Nitrogen and Irrigation Management

This new publication describes efficient management of nitrogen (N) fertility and irrigation in California processing tomato production. 

Improving the efficiency of N and irrigation inputs is increasingly important given the limited availability of irrigation water and increased regulatory activity designed to protect groundwater resources. In response to evidence of widespread nitrate pollution of groundwater, the Central Valley Region Water Quality Control Board has  adopted a regulatory program that requires growers to track and report N inputs. This information will be used to estimate a nitrogen balance, which compares the amount of N applied to fields with the amount of N removed from fields in harvested fruit. The greater the imbalance between applied N and N removed in harvested fruit, the greater the potential for N loss to the environment. Growers who consistently show a large imbalance between N application and harvest N removal are likely to come under increased scrutiny for potential contribution to groundwater nitrate degradation.

This publication focuses on managing drip irrigation, which is now the standard practice in processing tomato production. The practices outlined here are also relevant to fresh market tomatoes grown on ground beds for harvest at the mature green fruit stage. This type of fresh market production has similar growth patterns and fertility and irrigation requirements up to the point of harvest, which occurs approximately 4 to 5 weeks earlier than processing tomato harvest.