After having long discussions with other fellow researchers and agronomists, I have yet to find an answer to this question. I've read many papers that mention positive impacts of N fertilisation in water limited environments (i.e. Barraclough, P. B., Kuhlmann, H., & Weir, A. H. (1989). The effects of prolonged drought and nitrogen fertilizer on root and shoot growth and water uptake by winter wheat. Journal of Agronomy and Crop Science, 163(5), 352-360), while others mention that this would happen in wetter areas (more than 300 mm of annual precipitation; Sadras, V. (2002). Interaction between rainfall and nitrogen fertilisation of wheat in environments prone to terminal drought: economic and environmental risk analysis. Field Crops Research, 77(2-3), 201-215). I understand that increasing the Nitrogen nutrition index of any crop would result in increased water used efficiency. Thus, if water is scarce and we can use it more efficiently by increasing N fertilisation, this would be a preferred choice.
What are your ideas on this matter? Should farmers increase or decrease N fertilisation in dry years?
Dear Jose
Generally, the application of Nitrogen fertilizer improves the efficiency of roots to explore the soil and, therefore, the drought avoiding capacity of plants. checking attached paper could be useful:
Please consult our review: Article Nitrogen Nutrition, Its Regulation and Biotechnological Appr...
Jose, I know very little about this topic but it might be helpful to think about the general principles. To an extent you've answered the question yourself by observing that there is no single answer.
With sufficient soil moisture plants will root relatively deeply, which is likely to benefit them in a future dry season (assuming the plants are perennial). On the other hand, a possible increase in the shoot-root ratio in fertilized plants could increase their susceptibility to drought (at least sudden drought), and the fertilizer could accelerate the decomposition of soil organic matter and reduce soil moisture retentiveness. The same sort of uncertainties arise within a season, but presumably the drier the season, or the quicker the onset of seasonal drought, the greater these kind of risks.
Clearly there will be important interactions with soil type and agronomic factors, particularly cultivation history/practice as it affects root impedance and rooting depth, and the nature of any weed competition. So to conclude - be careful about drawing general conclusions from your field trials!
Philip
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