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Cover crops can expand ecosystem services, though sound management recommendations for their use within semiarid cropping systems is currently constrained by a lack of information. This study was conducted to determine agroecosystem responses to late-summer seeded cover crops under no-till management, with particular emphasis on soil attributes. Short-term effects of late-summer seeded cover crops on soil water, available N, near-surface soil quality, and residue cover were investigated during three consecutive years on the Area IV Soil Conservation Districts Research Farm near Mandan, ND. Mean aboveground cover crop biomass was highly variable across years (1430, 96, and 937 kg ha–¹ in 2008, 2009, and 2010, respectively), and was strongly affected by precipitation received within 14 d following cover crop seeding. During years with appreciable biomass production (2008 and 2010), cover crops significantly reduced available N in the 0.9-m depth the following spring (P = 0.0291 and 0.0464, respectively). Cover crop effects on soil water were subtle, and no differences in soil water were found between cover crop treatments and a no cover crop control before seeding cash crops the following spring. Late-summer seeded cover crops did not affect near-surface soil properties or soil coverage by residue. Soil responses to late-summer seeded cover crops did not differ between cover crop mixtures and monocultures. Late-summer seeded cover crops may enhance ecosystem services provided by semiarid cropping systems through biomass production and N conservation, though achieving these benefits in a consistent manner appears dependent on timely precipitation following cover crop seeding.

Crop sequence is an important management practice that may lower the risk for leaf spot diseases of spring wheat (Triticum aestivum L.). Field research was conducted near Mandan, ND, to determine the impact of crop sequences on leaf spot diseases of hard red spring wheat early in the growing season. Spring wheat was evaluated for disease severity following crop sequence combinations of 10 crops [buckwheat (Fagopyrum esculentum Moench), canola (Brassica napus L.), chickpea (Cicer arietinum L.), corn (Zea mays L.), dry pea (Pisum sativum L.), grain sorghum [Sorghum bicolor (L.) Moench], lentil (Lens culinaris Medik.), oil seed sunflower (Helianthus annuus L.), proso millet (Panicum miliaceum L.), and hard red spring wheat). Spring wheat leaves with distinct lesions were collected for determination of lesion number and percentage necrosis data, which were used to estimate leaf spot disease severity. Pyrenophora tritici-repentis (Died.) Drechs., the cause of tan spot, and Phaeosphaeria nodorum (E. Miiller) Hedjaroude, the cause of Stagonospora nodorum blotch, were the major leaf spot diseases and consistently present throughout the growing season. The frequency of isolation following alternative crops was generally lower compared with spring wheat following wheat. Leaf spot diseases on spring wheat were impacted by crop sequencing. Spring wheat following crop sequences with alternative crops for 1 or 2 yr had lower levels of disease severity compared with a continuous spring wheat treatment early in the growing season. Disease severity was apparently not related to the percentage of crop residue coverage on the soil surface associated with various crop sequence combinations. New alternative crops preceding spring wheat reduce levels of leaf spot diseases.

Future trends in population growth, energy use, climate change, and globalization will challenge agriculturists to develop innovative production systems that are highly productive and environmentally sound. Furthermore, future agricultural production systems must possess an inherent capacity to adapt to change to be sustainable. Given this context, adoption of dynamic cropping systems is proposed to meet multiple agronomic and environmental objectives through the enhancement of management adaptability to externalities. Dynamic cropping systems are a form of agricultural production that relies on an annual strategy to optimize the outcome of (i) production, (ii) economic, and (iii) resource conservation goals using ecologically-based management principles. Dynamic cropping systems are inherently complex, possessing larger crop portfolios and greater crop diversity and sequencing flexibility as compared with monoculture and fixed-sequence cropping systems. Greater crop diversity and sequencing flexibility within dynamic cropping systems may result in reduced weed and disease infestations, greater nutrient- and precipitation-use efficiency, decreased requirements of exogenous inputs, and lower production risk. The multiple interactions among management components of dynamic cropping systems demand greater management intensity than monoculture and fixed-sequence cropping systems. Further development of dynamic cropping systems is important for managing crop production systems in a sustainable manner. These systems can ultimately assist land managers to develop new and improved land-use strategies to the benefit of generations to come.

