Impacts of Changing Postharvest Agricultural Practices on Abundance of Waste Grain in California's Central Valley

Abstract

Abstract Agricultural waste grains are significant for providing nutrients for wintering waterfowl in California. Rice and corn comprise 56% of their nutrient needs in the Central Valley and changes to agricultural practices, such as postharvest treatments, could impact these food resources. Currently, limited data exist on how postharvest treatments in rice and corn fields affect the abundance of waste grain, yet these data are essential to determine the carrying capacity of agricultural lands for wintering waterfowl. To address this knowledge gap, we estimated the abundance of waste grain (kg/ha) using dry field transects, dry field soil cores, and flooded field (wet) soil cores. In 2016 and 2017, we sampled 84 rice fields and 47 corn fields. Our results indicate that the abundance of waste rice varied significantly among postharvest treatments. Fields that received no postharvest treatment (stubble left standing; no incorporation of straw) had the greatest amounts of waste rice, whereas fields that were disced, disced and rolled, or burned provided the least amount of waste rice. The average abundance of waste rice across all postharvest treatments was 320 kg/ha in dry fields (arithmetic mean; geometric mean = 228 kg/ha; soil core samples). Estimates of waste rice in flooded fields averaged only 169 kg/ha (geometric mean 98 kg/ha; soil core samples), significantly lower than in the same fields prior to flooding. Variation in the abundance of waste corn was greater than that of waste rice. Fields that did not receive any postharvest incorporation had the greatest abundance of waste corn, 233 kg/ha on average (arithmetic mean; geometric mean = 72 kg/ha), whereas fields that were incorporated (disced or disced and rolled) contained significantly lower abundance of waste corn, averaging 50–60 kg/ha (arithmetic mean; geometric mean = 5–10 kg/ha). The average, across all postharvest treatments, was 159 kg/ha of waste corn (geometric mean = 25–34 kg/ha). Our results suggest that postharvest practices affect the abundance of waste grain in rice and corn fields; changes in these practices could impact food availability for wintering waterfowl. Our results also indicate that the method of sampling waste grain can influence estimates of residual grain abundance.