Nutrient, Labor, Energy and Economic Evaluations of Two Farming Systems in Iowa

Farmer-researcher partnerships are needed to ensure soil and crop management practices are productive, environmentally safe, economically sound, and socially acceptable. We developed a farmer-researcher partnership to compare nutrient, labor, energy, and economic budgets for two “conventional” 40-acre fields where a 2-yr corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation is used with those for two adjacent fields where a 5-yr corn, soybean, corn, oat (Avena sativa L.), and hay rotation is used. Conventional fields received commercial fertilir and herbicides. Alternative fields received no herbicides and a mixture of animal manure plus municipal sewage sludge as the primary nutrient source. A 10-yr nutrient budget suggests that N, fixation would have to provide at least 53% of the N removed by soybean grain to prevent depletion of soil organic matter or other soil N sources from conventional fields. By assuming similar amounts of N fixation in the alternative fields, we show that 962 Ib N/acre, 244 Ib Placre, and 844 Ib Wacre were applied (or fixed) in excess of crop removal. Soil-test P, K, and organic matter changes reflect these applications. More fieldwork hours per acre per year were required to handle manure, avoid using herbicides, and harvest hay than to use conventional practices. Energy budgets were dependent on whether nutrients in the manure plus municipal sludge were considered as (i) an input cost for the crop, or (ii) a disposal cost that should be charged against an animal enterprise. Economic budgets were dependent on assumptions made regarding how to account for management costs. Overall, developing farmer-researcher partnerships was an effective method for evaluating alternative farming systems. How do conventional and alternative farming practices affect nutrient, labor, energy, and economic budgets on two central Iowa farms? This question was asked because the effects of alternative soil and crop management practices must be quantified to help identify agronomically productive, environmentally safe, economically feasible, and socially acceptable farming systems. The National Research Council's (NRC) Alternative Agriculture report was written to show that alternative farming methods were feasible and could be profitable. One criticism of the report was that the case studies were not supported by quantitative data. To obtain a better understanding of the complex interactions occurring between farming systems and the environment, it will be necessary to develop farmer-researcher partnerships in addition to conducting more traditional component research. This study was conducted on two adjacent 80-acre tracts in central Iowa that have been managed using conventional and alternative practices for several years. The alternative tract is part of the Richard and Sharon Thompson farm (Case Study no. 5 in the NRC report). Several component studies have provided quantitative information on profile N, water infiltration, aggregate stability, crop yield, and earthworm effects of the alternative farming practices; but nutrient, labor, energy, and economic assessments were needed to evaluate the economic feasibility and social acceptability (primarily labor requirements) of the practices. To make those assessments, a cooperative farmer-researcher partnership was implemented. What are the differences in the nutrient, labor, energy, and economic budgets for a well-managed conventional and alternative farming system in central Iowa? Nutrient budgets were developed for 1984 through 1993 by subtracting estimated crop removal from nutrient inputs supplied through commercial fertilizer or animal manure plus municipal sewage sludge. Estimated N-P-K application and removal by crops grown on the north and south fields under either management system differed by less than ±4% over the 10-yr. Our calculations show that more N was removed from the conventional fields than was applied through the fertilizer (Fig. 1). This was expected because the soybean crop was dependant upon residual nutrients from the fertilizer applied to the corn crop. Therefore, to achieve a simple N balance without depleting soil organic matter or other soil N sources, these data show that the soybean crop would have to obtain at least 53% of the N removed with the grain through dinitrogen fixation. Fig. 1A 10-yr N, P, and K balance, without including N fixation, for two conventionally managed (Conv.-North and Conv.-South) and two alternatively managed (Alt.-North and AM.-South) farming systems in central Iowa. For the alternatively managed fields, the total N that had to be accounted for in the fields receiving animal manure plus sludge was estimated by adding a similar N fixation credit for soybean and hay to the already surplus amount of N (Fig. 1). This required accounting for 962 lb N/acre, 244 lb P/acre, and 844 lb K/acre applied (or fixed) in excess of crop removal between 1984 and 1993. Soil-test records document increases in Bray P1 extractable P and ammoniumacetate exchangeable K, while excess N could be accounted for by higher soil organic matter concentrations in the alternatively managed fields. This increase was good for soil structure, but since organic matter releases N slowly, it may create a soil N reserve that is more difficult to manage for crop production than N supplied by inorganic fertilizers. Field time for the conventional operation averaged 1.06 h/acre per year, while for the alternatively managed fields, it averaged 1.90 Wacre per year. Increased labor was required for the alternative system because (i) more time was required to spread the manure and sludge than to apply commercial fertilizer, (ii) more cultivations were required to avoid the use of herbicides, and (iii) multiple harvests were required to include hay in the 5-yr rotation. This difference may be a factor that will influence a farmer's decision on adopting the alternative farming practices, especially if their operation involves large amounts of land or if they are committed to off-farm employment. Energy and economic budgets were highly dependent on whether the nutrients in the manure plus municipal sewage sludge were considered as an input cost for the crop or as a disposal cost to be charged against the animal enterprise. When averaged for the two extremes, there was little difference between the farming systems in estimated energy use. Economic assessments for 1989 through 1993, without including government deficiency payments for corn, showed that the return to management averaged $28.97/acre for the conventional operation and $30/acre for the alternative farming system in central Iowa. Economic comparisons at less than the whole farm level often assume that the management and labor requirement is essentially the same. For this study, however, the differences are important. The alternative system may have required more management because more crops were included, manure was used instead of commercial fertilizer, and more cultivations were used to avoid using herbicides. The $28.97 and $30/acre estimates for “return to management” were computed by subtracting estimates of all costs, including an arbitrary labor charge of $6h. With these assumptions, the difference in average economic return per acre for the two farming systems was small. However, by assuming the management requirement for both systems is the same and placing an arbitrary charge of $10/acre as a management fee, the direct crop labor cost would be $25.37/acre for the conventional system compared with $31.40lacre for the altemative system. Dividing the hours of direct crop labor for each farming system shows a return that is 44% greater for the conventional system ($23.82/hvs$16.53/h). The assumptions made with regard to computing the economic return for the two systems will undoubtedly reflect personal preferences. Overall, we conclude that both farming systems are sustainable based on the nutrient, labor, energy, and economic budgets. Furthermore, our results demonstrate the effectiveness of developing farmer-researcher partnerships to quantitatively evaluate the effects of alternative farming systems.