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. The economic loss of lower crop yields has been compounded by lower quality and higher disease and pest incidence. The drop in cereal production has also reduced the availability of feed, leading to a substantial reduction in livestock numbers and the availability of manure as an alternative source of soil nutrients. Although Asia's crop production, as calculated by K removal, is more than half total production worldwide, it consumes little more than a quarter of global potash.