Comparing crop rotations between organic and conventional farming

Abstract

Cropland use activities are major drivers of global environmental changes and of farming system resilience. Rotating crops is a critical land-use driver, and a farmers' key strategy to control environmental stresses and crop performances. Evidence has accumulated that crop rotations have been dramatically simplified over the last 50 years. In contrast, organic farming stands as an alternative production way that promotes crop diversification. However, our understanding of crop rotations is surprisingly limited. In order to understand if organic farming would result in more diversified and multifunctional landscapes, we provide here a novel, systematic comparison of organic-to-conventional crop rotations at the global scale based on a meta-analysis of the scientific literature, paired with an independent analysis of organic-to-conventional land-use. We show that organic farming leads to differences in land-use compared to conventional: overall, crop rotations are 15% longer and result in higher diversity and evener crop species distribution. These changes are driven by a higher abundance of temporary fodders, catch and cover-crops, mostly to the detriment of cereals. We also highlighted differences in organic rotations between Europe and North-America, two leading regions for organic production. This increased complexity of organic crop rotations is likely to enhance ecosystem service provisioning to agroecosystems.

Figure 1

Average ( ± standard error of the mean) rotation length [in years], total number of crop categories in organic (green), and conventional (orange) rotations and land-use, as well as the Shannon Index (H) and the Equitability Index (EH) calculated at the global scale and by global region using the rotation and the land-use datasets. H and EH are calculated based on the timeshare of each crop in the rotation (for the rotation dataset), or based on the relative harvested area of each crop category (for the land-use dataset). The total number of crop categories considered was n = 11 in the rotation dataset and n = 6 in the land-use dataset. **P < 0.01; *P < 0.05; ^†P < 0.1.

Figure 2

Difference (organic minus conventional, ± standard error of the mean) in crop categories between organic and conventional rotations at the global scale and by global regions (in % of the total rotation length) based on the rotation dataset. The cereal total is the sum of all cereal categories. The shaded sub-categories – ‘Primary cereal’, ‘Secondary cereal’ and ‘Cereal/Pulse’ - refer to primary cereals (wheat, rice, maize), secondary cereals (spelt, barley, rye, triticale, oat, sorghum, millet and pseudocereals), and cereals intercropped with a pulse, respectively. ‘Fodder’ crops refer to temporary fodder crops (such as alfalfa, clover and ryegrass). Number of observations (organic; conventional): Global (127; 111), Europe (53; 46), North America (63; 54), Others (11; 11). ***P < 0.001; **P < 0.01; *P < 0.05.

Figure 3

Difference (organic minus conventional, ± standard error of the mean) in crop categories between organic and conventional land-use at the global scale and by global region (in % of harvested area under each crop category in relation to the total cropland area farmed organically or conventionally, respectively) based on the land-use dataset. Number of countries: Global (50), Europe (29), North America (2), Others (19). ***P < 0.001; **P < 0.01; *P < 0.05; ^†P < 0.1.

Figure 4

Above: Average differences (organic minus conventional, ± standard error of the mean) between the organic and conventional share of fodders, catch and undersown cover crops (in % of the total rotation length) at the global scale and by global region. Below: Contribution of grass, mixed (any intercropping of legume and grass) and legume species to temporary fodders, catch crops and undersown cover crop compositions in organic and conventional rotations at the global scale and by global region. Number of observations (organic; conventional): Global (127; 111), Europe (53; 46), North America (63; 54), Others (11; 11). ***P < 0.001; **P < 0.01; *P < 0.05.