How well is your nitrogen managed?

Well for some crops, especially some horticultural crops the end of the season is fast approaching. As the harvesters run it may be a good time to reflect on the success and status of your nitrogen management program.

Nitrogen, although not the largest input cost in horticultural production should be managed to achieve maximum profit while minimizing environmental loss. The fall may seem like an unlikely time to reflect on nitrogen management, but from an environmental point of view it represents the time when there is the most risk of loss of nitrogen to groundwater. A term we often use in nutrient management to determine the risk of nitrogen loss to the environment is "residual soil nitrogen". This is the amount of nitrogen left in your soil after your crop is harvested. Residual soil nitrogen can come from two sources. One is the nitrogen left in the soil solution surrounding the root zone of your crop. This nitrogen is left over from fertilizer applied during the growing season. The second source of residual soil nitrogen is the crop residue remaining in the field. In horticultural crops this residue is normally very lush and green and can have a C:N ration of less than 25:1. This material contains much more nitrogen per tonne than any field crop residue that typically have C:N ratio ranging from 50-100:1. Research has shown that nitrogen rich horticultural residues can break down and release up to 100 lbs of N per acre over a 3 week period after harvest. This pulse of N is released at a time of year, when the soil moisture and aquifers are being recharged.

Managing fall residual soil nitrogen is key to maintaining ground water quality in horticultural production systems.

Growers to solve this problem have adopted several creative management strategies. One of the most successful has been to remove crop residue from the field, compost the residue with high carbon materials, such as straw and return the nitrogen and carbon back to the fields in a more stabilized form. In compost, the nitrogen is not as readily available for loss to groundwater, but is still available for next year's crop.

Another way is to incorporate a cover crop into your production system that can take up the residual soil nitrogen left in your field after harvest. Cover crops don't work in all rotations, but any growth and nitrogen uptake you do get, will at least keep the nitrogen higher up in your soil profile, keeping it away from groundwater longer.

Good management of residual soil nitrogen is the key to successful nutrient management in horticultural crops.

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