Six-year transition from conventional to organic farming: effects oncrop production and soil quality

Organic farming has become increasingly important in recent decades as the consumer has grown itsfocus on the food and environmental benefits of the technique. However, when compared to conventional farming systems, organic farm system are known to yield less.Presented in this paper are the results from two organic cropping systems following six years of organicmanagement. Fertilisation management differentiated the two systems; one was fertilised with greenmanure and commercial organic fertilisers, while the other was fertilised with dairy manure. A con-ventional cropping system, managed with mineral fertiliser as typical in the southern Piemonte region(Italy), served as the bussiness as usual crop management. The first hypothesis tested related to crop yieldvariation during the initial phase of organic management; we expected a sharp reduction in the earlyphase, then minor reductions later on. The second hypothesis tested related to soil fertility variation; weexpected enhanced soil fertility under organic management.Overall, the organic system produced less, relative to the conventional system in interaction with yeareffect. Yield reduction seemed related to the lower soil nutrient availability of organic fertilisers thatprovided nutrients consequent to mineralisation. Therefore, summer crops are well-suited to manure-fertilised organic farms as mineralisation happens at higher temperatures, as opposed to winter wheat,which is largely reduced in such systems. Commercial organic fertilisers can, however, limit this effectthrough their high nutrient availability in the winter and early springAlso shown was that soil quality, defined as a general decrease in soil organic carbon (SOC) over time inthe three analysed arable systems, can be mitigated by manure additions. Green manuring can maintainSOC and increase total N in soil, only if introduced for a sufficient number of years during crop rotation.Finally, soil fertility and Potential Mineralisable N in the different systems demonstrated that organicsystems managed with commercial organic nitrogen fertilisers and green manure do not improve soilquality, compared to systems managed with mineral fertilisers.