Randy L. Anderson

Cropping System Influence on Planting Water Content and Yield of Winter Wheat

wheat yields were reduced by 79 kg ha 1 for every centimeter that soil water at wheat planting was reduced by Many dryland producers in the central Great Plains of the USA sunflower (Helianthus annuus L.) ahead of wheat in express concern regarding the effect that elimination of fallow has on soil water content at winter wheat (Triticum aestivum L.) planting rotation. In southwestern Kansas, Norwood (2000) simiand subsequent yields. Our objectives were to quantify cropping syslarly showed lower winter wheat yields when the previtem effects (fallow weed control method and crop sequence), including ous crop was sunflower or soybean compared with corn corn (Zea mays L.) (C) and proso millet (Panicum miliacium L.) (M), or grain sorghum [Sorghum bicolor (L.) Moench]. These on soil water at winter wheat planting and subsequent grain yield, and reductions in wheat yield were related to lower soil to determine the frequency of environmental conditions which would water at planting. Lyon et al. (1995) showed that soil cause wheat yield to drop below 2500 kg ha 1 for various cropping water at planting was strongly correlated with yield of systems. Crop rotations evaluated from 1993 through 2001 at Akron, short season summer crops [pinto bean (Phaseolus vulCO, were W-F, W-C-F, W-M-F, and W-C-M (all no-till), and W-F garis L.), proso millet] but only weakly related to yield (conventional till). Yields were correlated with soil water at planting: of long season summer crops (sunflower, grain sorghum, kg ha 1 373.3 141.2 cm (average and wet years); kg ha 1 897.9 39.7 cm (dry years). Increasing cropping intensity to two corn). They attributed this result in part to shorter seacrops in 3 yr had little effect on water content at wheat planting and son crops having more soil water available at the critical subsequent grain yield, while continuous cropping and elimination of reproductive growth stage than longer season crops, fallow reduced soil water at planting by 11.8 cm and yields by 450 which used much of the initial soil water for stover to 1650 kg ha 1, depending on growing season precipitation. No-till production and did not have it available for grain develsystems, which included a 12to 15-mo fallow period before wheat opment. planting nearly always produced at least 2500 kg ha 1 of yield under In addition to differences in previous crop water use, normal to wet conditions, but no cropping system produced 2500 kg soil water content at wheat planting can also be affected ha 1 under extremely dry conditions. by differences in tillage and crop residue effects on precipitation storage efficiency. Precipitation storage efficiency increases as tillage is reduced during the sumT traditional wheat–fallow production system used mer fallow period before wheat planting (Smika and in the central Great Plains of the USA was develWicks, 1968; Tanaka and Aase, 1987; Norwood, 1999). oped in the 1930s as a strategy to minimize incidence of Crop residues reduce soil water evaporation by shading crop failures resulting from erratic precipitation (Hinze the soil surface and reducing convective exchange of and Smika, 1983). The use of herbicides to control weeds water vapor at the soil–atmosphere interface (Greb et in this system reduced or eliminated tillage, and led to al., 1967; Aiken et al., 1997; Van Doren and Allmaras, greater precipitation storage efficiencies, such that more 1978). Additionally, reducing tillage and maintaining frequent cropping could be successfully employed (Halsurface residues reduce precipitation runoff and invorson and Reule, 1994; Peterson et al., 1993; Anderson crease infiltration, thereby increasing precipitation storet al., 1999; Norwood et al., 1990; Smika, 1990; Farahani age efficiency (Unger and Stewart, 1983). et al., 1998). Both producers and agricultural lenders would like While more intensive cropping is gradually replacing to have a means of assessing the risk level that might W-F in the central Great Plains, many producers still be incurred in moving from conventional wheat–fallow express concern regarding the effect that more frequent production systems to more intensively cropped no-till cropping has on soil water content at planting and subsesystems. Part of that risk assessment involves quantifyquent winter wheat yields. Previous research has shown ing the effects of cropping system on wheat yields. Thererelationships between available soil water and yield of fore, the objectives of this study were to (i) quantify some crops. Nielsen et al. (1999) reported that winter effects of cropping system (crop sequence and fallowseason weed-control method [i.e., tillage vs. no-till]) on D.C. Nielsen, M.F. Vigil, R.A. Bowman, and J.G. Benjamin, USDAsoil water content at winter wheat planting and subseARS, Central Great Plains Res. Stn., 40335 County Road GG, Akron, quent effects on grain yield, and (ii) determine freCO 80720; R.L. Anderson, USDA-ARS, Northern Grain Insects Res. quency of environmental conditions that cause wheat Lab., 2923 Medary Ave., Brookings SD 57006; and A.D. Halvorson, USDA-ARS, Soil–Plant–Nutrient Research Unit, P.O. Box E, 301 S. Howes, Ft. Collins, CO 80522. Received 21 Jan. 2002. *Corresponding Abbreviations: CT, conventional tillage; W-C-F, wheat–corn–fallow; author (dnielsen@lamar.colostate.edu). W-C-M, wheat–corn–millet; W-F, wheat–fallow; W-M-F, wheat–millet– fallow; NT, no-till. Published in Agron. J. 94:962–967 (2002).

