Optimizing Application of Phosphorus and Potassium to Processing Tomatoes under Drip Irrigation

IPNI-2007-CAN-ON28

29 Feb 2008

2007 Annual Interpretive Summary

Optimizing Application of Phosphorus and Potassium to Processing Tomatoes under Drip Irrigation, 2007

Recent research has indicated that processing tomatoes require higher rates of N when grown with fertigation. The objective of this research is to determine optimum rates of P and K for the higher yields obtained in this production system. Four rates of P, from 0 to 180 lb P2O5/A, were applied in a factorial combination with four rates of K from 0 to 640 lb K2O/A, starting in the spring of 2006. Soil test levels were 45 to 50 ppm Olsen-P, considered high for tomatoes, and 140 to 180 ppm ammonium-acetate K.

Under fertigation, applying rates of 200 to 360 lb K2O/A produced optimal marketable yields over 50 t/A. Without irrigation, yields were less than half as high, but high rates of K boosted marketable yield by up to 4 t/A. Soil profile nitrate was lower following fertigation, confirming the high nutrient use efficiency of this very productive system. Soluble solids as measured by Brix increased linearly with applied K. Neither P nor K were found to affect lycopene in either 2006 or 2007. This project is planned to continue in 2008. ON-28