Effect of Clover Sward Management on Nitrogen Fixation and Performance of Following Spring- and Winter Wheat Crops; Results of a 3-Year Pilot Study

Abstract

Wheat yields in organic production are significantly lower than those achieved in conventional farming systems and in Northern Europe organic farmers also struggle to achieve the processing quality levels demanded by millers and bakers, especially in winter-wheat crops. Here, we report the findings of a 3-year pilot study which investigated the potential of increasing grain yields and both standard processing (e.g., grain protein levels and specific weights) and selected nutritional (tocopherol and tocotrienol isomers) quality parameters via (i) changes in the management of clover crops grown before wheat (Rhizobium seed inoculation, application of greenwaste compost to clover swards) and (ii) use of new varieties developed in both the UK and continental Europe. Results indicate that the use of compost amendment to preceding clover swards significantly increased the grain protein levels in the three winter-wheat, but not the four spring-wheat varieties, and also significantly increases grain yields in one winter-wheat variety (Greina). In contrast, the use of Rhizobium-inoculation was found to significantly reduce protein concentrations in the winter-, but not spring wheat varieties, and had no significant effect on grain yields in both winter and spring wheat. However, analysis of variance detected significant interactions between Rhizobium seed inocula in clover pre-crops and (a) compost application for grain specific weights in winter-wheat and grain hardness in spring wheat crops and (b) variety for grain protein content in spring wheat crops. No significant effect of clover pre-crop management on tocopherol and tocotrienol isomer profiles could be detected, although significant differences between varieties were detected in both winter and spring wheat. Results of this pilot study need to be confirmed in future trials, but indicate that both (a) changes in clover-management practices and (b) the selections of wheat varieties that are more suitable for organic farming systems has the potential to increase grain yield and allow organic farmers to more frequently achieve baking or milling grade quality.

Breeding Bread-Making Wheat Varieties for Organic Farming Systems: The Need to Target Productivity, Robustness, Resource Use Efficiency and Grain Quality Traits

“…Recent studies and reports from Northern Europe also suggest that combining the use of varieties from organic breeding programs with innovative agronomic protocols (e.g., the use of Rhizobium inocula and applications of green-waste compost in grass/clover leys grown before cereals to optimize N supply) can; (i) narrow the yield gap between organic and conventional production systems and/or (ii) substantially increase grain protein content and other processing quality parameters in organic wheat production [ 57 , 82 , 118 ]. This suggests that, different to intensive conventional cereal production, where yields in many European countries have plateaued since the mid-1990s, the productivity of organic production systems is still increasing in Europe.…”

“…Although significant progress can be achieved via improved breeding and selection methods, processors will also have to focus on innovation. This is of particular importance in regions with maritime/temperate climates, where it is often difficult for both organic and conventional farmers to achieve the concentrations and quality of protein specified by millers and bakers [ 4 , 6 , 9 , 48 , 57 , 58 , 74 , 82 , 119 ]. Conventional producers in these regions address this challenge by applying mineral N fertilizer at critical stages of crop growth and organic farmers have tried to mimic this approach by applying permitted organic fertilizers with a high water-soluble, readily plant available N content (e.g., cattle manure slurry or chicken pellets) to established crops [ 4 , 7 , 9 , 57 ].…”

“…Aszita had lower lodging resistance than Solstice, but, as in previous long-term, factorial field trials with the conventional variety Malacca [ 4 , 7 ], significant levels of lodging were only observed when mineral N fertilizer was used without protection by synthetic chemical fungicides and plant growth regulators [ 6 ]. Superior performance under organic farming conditions has been confirmed for Aszita and other Sativa organic bread-making wheat varieties in variety comparison trials in the UK and other locations in Northern Europe [ 57 , 77 , 82 ].…”

Effect of Different Cover Crops on Suppression of the Weed Oxalis pes-caprae L., Soil Nutrient Availability, and the Performance of Table Olive Trees ‘Kalamon’ cv. in Crete, Greece

“…The use of Rhizobium inoculation of legume seed was reported to increase symbiotic Nfixation by legume crops, soil fertility and yields of subsequent crops in arable production systems [4,7,22]. The finding that Rhizobium inoculation of vetch (V. sativa) seed resulted (a) in a reduction in vetch crop density, (b) no significant increase in N-fixation efficacy (based on parameters measured such as nodulation, size of nodules and proportion of active nodules) and (c) no significant increase in N-availability (assessed via leaf analysis), was therefore unexpected.…”

“…One approach to increase N-fixation and availability from cover crops may be to apply Rhizobium inoculum to legume seed. For example, the application of a commercial Rhizobium inoculum to clover seed was recently shown to further increase N-levels in soil and N-supply to subsequent wheat crops grown after clover leys in the UK [4,7]. However, this approach has not been evaluated for vetch (Vicia sativa), the main legume species used as cover crop in organic olive orchards in the Mediterranean region [8].…”