Fossil energy use in conventional and low-external-input cropping systems

Abstract

ErratumERRATUM low-external-input and conventional systems to refl ect the updated data set, as well as changing the primary energy input category from grain handling to fertilizer. Th e corrections change the quantitative results reported in the publication, but with the exception of a shift in the relative importance of grain handling and fertilizer, the general pattern of results and conclusions remains the same.My coauthors and I sincerely apologize for the error in the publication. -Michael CruseABSTRACT Conventional agriculture production systems in developed countries rely heavily on fossil energy, but emerging uncertainties in fossil fuel supply indicate a need to better understand energy effi ciency in conventional and alternative systems. We used 6 yr of data from a cropping systems experiment conducted in Iowa to compare energy use of a conventionally managed corn (Zea mays L.)soybean [Glycine max (L.) Merr.] system (a 2-yr rotation) with two low-external input (LEI) cropping systems that used more diverse rotations and manure, but substantially lower quantities of synthetic N fertilizer and herbicides. Depending on how fossil energy costs were assigned to manure, the two LEI systems (a 3-yr rotation of corn-soybean-small grain/red clover (Trifolium pratense L.), and a 4-yr rotation of corn-soybean-small grain/alfalfa-alfalfa, Medicago sativa L.) used between 14 and 53% less fossil energy than did the conventional system. In general, the primary category for fossil energy use was fertilizer. Th e conventional 2-yr system used substantially more fossil energy embodied in synthetic fertilizers and pesticides than did the LEI systems. Economic return, harvested crop weight, and potential energy production of the conventional 2-yr and LEI 4-yr systems were similar. Effi ciency ratios, including crop energy output and economic return per unit of fossil energy invested, were signifi cantly higher in the LEI 4-yr rotation than in the conventional system. In coming years, if fossil energy prices rise signifi cantly without concomitant increases in crop value, diversifi ed LEI systems may become preferable to conventional cropping systems and used more widely.

Using biodiversity to link agricultural productivity with environmental quality: Results from three field experiments in Iowa

“…Results of the experiment indicated that corn and soybean yields from the more diverse 3-and 4-year systems were higher than those from the conventional system, despite substantial reductions in the use of synthetic N fertilizer and herbicides [36][37][38] (Table 1). Fossil energy use decreased with increases in crop diversity due to reductions in the use of fertilizers and pesticides, gas to dry grain, and liquid fuel to power farm machinery 37 (Table 1). Weed suppression was highly effective in each of the three cropping systems as reflected by the very small amounts of weed biomass found in corn and soybean phases of the rotations 36 (Table 1).…”

“…Systems in which livestock are concentrated at high densities and isolated from the land base producing the crops that feed them are often characterized by high levels of pollution 114 . In contrast, integrated crop-livestock systems, including the diversification of cereal-based rotations with forage crops, the local application of manure, and pasture-based production, are likely to play an important role in reducing water contamination, soil erosion and fossil fuel dependence in agroecosystems, while maintaining high levels of productivity and profitability 13,37,[114][115][116] . With appropriate forms of crop diversity and integrated management systems, livestock products might be generated in a manner that permits food security to coexist with ecosystem integrity.…”

“…Choices of herbicides used in each system were based on the identities, densities and sizes of weed species observed in the plots. Sampling procedures and other details of farming practices used in the different cropping systems during 2003-2010 are described in Liebman et al 36 , Cruse et al 37 and Gómez et al 38 . Results of the experiment indicated that corn and soybean yields from the more diverse 3-and 4-year systems were higher than those from the conventional system, despite substantial reductions in the use of synthetic N fertilizer and herbicides [36][37][38] (Table 1).…”

“…Sampling procedures and other details of farming practices used in the different cropping systems during 2003-2010 are described in Liebman et al 36 , Cruse et al 37 and Gómez et al 38 . Results of the experiment indicated that corn and soybean yields from the more diverse 3-and 4-year systems were higher than those from the conventional system, despite substantial reductions in the use of synthetic N fertilizer and herbicides [36][37][38] (Table 1). Fossil energy use decreased with increases in crop diversity due to reductions in the use of fertilizers and pesticides, gas to dry grain, and liquid fuel to power farm machinery 37 (Table 1).…”

“…Harvest of alfalfa hay and concentrated feeds allowed integration with livestock production and fostered nutrient return to cropland through the application of manure 36 , further reducing production costs and fossil energy consumption 37 . In studies conducted by Randall et al 27 and Drinkwater et al…”