Recipient Organization
UNIVERSITY OF NEBRASKA
(N/A)
LINCOLN,NE 68583
Performing Department
Agronomy & Horticulture
Non Technical Summary
Water is the most limiting factor for crop production in Nebraska. Water availability for agriculture will become a more critical issue as additional restrictions are placed on irrigation development and use, particularly if climatic patterns become relatively drier. Adoption of no-till has reduced the amount of water lost to evaporation from tillage operations. However, the lack of tillage has created an environment favorable for the growth of winter annual weeds. Many Nebraska farmers do not control these weeds until the time of planting or later. Anecdotal evidence has shown that not controlling these weeds, particularly when they are allowed to grow until planting or beyond, can reduce crop emergence and restrict early-season crop growth in rainfed cropping systems. It is also known that winter annual weeds can harbor disease pathogens and insects pests. Weed scientists recommend that farmers plant into weed-free fields, but the impact of winter annual weed growth on the subsequent crop yield has not been reported in peer-review literature. Integrated Pest Management (IPM) is based on economic thresholds. Economic thresholds help the farmer determine if pest pressure will cause yield reductions that exceed the cost of control. Applying economic thresholds to pest management decisions will reduce production costs for the farmer and protect the environment by eliminating unnecessary pesticide applications. Quantifying the potential yield impact of uncontrolled winter annual weeds will define the economic value of controlling these weeds, and will enable farmers to make informed decisions about when it is economical to control those weeds. Uncontrolled winter annual weed growth may reduce the amount of soil moisture available to the crop. Water use by weeds is often attributed as one of the reasons why weeds reduce crop yields. The negative impact of water use by summer annual weeds has been demonstrated by measuring differences in soil moisture between crops grown in weed free and weedy treatments. However, the amount of water used by winter annual weeds and its impact on crop growth and yield has not been reported in peer-review literature. Technologies such as the neutron probe, watermark sensors, TDR, and other capacitance devices allow rapid, repeatable measurements of soil moisture. Greenhouse and field experiments can measure water use relative to plant growth to develop water use efficiency values for winter annual weeds. Quantifying how much water is used by winter annual weeds can be used to develop economic thresholds for winter annual weed control. When farmers are informed regarding the potential water use of winter annual weed growth, they can make informed decisions that may reduce groundwater extraction for irrigation and increase crop yields and farm profitability.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
A. Determine Nebraska farmers perspectives on the impact of winter annual weeds in crop production and document how they manage these weeds. B. Determine winter annual weed infestations in Nebraska fields. C. Determine the critical period for winter annual weed control in rainfed, no-till corn-soybean cropping systems across a precipitation gradient. 1. Measure corn and soybean yield when winter annual weeds are allowed to grow until late November, March 15, April 1, April 15, May 1, May 15, June 1, or June 15. D. Measure how winter annual weed growth and removal timings affect soil water availability. E. Measure how winter annual weed growth and removal timings affect crop emergence, crop growth and development, and nitrogen content of the crop. F. Develop water use efficiency coefficients for important common winter annual weeds: marestail (Conyza canadensis), tansymustard (Descurainia pinnata), field pennycress (Thlaspi arvense), henbit (Lamium amplexicaule), shepherdspurse (Capsella bursa-pastoris), Carolina foxtail (Alopecurus carolinianus), downy brome (Bromus tectorum), dandelion (perennial - Taraxacum officinale), and common lambsquarters (summer annual - Chenopodium album. G. Measure biomass production of common winter annual weeds: marestail, tansymustard, field pennycress, henbit, shepherdspurse, Carolina foxtail, downy brome, dandelion, and common lambsquarters. H. Develop economic thresholds for winter annual weeds based on weed density, weed water use efficiency, crop, yield potential, herbicide costs, tillage system, expected precipitation and irrigation availability. I. Determine if supplemental irrigation at planting to replenish water used by winter annual weeds will negate the negative effects of uncontrolled winter annual weed growth. J. Determine if tillage to control winter annual weed growth will result in less water loss than uncontrolled winter annual weed growth. K. Measure winter annual weed response to herbicides to improve recommendations for herbicides to use for winter annual weed control in Nebraska.
Project Methods
A. Survey Nebraska farmers on the prevalence of winter annual weeds, the perceived impact of those weeds on crop production, and the approaches used to manage those weeds. Use mail and/or internet survey instruments. B. Survey Nebraska no-till corn and/or soybean fields for winter annual weed populations in 2009 and 2010. Survey 240 fields over 2 years. Conduct weed counts in the first half of April. Record weed density in at least 10 locations in each field, following a prescribed spatial pattern for making counts. C. Determine the critical period for winter annual weed control along a precipitation gradient in SE, SC and WC Nebraska. Use no-till, rainfed fields on research farms in Lincoln, Clay Center, and North Platte. Weed removal timings will be mid-November, March 15, April 1, April 15, May 1, May 15, June 1, and June 15 in both corn and soybean plots. Treatments will be maintained weed free (e.g., newly emerged weeds will be controlled before they reach 4 inches tall). Corn and soybean will be planted in early May. Record weed density and size by species in two 0.5 m2 quadrats per plot where herbicides will be applied prior to each weed removal timing. Yields will be recorded for each plot using a small plot combine, and data will be used to fit Logistic and Gompertz models to describe the critical weed removal timing. D. Determine how winter annual weed growth affects soil water availability in the surface 3 feet by measuring soil moisture in the critical period study. E. Determine how winter annual weed growth affects crop emergence, growth and development, and soil and crop nitrogen availability by collecting germination, growth, and nutrient content analysis of the crops grown in the critical period study. F. Develop water use efficiency coefficients of key winter annual weed species: marestail, tansymustard, field pennycress, henbit, shepherdspurse, Carolina foxtail, downy brome, dandelion (perennial), and common lambsquarters (early spring annual). Plants will be grown in the greenhouse and water use efficiency will be determined by subjecting each species to various fraction of transpirable soil water levels. Plants will be harvested at flowering or physiological maturity, then dried and weighed to determine biomass production. Biomass weights will be plotted against cumulative water use to determine the water use coefficient for each species. G. Measure biomass production potential of key winter annual weeds in small plots (1.5 x 3 m) in the fall in Lincoln, Clay Center, and North Platte. Measure soil moisture and nitrate-N. Harvest plants for biomass in mid-May and early June. H. Develop an economic threshold tool that will help predict the optimum timing for winter annual weed control as affected by weed species, density, weed water use coefficient, precipitation, crop, crop yield potential, and cost of herbicide application.