Speaker
Description
Organic winter wheat is characterised by variable grain yield and quality. To bridge the yield and quality gap while minimising the potential environmental impact, nitrogen management needs to be improved. The aim of the study was to examine how organic farmers can achieve the bread making quality of winter wheat by modifying their management practices. A one season field study was con ducted on organic farms to understand the response of winter wheat grain yield and protein content to biogas digestate fertilisation depending on field properties and historical management. On-farm trials were set up on ten organic farmers’ fields in Västra Götaland County in southwest Sweden.
In 2021, the selected fields had a grass-clover ley, which was ploughed before winter wheat was planted in the autumn of 2021. The trials had a randomised block design with four replications, including three in cremental N rates from split doses of biogas digestate (60, 120, 180 kg N ha-1), and one unfertilised control treatment (N0). In addition to winter wheat grain yield and protein content, soil nitrogen supply (SNS) and general soil characteristics were also determined. To understand the variability across fields, information about the ley pre-crop was also recorded. Farmer fertilisation practices were investigated and compared to biogas digestate application.
The results showed that the application of biogas digestate significantly increased grain yield and protein content at all application rates. In contrast, in the unfertilised plots (N0) the grain yield was positively correlated to SNS, which ranged between 40-130 kg ha-1, whereas there was no signif icant relation to the grain protein content. When looking at individual fields, only a few farms were able to reach the optimum yield with the biogas digestate rates applied in the trials, i.e. the wheat crop could have responded further to a higher N-rate. The same pattern was observed for the grain protein content, where four out of ten trials gave a sufficient protein content (11.5%) to get the price premia for organic wheat, showing the po tential for targeted nitrogen management depending on site characteristics. The variation in field properties between the farms was mainly related to clay content, total soil carbon and mineral soil nitrogen concentration in the autumn, and total weed biomass. The nitrogen management practices that the farmers applied differed from field to field, with variations in choice of N source and N amount. As a result, the winter wheat yield between farms varied, with a six-fold increase from 2 to 12 tons ha-1, as did the protein content, from 8 to 14%. Results from the farmer practice plots did not reflect those obtained when applying similar amounts of N in the form of biogas digestate.
This study demonstrated how the bread making quality of organic winter wheat can be improved using grass-clover ley as a pre-crop in combination with biogas digestate application. The grain yield
was also dependent on the long-term build-up of soil fertility, which was affected by the soil nitrogen supply measured in the unfertilised plots.
Our findings raise the need to further investigate the potential
of alternative soil amendments and nutrient sources, potentially suitable for organic certification, and how they can contribute to the circular economy and sustainable nutrient management in organic farming systems.
| Keywords | biogas digestate, nitrogen, nutrient management, on-farm trial |
|---|
