Organic matter returns to soils must be higher under organic compared to conventional farming

Abstract

The aim of this paper is to discuss the demand of fresh organic matter (FOM) supply to maintain soil organic matter (SOM) levels and productivity of arable soils under organic management. The basic question is whether the different frame conditions in organic vs. conventional farming result in a different and system‐specific FOM demand. If this is the case, it would follow that the farming system has to be considered in the calculation of SOM balances. SOM balances are the most common decision support tools in organic matter management. A conversion to organic farming in practice usually leads to an increase of SOM levels as well as soil microbial activity over time. The system‐specific driver of this effect is the indispensable extension of the share of (perennial) legumes in crop rotations at the expense of non‐legumes such as cereals, row crops, and maize. Extended legume cropping is essential for N supply in crop rotations as the import of N fertilizer in total is limited by organic farming regulations and mineral N fertilizer may not be used at all. Based on this characteristic of organic management, we argue that the demand of FOM supply to soils must be higher than in conventional crop production. The most relevant factors are (1) the non‐existence of mineral N fertilizer as an external N source that supports the maintenance of SOM by decreasing the demand for SOM‐N, (2) benefits of increasing SOM stocks and turnover for soil productivity under organic management, and, (3) increased mass‐losses of FOM and easily degradable SOM compartments due to higher microbial activity in soils. These effects have to be quantified and must be considered in SOM balances in order to avoid misleading assessments and erroneous decisions.

Evaluation of soil health in organicvs. conventional farming of basmati rice in North India

“…To that end, nutrient depletion in organic systems may stimulate nutrient mining by fostering microbial activity at the expense of reduced effi-ciency and ultimately increase SOC loss (Ammann et al, 2007;Craine et al, 2007), where the effect can be more pronounced in the future warmer world . Leifeld and Fuhrer (2010) and Leithold et al (2015) further argued that higher SOC content in some organic farming systems is an artifact of the excessive and disproportionate application of organic fertilizers as compared to the conventional systems, rather than the proposed sustainable use of resources. Excessive application of organic fertilizers in organic systems has also been attributed to nutrient leaching to ground water (Bergströ m et al, 2008).…”

The Characteristics of Five Food Production Systems and Their Implications for Sustainable Landscapes

“…During any transition period to a traditional, certified organic, or agro-ecological system, productivity is expected to be low. While this is often attributed to an adjustment in soil health to an improving microbiological community (Tu et al, 2006;Leithold et al, 2015), there is evidence to suggest that it is not just soil that assists in greater yields over time, but also applied management techniques (Martini et al, 2004).…”

Overlooked side effects of organic farming inputs attract soil insect crop pests

“…), is likely to increase under organic farming (Leithold et al. ), and knowledge about the harmful effects of crop residues in regard to belowground insect crop pests remains meagre. Similarly, composting pits in proximity to farms (Fussell ), in which animal waste, leaves, vegetable refuse, and household waste are deposited for later application in the field, are believed to serve as ovipositional safe havens for soil insect pests that potentially cause enormous levels of crop damage because this concentration of source foods in a small space tends to promote the gregarious behavior of pests likely to cause outbreaks (all authors, personal observations ; Cappuccino ).…”