Soil Core Composition and Profiles Underlying Large Dairy Operations.

California is the largest US producer of milk and cheese with 1.8 million milking cows, making freestall dairy farms the state’s most prevalent concentrated animal farming operation (CAFO) industry. Typically in freestall dairies, all of the water used is collected into lagoons, and ultimately, manure solids and liquid manure water are land-applied as soil amendment and for fertilization of surrounding forage fields. In this study, we analyzed soil core samples up to 30 meter depth underlying three dairy operations in the southern San Joaquin Valley of California. One of the dairy operations is new (less than ten years old) and is sited on former crop land; the other two operations are older (one over 50 years, and the other over a century). Vadose zones are 25-60 meters thick and developed in sedimentary sequences dominated by alluvial fan deposits. Soil core samples were collected from 16 locations in and around dairy operations that were potentially affected by lagoons, corrals, and manure-applied fields. Soil samples from older dairy farms showed higher concentrations of SO4-S, Cl-, and exchangeable Na, and higher pH. Shallower soil samples at all dairy sites were elevated in electrical conductivity, SO4-S, Cl-, NO3-N, and Olsen P. NH4-N was below detection limit for approximately 50% of the samples, and 85% was less than 1 ppm. However, there were several samples within the upper 15 m that showed soil NH4-N above 100ppm. These may possibly be due to perched groundwater. Comparison between potential source facilities shows that soil samples affected by lagoons show the highest NH4-N concentrations followed by corrals, and manure-applied field. Soil cores located downgradient from lagoons and corrals show higher SO4-S and NO3-N and higher electrical conductivity than the field. The pH is highest in the field, which frequently receive manure.