Date of Graduation

12-2019

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Kristofor R. Brye

Committee Member

Lisa S. Wood

Second Committee Member

Travis Faske

Third Committee Member

Leandro Mozzoni

Keywords

Irrigation, Long-term Effects, Nematodes, Residue, Soil, Soybeans, Tillage, Water Management

Abstract

Soybeans (Glycine max) are one of the major row crops in the United States, particularly in Arkansas. Soybean cyst nematode (SCN, Heterodera glycines) and southern root-knot nematode (RKN, Meloidogyne incognita) are two of the most damaging pests that cause major economic losses in soybeans. Little is known concerning the effects of common and alternative agronomic practices on nematodes in fields with nematode population densities below threshold levels. Therefore, the objective of this study was to evaluate the effects of the combination of tillage (conventional tillage and no-tillage), irrigation (irrigated and non-irrigated), wheat (Triticum aestivum) residue burning (burned and no burned), and wheat residue level (high and low) on the natural nematode population density and change over the growing season and between years in a long-term, wheat-soybean rotation on a silt-loam soil in Arkansas. Nematodes were measured in the top 10 cm in July, August, and October 2017 and 2018. The SCN egg population density in the soil was numerically largest [P = 0.01; 2.9 nematodes (100 cm3)-1] in the conventional tillage (CT)-no-burn combination under irrigated conditions and lowest [0.1 nematodes (100 cm3)-1] in the CT-no-burn combination under dryland production. The SCN J2 population densities [1.1 nematodes (100 cm3)-1] was 3.4 times greater (P < 0.01) under the CT-burn than under the CT-no-burn and no-tillage (NT)-burn treatment combinations, which did not differ and averaged 0.49 nematodes (100 cm3)-1. Spiral nematode (Helicotylenchus spp.) population densities was 52.6 times greater (P < 0.01) under irrigated-CT [31.84 nematodes (100 cm3)-1] than under the irrigated-NT, dryland-CT, and dryland-NT treatment combinations in 2017, all of which had less than 0.6 nematodes (100 cm3)-1. Lesion nematode (Pratylenchus spp.) population density was 5.6 times greater (P = 0.02) under the dryland-burn than under the dryland-no-burn treatment combination, but was unaffected by burning under irrigated conditions. The RKN had small populations in the soil and could not be formally statistically analyzed. Traditional and alternative wheat-soybean management practices can influence nematode populations and should be carefully considered to maximize soybean production and profitability.

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