Rapeseed With Pulses and the Management of Nitrogen
Originally written by Gilles Sauzet and published in TCS in March 2016
When we include pulses or beans in the cropping system, either as a main crop or companion crop, nitrogen management is at the heart of the strategy. Knowledge of the evolution of nitrogen build-up and nitrogen flows mobilized by the different cultures that can use it, becomes a major asset, especially in low-availability environments.
The inclusion of legumes in cropping systems should naturally lead to a limitation of mineral nitrogen and reduce emissions of greenhouse gases, this more or less short term. Nitrogen is also not the only benefit emphasized. A more global vision, leading to environmental improvement is primarily expected. Structural quality, biological, organic soil is taken into account and becomes an essential element in our quest for success of the system, highly dependent on the quality of implementation of crops and intercropping. Soil is at the heart of the approach and its fertility should allow obtaining robust plants, able to develop and express a potential appropriate to the context.
The farmer must always act on the state and trends of the environment, soil and weather. In some areas, the more limited potential, it is in the interests of sustainability, reflecting the integration of levers able to pass a course in agro-economic performance, while moving towards an agroecological approach. Uncap yields under limited potential contexts is not impossible if the components of the environment is respected by integrating innovative levers suitable. The associated rapeseed now has some experience.
After several disappointments in particular linked to the absence of frost-free phases and non-destructive disabling plants in spring, it has become common practice in many farms of the AC networks. Expectations agronomic terms are the same as when rape is alone. However the associated plant should not compete with the crop. A balance needs to settle and why each species, in turn, must take advantage of the elements at its disposal.
Autumnal behaviour
The objectives in winter entrance, as rape either alone or combined are the same: quick lift, good stand structure, root growth capacity, to facilitate dynamic aerial growth of oilseed rape for accumulating nitrogen and set up vis-à-vis competition from weeds and insect management. The fear is of course to have a cover of legumes that would compete with the growth of rape. The cycle associated species is offset from the cycle of rapeseed which induces non-concurrent phases of growth.
The competition is rare once the implementation of rape is successful. It sometimes gets better behaviours associated rapeseed in biomass and accumulated nitrogen. This is the case in waterlogged soils crusty. The legume, especially faba beans, helps to improve the porosity and emergence. The partner rape is rarely if ever limited nitrogen input or output of winter, unlike the single rape, mid to low balances and this, no one can talk of dilution; accumulated aboveground biomass in both cases is very close. The competition rapeseed / legumes is extremely rare.
The experimental results show a decrease of 5 units of nitrogen absorbed, which can be attributed to a favourable variance of green biomass alone rape. However nitrogen contents of measures and visual field observations (leaf colour) show a better nitrogen status of partner rape without that we can evoke a division between plants, but a better root condition and perhaps, some rhizodeposition.
Behaviour in spring
The profit is expected in the spring. Indeed pulses, which normally must degrade in winter operation are assumed to improve the nitrogen stock in the spring, their C / N is low (9 to 15). The initial objective, through the introduction of legumes in the cropping system, either as a main crop, covered with intercropping or in combination, is to improve the availability of nitrogen to make profit crops, but also to enrich the rhizosphere and preserve the structural state, and organic soil pore. Early tests indicate that rape can itself benefit from this. Its fall and winter behaviour is modified (deeper rooting, better nitrogen status) and often allows a more dynamic growth recovery in late winter.
It therefore seems less dependent on the availability of mineral nitrogen fertilizers and biomass and nitrogen accumulated in bloom are consistently higher in partner rape. Behaviour associated rapeseed, as seen throughout the cycle is improved. Rape can benefit quickly from an additional source of nitrogen that allows her to express a priori identical potential. If we compare the differences in nitrogen CAU (apparent coefficient of use), there is a better use of rape in nitrogen associated with legumes. Certainly fertilization is lower and may explain this. However the best root exploration is also a justified explanation.
