The Influence of Flood Irrigation in Rice Systems On the Spatial Distribution of Soil Nutrients, Plant Nutrient Uptake and Yield.

An understanding of the underlying causes of the spatiotemporal variability of rice yield within rice fields is requisite to the development of effective precision management strategies. Currently, rice growers lack the information needed to manage spatial variability of soil nutrients and yield-limiting factors, such as soil salinity and nutrient deficiencies. Laser leveling and water management practices may be important factors influencing field variability. This presentation will focus on the influence of water management on the redistribution of soil nutrients, and its effect on plant nutrient uptake and productivity.  

A two-year, on-farm study was conducted in four commercial rice fields, ranging in size from 23 to 69 hectares, in the Sacramento Valley. To quantify the spatial variability of soil chemical properties, soil samples were collected across a geo-referenced grid. These samples were analyzed for organic carbon, total nitrogen, nitrate-nitrogen, Olsen phosphorous, extractable potassium, pH and electrical conductivity. To characterize the spatial distribution of water solute concentrations across a field, surface water samples were collected from irrigation boxes as water was flowing through the field. Water samples were analyzed for pH, EC, soluble nitrogen, P and K, and dissolved organic carbon. The spatial variability of yield within each field was measured by commercial yield monitors, and by hand-harvesting plots to confirm commercial yield monitor results.

Nutrient concentrations in flood water and soil generally increased with increasing distance from the inlets. Plant uptake of K was greatest in the bottom checks, suggesting that distinct management zones within fields may be appropriate.  However, there were mixed results for observed patterns of nutrient concentrations in both water and soils across fields. Field-leveling, water temperature and weed presence are other factors we are investigating, which may further elucidate the observed yield patterns.