The Influence of Nitrogen on the Growth and Maturity of Onions Grown on Organic Soil1

Abstract

Field experiments were conducted on organic soil for 3 years using relatively high rates of N to evaluate the influence of N on the growth and maturity of onions. In 2 years with low rainfall, maturity was not influenced, but yields declined with increasing rates of N. The decline in yield was originally attributed to ammonium toxicity, but observations with 3 sources of N indicated that high concn of fertilizer salts also could have caused injury to the plants. With high rainfall, yields increased with each increase in N, and as much as 240 lb. of N/acre was required for normal growth and maturation, while those onions receiving less than 120 lb. of N/acre were deficient in N and failed to mature properly. Utilizing different methods of incorporating N in the soil to evaluate the toxic response to N was unsuccessful in the wet season. Some indication of injury to the young seedlings occurred with the highest rates of N banded beneath the row, but these symptoms disappeared during subsequent periods of high rainfall.

Nitrogen-water Relationships of Onions Grown on Organic Soil1

“…With irrigation, increasing N levels increased yield and stimu lated earlier maturity. This response was obtained previously in the wet seasons (5) and is similar to other reports (4, 8) that onions will mature earlier with N applied in excess of that required for maximum yield. Yields with the greatest amount of N were equal to or greater than the corresponding treatments grown without irrigation suggesting the desirability of supply ing the crop with regular moisture to obtain maximum effec tiveness of N applications.…”

“…The response of onions to N applications with high and low moisture levels in this study was similar to that obtained pre viously with onions grown in different wet and dry seasons, that is: increasing N rates increased yields in the wet season but had no effect on or decreased yields in the dry season (5). Since seasonal differences other than moisture were difficult to evaluate in the previous study, this research was conducted with wet and dry conditions in the same growing season.…”

“…The effectiveness of N applications to onions grown on organic soil is determined by the amount of moisture received by the crop. Previous research (5) indicates that onions grown with varying amounts of N without adequate rainfall mature uniformly although yields may be reduced with high N appli cations. However, with adequate or excessive rainfall, increasing amounts of N are required for optimum growth and maturity.…”