Incompatibility between fertility building measures and the management of perennial weeds in organic cropping systems

Abstract

A B S T R A C TFertility building measures are important components in improving the productivity of organic cropping systems without livestock. However, some measures seem to be incompatible with the control of perennial weeds that can have adverse effects such as significant weed competition. The influence of fertility building measures (N 2 -fixing crops in the crop sequence, cover crops and manuring) and the abundance of perennial weeds were studied in a long-term crop rotation experiment at two locations in Denmark. The aim was to gain insight into the factors that influence the growth of perennial weed species occurring in mixed stands. Data were obtained from three cycles of four-year arable crop rotations comprising various cash crops in rotations with and without annual whole-year grass-clover as green manure and subjected to four treatment combinations: with and without animal manure and with and without cover crops. Severe outbreaks of perennial weed problems did not occur at the location that had the highest soil fertility, whereas the other site demonstrated dynamic growth of Cirsium arvense and Elytrigia repens. Grain legumes tended to promote the growth of C. arvense, while manuring was neutral to C. arvense but beneficial to E. repens. Cover crops assisted the growth of E. repens since prolonged mechanical interventions were not possible. Compatibility was only achieved with grass-clover and C. arvense, meaning that green manure crops suitable for cutting and mulching could offer an important management option against C. arvense but not against E. repens.

Nitrogen fertilizer replacement value of digestates from three green manures

“…Nutrients and especially nitrogen (N) availability and weed infestations are two major constraints to organic production in stockless systems. The inclusion of forage legumes in the rotation is a strategic way to increase the robustness of the system, by providing N through biological fixation and by competing against perennial weeds (Melander et al 2016). In stockless systems, forage biomass is a valuable green manure, and it is a common practice to leave the cuts on the field as mulch (Stinner et al 2008).…”

Nitrogen leaching: A crop rotation perspective on the effect of N surplus, field management and use of catch crops

“…In particular, an additional year of green manure was added in OGM, while hemp was introduced in OGL and CGL. Green manures suitable for mowing have been identified as a strategic option for managing perennial weeds (Melander et al, 2016), while hemp is known to be highly competitive against many weed species (Van Der Werf, 1994).…”

Influence of mechanical weeding and fertilisation on perennial weeds, fungal diseases, soil structure and crop yield in organic spring cereals

“…E. repens is exemplified by Håkansson (2003) as a species that responds positively to stronger fertilisation, but this was not shown in our study. However, other studies have demonstrated contradictory results with E. repens and its response to organic amendments when competing with arable crops (Rasmussen et al 2014;Melander et al 2016). Another species, S. arvensis is exemplified as a species that responds opposite, i.e.…”

“…Frequent mowing throughout the summer of a full-season green cover-crop manure did for instance control creeping thistle (Cirsium arvense) in succeeding cereal crops (Dock-Gustavsson 1997;Graglia et al 2006;Thomsen et al 2015). Other weed species such as couch grass (Elymus repens), however, may be poorly controlled in such cover crops (Vanhala et al 2006;Thomsen et al 2015;Melander et al 2016). Moreover, there are also concerns both regarding weeds, especially some perennial creeping species as E. repens (Thomsen et al 2015), mineralisation and leakage of nitrogen outside of the growing season (Korsaeth and Eltun 2008).…”

“…Earlier studies by Thomsen et al (2015) and Melander et al (2016) indicate that periods of soil cultivation, for example both in the autumn and in spring, may be required for controlling mixed stands of perennial weeds in cereal-dominated rotations, but there is a need to verify this with new studies. Furthermore, considerations to the total sustainability of the system are required.…”