Long-term agro-economic and environmental assessment of adaptive nutrient management on cropland fields with established structural conservation practices

Authors: Smith, Douglas; Harmel, Daren; Haney, Richard

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2019
Publication Date: 5/12/2020
Citation: Smith, D.R., Harmel, R.D., Haney, R.L. 2020. Long-term agro-economic and environmental assessment of adaptive nutrient management on cropland fields with established structural conservation practices. Journal of Soil and Water Conservation. 75(3):416-425. https://doi.org/10.2489/jswc.75.3.416.
DOI: https://doi.org/10.2489/jswc.75.3.416

Interpretive Summary: Conservation practices are often studied for their environmental impact; however, agricultural producers rarely adopt these practices based solely on their environmental performance. Thus, it is essential the information is available on both environmental and economic performance of conservation measures. The objective of this research is to report on the environmental and economic performance of adaptively managed agronomic and conservation practices that were a part of a 16-year study on poultry litter application to cultivated fields at the Riesel watersheds in Central Texas. One field was fertilized with commercial fertilizers, while the other five fields were fertilized with poultry litter with rates from 2-6 tons/ac. In 2009, nitrogen fertilizer rates were adjusted based on soil testing and in 2013, cover crops were introduced to minimize the amount of time the soil was left bare. Important results included: 1) Soil test recommendations that consider historical crop yields reduced N application but did not reduce profits; 2) interannual variability of economic and weather conditions contributed to the lack of statistically significant differences in profit, although profit reduction for high nutrient rate treatments was clear; and 3) litter application especially at rates in excess of crop P needs also increased runoff P losses indicating the need for careful management of organic nutrient sources. Results of this long-term study are important, because they showed that maintaining or increasing economic return does not have to be sacrificed to improve environmental impacts, which is an important consideration as producers make on-farm management decisions.

Technical Abstract: On-farm adoption of agricultural conservation practices or management alternatives depends on conservation ethic, social pressure, regulatory attention, and perceived impact on yield and economic return. Although agro-economic and environmental impacts are assumed to conflict, little research has been conducted to addresses potential tradeoffs and provide a scientific-basis for decision-making. Thus, this 16 yr evaluation of adaptive nutrient management was conducted on six fields with conservation practices already in place. Each field was randomly selected to receive either commercial fertilizer or poultry litter at rates of 4.5-13.4 Mg/ha. Two major nutrient management adaptations were made (i.e., soil test N rate recommendations in 2009, and reduction of fallow period length and cover cropping during prolonged fallow periods in 2013). Important results included: 1) Soil test recommendations that consider historical crop yields reduced N application but did not reduce profits; 2) interannual variability of economic and weather conditions contributed to the lack of statistically significant differences in profit, although profit reduction for high nutrient rate treatments was clear; and 3) litter application especially at rates in excess of crop P needs also increased runoff P losses indicating the need for careful management of organic nutrient sources. Results of this long-term study showed that maintaining or increasing economic return does not have to be sacrificed to improve environmental impacts, which is an important consideration as producers make on-farm management decisions.