Splitting closely studied
The results obtained confirm that bloom reduce the dose of 30 units does not disturb the growth and therefore in principle the establishment of the number of pods and seeds. In contrast to the stage G4, the associated rapeseed is less productive biomass and accumulated less nitrogen. Fractionation of nitrogen in combination situation definitely needs to be worked and reviewed. The good condition of winter rapeseed output associated not campaigning for a dose of the same nature that only rape, even in situations with low availability. However, we need to extend the absorption late flowering and maintain a more efficient LAI Post-bloom. At this level, the later contributions can be interesting.
As such, some tests have shown that eliminating the late contribution (point E) associated rapeseed could be limiting (Spring 2014) especially when the late flowering is watered. The results obtained confirm that bloom reduce the dose of 30 units does not disturb the growth and therefore in principle the establishment of the number of pods and seeds. Work on the fractionation is ongoing. Maintaining the leaf area index during the late flowering stage physiological maturity is important to try to improve the thousand grain weight, component until now very stable as rape either alone or associated.
To improve the productivity in grains, grain number is decisive. The PMG tends to decrease when the number of grains becomes too large. It is therefore necessary to find ways to maintain, even in non-optimal climatic conditions. In addition and to date, the sulphur fertilization, as rape is alone or in combination, is identical. This aspect of the route has not been worked.
Rarely unfavourable productivity to the association
By incorporating legumes covered the rape, it is hoped to benefit from ecological interests. Competition vis-a-vis weeds, disruption of insects, the optimized growth rapeseed, throughout the cycle should result in better overall behaviour, which provides for expression of a potential at least equal to that obtained by only rape, but with a reduced crop management inputs. The graphs below show against the associated productivity gaps between rape and alone, associated oilseed rape has received 30 units of nitrogen and less, weed control programs or fall insecticide reduced.
Certainly the differences are small but rarely associated adverse to rape. System robustness is noted in place. It gets as much or more with less. This is confirmed by tests performed by farmers plots (graphs below cons) in Berry. By incorporating legumes covered the rape, it is hoped to benefit from ecological interests. These comparisons confirm the reliability of this practice. When the associated rapeseed compared with a reduced route (nitrogen / insecticide / weeding) yields similar results to a single rape with complete ITK. This success is completely linked to the rape installed. Since its implementation is successful, his behaviour is optimized either alone or associated.
Of the association are expected agronomic and ecological benefits. By cumulative effects or interactions with the integration of other levers, improvements are expected on the ground and the culture system. In production areas where both agronomic and economic performance are average and irregular, this positive development of the environment and the care given to crop establishment, must be able to uncap insufficient returns. Inevitably, evaluating the potential created will influence the forecasts of nitrogen fertilization in particular.
Our goal is to characterize the evolution of fertility medium to produce more with less or much nitrogen. For this, it is appropriate to know the fate of nitrogen accumulated and returned by legumes in the cropping system. This work is ongoing with holdings in Berry in particular networks.
The introduction of legumes, an important issue
The place of rape is sometimes questioned or discussed in some areas it has been historical producted in. We must find new production methods, new sources of fertility. We must act on the course culture and its success depends on securing its implementation and introduction of new levers to improve its growth and behaviour with respect to bioaggressors.
The introduction of legumes is an important issue that we must evolve both in technical route productivity. There remain issues to work or refine as the optimal destruction phases covered, the amount of accumulated biomass necessary, assessing the performance target may be different from one rape, splitting nitrogen … This paradigm shift therefore suggests positive developments regarding rape culture but also the accompanying crops in the rotation.
Indeed the integration of legumes rapeseed will not by itself transform the usual results, but participate as well as the introduction of other innovative practices (intercropping covered more permanent cover, differentiated management of intercropping with work and not work, lengthening the rotation when possible …) to improve the environment and productivity. Establish robust crops on a carrier floor production should allow to increase the potential in a context of respect for the environment. Grow or so becomes an obligation in certain soil and climatic contexts. Changing practices across culture and system must facilitate this success.