The Effect of Large Applications of Manure on Movement of Nitrate and Carbon in an Irrigated Desert Soil

Abstract

AbstractFeedlot manure was applied in the field at rates of 0, 45, 90, 180, and 360 metric tons/ha to a Holtville clay under irrigated conditions. Holtville clay is a soil with restricted internal drainage. Ceramic cups were installed at various depths in the soil profile to monitor the movement of manganese, nitrate, and soluble organic carbon.The manure greatly increased the amount of soluble organic carbon in the soil solution. An increase in the manure application rate to 180 or 360 metric tons/ha increased the nitrate in the soil solution at 20 and 40 cm, but there were only small differences at 80 and 140 cm. The lack of movement of nitrate to the 80‐cm depth for the high rates of manure application appeared to be due to denitrification, because high nitrate levels were present in the surface soil and sufficient water was applied to leach to this depth. Nitrate leaching was less when manure was applied annually than when it was applied only the first year. Less movement of nitrate to the 80‐cm depth in treatments receiving manure annually seems to be the result of denitrification caused by the higher level of soluble organic carbon. The application of manure did not result in reducing conditions at 20 cm under regular irrigation as measured by redox potential, but the double irrigation schedule caused soil reducing conditions at 20 cm. At 80 cm, manganese in the soil solution was inversely correlated to nitrate level.