Differences in response of winter cereal varieties to applied nitrogen in the field I. Some factors affecting the variability of responses between sites and seasons

Abstract

The grain yield response of a range of winter cereal varieties to applied nitrogen was studied in five experiments under a range of field conditions in northern Syria. Significant yield differences (P > 95%) were found between varieties in their yields at zero applied nitrogen and in their yields at higher levels of nitrogen. Differences were also found in yield responsiveness to applied nitrogen (grain yield per unit of nitrogen applied) and in the nitrogen rates required to reach maximum grain yield. However, meaningful differences in the latter parameter were difficult to measure unless about eight rates of nitrogen were used.

Factors observed to modify differences in varietal response to nitrogen were, soil phosphate supply, initial soil mineral nitrogen, and possibly seasonal factors such as water supply and temperature. As a consequence of some of these factors the responses of only about half the varieties tested in two experiments could be considered repeatable leading to the conclusion that relatively uniform conditions are required for experiments of this type. However, reproducibility of nitrogen characteristics under a range of field conditions is considered desirable in potential parental genotypes and testing over a number of seasons is suggested. Experimental conditions suitable for detecting differences in the field are also suggested