David C. Nielsen

Oilseed crops for semiarid cropping systems in the Northern Great Plains

oilseed crop produced in the USA, canola is the dominant oil crop in Canada. The cool climatic conditions Oilseed crops are grown throughout the semiarid region of the characteristic of the Canadian prairies provide an ideal northern Great Plains of North America for use as vegetable and industrial oils, spices, and birdfeed. In a region dominated by winter environment for Brassica spp. oilseeds and flax (Table and spring wheat (Triticum aestivum L. emend. Thell.), the accep2) while the climate found in the USA is better suited tance and production of another crop requires that it both has an to the warm season crops like soybean and sunflower. agronomic benefit to the cropping system and improve the farmers’ In the northern Great Plains, soybean is a relatively economic position. In this review, we compare the adaptation and new crop finding a place in semiarid cropping systems rotational effects of oilseed crops in the northern Great Plains. Canola with the development of early maturing, low heat–unit (Brassica sp.), mustard (B. juncea and Sinapis alba L.), and flax cultivars (Miller et al., 2002). As a result, the vast major(Linum usitatissimum L.) are well adapted to cool, short-season conity of soybean production in both the USA and Canada ditions found on the Canadian prairies and northern Great Plains occurs in wetter regions east of the Great Plains. Howborder states of the USA. Sunflower (Helianthus annuus L.) and safflower (Carthamus tinctorius L.) are better adapted to the longer ever, for the other oilseed crops listed in Table 1, the growing season and warmer temperatures found in the northern and majority of production occurs within the northern Great central Great Plains states. Examples are presented of how agronomic Plains. practices have been used to manipulate a crop’s fit into a local environDiversification within cereal-based cropping systems ment, as demonstrated with the early spring and dormant seeding can be critical to breaking pest infestations that are management of canola, and of the role of no-till seeding systems in common with monoculture (Bailey et al., 1992, 2000; allowing the establishment of small-seeded oilseed crops in semiarid Elliot and Lynch, 1995; Holtzer et al., 1996; Krupinsky regions. Continued evaluation of oilseed crops in rotation with cereals et al., 2002). Results of crop rotation studies in the Great will further expand our understanding of how they can be used to Plains revealed that where oilseeds are adapted, their strengthen the biological, economic, and environmental role of the region’s cropping systems. Specific research needs for each oilseed inclusion in rotation with cereals could increase net recrop have been recommended. turns and reduce risk through improved production stability (Lafond et al., 1993; Dhuyvetter et al., 1996; Zentner et al., 2002). In addition, the yield of wheat was increased when following oilseeds in rotation, confirmO crops are grown throughout the semiarid region of the northern Great Plains of North ing that monoculture systems are the least effective America for use as vegetable and industrial oils, spices, means of optimizing wheat production (Lafond et al., and birdfeed. In a region dominated by winter and 1992; Brandt and Zentner, 1995; Anderson et al., 1999). spring wheat (Triticum aestivum L.), the acceptance and The use of minimum and no-till seeding systems has production of another crop requires that it both has an been found to provide an effective means of controlling agronomic benefit to the cropping system and improves soil erosion in various regions of the Great Plains (Black the farmers’ economic position. Given that most oilseed and Power, 1965; Lindwall and Anderson, 1981). Imcrops have an indeterminate growth habit, adaptation provements in seed yield with conservation tillage have is influenced by tolerance to high temperature and been reported as a result of increased levels of plantdrought stress and by crop management to take advanavailable water throughout the soil profile in the spring tage of optimum environmental conditions for flowering (Aase and Reitz, 1989; Brandt, 1992; Lafond et al., 1992) and seed fill. The increasing area of oilseed crop producand increased water use efficiency due to favorable mition is an indication of the success of plant breeders croclimate conditions created by standing stubble (Cutand agronomists in developing suitable cultivars and forth and McConkey, 1997). Some oilseed crops are production methods in this semiarid region (Table 1). small seeded, requiring good surface soil moisture for While soybean [Glycine max (L.) Merr.] is the major seed germination and crop establishment, as is effectively provided in direct-seeding systems in the northern A.M. Johnston, Potash and Phosphate Inst. of Canada, 12-425 PineGreat Plains. As a result, adoption of conservation tillhouse Dr., Saskatoon, SK, Canada S7K 5K2; D.L. Tanaka, USDAage management not only reduces soil loss by erosion, ARS, Northern Great Plains Res. Lab., Box 459, Mandan, ND 58554; but also can facilitate extending the crop rotation and P.R. Miller, Montana State Univ., Dep. of Land Resour. and Environ. Sci., P.O. Box 173120, Bozeman, MT 59717-3120; S.A. Brandt, Agric. allowing for diversification of the crops grown. Ecoand Agri-Food Can., Box 10, Scott, SK, Canada S0K 4A0; D.C. Nielnomic success with a diversified crop rotation has been sen, USDA-ARS, Cent. Great Plains Res. Stn., 40335 Country Rd. reported to be improved with the implementation of GG, Akron, CO 80720; G.P. Lafond, Agric. and Agri-Food Can., Box conservation tillage practices, such as minimum and zero760, Indian Head, SK, Canada S0G 2K0; and N.R. Riveland, North Dakota State Univ., Williston Res. Ext. Cent., 14120 Hwy. 2, Williston, tillage (Lafond et al., 1993; Rossetti et al., 1999; Zentner ND 58101-8629. Saskatoon Res. Cent. Publ. 1421. Received 1 Dec. et al., 2002). 2000. *Corresponding author (ajohnston@ppi-ppic.org). The objective of this review is to summarize information on the adaptation and production potential of some Published in Agron. J. 94:231–240 (2002).

