Information from 2001 Missouri Rice Research Update, February 2002.

University of Missouri Soil Test Recommendations for Rice Production

Gene Stevens and David Dunn


Most of the Current University of Missouri soil test recommendations has been adopted from Arkansas. During the past 5 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 3 year period.

Currently 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 soybean yields were increased 25% when 1 ton/a of lime was applied before soybeans were planted at the Missouri Rice Research Farm.

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 Bullatin Board at Table 1 gives the nitrogen recommendations for 4 popular varieties.

Table 1. Nitrogen recommendations for 4 popular rice varieties.

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

Phosphorus (P)

The soil test used to determine P levels is the Bray 1 method. Results are expressed in lbs P/a. Phosphorus recommendations are based on a target level of 30 lbs P/a. A rice crop will remove .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 lbs K/a. Potassium recommendations are based on a target level of 5X CEC. For silt-loam soils this is about 75 lbs K/a. For gumbo soils this number is about 100 lbs K/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 added in. 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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