1a. Objectives (from AD-416):
1) Develop integrated multi-tactic weed management programs which will include cover crops, cultural practices, and bio-herbicides for reduced-tillage production systems. 2) Determine the ecological mechanisms by which crop and soil management impact crop and weed establishment and growth processes.
1b. Approach (from AD-416):
A multi-tactic approach will be developed for reduced-tillage corn production that combines the optimum hairy vetch-rye cover crop mixture for suppressing weeds with poultry litter injection that supplements nitrogen required by the crop, but localizes it in space and time to minimize utilization by weeds. Soil properties, mulch characteristics, and weed sizes will be determined that optimize the postemergence destruction of weeds with a high-residue cultivator, minimize disturbance of the surface residue, and maximize soybean yield. Methods will be developed to augment and purify naturally-produced bacterial phytotoxins and test their efficacy as a postemergence herbicide. Basic research will be conducted to increase our understanding of weed suppression by cover crop mulches in relation to potentially allelopathic compounds leached into the soil and their duration of soil activity. Basic research also will be conducted to determine the effect of soil organic matter on mitigating the competitive effects of weeds on crops.
3. Progress Report:
The third year of a component experiment was completed that determines the optimal cover crop species composition (cereal:legume), poultry litter rate, and placement method that minimize weed competition and maximize nitrogen use efficiency in corn. Results analyzed to date indicate that greater cereal biomass favors weed control while greater legume biomass results in higher N fertility. Initial soil N levels will greatly influence cover crop composition regardless of initial seeding rates. This experiment has attracted a broad multi-disciplinary team from ARS and land grant universities and has been included in two funded grant applications. Three University of Maryland Masters Degree students have selected this experiment for their thesis work. Experiments were continued to determine the role of components in the Gac/Rsm regulon in production of tagetitoxin. Plasmids created to overexpress five rsmX genes in P. syringae pv. tagetis (Pst) were used in experiments with plants to study the role of these rsmX genes in regulation of tagetitoxin. These experiments were inconclusive. Creation of plasmids to demonstrate the role of rsmX, as well as rsmY and rsmZ, in regulation of tagetitoxin continues to be a challenge. In experiments with collaborators at the University of Nottingham, United Kingdom, it was demonstrated that the Gac/Rsm regulon in Pst is important for the production of acyl-homoserine lactones. We are currently determining if the Gac/Rsm regulon regulates tagetitoxin production via these acyl-homoserine lactones. Experiments were initiated with an ARS collaborator at the Beltsville Agricultural Research Center to finalize sequencing of the Pst genome. These sequencing experiments will potentially identify genes involved in regulation of tagetitoxin and also identify genes involved in the synthesis of this phytotoxin. Work on this aspect of the project was slowed due to the death of a collaborator. Results from previous allelopathy experiments provided new insights on the activity of allelochemicals in soil. For example, solution-phase availability of allelochemicals was found to be critical and needs more careful evaluation. Consequently, we deferred initiation of microplot and allelopathy research outlined in the project plan, and initiated a new direction of research that includes a more careful analysis of the contributions of roots to the production of allelochemicals. A two-phase, two year greenhouse pot experiment was completed. The first trial examined the effects of soil from long-term conventional and organic cropping systems on the functional densities required for nitrogen utilization of crop and weed species. We observed a 10:1 ratio of weed to crop functional density based on nitrogen utilization. Results from these experiments were used to design a weed-crop competition experiment with the same soils. The competition experiments showed higher productivity in the organic soils but only small differences between species (weed and crop) utilization of nitrogen within a given soil type. Data have been analyzed, and the first manuscript is in preparation.
1. Development of cover crop-based, no-till- and reduced-tillage- corn and soybean production systems for weed control. No-till crop production is one of the most important and effective approaches to conserving soil resources in conventional production systems. However, no-till crop production systems (e.g. corn and soybean) that consistently use the same herbicides can lead to herbicide resistance in weeds. Diversifying selection pressures against weeds through the use of cover crops can mitigate these herbicide resistance problems. Weed management is also problematic in organic grain production systems. Weed management is very labor intensive in these production systems, ultimately limiting the ability of organic farmers to meet market demand for organic grain. Our studies have shown that the use of cover crops can reduce labor requirements in organic corn and soybean production systems. These cover crop-based, no-till and reduced-tillage corn and soybean production systems are being adopted by both conventional and organic growers. Our cover crop-based approach to reducing tillage in low-herbicide and organic corn and soybean production systems will ensure the long-term sustainability of corn and soybean crop production.
Rice, C., Cai, G., Teasdale, J.R. 2012. Concentrations and allelopathic effects of benzoxazinoid compounds in soil treated with rye (Secale cereale) cover crop. Journal of Agricultural and Food Chemistry. 60:4471-4479.