Martina Keller

Development and Testing of a Decision Making Based Method to Adjust Automatically the Harrowing Intensity

Harrowing is often used to reduce weed competition, generally using a constant intensity across a whole field. The efficacy of weed harrowing in wheat and barley can be optimized, if site-specific conditions of soil, weed infestation and crop growth stage are taken into account. This study aimed to develop and test an algorithm to automatically adjust the harrowing intensity by varying the tine angle and number of passes. The field variability of crop leaf cover, weed density and soil density was acquired with geo-referenced sensors to investigate the harrowing selectivity and crop recovery. Crop leaf cover and weed density were assessed using bispectral cameras through differential images analysis. The draught force of the soil opposite to the direction of travel was measured with electronic load cell sensor connected to a rigid tine mounted in front of the harrow. Optimal harrowing intensity levels were derived in previously implemented experiments, based on the weed control efficacy and yield gain. The assessments of crop leaf cover, weed density and soil density were combined via rules with the aforementioned optimal intensities, in a linguistic fuzzy inference system (LFIS). The system was evaluated in two field experiments that compared constant intensities with variable intensities inferred by the system. A higher weed density reduction could be achieved when the harrowing intensity was not kept constant along the cultivated plot. Varying the intensity tended to reduce the crop leaf cover, though slightly improving crop yield. A real-time intensity adjustment with this system is achievable, if the cameras are attached in the front and at the rear or sides of the harrow.

Integrating Economics in the Critical Period for Weed Control Concept in Corn

Abstract The effect of weed interference on corn yield and the critical period for weed control (CPWC) were determined in Germany and Benin. Treatments with weed control starting at different crop growth stages and continuously kept weed-free until harvest represented the “weed-infested interval.” Treatments that were kept weed-free from sowing until different crop growth stages represented the “weed-free interval.” Michaelis–Menten, Gompertz, logistic and log–logistic models were employed to model the weed interference on yield. Cross-validation revealed that the log–logistic model fitted the weed-infested interval data equally well as the logistic and slightly better than the Gompertz model fitted the weed-free interval. For Benin, economic calculations considered yield revenue and cost increase due to mechanical weeding operations. Weeding once at the ten-leaf stage of corn resulted already profitable in three out of four cases. One additional weeding operation may optimize and assure profit. Economic calculations for Germany determined a CPWC starting earlier than the four-leaf stage, challenging the decade-long propagated CPWC for corn. Differences between Germany and Benin are probably due to the higher yields and high costs in Germany. This study provides a straightforward method to implement economic data in the determination of the CPWC for chemical and nonchemical weed control strategies. Nomenclature: corn, Zea mays L.

Yield losses in vegetable and arable crops caused by yellow nutsedge (Cyperus esculentus) in farmers fields in Switzerland

Cyperus esculentus has become a serious weed in Switzerland. Despite intensive awareness training unaffected farmers tend to underestimate the consequences of C. esculentus infestation, especially the potential yield losses. Hence, countermeasures are often taken hesitantly. Yield loss data from abroad is widely available. However, this data was of limited value to raise awareness in Switzerland, because its transferability to our production systems was questioned. To close this gap yield losses caused by C. esculentus were determined for different crops in farmers’ fields in Switzerland (2013-2016). Yield was assessed with and without C. esculentus infestation and its coverage was estimated. Standard herbicides had been applied in the fields. For sugar beet and potatoes average, actual yield losses of 67% and 34% were detected at C. esculentus coverages of 68% and 44%, respectively. High infestation (80-100%) in leek, onions and Brussels sprouts caused losses of 86%, 90%, 93%, accordingly. In carrots: A high infestation led to 61% yield loss. At these infestation levels yield quality was also negatively affected. In Switzerland, these figures are employed to further train farmers. The findings are presented here to make this more recent yield loss data available to colleagues facing the same problem in their countries.

Validation of yellow nutsedge (Cyperus esculentus) control strategies in maize in an on-farm, large-scale field trial

A large on-farm field trial was carried out between 2013 and 2015 to investigate the effect of repetitive maize cropping on Cyperus esculentus infestation over time. Intensive control strategies, developed and investigated in small-scale trials, were validated. Four C. esculentus treatment strategies were installed. Soil samples were taken each year put in the greenhouse and the number of C. esculentus sprouts was assessed. Initial infestation was patchy. Field areas were flooded several times due to heavy rainfall. Despite the inherent variability and the adverse weather conditions following conclusions can be drawn: Growing maize combined with intensive weed control (2-4 passes), reduced infestation on average by 80%. Principal components for Cyperus esculentus control strategies are hoeing, the active substances S-metolachlor, mesotrione, terbuthylazine, rimsulfuron, bentazone, and a herbicide containing foramsulfuron, thiencarbazone and iodosulfuron. Growing maize combined with high intensity weed control is an effective approach to manage and reduce C. esculentus infestation. Yield depressions due to this highly intensive weed control cannot be rule out. Nevertheless, farmers in the affected region have adopted these approaches.