Seasonal and Soil Fertility Effects on the Response of Waterlogged Cotton to Foliar‐Applied Nitrogen Fertilizer

The majority of irrigated cotton ( Gossypium hirsutum L.) soils in Australia are poorly drained, and the short‐term waterlogging associated with extended furrow irrigation reduces cotton yield, partly by reducing the uptake of N. Foliar application of N before irrigation can overcome a transient shortage, but yield responses have been variable. Seasonal and soil N fertility effects on the response of waterlogged cotton to foliar‐applied N fertilizer were studied over three seasons at Narrabri, N.S.W., Australia. A cracking grey clay soil (Typic Pellustert) was waterlogged by furrow irrigations lasting 4 to 32 h. Climatic and soil fertilizer conditions included a cool, moist season with optimal soil fertilizer N; a hot, arid season with high soil fertilizer N; and a hot, arid season with a wide range of soil fertilizer N. Foliar N was applied at 0, 5, 10, and 20 kg ha −1 in the first season, 0, 15, 30, and 60 kg ha −1 in the second season, and 0, 60, 120, and 180 kg ha −1 in the third season. Increased waterlogging reduced N uptake and lint yield. Nevertheless, there was no response to foliar N in the cool, moist season because factors other than N limited growth and yield whether or not N was supplied to the foliage. Lack of response to foliar N in the hot, arid season with high soil N fertility was attributed to high uptake of N (163 kg N ha −1 ) by untreated shoots, which compensated for reduced uptake by the roots during waterlogging. A three‐factor interaction in the third season confirmed that more cotton yield was recovered by applying foliar N under more severe waterlogging when soil N levels were not high. At N rates of 120 and 180 kg ha −1 , shoots recovered more soil‐applied N than foliar‐applied N. Recoveries were similar at 60 kg N ha −1 . The results confirmed that foliar N can ameliorate the effects of waterlogging in cotton, defined some of the conditions under which responses to foliar N occur, and explained some of the variability in response to foliar N found under commercial conditions.