The Efficiency of Nitrogen Fertilization of Spring Wheat Depending on Seasonal Rainfall

Aims: The main objective was to determine the influence of nitrogen fertilization on spring wheat grown after catch crops or without them.

Study Design: The split-plot experimental design with four replications was used.

Place and Duration of Study: A field experiments were carried out in the years 2005-2008 at Mochełek (17º 51′ E; 53º 13′ N) – an Experimental Station of the University of Technology and Life Sciences in Bydgoszcz.

Methodology: A two-factor, field experiment was conducted on Alfisols formed of a sandy loam in the north-central Poland. The N rates were [kg·ha-1]: 0, 40, 80, 120, 160. The second factor was the catch crops – that were investigated – field pea (Pisum sativum var. arvense L.), oilseed radish (Raphanus sativus var. oleiformis L.), and a control without a catch crop. The main studied features were spring wheat yield and its components, depending on nitrogen rates. Moreover the most economic rate of nitrogen for spring wheat in years with different amount of rainfall were calculated.

Results: The optimal rate of nitrogen in spring wheat cultivation depended mainly on the total precipitation that prevailed during its growth. The highest grain yield of this plant grown after catch crops could be obtained applying 140-160 kg N∙ha-1 in the year with a very good supply of rain water and 41-42 kg N∙ha-1, in the extremely dry year.

The effect of catch crops on the yield of spring wheat depended on the rate of nitrogen. Very large increase in grain yield was obtained when no nitrogen was applied. After the application of 120 and 160 kg N∙ha-1 there was no effect of catch crops on spring wheat productivity.

Conclusion: The most economic rate of nitrogen for spring wheat was lower than the agronomically optimal rate by about 30% in the year with a favourable rainfall distribution. In the extremely dry year, the nitrogen fertilization of spring wheat grown after catch crops was economically unjustified. The effect of catch crops on grain yield was positive only in spring wheat fertilized with nitrogen at a rate of up to 80 kg∙ha-1.