Crops respond quickly, growing taller, greener and more lush.
From the '70s to the early '90s, many farmers fed their fields with more nitrogen than was removed in harvested crops. And, in the last few years, the upward trend in the use of nitrogen fertilizer has resumed. Phosphate use reveals a similar story but potash tells a different tale. Global trends are interesting and may be informative, but nutrient need and, more particularly, fertilizer use, depend on factors that have more relevance at a regional level. Whether farmers apply fertilizers or not, and whether they have the necessary knowledge, money, credit or, indeed, whether fertilizers are locally available, depends as much upon political and economic history as in the inherent fertility of their soils or the nutrient demands of their crops.