Balancing nutrient pools

Edward Crompton, a soil scientist now deceased, introduced the term 'Grow the soil to grow the grass'. Behind this phrase was the idea that we need to know about our soils in considerable detail, and to be able to match soils well to particular uses. One of the challenges is to learn to put whatever nutrients in the soil are necessary to support a particular crop or range of flora without creating excesses that can be washed over the soil surface or down through and out of the bottom of the soil where they then cause problems for the wider environment.

Certainly where agriculture is concerned we need to be increasing crop production worldwide to ensure that we can feed the growing population. But this has to be done in a sustainable way and in a way that safeguards the environment. We now know a lot about our soils. Farmers, in particular, from years of experience know a great deal about their soils. Hopefully we are past the period when hugely excessive amounts of fertilisers are added to the crops, achieving high yields, but setting up a system whereby excess nutrients leave the soil to cause problems in the wider environment. We need to manage the nutrient cycle more specifically, putting on just enough fertiliser to meet the crop's requirement without adding an overdose. Both economically and environmentally this makes sense. We should 'grow the soil to grow the crop'. We need to manage the nutrient cycle more carefully.

It is also important to consider how fertilisers are being used in parts of the world that are still trying to develop their agriculture. In many parts of Africa farmers are unable to afford fertiliser. The fertility of many of the soils gets less and less as farmers struggle to obtain crops from their land but are unable to afford to replenish the nutrients. Under this agricultural practice where nutrients cannot be put back in the soil, there is a downward spiral for crop production in many areas where food is desperately short. As attempts continue to raise crops to provide food for the people to eat, so the soils continue to weaken, not only because of low nutrients but also their proneness to erosion. This is a different type of dilemma to that facing the farmers in the more affluent developed countries - it is one of underfertilisation of the precious soils rather than overfertilisation. Both problems need to be addressed.