Evaluation of nitrate distribution in long-term no tillage corn production under three cover situations and three rates of nitrogen

Author

Wickson Temwa Kawonga

Date of Award

12-1990

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

John G. Graveel

Committee Members

Don Tyler, Paul Denton, Bob Duck

Abstract

Nitrate-nitrogen distribution to a depth of 274 cm was evaluated in long term no-tillage corn plots subjected to three nitrogen rates and three cover situations. The soil on the experimental area was mapped Memphis silt loam (fine-silty, mixed, thermic, Typic Halpudalfs). The design of the experiment was randomized block with split-plot arrangement of treatments. The treatments were five levels of nitrogen and five cover situations. Main plots consisted of nitrogen rates and cover crops formed sub-plots. Soil samples were collected at 15 cm depth intervals down to 90 cm and at 30 cm intervals from 91 to 274 cm. Soil solution was obtained using vacuum displacement and nitrates determined by ion chromatography.

Corn (Zea mays L.) yield increased with an increase in nitrogen rate. Beyond 168 kg N ha^-1 there were no significant differences in corn yield. Below 112 kg N ha^-1 yields of corn following hairy vetch (Vicia villosa Roth.) were significantly greater than those following wheat (Triticum aestivum L.) and corn stubble. Nitrate-nitrogen accumulation was highest where 224 kg N ha^-1 was applied and where hairy vetch was seeded as a cover crop. The highest NO₃ concentration in soil solution occurred in August. Mean NO₃-N concentration from vetch, wheat and no cover were 32, 25, and 28 μg mL^-1 respectively. The top 30 cm of soil contained 37% of the total NO₃-N. At 0 kg N ha^-1 there were no significant differences in NO₃-N accumulation at each depth interval from 0 to 274 cm. At 168 kg N ha^-1, significant NO₃-N accumulation occurred at depths below 122 cm. Raising the nitrogen rate to 224 kg ha^-1 resulted in no significant differences among depths for NO₂-N accumulation for all cover situations. Plots seeded to wheat had the least NO₂-N accumulation at all depths. Electrical conductance followed the trend of NO₂-N distribution. Soil pH varied greatly in April and was constant in August and November. Significant differences existed among depth intervals for both pH and electrical conductance. No significant differences were observed among cover crops.

Recommended Citation

Kawonga, Wickson Temwa, "Evaluation of nitrate distribution in long-term no tillage corn production under three cover situations and three rates of nitrogen. " Master's Thesis, University of Tennessee, 1990.
https://trace.tennessee.edu/utk_gradthes/7125