Reduced tillage is increasingly promoted to improve sustainability and productivity of agricultural systems. Nonetheless, adoption of reduced tillage by organic farmers has been slow due to concerns about nutrient supply, soil structure, and weeds that may limit yields. Here, we compiled the results from both published and unpublished research comparing deep or shallow inversion tillage, with various categories of reduced tillage under organic management. Shallow refers to less than 25 cm. We found that (1) division

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The nitrogen supply can be a yield-limiting factor in organic farming, especially when reduced tillage is applied. An organic field experiment was conducted from 2007 to 2013 to analyse the potential of the nitrogen supply through the efficient use of green manure crops in different tillage systems. Three farming systems were compared: a stubble cleaner system (SC) and a plough system (PL), both in a cereal-based crop rotation, and another plough system in a crop rotation that included alfalfa grass ley (PLALF). In the fifth year of the experiment, the experimental design was extended into a split plot design, and seven green manure treatments (Lolium perenne, Phacelia tanacetifolia, Sinapis alba, a mixture of Sinapis alba and Trifolium resupinatum, Trifolium resupinatum, Vicia sativa, and bare fallow as the control) were integrated into each of the three systems. The effects of the three systems and the green manure treatments on N mineralization, the soil microbial biomass and the yield of the main crops of oats and field beans in the sixth and seventh years of the experiment were analysed. The results showed that the choice of green manure species was of minor importance in the PLALF system. This system generally successfully supplied N to the oats with oat yields from 3.6 to 5.1 t per ha.Vicia sativa was the most promising green manure crop in the SC and PL systems, with the N min values and oat yields (4.0 and 4.6 t per ha) being similar to those in the PLALF system. In the subsequent year, the PLALF system again was more successful in most of the N min assessments than the PL and SC systems, which often had rather similar results. In addition, a main crop of field beans was able to compensate for the differences in the N min content, and the yields were similar in all three systems (3.1 to 3.7 t per ha). The microbial biomass in the top soil was significantly increased in the reduced tillage system compared to the plough systems. In conclusion, reduced tillage in organic farming can promote soil microorganisms and be competitive if the nitrogen supply is improved through the efficient use of green manure or an adequate leguminous main crop.

Factorial field trials were carried out on an experimental farm near Kassel, Germany, in two consecutive seasons (2003 and 2004) in order to examine the impact of leguminous and cereal preceding crops (i) on soil N availability under subsequent potatoes and (ii) the effect of preceding crop and pre-sprouting of seed tubers on crop development, N uptake, N utilization efficiency and total and size-graded tuber yields relevant for processing into either crisps or French fries. In addition, an approach to analyse complex field experiments using mixed models is discussed. Soil mineralized nitrate-N at emergence of the potato crop was affected by the preceding crop and was highest when potatoes followed peas, while the short-term alfalfa/grass/clover ley appeared too sensitive to environmental conditions in the preceding cropping season, and its efficiency in terms of N supply may be hard to predict. Pre-sprouting advanced crop development and dry matter accumulation of the canopy, translocation of assimilates and N from canopy into tubers and allowed an increased N utilization efficiency. The positive effect of pre-sprouting on total tuber yield was compensated up to the final harvest, but a higher percentage of marketable tuber yield for French fries (>50 mm) was found independently of the date of harvest. An increasing N supply (after peas and a following catch crop) may be efficient in terms of higher yields of the marketable size-grades (40-65 mm) for crisps, but increase oversized tuber yields in seasons not affected by Phytophthora infestans. Average tuber fresh weight responded consistently and positively to seed-tuber preparation (pre-sprouting), cultivar (cv. Agria) and an increased N supply (after peas).