Nitrogen Availability from Compost in High Tunnel Tomato Production

High tunnel use for tomato cultivation is on the rise in the northeastern United States. Use of high tunnels both extends the growing season and increases yield. This study was designed to provide data to help predict the nitrogen-supplying ability of compost in high tunnel production. Four finished composts from commercial producers in Maine were analyzed for nutrient content, pH, conductivity, lignin and soluble C. The four compost treatments were compared with an unamended control and a control receiving inorganic nutrient in a field study with randomized complete block design and four replications. Composts were applied at the rate of 122 kg of total N acre-1,and inorganic NPK fertilizer was applied at the rate of 45 kg N acre-1. Tomatoes were grown in these treatments in high tunnels at the Highmoor Farm Maine Agricultural and Forest Experiment Station in Monmouth, ME during the summers of 2013 and 2014. Soil NO3 - N, NH4+-N and moisture were measured throughout the growing season, along with total marketable yield and plant N uptake. Compost did not affect soil moisture on any sampling date during the growing seasons. Compost inorganic N and other properties were significantly different between composts and between years. Compost inorganic N concentrations were positively correlated with plant yield, biomass and N uptake. When compost inorganic N was supplied at over 39 kg ha’1, marketable yield was significantly greater than that of the unamended treatment and was not significantly different than that of the inorganic NPK treatment. When compost inorganic N was supplied at less than 10 kg ha-1, marketable yield was not significantly different than that of the unamended treatment. Rainfall and temperature influenced plant growth to some extent, even in the protected high tunnel setting. The percentage of compost organic N mineralized was not significantly different between treatments, and varied widely between replications. Mineralized organic N was not significantly correlated with compost C:N ratio, %C, %N, total inorganic N, NO3 -N, NH4+-N, DOC nor lignin. The amount of compost NO3--N applied was positively correlated with the soil NO3 -N concentration on many sampling dates. The amount of compost NH4+-N applied was positively correlated with the soil NH4+-N concentration on many sampling dates, and was correlated with the soil NO3--N concentration in 2014. Unlike compost inorganic N, compost organic N appeared to have little effect on plant growth and yield the first growing season after application