Soil Protection Through Organic Farming: A Review

Abstract

About 17% of the total land area in Europe is affected by erosion, and an estimated 45% of European soils have low organic matter content. Because agriculture occupies the largest proportion of land, agricultural management is decisive for soil conservation and soil quality. Here we evaluate, on the basis of published research, whether or not organic farming might be a way to maintain and restore soil quality. Results of field experiments and studies of practical farms show concordantly that soil organic matter typically increases or is conserved better with organic than with conventional farming practices, with differences becoming exceedingly pronounced with time. Soil organic carbon was 6-34% higher under organic than under conventional management, with two studies finding no pronounced differences and two studies with very old organic farms exhibiting 50-70% more soil organic C than their conventional neighbors. This goes along with an increase in soil total nitrogen content of up to 21% (47% on one of the old organic farms), which nevertheless was shown not to lead to increased nitrogen losses to the groundwater due to nitrogen-conserving practices used in organic farming. In the "plant available" soil contents of phosphorus and potassium, there appears to be no general trend under "organic" as compared to conventional management. Soil structure is typically positively affected by organic farming practices. There were up to 70% more stable macroaggregates in organic farming, and infiltration rates were up to twice as high as under conventional management. Soil water content increased by 5-72% in the studies analyzed, and an increased soil water content was reported to account for 30% higher yields in the organic systems during the extremely dry years experienced during the Rodale Farming Systems Trial. Erosion, as assessed by measuring topsoil thickness, was lower under organic management, resulting in 2-16 cm thicker topsoils. When the universal soil loss equation (USLE) method was used to model erosion, between 15% and 30% less erosion under organic management was reported. In summary, the research analyzed shows that organic management protects and improves soil quality. The main factors responsible for these benefits were identified as larger inputs of organic matter (manure, compost); more diverse crop rotations, including cover crops and green manures; and a longer time span of soil cover. Because organic farming is the only farming system that is legally defined and controlled, these benefits of organic farming can be relied on, although there is some differentiation within organic farming by different farm types and production intensities.