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).

Quantifying effects of soil conditions on plant growth and crop production

Soil management decisions often are aimed at improving or maintaining the soil in a productive condition. Several indicators have been used to denote changes in the soil by various management practices, but changes in bulk density is the most commonly reported factor. Bulk density, in and of itself, gives little insight on the underlying soil environment that affects plant growth. We investigated using the Least Limiting Water Range (LLWR) to evaluate changes in the soil caused by soil management. The LLWR combines limitations to root growth caused by water holding capacity, soil strength and soil aeration into a single number that can be used to determine soil physical improvement or degradation. The LLWR appeared to be a good indicator of plant productivity when the full potential of water holding capacity on available water can be realized, such as with wheat (Triticum aestivum, L.) grown in a no-till system when the wheat followed a fallow period. A regression of wheat yield to LLWR gave an r 2 of 0.76. The LLWR was a poorer indicator of plant productivity when conditions such as low total water availability limited the expression of the potential soil status on crop production. Dryland corn (Zea mays, L.) yields were more poorly correlated with LLWR (r 2 =0.18), indicating that, under dryland conditions, in-season factors relating to water infiltration may be more important to corn production than water holding capacity. An improved method to evaluate in-season soil environmental dynamics was made by using Water Stress Day (WSD). The WSD was calculated by summing the differences of actual water contents in the field from the limits identified by the LLWR during the growing season. A regression of irrigated corn yield with LLWR as the soil indicator of the soil environment resulted in an r 2 of 0.002. A regression of the same yield data with WSD as the indicator of the soil environment resulted in an r 2 of 0.60. We concluded that the LLWR can be a useful measure of management effects on soil potential productivity. Soil management practices that maximize the LLWR can maximize the potential of a soil for crop production. Knowledge of the LLWR for a soil can help the farm manager optimize growing conditions by helping schedule irrigation and for making tillage decisions. The WSD, calculated from the LLWR and in-season water dynamics, allows us to evaluate changes in the

Use of crop water stress index for monitoring water status and scheduling irrigation in wheat

The crop water stress index (CWSI) is a valuable tool for monitoring and quantifying water stress as well as for irrigation scheduling. This study was conducted during the 1990 and 1991 growing seasons at the Colorado State University Horticulture Farm near Fort Collins, CO, USA (40835 0 N latitude, 105805 0 W longitude and 1524 m elevation). The main objective was to develop a baseline equation, which can be used to calculate CWSI for monitoring water status and irrigation

Scheduling irrigations for soybeans with the Crop Water Stress Index (CWSI)

