Effects of tomato cannery water forage irrigation on nitrogen and carbon in a clay loam soil

Land application is a common method for treatment and disposal/reuse of process water and solids from food processing in Central Valley California, USA. Application rates are commonly based on N as contamination of ground and surface waters are of environmental concern. Contemporary disposal practices employ a crop to consume the N applied. Tomato processing wastewaters and semi-solid wastes were evaluated using homogeneous soil columns, and long-term monitoring of the cannery land application site. The 105-day outdoor column study included the smectitic field soil of clay loam texture, Bermudagrass, and three cannery water (CW) loading rates and a control (urea) applied weekly. NO3− and BOD leaching were low during the simulated irrigation season. Based on N grass uptake, leaching losses, and soil N, gaseous N losses were 50, 64, and 61% of the N applied from 313, 471, and 627 kg N ha−1 CW applications. However, gaseous N losses exceeded N applied by all treatments and included significant native soil N loss ranging from 1500 to 2600 kg ha−1. N losses indicated a “priming effect” due to mineralizable organics, and a significant decrease in soil C was seen in all treatments. The study results point toward denitrification as the major cause of gaseous N losses where ammonia volatilization was found to be a lessor cause of N loss. Long-term field monitoring results showed greater N impacts from land incorporation of semi-solid wastes than from wastewater irrigation, consistent with the soil column findings. The study demonstrated that CW having high amounts of labile organics applied to a soil of low permeability can result in heightened gaseous N loss rates, especially by denitrification. Gaseous N losses in addition to crop N uptake lessened the possibility of contamination of ground and surface waters.

► Gaseous N losses were > 50% of the applied tomato cannery wastewater N. ► A “priming effect” resulted in significant gaseous losses to both soil C and N. ► NO3− and BOD leaching were found to be low with the prescribed management practices. ► Land application of tomato biosolids can pose a greater N concern to the environment than wastewater irrigation. ► Labile C applied to a low permeability soil resulted in high denitrification rates. ► The study would support that contemporary disposal practices for the tomato cannery waste can be environmental benign where plant uptake and gaseous N loss are acceptable fates.