DEVELOPMENT OF A CRITICAL MEHLICH 3 SOIL ZINC CONCENTRATION FOR RICE IN ARKANSAS

Abstract

Zinc (Zn) fertilizer recommendations for rice (Oryza sativa L.) in Arkansas have been based on soil pH since the 1970s and have not accounted for the residual carryover of previous Zn fertilizer applications. Continuous application of Zn fertilizer to soil in some fields cropped to rice has resulted in very high Mehlich 3 extractable Zn (M3Zn) concentrations in soil and illustrates the need to develop improved recommendations. The objective of this research was to develop a critical M3Zn soil concentration for making Zn fertilizer recommendations to rice. The relationship between relative yield (RY), soil pH, and soil M3Zn concentration was determined from 36 Zn fertilizer studies conducted on silt loam soils between 1992 and 2000. Multiple regression analysis showed that soil pH, M3Zn concentration, and their interaction best described rice yield response to Zn fertilization. When soil pH was >5.5, a yield response to Zn fertilization was possible, but depended on the soil's M3Zn concentration. The critical M3Zn concentration required to produce 90% RY, without Zn fertilizer application, for soils with pH values of 6.2, 7.0, and 7.8 was 1.3, 3.5, and 4.2 mg M3Zn kg soil−1, respectively. Results suggest that soil pH and M3Zn concentration should be used together when making Zn fertilizer recommendations for rice to prevent yield loss from Zn deficiency and economic loss from needless Zn fertilizer applications. Zinc fertilization is not needed on soils high in M3Zn concentration, regardless of soil pH, and rice yields could possibly be reduced by application of Zn fertilizer in these fields.