NITROGEN-BALANCE IN SOUTHERN SAN-JOAQUIN VALLEY

A N balance for the southern San Joaquin Valley of California [USA] was calculated, using techniques and methodology developed for the Upper Santa Ana River Basin of southern California. The 2 areas differed considerably in both size (the latter being much smaller) and agricultural function. Data were compiled on N inputs, use and outputs for many sources within the study area. Such data enabled construction of a flow diagram depicting best estimates of N pools and fluxes within the San Joaquin Valley basin. N inputs into the study area from various sources were somewhat greater than output to the atmosphere and by plant removal. Inputs to the soil N pool were about 9 kg/ha more in 1971 than in 1961. Since the soil N pool was estimated to be about 11 metric tons/ha, this represented an increase of about 0.1%. Since the increases of N are not evenly distributed over the study area, high N concentrations can develop in some local areas.