Abstract A Crop Water Stress Index ( CWSI ) has been related to water use and plant water-stress parameters, but irrigation scheduling based on CWSI values has only been reported for corn and wheat. The objectives of this study were to evaluate irrigation scheduling of soybean ( Glycine max L. Merrill) with CWSI as computed from measurements of infrared canopy temperature, air temperature, and vapor-pressure deficit, and to determine if amount of water applied per irrigation influenced water use and yield obtained from irrigation scheduling by CWSI . Soybeans were grown in field plots with drip irrigation (25 mm water per irrigation) and under a rainout shelter with flood irrigation (25 or 51 mm water per irrigation). Irrigations were initiated when CWSI reached threshold values of 0.1, 0.2, 0.4, or 0.6. Analysis of the data showed the CWSI baseline equation to be incorrect. A new baseline was computed and reanalysis of the CWSI data showed true irrigation thresholds had been 0.2, 0.3, 0.4, and 0.5. These four threshold values resulted in total irrigation amounts of 181, 180, 174, and 145 mm applied to the drip-irrigated plots, respectively. Under the rainout shelter, total irrigation amounts of 347, 271, 195, and 195 mm when 25 mm was applied per irrigation, and 406, 356, 356, and 305 mm when 51 mm was applied per irrigation, resulted from the 0.2, 0.3, 0.4, and 0.5 CWSI thresholds, respectively. Respective yields for these plots were 2656, 2566, 2430, and 2189 kg ha −1 for the drip-irrigated plots, 3375, 2826, 2435, and 2365 kg ha −1 for the rainout-shelter plots with 25 mm per irrigation, and 3575, 3551, 3110, and 2108 kg ha −1 for the rainout-shelter plots with 51 mm per irrigation. Under deficit-irrigation conditions the relationship between CWSI , soil water content, and leaf water-potential appears to change. Knowing how much water to apply per irrigation is important information for effectively using CWSI to schedule irrigations in soybeans. Cloudy sky conditions do not occur with sufficient frequency in the central Great Plains to inhibit the timely use of the infrared thermometer for irrigation scheduling.

Non water-stressed baselines for sunflowers

Abstract Effective use of the Crop Water Stress Index (CWSI) to quantify water stress requires knowledge of a non water-stressed baseline (NWSB). This study was conducted to determine effects of plant population, plant development, leaf temperatures, canopy temperatures, and time of measurement on NWSB for sunflower (Helianthus annuus L., “Triumph 560-A, 822B-R”). Measurements of canopy and single leaf temperatures were made with an infrared thermometer (IRT) throughout the growing season on plants in three populations (2.6, 5.3, and 7.9 plants·m−2) grown under full irrigation to provide a range of ground cover conditions. Plant population only affected NWSB based on canopy temperatures when leaf area index (LAI) was less than 2.0. Non water-stressed baselines based on single leaf temperatures were not affected by plant population. Slopes of NWSBs were similar during vegetative and flowering growth stages, but declined in absolute value during grain-filling. Non water-stressed baselines derived from midday temperature and vapor pressure deficit (VPD) measurements were not different from NWSBs derived from diurnal measurements. Measurements of single leaves of sunflower plants made with an IRT can be used to evaluate water stress early in the growing season before canopy closure occurs, or in non-irrigated production areas where canopy closure may not occur, and during grain-filling when heads become very warm and disrupt canopy temperature measurements.

Cover Crop and Irrigation Effects on Soil Microbial Communities and Enzymes in Semiarid Agroecosystems of the Central Great Plains of North America

Cover crops can have beneficial effects on soil microbiology by increasing carbon (C) supply, but these beneficial effects can be modulated by precipitation conditions. The objective of this study was to compare a fallow-winter wheat (Triticum aestivum L.) rotation to several cover crop-winter wheat rotations under rainfed and irrigated conditions in the semiarid US High Plains. Experiments were carried out at two sites, Sidney in Nebraska, and Akron in Colorado, USA, with three times of soil sampling in 2012–2013 at cover crop termination, wheat planting, and wheat maturity. The experiments included four single-species cover crops, a 10-species mixture, and a fallow treatment. The variables measured were soil C and nitrogen (N), soil community structure by fatty acid methyl ester (FAME) profiles, and soil β-glucosidase, β-glucosaminidase, and phosphodiesterase activities. The fallow treatment, devoid of living plants, reduced the concentrations of most FAMEs at cover crop termination. The total FAME concentration was correlated with cover crop biomass (R = 0.62 at Sidney and 0.44 at Akron). By the time of wheat planting, there was a beneficial effect of irrigation, which caused an increase in mycorrhizal and protozoan markers. At wheat maturity, the cover crop and irrigation effects on soil FAMEs had subsided, but irrigation had a positive effect on the β-glucosidase and phosphodiesterase activities at Akron, which was the drier of the two sites. Cover crops and irrigation were slow to impact soil C concentration. Our results show that cover crops had a short-lived effect on soil microbial communities in semiarid wheat-based rotations and irrigation could enhance soil enzyme activity. In the semiarid environment, longer time spans may have been needed to see beneficial effects of cover crops on soil microbial community structure, soil enzyme activities, and soil C sequestration.