Many organic vegetable producers have been relying heavily on livestock composts as a source of fertility on farms. Often, high rates of compost are applied to meet the nitrogen (N) needs of crops. When this strategy is implemented, it can lead to over application of phosphorus (P) and potassium (K). As an example, a grower may apply poultry manure at 6 tons ac-1 per year to supply vegetable crops with adequate N. This can contribute as much as 180 lbs ac-1 of P per year, where vegetable crop removal of P ranges from 10-80 lbs ac-1 per season. In this scenario, there is an over application of P, leading to an excess of 100 lbs ac-1 of P or more each year the poultry manure is applied. This type of application rate can cause rapid build-up of P in soil and subsequently increase the potential risk of P loss to nearby surface water. Phosphorus loading and associated risk of loss depends on many factors including soil type, slope, and proximity to water. However, with impending water quality regulations, farmers will be required to account for their nutrient balance and work towards minimizing potential nutrient losses into the environment.
Vermont, University of Vermont
Darby, Heather; Gupta, Abha; Cubins, Julija; Emick, Hillary; and Ziegler, Sara, "Vegetable Fertility Management Trial" (2016). Northwest Crops & Soils Program. 185.