Date of Graduation

8-2016

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Trenton L. Roberts

Committee Member

Nathan A. Slaton

Second Committee Member

Jarrod T. Hardke

Third Committee Member

Michael D. Richardson

Keywords

Biological sciences, Clay soil, N-star, Soil sampling

Abstract

The two methods for determining N-fertilizer recommendations for rice (Oryza sativa L.) in Arkansas are the standard N recommendation (SR) based on soil texture, previous crop, and rice cultivar, and the Nitrogen-Soil Test for Rice (N-STaR) which quantifies the potentially mineralizable-N of the soil and provides a site-specific N recommendation. The N-STaR program has recently been developed, and the validation of N-STaR for clay soils is an important step in ensuring that N-STaR predicts correct N-fertilizer rates for rice under a delayed-flood production system. Small-plot trials located across Arkansas compared the N-STaR 95 and 100% relative grain yield (RGY) N rates applied as a single preflood (SPF) and a 2-way split (2-WS) application to the SR. The N-STaR N-fertilizer rate recommendations were equal to or less than the SR at all locations with differences ranging from -224 to 0 kg N ha-1. At all 13 sites, rice receiving the N-STaR 100% RGY N-fertilizer treatments yielded equal to or greater than the SR. Similar results were seen for the N-STaR 95% RGY fertilizer-N treatments, although rice receiving the 95% RGY SPF fertilizer-N rate yielded lower than the SR at three locations. The second objective was to examine potential sampling tools for their accuracy in collecting N-STaR soil samples while having the greatest ease-of-use. Alkaline hydrolyzable-N (AH-N) from soil samples collected by the N-STaR bucket and drill (BD), Kleen Hole Spade dry (KHS-D), Kleen Hole Spade lubricated with water (KHS-W), and Kleen Hole Spade lubricated with WD-40 (KHS-40) were compared against the dutch auger (DA) control. The alternative sampling methods were not statistically different in AH-N concentration from the DA, although all alternative methods had a tendency to overestimate AH-N compared to the DA and a correction value should be considered. The KHS-D showed the greatest utility in sampling clay soils and would be the best alternative method for encouraging the use of N-STaR in rice production on clay soils. In conclusion, this research validates the N-STaR N rate recommendations for rice on clay soils in Arkansas and highlights alternative sampling methods that may be employed in N-STaR soil sampling.

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