AGRI-BRIEFS   AGRONOMIC NEWS ITEMS

From Agronomists of the Potash & Phosphate Institute 655 Engineering Drive, Suite 110 Norcross, Georgia 30092-2837 Phone (770) 447-0335

Fall 2001, No. 7

Balanced fertility results in increased nutrient use efficiency and therefore less likelihood of nutrient loss to the environment due to leaching and/or runoff. This effect has been demonstrated in a long-term irrigated corn study in western Kansas. Yearly application of phosphorus fertilizer at a rate of 40 pounds P₂O₅ per acre increased average nitrogen use efficiency by more than 40 percent over the first 30 years of the study. This resulted in less residual nitrogen in the soil where phosphorus was applied, thus less chance of fertilizer nitrogen entering groundwater or surface water. In fact, at the economic optimum nitrogen rate, (160 pounds per acre), there was 66 percent less nitrate-nitrogen in the upper 10 feet of soil after 30 years of production where phosphorus was applied.

Crop water use efficiency (WUE) is improved by adequate and balanced fertility since more yield can be produced with the same amount of water. A well-fed crop produces a healthier and more extensive root system that is capable of extracting water and nutrients more efficiently than a nutrient deficient crop. The effect of fertilization on WUE has been clearly shown in numerous studies across the country. For example, a recent southwest Texas irrigated ryegrass study showed that nitrogen fertilization alone increased WUE by as much as 90 percent. Where nitrogen and phosphorus applications were balanced, WUE was increased by over 200 percent. This research was conducted in an area where there is increasing competition between large cities and agriculture for limited groundwater resources. The long-term benefits of balanced fertilization to the urban population, not to mention the producer, are obvious.

Several other environmental concerns are affected by balanced fertility. Increasing levels of soil organic carbon can reduce atmospheric enrichment of the greenhouse gas carbon dioxide. Balanced fertility management, as well as other management practices such as reduced tillage, can play a positive role in increasing carbon sequestration from the atmosphere by crops and storage of carbon in soils.

Good fertility management also reduces the potential for soil erosion by producing a more healthy and vigorous crop that closes the canopy and covers the soil more rapidly. It also ultimately provides more surface residue that may reduce the potential for erosion and nutrient runoff into surface water. Additionally, high yield production and the fertilizer inputs it requires reduce the total number of acres necessary for agriculture, thus rendering more land available for recreational purposes and wildlife habitat. This benefit becomes increasingly important as world population grows.

While adequate and balanced fertilization certainly has distinct environmental protection benefits, it’s important to remember that misuse of nutrients can lead to impairment of the environment. Best management practices such as soil testing and proper fertilizer placement and application timing are necessary to maximize the benefits and minimize the potential for damage.