Relative yield of food and efficiency of land-use in organic agriculture - A regional study

Abstract

CONTEXTMost information on relative yield of organic (OA) and conventional agriculture (CA) is from plot experiments of individual crops grown with organic or inorganic fertilizers, respectively. Commonly reported values are 0.75–0.91, a relatively small difference. But organic manures are produced through biological nitrogen fixation (BNF) by legumes. How much and what else does that land in legumes contribute to overall yield? OBJECTIVEEstablishment of OA/CA yield ratios for crop-dairy production at regional scale accounting for proportions of land in crop and fodder production and their contributions to overall food yield using human metabolizable energy (HME) as a unifying parameter of yield of grain and milk. METHODSAverage yield of grain and fodder crops per unit farm area for OA and CA in eight regions of Sweden were converted to human (HME) and ruminant metabolizable energy (RME), respectively. Two diets for dairy cattle were constructed to maximize either yield of HME in grain plus milk (maxHME) or in milk (maxmilk) from all grown fodder supplemented by crop products while maintaining overall diet quality at 15% crude protein (CP). RESULTS AND CONCLUSIONSAverage regional annual primary production (dry biomass), including crop residues, of 6361 (range 4862–7793) kg/ha for OA was less than 9223 (range 6337–12,910) kg/ha in CA. OA had greater proportion of land in fodder crops and pasture (65%, range 38–87%) than CA (30%, range 11–86%). Total HME yields (grain plus milk) were less in OA than CA but with large variation between regions, maxHME OA 21.2 (range 11.0–30.4) GJ/ha and CA 43.6 (16.2–82.1) GJ/ha and maxmilk OA 19.9 (range 9.1–27.4) GJ/ha and CA 42.9 (range 16.0–80.9) GJ/ha. Regional OA/CA HME-yield ratios ranged from 0.43 to 0.74, with greater values in northern regions of low productivity where crop intensification is constrained by low temperature. SIGNIFICANCEThis analysis establishes smaller relative yields of OA than are commonly reported. Smaller yields per crop area in OA are further reduced at farm (system) level relative to CA by the larger proportion of land required in legume-based crops and pastures. Ruminant animals provide some compensation for that land by converting human-inedible fodder to human food. Consequently, transformation of CA farmland to OA would require additional land, up to 130% in productive southern and central regions, to maintain equal overall yield. More such comprehensive data are required for calculation of OA/CA yield ratios at the system level.