Farm Table says:
What is the problem?
A heightened focus on greenhouse gas emissions and the cost of N fertilizer has prompted greater attention to the efficient use of N fertilizers. While most cotton crops require N fertilizer to achieve high yields, producers must ensure that N fertilizer inputs are used appropriately analysis and/or in-crop tissue analysis. Because of the global consequences of greenhouse gas emissions, greater attention is being given to N fertilizer management.
What did the research involve?
Internal crop N use efficiency (iNUE) was measured within two N fertilizer rate experiments that covered a wide range of N fertility over six cropping seasons. Internal crop iNUE was determined by dividing lint yield by crop N uptake. No nutrients other than N limited cotton growth or yield and the crops were not drought-stressed. Crop NUE was measured over five cropping seasons within an N fertilizer rate experiment that provided a wide range of soil N fertility. The optimal N fertiliser rates were determined from fitted quadratic functions that related lint yield with N fertilizer rate for each cropping system in each year.
What were the key findings?
When the optimal N fertilizer rate was applied, crop iNUE averaged 12.4+0.3 kg lint/kg crop N uptake. The crop iNUE was then related to the economic N fertilizer rate N fertilizer rate to determine the degree to which N fertilizer was under or over-applied. Low iNUE values were a consequence of excessive N fertilizer application. Crop iNUE was determined in 82 commercial cotton crops in five valleys over the final 4 years of this study. Information on crop iNUE enables cotton producers to assess their N fertilizer management and adjust N fertilizer rates for future crops.
This study demonstrated that there is scope to substantially reduce N fertilizer inputs to Australian cotton fields without reducing yields.