Yunian Huang

Document Type

Dissertation - University Access Only

Award Date

1995

Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

Abstract

Groundwater is an important source of drinking water. Nitrate nitrogen concentrations in excess of 10 mg L-1 have been found in groundwater in South Dakota. Agriculture is the most widespread non-point source of groundwater contamination. A three year study was established in 1990 on an Estelline silt loam (Pachic Odie Haploboroll) soil, located in eastern South Dakota. The objective was to compare the use of different crops for the removal of soil nitrates deep in the soil profile. The project was superimposed on a site which was included in a study to determine the effects of management on nitrate leaching in corn-producing soils (1987-1989). The study conducted from 1987 to 1989 included different fertilizer nitrogen rates (0, 65, 130, 195, and 260 kg N ha-1) and tillage treatments (moldboard plow, chisel plow, and ridge-till). In 1990, 'removal crops' were superimposed. Included in this study were alfalfa (Medicago saciva L. ' Saranac 7061' ), ineffective alfalfa (Medicago saciva L. 'In Saranac 7496'), and switchgrass (Panicum virgacum L. ' Sunburst'). Corn (Zea mays L. 'Pioneer 3732') was used as the row crop control. Tillage treatments in the corn plots were continued as in the previous study, but without fertilizer application. The 20% enriched 15 N K N03 was injected at 1. 2 m depth in the soil profile to study plant nitrogen uptake and redistribution of soil N03- N from deep soil position. Four points were injected in each plot of previous nitrogen rate 195 kg N ha-1 treatment with· four replicates. Tillage treatments affected soil N03- N distribution under corn, but not under the removal crops. Corn maintained normal growth by using existing soil N only in the first year. Nitrate which had leached into the lower profiles provided adequate nitrogen for normal growth of switchgrass, alfalfa and ineffective alfalfa during the entire period of the experiment. Within three years, the amount of N0 3- N in the 0-120 cm soil profile decreased 225, 276, 284, and 442 kg ha-1 for corn, alfalfa, ineffective alfalfa, and switchgrass, respectively. In 1990, nitrogen accumulation in herbage biomass was 88 kg N ha-1 for corn, and 46 kg N ha-1 for switchgrass. In 1991, nitrogen accumulation was 81, 154, 126, and 192 kg N ha-1 for corn, alfalfa, ineffective alfalfa, and switchgrass, respectively. In 1992, nitrogen accumulation was 22, 349, 141, and 163 kg N ha-1 for corn, alfalfa, ineffective alfalfa, and switchgrass, respectively. From the tracer study it was determined that of the total nitrogen accumulation in the plants, 1. 0% was taken up by corn from the soil profile below 120 cm, as compared to 4. 5% by alfalfa, 6. 5% by ineffective alfalfa, and 22. 3% by switchgrass. The tracer study also indicated that soil nitrates moved toward the freezing front during winter months. Use of deep-rooted switchgrass appears to be effective in removing N03-N from deep soil locations.

Library of Congress Subject Headings

Groundwater -- South Dakota -- Quality Soils -- Nitrate content Soils -- Leaching

Format

application/pdf

Number of Pages

151

Publisher

South Dakota State University

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