Producers need to know how to sequence crops to develop sustainable dynamic cropping systems that take advantage of inherent internal resources, such as crop synergism, nutrient cycling, and soil water, and capitalize on external resources, such as weather, markets, and government programs. The objective of our research was to determine influences of previous crop and crop residues (crop sequence) on relative seed and residue yield and precipitation-use efficiency (PUE) for the no-till production of buckwheat (Fagopyrum esculentum Moench), canola (Brassica napus L.), chickpea (Cicer arietinum L.), corn (Zea mays L.), dry pea (Pisum sativum L.), grain sorghum (Sorghum bicolor L.), lentil (Lens culinaris Medik.), proso millet (Panicum miliaceum L.), sunflower (Helianthus annus L.), and spring wheat (Triticum aestivum L.) grown in the northern Great Plains. Relative seed yield in 2003 for eight of the 10 crops resulted in synergistic effects when the previous crop was dry pea or lentil, compared with each crop grown on its own residue. Buckwheat, corn, and sunflower residues were antagonistic to chickpea relative seed yield. In 2004, highest relative seed yield for eight of the 10 crops occurred when dry pea was the previous crop. Relative residue yield followed a pattern similar to relative seed yield. The PUE overall means fluctuated for seven of the 10 crops both years, but those of dry pea, sunflower, and spring wheat remained somewhat constant, suggesting these crops may have mechanisms for consistent PUE and were not as dependent on growing season precipitation distribution as the other seven crops. Sustainable cropping systems in the northern Great Plains will approach an optimal scheme of crop sequencing by taking advantage of synergisms and avoiding antagonisms that occur among crops and previous crop residues.

Dynamic cropping systems principles require that farmers consider climatic, market, and ecological factors on an annual basis in making crop choices. Our objectives were to determine variability of seasonal soil water depletion (SWD) and spring soil water recharge (SWR) among crops and to apply results to dynamic cropping systems practice. A 10-species crop sequence project was conducted under notillage on silt loam Haplustoll soils in North Dakota. Mid-May to midSeptember SWD and following April SWR were determined from 2002 to 2005 by neutron moisture meter to the 1.8-m depth. Crops studied and average SWD amounts (cm) were: sunflower (Helianthus annuus L.), 13.5; corn (Zea mays L.), 12.6; sorghum [Sorghum bicolor (L.) Moench], 11.0; spring wheat (Triticum aestivum L.), 10.6; canola (Brassica napus L.), 10.0; millet (Panicum miliaceum L.), 9.6; buckwheat (Fagopyrum esculentum Moench), 9.4; chickpea (Cicer arietinum L.), 8.5; lentil (Lens culinaris Medik), 8.1; and dry pea (Pisum sativum L.), 5.0, with highest and lowest being 29 and 11% of average May soil water, 46 cm. Because the period of the experiment was relatively dry, recharge was less than depletion. Spring soil water was 10 cm greater following pea than following sunflower. Ranking of crops for water storage roughly followed reverse SWD rank, with several exceptions, notably wheat, which had greater water from snow capture. Lower soil water following crops such as sunflower and corn was linked to negative crop sequential effects in this project. Choosing to seed a lower water-using crop in the spring after the occurrence of below-average SWR on land that had a higher water-using crop the previous season illustrates an application of information reported here along with the principles of dynamic cropping systems.

Field research was conducted to determine the influence of crop and crop sequencing on crop residue coverage of soil with 10 crops [buckwheat (Fagopyrum esculentum Moench), canola (Brassica napus L.), chickpea (Cicer arietinum L.), corn (Zea mays L.), dry pea (Pisum sativum L.), grain sorghum [Sorghum bicolor (L.) Moench], lentil (Lens culinaris Medik.), oil seed sunflower (Helianthus annuus L.), proso millet (Panicum miliaceum L.), and hard red spring wheat (Triticum aestivum L.)]. Crop residue production was obtained. Crop residue coverage of the soil surface was measured with a transect technique at the time of seeding spring wheat. Crop residue coverage varied and was more clearly associated with the second-year crop than with the first-year crop of a 2-yr crop sequence. Crop sequences composed of spring wheat, proso millet, and grain sorghum had higher crop residue coverage compared with sequences composed of the other crops. When these three crops and three crops that provide lower crop residue coverage of soil the subsequent year (lentil, chickpea, and sunflower) were analyzed as a subset to compare various sequences of crops providing a range of residue coverage, for example, lower (first yr)/lower (second yr), the surface residue coverage ranged from 65% for the lower/lower combination to 93% for the higher/ higher combination in 2004 and from 56 to 94% in 2005, respectively. A producer operating on more fragile soil and concerned about reducing soil erosion hazards would be advised to grow crops that provide higher residue coverage in the year before crops that provide lower residue coverage.

