Nitrate Contents of Sudangrass and Barley Forages Grown on Plots Treated with Animal Manures

In areas of high concentrations of domestic animals, such as the Chino-Corona Basin in southern California, there is a tendency to use large amounts of manures on adjacent croplands. In these situations, there is a need to know the upper safe limits of manure use for protection of animals from excess nitrate (NO⁻₃) in forage and for the protection of groundwater from NO⁻₃ and soluble salts. A field trial on the Moreno Farm of the Univ. of California, Riverside was conducted to respond to these needs. This paper presents the results of this experiment relative to the upper safe limits for NO⁻₃ in barley and sudangrass forages used by the dairy industry. Barley grown in the winter of 1972–73 and sudangrass grown in the summer of 1973 were analyzed for NO⁻₃. These Crops represented the third year of an experiment with two manures (dry dairy corral manure and liquid manure from a feedyard) and two irrigation treatments (ET and 1.33 ET) on a Hanford sandy loam. Nitrate concentrations in barley decreased progressively as the crop grew, were higher with liquid than with dry manure, and were not affected by irrigation level. The NO⁻₃ concentrations in sudangrass generally increased as the crop grew until just prior to emergence of flower heads from the boot and then decreased, were higher with liquid than with dry manure, and were higher with the lower water level. Based on the NO⁻₃ content of sudangrass the safe annual rate of liquid manure, which had 4.8% N on a dry weight basis, for the particular management system in which half of the manure was applied at the time of planting of barley in the fall and the other half at time of planting of the sudangrass, was about 8.6 metric tons of dry weight/ha/year. The safe limit of dry manure, which contained 1.8% N on a dry weight basis, for the same croppingmanagement system was about 29 metric tons of dry matter/ha/year.