Management Options for Organic Winter Wheat Production under Climate Change

An effective adaptive strategy for reducing climate change risks and increasing agro-system resiliency is broadening cropping system diversity, heightening the flexibility of cultivation and tillage methods. Climate change impacts on standard cultivation practices such as mineralisation and nitrate leaching due to mild and rainy winters, as well as frequent drought or water saturation, not only limiting fieldwork days, but also restricting ploughing. This calls for alternative methods to counteract these propensities. From 2010 to 2013, a farming system experiment was conducted on a distinctly heterogeneous organic farm in Brandenburg, Germany. With the intention of devising a more varied and flexible winter wheat cultivation method, standard organic farming practices (winter wheat cultivation after two years of alfalfa-clover-grass and ploughing in mid-October) were compared to four alternative test methods, which were then evaluated for their robustness and suitability as adaptive strategies. Two of the alternative methods, <em>early sowing</em> and <em>catch crop</em>, entailed moving up the date for alfalfa-clover-grass tilling to July. Instead of a plough, a ring-cutter was used to shallowly (8 cm) cut through and mix the topsoil. In the <em>early sowing</em> test method, winter wheat was sown at the end of August, after repeated ring-cutter processing. With the <em>catch crop</em> method, winter wheat seeding followed a summer <em>catch crop</em> and October tillage. The two <em>oat</em> methods (<em>oat/plough</em>; <em>oat/ring-cutter</em>) entailed sowing winter wheat in September, following oat cultivation. Overall, the cultivation methods demonstrated the following robustness gradation: standard practice = <em>catch crop</em> ≥ <em>early sowing</em> > <em>oat/plough</em> > <em>oat/ring-cutter</em>. When compared to standard procedures, the<em> catch crop</em> and <em>early sowing </em>test methods showed no remarkable difference in grain yields. Measured against <em>early sowing</em>, the <em>catch crop</em> test method was significantly more robust when it came to winterkill, quality loss, and weed infestation (40% lower weed-cover). High N_min-values (up to 116 kg N ha^-1) in autumn could have caused the chamomile and thistle infestation in both <em>oat/plough</em><em>oat/ring-cutter</em> test methods, which led to crop failure in the hollows. Compared to standard practices, the <em>oat ring-cutter</em> test method brought in over 50% less grain yield. This was attributed to ring-cutter processing, which reduced N mineralisation and caused high weed infestation. However, the ring-cutter effectively regulated alfalfa-clover-grass fields in both exceedingly wet and very dry weather; a temporal flexibility which increases the number of fieldwork days. The <em>catch crop</em> and <em>early sowing</em> test methods contributed most to boosting future agronomic diversity.