Nitrogen challenges in dryland agriculture
1997
El Gharous, M. (INRA, Settat (Morocco))
Nitrogen is the most spectacular of all essential nutrients in its effects on plant growth. Because of the transitory nature of N in soil, and its potential for becoming a pollutant of air and water, it should receive more care in its overall management than any other major or minor plant nutrient. In this paper, a few aspects of N management in dryland agriculture are reviewed. While the observations are largely based on the author's experience in Morocco, they are pertinent to the broad West Asia-North Africa region as a whole. The effect of N on crop production is well documented and has been discussed briefly in this paper. Methods of estimating crop N fertilizer needs are still not well developed and require more attention. Also, in relation to the estimation of the amount of N fertilizer to apply to a crop, more work is needed in order to determine the quantity of mineral N coming from soil organic matter during a growing season, and to improve N use efficiency. Spatial variability is another area of research which is not well documented in dryland regions. Nitrogen recommendations based on soil tests require a representative soil sample and appropriate soil testing methods. Furthermore, dryland regions are characterized by small farms with different management and this enhances physical and chemical spatial variability. Therefore, an appropriate soil sampling method which includes the number of soil samples to be taken per homogenous unit area, depth of the sample, and time of sampling is necessary. While much has been achieved in N research, some gaps in our knowledge remain to be refined and elucidated
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