Improving the agronomic management and utilisation of organic bread making wheat

Abstract

Yield of wheat produced under organic standards has been repeatedly shown to be 20-40% lower than achieved in conventional farming systems, with reduced protein levels. This has mainly been linked to the inability to (a) control certain diseases and (b) use foliar applications of mineral N-fertilisers late in the growing season. The organic bread making sector in the UK has therefore been unable to meet the requirements of the market without utilising imported high protein organic wheat to augment the lower protein content of the UK crop. A large scale field trial carried out between 2003 and 2005 at Gilchesters Organic Farm in Northumberland was used to investigate the effect of applying a Rhizobium inoculant and green waste compost (GWC) amendments to two-year clover swards. The trial also evaluated the effect of the agronomic management of the pre-crop fertility building on the performance and quality of subsequent wheat varieties. This consisted of three winter and four spring bread making wheat varieties, selected from a range of European wheat breeding programmes. Results identified that the addition of Rhizobium inoculant to red clover seeds improved the establishment of the clover crop, total rhizobia number per plant and rhizobia volume. The establishment of clover plants was significantly higher with inoculum (190 plants m-2) than without (152 plants m-2). The numbers of nodules per plant in the year of crop establishment were also significantly higher with inoculum than without. The nodule volume was also significantly higher with the use of inoculum than without, with a 50% increase in the size of nodules. In the second year of growth the established clover swards in the absence of inoculum had a mean plant count of 150 m-2, with a maximum predicted nodule number being achieved from 425 plants m-2. Clover swards established with the inoculant had a mean plant count of 200 m-2, with the maximum predicted nodule number achieved with 350 plants m-2. Results from the subsequent wheat variety trial showed that variety choice had a clear effect on both winter and spring wheat yields, but the improvements to fertility management practices also significantly affected yield and protein quality. For the winter wheat varieties use of Rhizobium inoculant significantly increased grain yield by 0.64 t ha-1, while use of GWC improved yield by 0.35 t ha-1 . For the spring wheats, grain yield was higher in the presence of clover inoculum (7.04 t ha-1) than in the absence (6.77 t ha-1) by 0.27 t ha-1, but the use of GWC had no effect on yield. This demonstrates clearly that yields in organic wheat production can be significantly increased by improved variety choice and fertility management regimes. Protein content for the winter wheat varieties was significantly higher in the absence of the inoculum (12.5 %) than with inoculum (11.6 %) but from grains with a smaller specific weight. The addition of GWC also significantly increased the protein content (from 11.82 % without GWC to 12.38 %). In the absence of the inoculum, grain specific weights were improved by the addition of GWC for all three winter wheat varieties. For the spring wheat varieties Rhizobium inoculum and GWC amendment had no significant effects on any of the grain quality parameters. An additional variety trial at Gilchesters Organic Farm evaluated the field performance of six spring wheat varieties from a range of European breeding programmes for their performance and grain quality in both 2006 and 2007. Results identified that variety choice had a considerable impact on yield and grain quality with large differences between seasons. The year 2006 was the best year for agronomic performance with favourable growing conditions, but yields in 2007 were significantly lower because of heavy rainfall combined with lower solar radiation levels during grain fill. Paragon and Fasan were the top yielding varieties in both years but Tybalt and Fasan produced grains of the highest grain quality. The baking performance of the varieties was in contrast to the grain quality results, i.e. Zebra, Fasan and Paragon all produced high volume loaves with high bulk fermentation after proving despite the grain analysis suggesting they were below the NABIM (National Association of British and Irish Millers) standard required for bread making. Tybalt, however, failed to hold the bulk fermentation after proving, collapsing prior to baking despite the grain quality results identifying good baking quality characteristics. Varieties Paragon and Fasan produced the best overall yield and baking results. A fertility trial was also used to evaluate the potential for additional amendments of organic manures and fertilisers, i.e. Farm Yard Manure (FYM), Green Waste Compost (GWC), Chicken Manure Pellets (CMP) and a combination of FYM + CMP applied at rates of 250 and 125 kg ha-1, on the performance of the spring wheat variety Paragon in 2006 and 2007. Results showed no significant benefits from the rate or type of fertiliser to the yield or grain quality. Although responses to fertility inputs were small in the current season of application, there are likely to be cumulative benefits later in the rotation as organic N becomes mineralised. Fertility management in an organic system is a long-term strategy based on progressively building fertility by growing N-fixing crops and supplementing this with available organic manures, as appropriate for any given organic rotation.