Wednesday, November 7, 2007 - 9:30 AM
318-1
Soil Based Nitrogen Tests for Rice Production: Taking it to Another Depth.
Conventional crop production has relied on yield goal estimates for determining N fertilizer needs, which can often lead to over-fertilization of crops and potentially higher impacts on the surrounding environment. Nitrogen fertilizer recommendations in rice have traditionally been based on yield goal and soil texture, but increasing costs of production and pressure from competing crops such as soybeans has led to the demand for a soil based nitrogen test for rice fertilizer applications. Recent developments in soil testing such as the ISNT and Direct Steam Distillation have been met with much criticism due to inconsistencies and inability to predict yield. During the early stages of development a trend between relative grain yield and ISNT and DSD were found, but with coefficients of determination <0.50. Sampling 15cm deep was not providing the information necessary to develop a successful soil based nitrogen test and a new sampling procedure was incorporated. Soil cores were taken in 15cm increments to a depth of 60cm and analyzed using either the ISNT or DSD. Initial results show a strong correlation between total N uptake and ISNT as well as percent relative grain yield and ISNT at the 0-45cm depth. These results suggest that sampling depth can play a major role in a soil tests ability to predict potentially mineralizable soil nitrogen and its ability to predict agronomic factors such as grain yield. Good correlations were also seen for grain yield and total N as well as total C. The plants ability to access mineralized N plays an important role in the success of a soil based nitrogen test and should be taken into consideration when determining sampling depth protocol. Rooting depth should be taken into account to select the proper depth for correlation of soil based nitrogen tests.
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