ILVO: Potential of grass-clover as a green-manure and a cut-and-carry fertilizer under conventional and reduced tillage regimes in organic vegetable production

WP0: Various actions were made to disseminate project results to the stakeholders, i.e., the translation to Dutch of the project brochure, a contribution to the technical leaflet with regard to the findings of WP5, open field visits and network events with discussion among farmers on the project results, poster presentation on the Organic Producers Conference in Birmingham, two articles in a professional journal. WP1/WP2: Data from a former mid-term field trial, conducted at ILVO in duplicate on two adjacent fields, were collected and transmitted to Newcastle University for the meta-analysis on crop and soil effects of reduced soil tillage under organic farming conditions. Belgium was one of the nine countries where organic farmers were interviewed on their experiences with and knowledge on reduced tillage and green manure use, which resulted in a classification of the farmers into groups showing a particular behavior. Inagro performed the interviews in the frame of a parallel national funded project.WP3: ILVO performed CO2 emission measurements (non-continuously) in the short-term trial (see below) in both 2012 and 2013. In 2013, the experiment was used by the Gabriel Lippmann Institute for measurements of the emissions of a range of greenhouse gasses On spring-sampled soil (2013), microbial carbon (C) and nitrogen (N) were determined in collaboration with FiBL.WP5: Core research activities of the Belgian partners concerned the investigation of nutrient dynamics under reduced tillage practice and with grass-clover as a green manure and a cut-and-carry fertilizer. At ILVO, a newly established field trial was used by which was focused on the interaction of reduced tillage and green manure use. In 2012, the experiment started with the tillage and green manure factors and in 2013, farm compost application was added as additional factor. A grass-clover ley (Lolium perenne, Trifolium pratense and Trifolium repens), established in autumn 2010 was destroyed in spring 2012, either in March (gm1, early destruction) or in May (late destruction). In case of late destruction, two variants occurred: i) removal of a full-grown sward (gm2) and ii) 3 times repeated mulching (gm3). Destruction was done with a cultivator with goosefoot shovels in a shallow setting and a rotary harrow. Two types of preparatory soil tillage were used before planting leek (Allium porrum) in June: i) conventional tillage with a mouldboard plough (CT) and ii) reduced tillage (RT) with a chisel plough (Actisol). The trial design was a split-plot and had tillage as main plot factor and green manure as subplot factor. All treatments were performed in four replicates. Individual subplots (24 in total) measured 7.5 by 30 meter. The N input by the grass-clover green manure (below- and aboveground plant parts) was determined for the different green manure variants (gm2 (61 kg N ha-1) < gm1 (108 kg N ha-1) < gm3 (194 kg N ha-1)). The leek crop was not additionally fertilized. In 2012, the net N release from the grass-clover green manure and its utilization by the leek crop were examined. In 2013, celeriac (Apium graveolens var. rapaceum) was grown and fertilized with grass-clover silage (cut-and-carry fertilizer) in following dosages: zero (gm2), 9.8 (gm1) and 19.6 Mg ha-1 (gm3), which corresponded with zero, 96 and 191 kg N ha-1. Farm compost was applied in spring 2013, half of each subplot receiving zero or 32.9 Mg ha-1. Compost was prepared at ILVO and composed of poplar bark, wood chips, grass clippings, hay, cereal straw and chicken manure. The main tillage operation, either conventional or reduced was conducted just before planting. Effects of each of the three factors on N availability, crop yield, and N uptake were assessed.At Inagro, an existing demonstration mid-term tillage experiment was used. It consists of two strips on which conventional ploughing was compared with non-inversion since 2006. In 2012, timing of grass-clover sward destruction was added as an extra factor to this experiment, i.e., early destruction (gm 1) and late destruction without removal of biomass (gm 3). The whole field received cattle manure with straw bedding at a rate of 30 t ha-1. In 2013 variants of the green manure factor were 10 and 20 ton ha-1 of the grass-clover cut-and-carry fertilizer applied before the main tillage an celeriac planting. Individual plots in this trial measured 18 by 25 m. Compared to the ILVO experiment, the same plant and soil assessment was carried out.Data of the ILVO trial and data from a long-term fertilization trial of Inagro were transmitted to Louis Bolk Institute for calibration of NDICEA for N and C. Reports on trial results were produced in close collaboration with Louis Bolk Institute.Main results and experiences from the Belgian field trials:-Successful mechanical destruction of the grass-clover sward and subsequent establishment of the main crop leek under reduced tillage with no excess of regrowth of the destructed sod.-In case of late destruction of the grass-clover, N mineralization was better matched to leek N demand, which may lower the risk of N losses. Crop yield and N uptake were proportional to the input of recently-formed organic N in grass-clover.-Under reduced tillage, the soil mineral N stock was located higher in the soil profile.-When soil compaction due to harvesting activity was not relieved and no cover crop was sown in autumn, deep, non-inversion tillage could not restore soil structure in spring, by which celeriac showed a lower rooting depth and apparently, an earlier, higher sensitivity to leaf spot disease (Septoria apiicola), both resulting in a lower tuber yield.-The effectiveness of ensilaged grass-clover as a cut-and-carry fertilizer was proved.-Yield increase by a one-time compost application was found.-No interactions were found between the tillage and green manure factor for their effects on soil mineral N stock and crop performance.-In 2012, early destruction induced higher soil respiration in spring with values comparable to summer CO2 fluxes for late destruction. In August, both 2012 and 2013, a significant higher CO2 flux was measured on conventionally ploughed plots compared to plots under reduced tillage, whereas in September 2013 the reverse was found. Cut-and-carry fertilizer and compost application significantly positively affected CO2 fluxes.