An ecological approach to strengthen weed management in the semiarid great plains

Abstract Cropping systems in the semiarid Great Plains are rapidly changing. Previously, winter wheat–fallow was the prevalent system; now, because of no-till practices, producers are diversifying their rotations to include alternative crops. Yet, weed management is often ineffective because of herbicide-resistant weeds and low profit margins. A possible solution is ecologically based weed management, where cropping systems are designed to lower weed community densities and improve crop competitiveness to weeds. Both winter and summer annual crops are grown in the Great Plains, which can help manage weeds because growth periods differ considerably between crop types. Designing rotations to include two winter/spring crops followed by two summer annual crops can reduce weed community density 12-fold compared to less diverse rotations. This rotation design favors natural weed seed decline in soil yet avoids proliferation of weed densities in crops with similar life cycles. However, tillage minimizes the effect of rotation design on weed community. A second component of the ecological approach is to strengthen crop competitiveness with cultural practices. Combining three practices together improved crop competitiveness three- to five-fold. With some crops, such as proso millet, cultural systems are so effective that herbicides may not be needed for in-crop weed control. Designing rotations based on a cycle-of-four with winter and summer annual crops also accrues ancillary benefits such as increased yields and economic returns as well as improved resource-use-efficiency. Furthermore, the ecologically based approach will enable producers to ameliorate the negative impacts of herbicide-resistant weeds and rising input costs.

A rotation design to reduce weed density in organic farming

Weeds are a major obstacle to successful crop production in organic farming. Producers may be able to reduce inputs for weed management by designing rotations to disrupt population dynamics of weeds. Population-based management in conventional farming has reduced herbicide use by 50% because weed density declines in cropland across time. In this paper, we suggest a 9-year rotation comprised of perennial forages and annual crops that will disrupt weed population growth and reduce weed density in organic systems. Lower weed density will also improve effectiveness of weed control tactics used for an individual crop. The rotation includes 3-year intervals of no-till, which will improve both weed population management and soil health. Even though this rotation has not been field tested, it provides an example of designing rotations to disrupt population dynamics of weeds. Also, producers may gain additional benefits of higher crop yield and increased nitrogen supply with this rotation design.

Improving Sustainability of Cropping Systems in the Central Great Plains

ABSTRACT Rotations are changing in the semiarid Central Great Plains because of no-till systems and crop residue management. With improved precipitation storage in soil, producers now grow corn (Zea mays L.), proso millet (Panicum miliaceum L.), or sunflower (Helianthus annuus L.) in sequence with winter wheat (Triticum aestivum L.) and fallow. A long-term cropping systems study was started at Akron, Colorado in 1990 to evaluate rotations comprised of a diversity of crops, with the goal of developing rotations that minimize frequency of fallow. After 10 years, we examined ecological trends associated with soil structure, nutrient cycling, and pest management as affected by rotations. Soil structure and nutrient cycling improved with continuous cropping, whereas, arranging winter and summer annual crops in a cycle-of-four improved pest management. Producers are seeking rotations that not only are economical, but also improve soil quality; they view fallow and tillage as detriments to long-term sustainability. Therefore, we also suggest options for developing rotations with continuous cropping, based on insight gained from the Akron study. Soils in the Central Great Plains were severely damaged during the Dust Bowl era; producers seek to repair this damage with continuous cropping and no-till. But, a concern with continuous cropping is yield variability and financial risk, which producers previously managed with fallow. Crop diversity and sequencing in conjunction with residue management and no-till may provide advantages that minimize need for fallow in risk management.

Synergism: A Rotation Effect of Improved Growth Efficiency

Abstract Cropping systems in the Great Plains are changing because of no-till. Rotations now include a diversity of crops in contrast with rotations in tilled systems that grow only one or two crops. This diversity of crops often leads to yield increases because of the rotation effect. We have observed that crop response to the rotation effect can be categorized as either improving resource-use efficiency or increasing plant size and yield capacity. An example of the efficiency response, which we term synergism, is that some crops improve water-use efficiency (WUE) of following crops. Crops produce more grain with the same water use in synergistic sequences; in contrast, crops that increase yield capacity consume more water to produce more grain. Further, synergism among crops increases tolerance of weed interference because of improved resource-use efficiency. Synergism is more prominent in low-yielding environments due to stresses such as drought, and appears to be rare among crop sequences. The cause of synergism among crops is likely related to a multitude of interacting factors such as microbial changes, growth-promoting substances, and altered nutrient cycling. Quantifying WUE as affected by preceding crop may provide a method to identify synergism among crops. No-till rotations that include synergistic crop sequences are improving land productivity, farm economics, soil health, and resource-use efficiency in the semiarid Great Plains.

