Wednesday, November 7, 2007
296-26
Flooded Rice Yield Response to Phosphorus Fertilizer Application.
The regulated changes in rice straw management from straw-burning to straw-incorporation are not reflected in current nutrient management plans for California rice. The current phosphorus (P) fertilizer recommendations for rice were developed over three decades ago on soils that were typically burned after harvest. The current recommendation is to apply P fertilizer if the Olsen-P soil test is less than 6 mg kg-1 (i.e. the critical level). The objectives of this study were to (1) determine the yield response of rice to P fertilizer application among fields of varying straw management (burn, incorporated, bailed) and (2) determine the relationship between soil P tests and rice yield response to P fertilizer application. This study was conducted on 20 rice grower fields located throughout California’s Sacramento Valley (5 in 2005 and 15 in 2006). The experimental design was a randomized complete block with three replications. Treatments were application of 0 or 40 kg-P ha-1 (as triple superphosphate). Only two of the fields had a significant yield increase after P fertilization (α=0.05). Among all fields, the median Olsen-P soil test was 8.1 mg kg-1, with a range of 2.2 to 32.4 mg kg-1 (nine of the fields were below the critical Olsen-P level of 6 mg kg-1). Among all sites, Olsen-P, Bray-P, soil organic matter content, and pH were not significantly correlated with rice yield response to P fertilization. For the past decade or more, rice fields have been receiving annual inputs of both rice straw and P fertilizer. These results suggest that in soils above the critical P level, there is no need for P application, as soils may be above the maintenance limit. Overall, it appears that it is necessary to update the critical P value for California rice.
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