Nutrient uptake by rice in response to water management

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Abstract
All rice (Oryza sativa L.) production in the United States utilizes flood irrigation. Yet, depletion of the aquifer in eastern Arkansas may necessitate the adoption of rice production practices that reduce water inputs. Field studies were conducted to evaluate reductions in the duration of floodwater application on nutrient uptake by lowland irrigated rice. Three water management treatments, (i) recommended application of a flood applied at the 4‐ to 5‐leaf stage of development (normal flood), (ii) a delay in the application of the flood until panicle differentiation (delayed flood), and (iii) full‐season intermittent flush irrigation (flush irrigated), were imposed on the cultivar Tebonnet’ grown on a Crowley silt loam (Typic Albaqualfs). Nitrogen (N) was applied as a recommended three‐way split to all treatments. Uptake and tissue concentration of N, phosphorus (P), potassium (K), zinc (Zn), iron (Fe), and manganese (Mn) were determined. Rice subjected to normal flooding consistently responded with the highest nutrient uptake and flush irrigated rice with the lowest uptake. Differences in nutrient uptake were generally measured by booting in 1989 and panicle initiation in 1990. Differences in uptake response measured earlier in the 1990 growing season are attributed to greater water deficit stress prior to panicle differentiation from lower rainfall. Reductions in tissue concentrations of Mn, Zn, and K in response to delayed flood or flush irrigation were measured in 1990 and in 1989 for Mn only. This reduced uptake of these elements is attributed to lower shoot dry matter production and reduced soil availability. In contrast, since tissue concentrations of N, P, and Fe were hot affected by water management, differences in uptake are attributed to lower dry matter production. There was no yield difference between rice subjected to normal or delayed flood, however, yield was reduced by flush irrigation. Although a delay in the timing of the floodwater application resulted in reduced nutrient uptake compared to normal flooded rice, sufficient nutrient uptake for optimum yields occurred. In contrast, maintaining soil water content at levels considered satisfactory for most upland crops by flush irrigating throughout the season, dramatically lowered nutrient uptake and yields. These data suggest that paddy rice requires the presence of a flood at least during reproductive growth for optimum growth, nutrient uptake and yields.