Response of soil health indicators to long-term dairy manure in a semiarid irrigated cropping system

Dairy manure fertilization is an important practice to return nutrients to agricultural soils, but there is limited knowledge regarding the effect of manure on soil health metrics in semiarid irrigated row crops. The objective of this research was to determine how long-term dairy manure application affects biological and chemical indicators of soil health in a field experiment in southern Idaho. The treatments were no fertilizer, inorganic fertilizer (IF), and dairy manure applied annually or biennially at rates of 17, 35, and 52 Mg ha(-1) on a dry weight basis. Spring soil samples were collected 7 yr after project initiation at depths of 0-15 cm and 15-30 cm and analyzed with soil health metrics that are commonly used to quantify organic matter pools and biological nutrient cycling via enzyme activities and N transformation rates. Soil organic C increased with increasing application rate and more than doubled after 7 yr of annual manure at the highest application rate. In general, C and N pools, enzyme activities, and N transformation rates were greater at 0-15 cm than deeper in the soil profile. Compared with IF, annual and biennial manure treatments had a significant effect on most indicators at both soil depths, which increased with increasing manure application rate. Because of the strong response of the indicators to dairy manure, all were found to be positively and significantly correlated with each other, suggesting that only a small subset of the metrics tested could potentially be used to evaluate the influence of manure on soil health in the region.