walter Gordan

Document Type

Dissertation - University Access Only

Award Date

1990

Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

Abstract

The use of conservation tillage methods, including ridge tillage, has increased dramatically in recent years. There is also great concern that farmers are applying more nitrogen (N) fertilizer than is environmentally sound. Nitrates are considered to be the most widespread non-point source of groundwater contamination. Groundwater nitrate nitrogen (No3 -N) concentrations in excess of 10 mg/L are found commonly in South Dakota. A three year study was established in 1987 on an xiii HILTON M. BRIGGS LIBRARY South Dakota State University Brookings, SD 57007-10?8 Estelline silt loam (Pachic Udic Haploboroll) and an Egan silty clay loam (Udic Haplustoll) soil, located in eastern South Dakota to investigate the effects of tillage and N rate on plant N uptake and N requirement for maximum yield of corn, soil N03 -N levels and movement through the soil profile and to evaluate a N03 -N soil test for making N fertilizer recommendation treatments. Five rates of N (0, -1 65, 130, 195, and 260 kg ha ) were applied to plots managed with 3 tillage systems: chisel, moldboard, andridge. The N source urea was banded beside the row 3 weeks after planting and immediately incorporated by cultivation. On the Estelline soil, corn grain yield and total N uptake were affected by a tillage X nitrogen interaction in 1988. Maximum yield within the ridge was achieved at the 130 kg ha-1 N rate; while in the chisel and moldboard systems, yields continued to increase with increasing N rate. In 1989 grain yields were significantly higher in the ridge system than in the other tillage systems at all N rates except the 65 kg ha-l N rate. On the Egan soil, tillage did not affect total N uptake or grain yields in either 1988 or 1989. In both years corn grain yield increased with increasing N-rates -1 up to the 195 kg ha N rate. On the Estelline soil, xiv significantly more N03 -N was found in the lower portion (60-120 cm) of the ridge till soil profile than in the moldboard and chisel systems. No differences were seen in No3 -N movement among tillage systems on the Egan soil. Fall No3 -N content in the 0-60 cm increment best correlated with corn grain yields on both soils. In general, the correlation coefficients explained less than half of the variability in yields. Multiple regressions, with applied N, N03 -N in either the spring or the fall, and with soil moisture content in the spring as dependent variables, revealed that soil No3 -N did not significantly explain any more of the variability in yield than did applied N alone.

Format

application/pdf

Number of Pages

146

Publisher

South Dakota State University

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