Responses of a Forage Hay Crop to the Residual Effects of Nitrogen and Phosphorus Fertilizers in On-Farm Trials in Northern Syria

Abstract

Fourteen on-farm sites used in barley fertilizer trials were retained for a second year and, without further fertilizer, sown with a mixed vetch/barley forage crop. Rainfall at the sites ranged from 149 to 451 mm, and linear regression on rainfall accounted for 76% of the variation in hay yield between the sites, with a greater rain-related increase in vetch than barley. Soil nitrogen and phosphorus content at planting time in the second year was significantly affected by the rate of fertilizer application in the previous year. Previous phosphate fertilization tended to increase hay yields, particularly at sites where levels of native available phosphate were poor. However, responses to residual fertilizer nitrogen were small and variable