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Fluid Journal : Spring 2017
12 The Fluid Journal Spring 2017 the critical level for rice to match that of soybeans (220 + 5 X CEC). Rice production in the Missouri Boot Heel is either on silt loam soils west of Crowley’s Ridge, or clay soils generally found to the east of Crowley’s Ridge. The clay soils generally have high native available K levels (500 to 600 lbs K/A) and do not require K fertilization. Many of these clayey soils have been recently land leveled and have a limited history of rice production. If intensive rice and soybean production continues on these soils, they will eventually require K fertilization. Results Grain yield. Of primary concern to rice producers is grain yield. Here proper K nutrition is a key to maintaining optimum yield levels. Data pooled over the 19 years studied show that yields are reduced 20% when K is not included in the fertilizer mix. Table 1 shows a typical response curve from a three-year evaluation conducted on a silt loam soil. The pooled data indicate that growing rice on a soil testing 100 lbs. below the current critical level of 125 +5XCECinKcouldleadtoa30-35 bushel reduction in yield. At current rice prices this represents a $150 per Figure 1. Apparatus used to measure rice stalk breaking strength. Table 1. Rice yields for pre-plant K treatments 2010-2012 on a silt loam soil, Qulin, MO % of soil test rec K applied Rice yield Bu/acre 2010 Bu/acre 2011 Bu/acre 2012 Bu/acre 3-year average % relative yield 0 114 123 116 78 50% 138 134 141 91 75% 149 134 140 94 100% 161 138 154 100 Figure 2. Relationship between stalk breaking strength and stalk K content for rice. acre cost. Grain quality. A second yield consideration for rice producers is milling quality. As rice is often used for direct human consumption, visual qualities have a bearing on the price that producers receive for their crop. The premium product is a whole, unbroken kernel of the appropriate length with a uniform pearly white translucent color. Broken, “chalky”, or discolored kernels result in steep price reductions. Before rice is sold at the elevator, a sample is milled by sequentially removing the husk and bran. The percentage of rice remaining after this process is calculated and referred to as “Head rice”. Next, as the whole kernels are separated and their percentage calculated, this portion is referred to as “whole rice”. By combining these two numbers, a value of the rice can be determined. Good milling rice has the numbers for Head and Whole totaling greater than 125. The last step for value determination is color evaluation. Potassium fertility has a positive effect on rice milling quality. Table 2 shows the milling results for two different years. For this trial, a different harvesting schedule was employed each year. In 2010, our primary goal was to evaluate lodging effects, while in 2011 we sought to evaluate milling effects. This led to distinct differences in milling values for the different years. However, the increase in milling quality was consistent over both years. Lodging. Rice producers also consider the non-yield benefits of potassium fertilization. Lodging is a major issue for rice producers. Fallen rice is much slower to harvest and the quality of grain is reduced. In our studies, lodging was not consistently reduced with proper preplant soil- applied K fertilization. In our opinion, this is due to reduced grain weight when soil-available K is inadequate. “Proper K nutrition critical for modern rice production.”