What organic materials boost soil nitrogen?
Written by
Michael Sullivan
Reviewed by
Prof. Martin Thorne, Ph.D.Soil nitrogen can be replenished with organic materials such as aged manure and alfalfa meal without chemicals. I've revived depleted vegetable plots with the rate of 10 tons per acre of composted chicken manure at 2.8% N which doubled bean yield in 8 weeks. When using raw manure it will burn roots, so always age for 6 months before use.
Aged Manure
- 1-3% nitrogen depending on animal source
- Compost 6 months to kill pathogens
- Apply 4" layer pre-planting for 90-day N release
Alfalfa Meal
- 2.5% nitrogen + trace minerals
- Mix 5 lb/100 sq ft into topsoil
- Feeds microbes for 4-6 weeks
Worm Castings
- 1% nitrogen with 60% organic matter
- Top-dress 1/2" monthly for container plants
- Enhances water retention in sandy soils
Layer materials for prolonged nitrogen. The vineyard with which I consult applies 3" of composted manure (2% N) and 1" of alfalfa meal (2.5% N) under the vines. This combination provides a nitrogen release of about 120 days to take the need for synthetic mid-season applications out of play. Soil tests also show that nitrates remain stable around 30 ppm.
Don't overdo your worm castings as their 1% N is more effective in combination with legumes. One of my clients grew tomatoes in a greenhouse using 30% worm castings and 70% peat moss and they stayed compact until we added blood meal (12%N) to the program! So even organic growers need their formulations balanced.
Read the full article: Nitrogen Deficiency in Plants: Signs & Solutions
