Crop Nutrition

Improving Rice Yields and Quality with Potassium

eKonomics News Team

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Higher prices and changing crop rotations have led a Missouri researcher to re-evaluate the role that potassium plays in rice production.

According to David Dunn, soils lab manager at the University of Missouri Fisher Delta Research Center, higher soybean prices in recent years have caused many farmers in the area to change their rotation. The traditional rotation was two years of rice followed by one year of soybeans. Now, it is becoming more common to plant one year of rice and two years of soybeans.

These findings have been corroborated by the eKonomics Nutrient Removal Calculator. Using average yields for the area, soybeans remove more than double the amount of potassium per acre than rice does. This has led to lower soil potassium levels, especially in the silt loam soil in Southeast Missouri.

“We are not supplying as much as we are taking off,” said Dunn. “Even if the recommended potassium rates are followed, farmers may still have reduced yield and quality in their rice crops.”

Impact on Yield and Quality

With his research, Dunn has shown that growing rice on soil testing 100 pounds below the critical level of potassium could lead to a 30 to 35 bushel per acre yield reduction. With current prices, that represents $150 per acre loss of profit to the farmer.

Milling quality is an important consideration for farmers. If a farmer’s rice quality is low, they might be docked in price. Dunn found higher potassium levels led to higher quality rice. Soils with higher potassium levels produced more “head” and “whole” rice, which is how elevators and processors determine quality.

Effects on Lodging and Stalk Strength

Lodging can be a major problem for farmers as it can slow harvest and reduce grain quality. In his research, Dunn found that foliar applied potassium in one study reduced lodging from 40 percent to 15 percent — even in fields with adequate soil applied potassium.

Dunn also devised a way to measure stalk strength and relate it to reduced lodging and concluded that rice stalks from areas with higher potassium levels had both stronger stalks and less lodging. When applying the full potassium fertilizer rate, stalk strength was double the stalk strength when no potassium fertilizer was applied. Lodging was reduced from 30 to 18 percent when a full potassium rate was applied compared to no potassium fertilizer application.

Updating Potassium Rates

Dunn states that farmers in Missouri should adjust rice potassium rates to maintain productivity and ensure good quality harvestable grain.

In the late 1990’s, the critical rice potassium rate was updated to 125 pounds of potassium plus five times the soil CEC (cation exchange capacity). Now, farmers should use an updated rate of 220 pounds of potassium plus five times the soil CEC for rice production, which is the same as the recommended rate for soybean production in Dunn’s area. In southeast Missouri, silt loam soils have a CEC from 7.5 to 18 and clay-based soils have a CEC of 18 or more.

With the changes in crop production, farmers should monitor and manage their soil fertility levels using a number of tools, including soil testing and online tools such as the eKonomics Nutrient ROI Calculator 2.0 to estimate their crop nutrients needs.