Maintaining soil fertility is an important step in creating a sustainable agriculture. Before stating how soil fertility is maintained, the causes of soil fertility decline must be stated.
Farmers mine soil. In natural ecosystems soil minerals basically stay in place. Trees uptake minerals, pass the minerals to the leaves, and the leaves fall back to the earth where the process starts all over again. Farmers remove the crops before the minerals can be replaced in the soil. There are ways to lesson the mineral loss, but there is no way to stop it from happening completely. Minerals must be replaced from the outside.
The first method to replenish minerals is through the application of fertilizers. There are two basic types of fertilizers organic and inorganic. Organic fertilizers are derived from organic matter, while inorganic fertilizers are generally mined and processed. Both types of fertilizers are required.
Synthetically made oganic fertilizers are also used. These fertilizers work well in producing crops. There is a concern that while the synthetics add similar beneficial minerals that other fertilizers do, they also may add other undesireable molecules. The benefit of their use is their low cost and ease of application.
NPK stands for the most important three minerals that must be present for crop growth. These are nitrogen, phosphorous, and potassium.
Different crops remove different amounts of minerals. Bananas which are known to be high in potassium, remove high amounts of it. This potassium must be replaced. Corn depletes high levels of maganese.
One problem environmentalist have with fertilizers is that agricultural run-off can be disasterous to water ecosystems. If an overbundence of nutrients is located within a water source, eutrophication can set in. The water's oxygen content is used up by microbial organisisms and fish die-off. Since fertilizers are highly necessary, improvements in its application are necessary to reduce collateral ecological damage.
Precision agriculture is developing which will hopefully reduce ecological damage from agricultural practices. Precision agriculture is the process of braking farm plots into small sections and analysing them to find out what sections need certain fertilizers and pesticides. Chemical applications are expensive, and if farmers can use more exact amounts of what is required, then farming will be cheaper and less damaging run-off will result.
Crop rotation is also used to decrease mineral deficiency. Different crops use and replenish different minerals. By rotating crops the some mineral loss is decreased. Crop rotation is not always economically feasible, but if it is, three common crops to rotate in the Mid-West is corn, soybean, and a legume. This lessons the need for fertilizer in-put, but it does not completely solve the problem.
Farmers can also leave crop residue on the field after harvesting. As in erosion control, farmers can leave corn stalks on the field. The minerals within the corn stalks decompose back into the soil. Again, the farmer must apply more pesticides with this procedure.
Placing mulch on fields and letting fields lie fallow for a season helps to replenish their vitality. The problem with this is that a fallow field earns no income yet carries cost. Mulch requires more labor and time. Farmers cannot work as much land with mulching systems. Mulch also works better in sandy soils than heavy clays. Timing is also critical in mulching. If mulch is applied to early and covers a plant, its growth can stunted. One benefit of mulching is that it can smother out competive plants.
To maintain yields soil fertility must be maintained. Alternative methods to fertilizer can reduce the need for fertilizers, but they cannot eliminate the need. Precision agriculture will help reduce damage caused by agricultural run-off.