A cultural system to reduce weed interference in organic soybean

Organic producers are seeking alternative tactics for weed control, so that they can reduce their need for tillage. In this study, we examined cultural strategies for controlling weeds during the transition from a cool-season crop to soybean. The study was arranged as a two-way factorial, with factors being choice of cool-season crop and tillage treatments. The cool-season crops were either spring wheat harvested for grain or an oat–pea mixture harvested for forage. Five tillage treatments, ranging from intensive tillage to no-till, were established following each cool-season crop. Two tillage treatments included the cover crops, oat plus oilseed radish. Soybean was planted the following growing season. Each soybean plot was split into two subplots: weed-free and weed-infested. A cultural system comprising oat/pea as a preceding crop with no-till and cover crops reduced weed biomass in soybean 63% compared to intensive tillage. Reduced weed biomass resulted because of delayed weed emergence and lower weed community density. Consequently, soybean yielded 14% more in this treatment than with the intensive tillage treatment when weeds were present. Weed community composition also differed between the two systems; horseweed and field dandelion were prominent in no-till, whereas common lambsquarters, redroot pigweed and buffalobur were prevalent in the tillage control. Other treatments did not control weeds better than intensive tillage. A cultural system approach may minimize the need for tillage during the interval between cool-season crops and soybean.

Suppressing weed growth after wheat harvest with underseeded red clover in organic farming

Organic producers are seeking alternative tactics for weed control so that they can reduce their need for tillage. In this study, we examined cover crop strategies for suppressing weed growth after harvest of wheat. Three cover crop treatments, red clover (mammoth type), a mixture of oat and dry pea, and a control were compared. Treatments were established in both winter and spring wheat, resulting in six treatments arranged in a randomized complete block design. Red clover was underseeded in wheat by drilling in the spring, and the oat/pea mixture was planted in August. Oat was planted uniformly across all treatments in the following growing season. The red clover treatment effectively suppressed weeds, reducing post-harvest weed biomass, density of volunteer winter wheat, and seed production of downy brome by more than 99% compared with the control. Oat/pea was not effective for weed management, likely because of less fall growth and competition compared with red clover. Underseeding red clover did not affect winter wheat yield, but reduced spring wheat yield by 17%. Oat yield, however, was reduced by volunteer crop plants and downy brome infestations in all treatments. Underseeding clovers in winter wheat may effectively manage weeds and, if they winterkill, can replace the need for tillage to control weeds after wheat harvest.

Impact of preceding crop on alfalfa competitiveness with weeds

Organic producers would like to include no-till practices in their farming systems, but they are concerned about managing weeds without tillage. We are seeking to develop a continuous no-till system for organic farming, based on a complex rotation that includes a 3-yr sequence of alfalfa. In this study, we evaluated impact of preceding crop on weed infestation in alfalfa. Alfalfa was established with no-till following spring wheat, corn or soybean. The study involved a 4-yr interval, with weed dynamics measured in the fourth year. Alfalfa established after soybean suppressed weeds more than alfalfa established after spring wheat or corn. Weed biomass in alfalfa following spring wheat was 18% of the plant community, but only 1% when alfalfa followed soybean and 6% when alfalfa followed corn. Weed biomass increased because alfalfa density following spring wheat was only 71% of alfalfa following soybean. Weeds such as downy brome ( Bromus tectorum L.) and dandelion ( Taraxacum officinale Weber) were able to establish and produce biomass where alfalfa stand was sparse. Alfalfa forage yield across 3 yr was also higher following soybean than either spring wheat or corn. Alfalfa competitiveness with weeds can be improved by choice of preceding crop.

A mowing strategy to convert red clover to annual crops in organic farming

Organic producers are interested in no-till cropping systems. In this study, we found that perennial clover can be converted to corn without tillage. Conversion tactics involved fall mowing in the third year of red clover, followed by between-row mowing of weeds and volunteer red clover in corn grown during the fourth year. Corn yielded 85% of the weed-free control with mowing conversion. In contrast, weed interference in tillage-based conversion and between-row tillage reduced corn yield 53%. Weed emergence was sixfold greater in the tilled conversion. Weeds were present in the corn row with mowing, but recently developed implements could control these weeds and further support a no-till conversion method.

Converting perennial legumes to organic cropland without tillage

Organic producers are interested in developing a no-till system for crop production. In this study, we examined management tactics to convert perennial legumes to annual crops without tillage. Our hypothesis was that reducing carbohydrate production in the fall by mowing would favor winterkill. Mowing treatments were imposed in the fall of the third year of alfalfa or red clover, and corn planted in year 4. The conventional practice of tillage to convert legumes to cropland was also included as a treatment. Mowing in autumn reduced red clover biomass 93% compared with alfalfa when measured 3 weeks after corn planting (WAP). Red clover biomass was still 75% less than alfalfa 6 WAP. Fall mowing suppressed red clover sufficiently to enable corn seedlings to establish, but corn seedlings did not survive in mowed alfalfa due to alfalfa competition. Corn grain yield following red clover was similar in the mowed and tilled treatments when weeds were present. Late season clover and weed growth reduced corn yields 46% compared with weed-free corn. Weed emergence in corn was three times higher after tillage compared with the mowed treatment. Converting red clover to annual crops with fall mowing will support a no-till system for organic farming.