As I’ve reported here a number of times, input prices for farmers have been rising steadily. If the economy collapses, we can expect those prices to decline – but commodity prices will also likely decline in that eventuality, leaving farmers in the same boat. If the economy recovers – everybody cross your fingers – then inputs are likely to continue increasing as a share of farm operational costs.

With that in mind, many farmers have begun exploring their options regarding fertilizer use, with an eye toward reducing use to the necessary minimum. While this can save quite a bit of money, it is important for farmers to be aware of the risks of reducing fertilizer inputs beyond a certain point. Most farms probably do have some “slack” in the fertilizer budget – but it’s critical not to cut out too much. Suboptimal fertilization levels can have detrimental impacts on yield, stress tolerance, and standability of crops.

One principle to follow – believe the science. Soil tests provide hard data, not just a general “feel” for how soil is developing, and should be done by any farmer planning a reduction in fertilizer input. Don’t assume that a test result will stay valid over time, however – remember that every plant harvested is taking some nutrients out of the soil. Even if your soil has a buffer of built-up fertilizing agents that might allow you a light year for new applications, that won’t necessarily apply during the next growing season.

Another thing to bear in mind is that different crops remove nutrients at different rates. Just one bushel of corn removes 0.29 pounds of K2O and 0.4 pounds of P2O5, while a bushel of soybeans on the same land will remove 1.45 pounds of K2O and 0.85 pounds of P2O5. Know the figures for the crops you intend to grow, and take that into account in your fertilizer plan.

Aside from direct fertilizer use, remember that pH levels will have an impact on the bioavailability of existing (and added) nutrients. If you fail to apply enough lime, absorption rates for N, P and K can decrease, sometimes dramatically. The pH must be 5.9 or higher for N and K, and 6.4 for P. A low pH level can also increase the risk of herbicide carryover for imidazolinone-based applications.

The consequences of low fertilizer levels can be quite devastating to a crop, particularly if the weather doesn’t cooperate. Insufficient P doesn’t produce many immediately visible effects, which may lead you to conclude that levels are adequate, but P levels directly affect the ability of your plants to handle stress. Insufficient K levels mean that plants have a harder time absorbing water and nitrogen from soil, which makes the crop more vulnerable to drought conditions. In soybeans, inadequate K can cause reduced nodulation and increased damage from disease and pests.

To summarize, decreasing your fertilizer application may well decrease your cost – but it may not improve your bottom line if you aren’t careful. It doesn’t make sense to knock $50,000 off the fertilizer bill if it means your stunted crop brings in $60,000 less than last year. Check soil levels carefully and accurately calculate the nutritional needs of your planned crop before taking this step.