Date of Graduation

12-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norman, Richard J.

Committee Member

Slaton, Nathan A.

Second Committee Member

Gbur, Edward E. Jr.

Third Committee Member

Wilson, Charles E. Jr.

Fourth Committee Member

Snyder, Clifford S.

Keywords

Nitrogen content; Rice production; Soil fertility

Abstract

Several potential indicators of rice (Oryza sativa L.) response to nitrogen (N) fertilization include the soils alkaline hydrolyzableN (AHN) concentration, seeding date, and the soils clayfixed NH4N content. Three studies were conducted to: (1) correlate AHN, determined using Illinois Soil Nitrogen Test (ISNT) or Nitrogen Soil Test for Rice (NSTaR), to plant parameters of interest and develop a fertilizer N rate calibration curve capable of predicting the 95% relative grain yield (RGY) fertilizer N rate for rice grown on clayey soils; (2) evaluate the influence of seeding date and N fertilization on rice plant growth and grain yield; and (3) evaluate the plantavailable portion of clayfixed NH4N using NSTaR and quantify total clayfixed NH4N using dry combustion. Alkaline hydrolyzableN, quantified using ISNT or NSTaR in the first study, explained 83% of the variability in calibration based on a 0 to 30cm sampling depth. The second study revealed that grain yield exhibited a tendency to be greater for rice seeded in April or May compared to June seeding dates in Arkansas. Results of the third study indicated a low percentage (46%) of total clay fixed NH4N was predicted to be plantavailable NH4N based on NSTaR. Fertilizer N rate recommendations based on the ISNT or NSTaR soil test methods evaluated in the first study revealed the potential of soilbased tests to improve economic, agronomic, and environmental aspects of rice produced on clayey soils. Seeding date selection can influence rice grain yield which may in turn influence fertilizer N management. However, the fertilizer N rate required to maximize grain yield when seeding date was delayed remained unclear following completion of the second study and continued research is required to identify the influence of seeding date on the yieldmaximizing, fertilizer N rate for rice grown in Arkansas. The recovery of clayfixed NH4N by NSTaR indicated a portion of total clayfixed NH4N was expected to be available for plant uptake. However, additional research is required to verify the low recovery of clayfixed NH4N and the influence of clayfixed NH4N on the quantity of AHN determined by NSTaR.

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