Guest Commentary: Fertilize More Efficiently to Benefit the Environment

November 8, 2018 1:49 PM0 comments

By Lynton S. Land

Despite decades of concern, beginning seriously with the passage of the Clean Water Act in 1977, water quality improvement in the Chesapeake Bay after 40 years is disappointingly small.

Most of the action has been focused on reducing urban point-source pollution — wastewater treatment plants, that is. The reason water quality has not improved significantly is simple. The largest source of pollution, inefficient crop fertilization, has never been meaningfully addressed.

Farmers, supported by the powerful agricultural lobby, seek to maximize their harvest (profit) without paying for the pollution they cause. Society benefits from the cheap food they produce. Most of the grain produced in the Bay watershed feeds animals raised for meat, not humans.

What must be done to ensure that water quality improves significantly, indisputably and permanently? The answer is the same worldwide — fertilize more efficiently so crops use more of the applied nutrients, thus reducing environmental nitrogen and phosphorus pollution.

All scientific publications stress that continued nutrient reduction is necessary if additional Bay water quality improvement is to be realized. Reduced nutrient pollution cannot continue to focus on urban areas. That low-hanging and expensive fruit has already been picked.

Reducing pollution from chemical crop fertilization is necessary, although many complex issues are involved. How many people know that conventional chemical fertilization efficiency is typically no better than about 65 percent when the fertilizer is applied at the time of planting?

Fertilizer application should closely match plants’ needs throughout the growth cycle. This has been expressed as the “4 Rs” – apply fertilizer from the right source at the right rate, at the right time and in the right place.

That is easier said than done. Applying fertilizer in increments as the plants grow is more efficient than a single-application at the time of planting. Controlled- (timed-, delayed-, stabilized-, encapsulated- or slow-) release fertilizers can significantly increase fertilization efficiency, but they are more expensive. Could they be subsidized?

Chemical crop fertilization will always be “leaky,” but it can be made much more efficient. Modern encapsulated fertilizer, on-the-go variable rate applicators and strains of grain that scavenge nutrients and use less water can raise fertilization efficiency considerably. Rotating a variety of crops, producing biofuels from perennial crops instead of corn can also considerably reduce nutrient pollution, as can vegetative buffers alongside creeks and rivers.

The 2005 Virginia Cooperative Extension On-Farm Corn Test Plots Report documents an average yield of 174 bushels of grain per acre using 192 pounds of nitrogen fertilizer for an efficiency of 64 percent. In the 2015 report, yields increase to 214 bushels per acre using only 168 pounds of nitrogen fertilizer for an efficiency of 89 percent. The extent to which these “test plots” reflect average fields is unknown, but the data show conclusively that a significant increase in chemical fertilization efficiency is possible. The fertilization efficiency of small grain test plots also increased over the same decade, from 57 percent to 76 percent.

But none of that gets at the problem of massive pollution from the disposal of manure by land application. Manure is an extremely inefficient fertilizer because the nutrients, nitrogen and phosphorus, must be released from organic compounds by microbes in order to be available to the crop. Nothing can be done to change that or to increase the efficiency of the fertilizer. When sewage sludge is applied to land in Virginia, it is assumed that only 30 percent of the nitrogen will be available to the crop. Most of the remaining 70 percent of the nitrogen causes pollution, amounting to hundreds of pounds of nitrogen per acre.

The phosphorus “cap” is astronomical, so all of the phosphorus is disposed whether the crop needs it or not. Lawmakers are obviously more concerned with the profits of the manure producers and a few farmers than they are about water quality. They need to be held accountable.

Current permissive and complex regulations that permit phosphorus disposal in excess of crop needs are merely excuses for cheap waste disposal. The simplest fix would be to limit the land application of poultry litter, sludge and manure to the amount actually needed by the crop, as determined by soil analysis. This waste can be a source of methane that will not contribute to global warming, even from a properly designed landfill.

Urban areas bear most of the burden of Bay nutrient reduction because wastewater and stormwater are regulated. Bay water quality can only improve significantly when the largest source of pollution, crop fertilization, becomes much more efficient.

Every study concludes that the worth of a healthier Bay based on the value of seafood, recreation and property far exceeds the worth of the most highly polluting agricultural entities. Anyone, including nongovernmental organizations and elected officials, who wants real improvement in Bay water quality should actively advance the strategy to ban manure.

Unless there is a groundswell of focused opposition to the most easily addressed source of substantial Bay pollution, the land application of manure will continue for the usual political reasons, and improvements in Bay water quality will remain small.

 


Lynton Land, for the Bay Journal News Service, is emeritus professor of geological sciences at the University of Texas in Austin. 

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