Presidedress Soil Nitrate Test for Fall Cabbage

Presidedress Soil Nitrate Test for Fall Cabbage

Summary

Summary
Efficient use of N fertilizer is important to achieve optimum crop yield, farm profitability, avoidance of water pollution, and conservation of natural resources. The Presidedress Soil Nitrate Test (PSNT) is commonly used to improve N management in field corn and sweet corn. Fall cabbage is planted after harvest of spring vegetable crops such as sweet corn, snap bean, and lettuce. These crops often leave significant amounts of carryover N in the soil. The PSNT may be useful to improve N management with fall cabbage (or other cole crops) grown as a “catch crop” to utilize residual N. Our 2-year study is evaluating the PSNT for use with fall cabbage adn determining the effectiveness of cabbage for utilization of carryover N from spring crops. Implementation of the PSNT by vegetable growers on an additional crop is expected to improve N recommendations, reduce nitrate leaching losses and enable more efficient, economically viable crop production.

Key Findings
The PSNT appears to have potential as a tool for predicting the need of fall cabbage for sidedress N and significantly reducing production cost. When sidedress N is not needed, the potential savings for cabbage is about 150 lbs. N/acre or $30.00/acre.

Indications are that cabbage is an effective crop for removing residual N from the soil, thus reducing the potential for movement of residual soil nitrate into groundwater.

Preliminary results indicate that the PSNT may be useful on crops other than corn, the crop for which this soil test was originally developed.

Objectives
1.Evaluate the usefulness of the PSNT to accurately identify N responsive and non-responsive fields planted in fall cabbage.

2.Measure fall cabbage yield response to fertilizer N rates following harvest of early season crops such as sweet corn, snap bean, or lettuce.
3.Measure recovery of residual mineral N from soil by fall cabbage.

Methods and Findings
Twenty-six field experiments to calibrate the presidedress soil nitrate test (PSNT) for use with fall cabbage were conducted in three states (New Jersey, Delaware, Connecticut). Cabbage yield response for each site appear to be closely related to the PSNT values. Most field sites had low PSNT values due to excessive rainfall. PSNT values less than 15 ppm NO3-N exhibited significant cabbage head yield responses to sidedress N fertilizer. PSNT values greater than 30 ppm exhibited no response to sidedress N.

Results already suggest that the PSNT should be useful to predict the need of cabbage for sidedress N. However, additional calibration data is needed, especially from sites having PSNT values in the range of 15 to 30 ppm.

Total N uptake for fall cabbage may be as high as 190 lbs. N/acre. This indicates that cabbage is an effective crop for removing residual N from the soil.

Most of the field trials followed the harvest of an early sweet corn crop. Three trials were planted on summer fallowed land. The weed control program for sweet corn used herbicides that would allow the fields to be cropped to fall cabbage. The sweet corn plant populations averaged 22,000 plants/acre. Nitrogen fertilizer applied to the sweet corn included 20 lbs. N/acre with the corn planter and 100 to 150 lbs. N/acre sidedressed when plants were about 12 inches tall.

After the fields were completely harvested of marketable ears, the corn stalks were chopped and plowed under to prepare the soil for cabbage. Fertilizer was broadcast at 100 lbs. K/acre, 50 lbs. S/acre, and 2 lbs. B/acre and incorporated with tillage. Cabbage (CV. Blue Bayou) bedding plants were grown in the greenhouse before being transplanted to the field between August 1 to 15.

While in the greenhouse the bedding plants were fertilized weekly with Miracle-Gro 15-30-15 and one final application was made immediately before transplanting into the field. Zero N fertilizer was applied to the field soil at the time of transplanting.

Between two and three weeks after the cabbage was established in the field, PSNT soil samples were analyzed for nitrate and ammonium. Sidedress N rate treatments (0, 40, 80, 120, 160 lbs. N/acre) were applied following PSNT sample collection. Cabbage heads were harvested in late October and early November.
Reported December 1997.

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