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Microplot Size and Retainer Effects on Rice Growth and Nitrogen-15 Accumulation

Dep. of Agronomy, 104 M.B. Sturgis Hall
Rice Res. Stn., Louisiana State Univ. Agric. Ctr., P.O. Box 1429, Crowley, LA 70527
Dep. of Agronomy, 104 M.B. Sturgis Hall
Nuclear Science Ctr.
Dep. of Experimental Statistics, Louisiana State Univ., Baton Rouge, LA 70803

^* Corresponding author (pbollich{at}agctr.lsu.edu).

Nitrogen studies on flooded rice (Oryza saliva L.) often use ¹⁵N as a tracer, which is usually contained within microplots and retainers to restrict root growth and to prevent ¹⁵N movement in floodwater and the soil solution. Little research has addressed the effects of the microplot and retainer on plant growth, N accumulation, and plot microclimate. The objectives of this field study were to (i) determine the effects of microplot size and retainer on plant growth, N accumulation, floodwater and soil temperature, and floodwater and soil pH and (ii) determine the size of microplots with and without retainers that most closely simulate a field plot. ‘Cypress’ rice was drill-seeded in a Crowley silt loam soil (fine, smectitic, thermic Typic Albaqualf) in circular microplots (15, 35, and 60 cm in diameter) with retainers, and square microplots (75 cm long) with and without retainers. Nitrogen-15-labeled urea was applied preflood at 151 kg N ha^–1. The control was a 2.1- by 7.6-m field plot fertilized with unlabeled urea at 151 kg N ha^–1. All plots were harvested at 90% heading. Plants in 15-, 35-, and 60-cm microplots were 8.5 to 25.4 cm shorter than plants in the field plot in at least one year. Plant dry matter and total N accumulation in microplots did not differ from the field plot, except for total N accumulation in the 15-cm microplot and dry matter in the 35-cm microplot. Water and soil temperature in microplots with retainers were 1.0 to 3.5°C lower than in the field plot. Water and soil pH did not differ between microplots and the field plot. The 75-cm square microplot with a retainer was found to be the best substitute for the field plot.

Received for publication February 19, 1996.

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