Interactions between green manure and amendment type and rate: Effects on organic potato and soil mineral N dynamic

A field experiment was carried out in Tuscany (Central Italy) to assess the contribution of different amendments in combination with a green manure legume cover crop (Trifolium subterraneum L.) to organic spring potato (cv. Monna Lisa) nutrition. The experimental field was divided into three blocks (replicates) and each of them was split in two main strips, representing different management systems, in which a subterranean clover (Trifolium subterraneum L.) green manure was cultivated or not. Within each strip, elementary plots, which received farmyard cattle manure or green compost at three different rates, corresponding to an amount of N 0, 50 and 100 kg ha-1, were randomly distributed according to a split-plot layout. Potato yield, N uptake and use efficiency were measured during the cropping cycle and at crop harvest. Furthermore, soil mineral N dynamics was studied to evaluate the potential impact on the environment by combination of compost application and leguminous green manure. Results obtained demonstrated that the cultivation of clover green manure and the application of farmyard manure substantially increased the total potato yield of 22.5% and 25.1%, respectively. The highest dose of organic amendments applied to the crop enhanced the potato production and N use efficiency by 43.3% and 16.9%, compared with the unfertilized control. However, the combination of clover green manure and amendments distribution did not increase the soil mineral N at the end of potato cropping cycle. These findings indicate that it is possible to modify the agronomical practices in organic potato production without enhanced potential environmental risks due to N leaching. On the basis of these results, effective strategies based on legume green manure combined with organic amendments application can be developed for establishing both new agronomical practices and N fertilizer methodologies applied to organic potato production.