Fertilizer Guidelines for Processing Tomatoes

Gene Miyao, Farm Advisor, Yolo, Solano, & Sacramento Counties

Fertilization application rates vary widely among California tomato growers. Typical seasonal application rates are 125 to 250 pounds of nitrogen per acre, 60 to 120 pounds of P2O5 per acre and 0 to 120 pounds of K2O per acre. Soil tests are valuable to provide background levels of soil fertility especially for P, K and zinc.

Nitrogen: University research has shown that under normal conditions, maximum yield can be obtained with approximately 140 to 180 pounds of N per acre. N applications as a sidedress at or prior to layby of 120 to 150 pounds are very sufficient. Recent studies by Veg Crops Specialist Jeff Mitchell demonstrated that soils with over 16 ppm nitrate-N in the top foot prior to sidedressing did not respond to additional N applications beyond that supplied as a starter fertilizer. Luxuriant levels of N are not necessary.

Phosphorus: Soils with bicarbonate-extractable phosphorous greater than 12 to 15 ppm are unlikely to respond to P application, although a temporary early growth response to preplant P may be seen in early spring conditions. An early seedling growth response can favorably result in earlier maturity. Below 12 ppm, a yield response to applied P would be expected.

Potassium: Many California soils have adequate potassium for high yield tomato production. However, on soils with ammonium-acetate-extractable K less than 150 ppm, K applications may be required; seasonal rates would vary from 60 to 150 pounds of K2O per acre.

Zinc: If zinc is limiting, (below 0.3 ppm), supplemental applications in the starter fertilizer or higher rates broadcast are recommended. Above 0.5 ppm, no additional zinc is recommended.

Starter Fertilizer: Placement of the starter fertilizer is important. A band 1 to 2 inches directly below the seed is best. Since initial roots grow directly downward, placement of the fertilizer to the side will delay pickup. Fertilizer located 2 inches to the side of the seed line is not efficient. Mechanics of fertilizer placement may be a concern. Disturbance of the seedbed by a fertilizer knife ahead of the planter can affect ideal seed-to-soil contact. Offsetting the knife 1/2 inch to the side of the seed line or angling the knife from the side are techniques to reduce disturbance of the seed line when attempting to plant without supplemental moisture for emergence. Placing the seed in direct contact with conventional fertilizers will result in poor germination and/or delayed emergence.

Pop-up applications are special techniques for suboptimal conditions where soils may be too wet to effectively place fertilizer below the seed. Starter fertilizer placement as a band below the seed is the superior method especially in low phosphorus soils and cool temperatures. Pop-up starter fertilizer application at rates of 11 gpa per seed line of a solution of 1 gallon of 10-34-0 diluted with 5 gallons of water is an alternative supplemental application method in fields still too wet to shank in starter at higher rates below the seed. On-seed application rates should be low so as not to create salt hazards that can inhibit germination. Some delay in rate of emergence and reduction in stand has occurred with the on-seed fertilizer application. The yield gain as well as seedling growth benefit will offset the stand reduction if phosphorus is needed. Higher rates and exotic blends with various pesticides should be avoided with on-seed placement. Leaving nontreated check strips are highly recommended.

For transplants, the conventional preplant rates fit into the program. Placement would be deeper and could be offset to the side slightly to reach developing roots growing out of the root ball. While not exact, maintaining dilute solutions of a material like 10-34-0 at rates of 8 gallons per 400 gallons of water per acre are reasonable when fertilizing with the transplant water. Solutions with K salts should be avoided.

Fertilizer Timing: Regardless of irrigation technique, most P is applied preplant, usually in a banded application. Where drip irrigation is used, N and K (if needed) are applied in numerous small fertigations throughout the season. In conventionally irrigated fields, N and K (if needed) are applied preplant and in one or more sidedress applications. Supplemental foliar feeding of N, P and K have had little economic benefit and impact on processing tomato production.

Summary: Even in 1979, the respected UC Cooperative Extension processing tomato team of Bill Sims, Mel Zobel, Don May, Bob Mullen and Phil Osterli realized in their numerous field tests "there would have been few crop failures even if only starter fertilizers had been applied." In general the soils in our Central Valley are fertile. For profitable tomato production, a little starter fertilizer and a moderate level of sidedress N are sufficient. Our production system is not bottlenecked due to lack of applied N.

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