Optimizing Application of Phosphorus and Potassium to Processing Tomatoes under Drip Irrigation
IPNI-2007-CAN-ON28
25 May 2007
Justification
Processing tomatoes, a major high-value crop in Ontario, are high in nutrient demand. The nutrient needs can further increase with drip irrigation/fertigation, a local common practice, due to the largely enhanced yield potential (Zhang et. al, 2003, 2005). Our studies in past 5 years show that fertilizer nitrogen (N) rate required for processing tomato production with drip fertigation should be 270 kg N/ha. This N rate is 3 times as much as the current provincial recommendation. As implicated by the “Role of Minimum Nutrient”, with increased need for fertilizer N, other nutrients, such as phosphorus (P) and potassium (K), must be supplied accordingly in sufficient amounts to develop the maximum yield potential.
On the other hand, over application of nutrients, especially P, can cause build-up in soil, and consequent contamination of water resource, as P is the key element controlling eutrophication of water bodies. Application of fertilizer P and K for processing tomatoes must be optimized in a way that minimizes adverse effect on water quality, while maintaining product quality and maximum marketable yield. The provincial government of Ontario has made the protection of source water as one of its top priorities, and passed the Nutrient Management Act (ON. REG. 267/03) in 2002. The regulation restricts land application of nutrients and encourages adoption of BMPs to mitigate the potential impacts on water quality. The OMAFRA-NMN series of nutrient management computer programs have been developed to assist producers with nutrient management planning. Optimum fertilizer rates along with crop nutrient removal are the key variables of OMAFRA-NMN. However, data on P and K is not available for processing tomatoes with drip irrigation, and have to be developed for the Ontario conditions.
More and more demand on quality of processing tomatoes has become an emerging issue to producers from both processors and consumers. The major food quality variables related to processing tomatoes include soluble solids, lycopene, and vitamin C. However, information on the roles of P and K in the formation of these food quality variables are limited and often in controversy, depending on the soil and weather conditions. There is no data available with this regard in Ontario, especially under drip irrigation/fertigation.
The industries (OTRI - Ontario Tomato Research Institute, IPNI – International Plant Nutrition Institute & OPVG - Ontario Processing Vegetable Growers) have identified that optimization of P and K application for processing tomatoes in an environmentally responsible manner to maximize yield and quality as top research priority.