Information from 2000 Missouri Rice Research Update, February 2001.

University of Missouri Soil Test Recommendations for Rice Production

Gene Stevens and David Dunn
Delta Research Center, University of Missouri - Columbia

Introduction

Most of the Current University of Missouri soil test recommendations have been adopted from Arkansas. During the past several years a team of scientists including Dr. Gene Stevens, Dr. Michael Aide, Dr. Paul Tracy, and David Dunn have carried out field evaluations of these recommendations. These evaluations are continuing today thanks to support from the Missouri Rice Research and Merchandising Council.

pH and soil acidity

In Missouri soil acidity is measured on the basis of Salt pH (pHs). The pH s indicates the need to apply lime. The lime requirement is measured by the Woodruff Buffer method. Missouri lime recommendations are given in lbs. of Effective Neutralizing Material (ENM) per acre. ENM is an estimate of how much soil acidity the lime will neutralize in a three-year period.

The University of Missouri does not recommend liming before rice is grown. Liming is necessary to maximize soybean yields in the rice-soybean rotation. Last year at the Missouri Rice Research Farm soybean yields were increased 25% when 1 ton/a of lime was applied before soybeans were planted

Nitrogen (N)

Currently the University of Missouri recommendations for nitrogen are variety specific. These recommendations are available from your County Extension Agent and are posted on the Ag Electronic Bulletin Board (AgEBB) at http://agebb.missouri.edu/murice/index.php. Table 1 gives the nitrogen recommendations for four popular varieties.

Table 1. Nitrogen recommendations for four popular rice varieties.

Variety Total N Preflood Mid-season
Cypress 150 90 30+30
Drew 135 75 30+30
Lemont 180 120 30+30
Cocodrie 150 90 30+30

Phosphorus (P)

The soil test used to determine P levels is the Bray 1 method. Results are expressed in pounds P2O5/a. Phosphorus recommendations are based on a target level of 30 lbs P/a. A rice crop will remove 0.30 lb. of P2O5 per bu per acre. To account for this loss a crop removal factor is included for soils testing between 30 and 55 lb. P/a. Recommendations are given in lbs. of P2O5 per acre.

Potassium (K)

The soil test used to determine K levels is an extraction with neutral, one normal ammonium acetate. Results are given in pounds K2O/a. Potassium recommendations are based on a target level of 5 x CEC. For silt-loam soils this is about 75 lbs. K2O/a. For gumbo soils this number is about 100 lbs. K2O/a. Rice yields drop off quickly when a soil tests below these levels. For low-testing soils a factor for building the soil up to maximum productive levels is included in the fertilizer recommendation. The current recommendation package allows the producer to choose how quickly to build up the soil K levels. A rice crop removes 0.2 lb K2O per bushel per acre. A crop removal factor is included to account for this. Recommendations are given in lbs. of K2O per acre.

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