Biological weed control in cereals by improved spatial uniformity and higher densities (Biologisk ukrudtsbekæmpelse i kornafgrøder med forøget rumlig uniformitet og høj afgrødetæthed)

Publication Type

Book

Authors

Olsen J. M., Griepentrog H.W., Pedersen S.M., Oerum J.E., Weiner J.

Year of publication

2011

Editor

Miljoestyrelsen (Ministry of Environment)

Series/labeling

Bekaempelsesmiddelforskning

A series of experimental studies over recent years have demonstrated that cereal crops have more ability than previously thought to suppress weeds, and that this ability can be realized if the crops are sown (1) at much higher densities than current practice and (2) in a highly uniform spatial pattern, rather than rows. Development and deployment of high density/high uniformity sowing systems would allow farmers to reduce herbicide application by 50-100%, without yield loss. In addition to this reduction in herbicide application, there are many additional advantages for the environment, including reduced traffic on the field, reduced fuel consumption and CO2 production, increased biodiversity and biomass production. Crop density and spatial uniformity is the only form of weed management that has only positive and no negative environmental impacts.
The goal of the current project has been (1) to develop more knowledge about the relationship between crop density, uniformity and weed suppression, (2) to investigate how this approach can be developed in the most effective way, and (3) to investigate the economic consequences of such a strategy for farmers under current and alternative price and support structures.

The report presents results from four areas investigated:
I) Small-scale field experiments to investigate the degree of spatial uniformity necessary to obtain a satisfactory degree of weed suppression
II) Spatial analyses of simulated crop sowing patterns, to investigate the degree of uniformity generated by different sowing strategies
III) Large-scale field experiments, comparing organic and conventional production systems with respect to weed management, and increased density and uniformity as an alternative or supplement to current strategies.
IV) Business economic analysis of the possibility of applying these methods, including a comparison of different strategies.

The results show that increased crop density always has a negative effect on reduced weed biomass and resultant yield loss. Increased uniformity also had a negative effect on reduced weed biomass, but not in all most cases. Under spring drought conditions, which occurred in two of the three years, the effect of spatial uniformity was smaller than under non-drought conditions or even non-existent - in one case there was no effect. This observation has contributed to our theoretical understanding of the mechanisms of crop-weedcompetition and the application of this knowledge to weed management. Increased crop density can be used to improve weed suppression. Increasedcrop spatial uniformity maximized the effect of density when abiotic stress(e.g. drought) does not limit total biomass production.The spatial analyses of simulated sowing patterns investigated how decreasedrow distance and improved uniformity of placement within rows contribute toincreased 2-dimensional spatial uniformity. Reducing row distance increases spatial uniformity greatly. After the "optimal" row distance for a given density is reached, further improvements in uniformity can be achieved by improving the uniformity of spacing within the row. Narrow row spacing is already possible but development of an inexpensive, non-energy requiring method for improving the distribution of seeds within the row should be a focus of research and development in sowing technology.
Both the effects of density and uniformity appear to be continuous, rather than threshold, effects. This means that improvements in weed suppression can be achieved to the degree that the technology and costs permit.
The spatial analyses of simulated sowing patterns shows that a completely 2- dimensional random pattern ("broadcasting") represents a huge increase in uniformity compared with standard rows. Previous studies as well as the current project show that most of the beneficial effects of increased uniformity pattern are achieved in the random pattern. This opens up the possibility of broadcasting at high density, when the technology is available and costs are appropriate. It also suggests that a degree of uniformity equivalent to totally random, which can be achieved through narrow ("optimal") row spacing, combined with improved but not precision seed distribution within the row, is a reasonable, achievable goal for the engineering of sowing machines for increased weed suppression.
The production economic analysis indicates that a change in cropping systems/technology, seed density and sowing pattern may have a significant economic impact. In spring wheat it seems to be economic viable to reduce the row distance from the conventional 12,5 cm to 4 cm in both conventional and organic farming systems. In organic farming, it may additionally be economically viable to apply higher amounts of seed, which may exclude eliminate the need for mechanical weeding. In conventional farming, an exclusion elimination of weeding, regardless of the seed density and row distances, may result in an increased number of weeds that survive. Increased seed density and a reduced row distance will therefore reduce the need for herbicides in conventional spring wheat under current cropping practices. The strategy investigated in this report can be further advanced though the development of "high density" varieties bred for such a system. High-density, high uniformity cropping with varieties developed for this purpose, combined with appropriate crop rotations, offer the possibility of eliminating herbicide use in cereals in Denmark.