Cropping systems need to be inherently flexible to take advantage of economic opportunities and/or adapt to environmental realities. A dynamic cropping systems concept-characterized by a management approach whereby crop sequencing decisions are made on an annual basis-has been proposed to improve the adaptability of cropping practices to externalities. A symposium on dynamic cropping systems was held at the 2005 ASA-CSSA-SSSA annual meetings in Salt Lake City, UT. Presentations at the symposium reviewed research results from a recent experiment near Mandan, ND, investigating short-term crop sequence effects on crop production, plant diseases, soil residue coverage, and soil water depletion. This paper briefly reviews each of the presentations at the symposium. Future research opportunities on dynamic cropping systems abound, and may have increased impact if emerging issues in agriculture (e.g., increased use of biofuels; livestock integration in cropping systems) are incorporated in evaluations.

cruited tillers in mid-May, July, and September. Tiller replacement has also been shown to be the primary means of persisratios,whichincorporatedcumulativerecruitmentandmortality,were greatest on plots grazed during early vegetative and mid-culm elonga- tence in many perennial grasses (Hendrickson and Briske, tion. Tiller recruitment, tiller mortality, and tiller replacement ratio 1997). Because perennial grass plants are essentially a had a year treatment interaction. In 2000, grazing during the early collectionoftillers,anunderstandingoftillerpersistence vegetative stage resulted in significantly higher tiller replacement ra- should give managers an understanding of how their graztios than grazing during late boot or no grazing, and grazing during ing strategy may affect stand persistence. Olson and mid-culm elongation and late boot had greater tiller recruitment but Richards (1988) used a tiller replacement ratio, which also greater tiller mortality than the other two treatments. Tiller re- incorporates new tiller emergence and tiller mortality placement ratio had a grazing treatment entry interaction in 2001. to determine persistence of tiller populations. ‘Mandan 1871’ had the greatest tiller replacement ratio and tiller The morphological stage of intermediate wheatgrass recruitment among entries. The results indicate time of grazing and development shouldbe considered in planninga grazing cultivar selection influence the persistence of tillers of intermediate

Approaches to assess the effects of management practices on agroecosystem functions are needed. This paper describes a computer program designed to assess the relative sustainability of management practices using agronomic and environmental data. The program, entitled AgroEcosystem Performance Assessment Tool (AEPAT), utilizes performance-based index methodology to derive a relative ranking of agroecosystem performance among management practices for functions and indicators included in the procedure. The program is organized into eight major steps: Introduction, Input Files, Assign Indicators to Functions, Describe Indicators, Assign Weights, Select Output File, Calculate Agroecosystem Performance Scores, and Save Agroecosystem Project. Help windows as well as a tutorial are provided within the program to assist users through each step. Users must keep in mind the assumptions and drawbacks inherent to performance-based indices while using AEPAT. Additionally, the program requires data on many indicators to provide useful information on agroecosystem performance. Therefore, its use is intended primarily for clientele conducting long-term agroecosystem experiments.

Research to integrate the vast array of information needed by producers to make decisions allowing them to remain sustainable in our ever-changing agricultural environment is in its infancy. Present research has not provided crop production and soils information that is adequately comprehensive and holistic for producers to make critical decisions. We propose a dynamic cropping systems approach to help producers make those critical decisions they need to remain sustainable. Our definition of a dynamic cropping system is a long-term strategy of annual crop sequencing that optimizes crop and soil use options and the attainment of production, economic, and resource conservation goals by using sound ecological management principles. Implicit to this strategy is the need for producers to possess information necessary to respond to continual change. Key factors associated with dynamic cropping systems are diversity, adaptability, reduced input cost, multiple enterprise systems, and awareness of environment and information. Development of a dynamic cropping systems research program involves creating a crop portfolio, crop sequence evaluation, and multidirectional flow of information among research, extension, and producers. Dynamic cropping systems approach relies on responsiveness and provides producers with management flexibility for developing their own long-term sustainable crop, soil, and land use systems.

Evaluating the impact agricultural practices have on agroecosystem functions is essential to determine the sustainability of management systems. This paper presents an approach to determine the relative sustainability of agricultural practices. A simple ranking procedure using a relative scoring method is proposed to discriminate among treatments based on the status of crop and soil parameters within different agroecosystem functions. Summing scores across agroecosystem functions allows for the identification of agricultural practices that are performing optimally based on functions included in the procedure. An example, using data from a long-term cropping systems experiment in the western Corn Belt, found the indexing procedure to successfully discern differences in overall performance across four agroecosystem functions between conventional [continuous corn (Zea mays L.) cropping sequence at a fertilization rate of 180 kg N ha -1 ] and alternative [corn-oat (Avena sativa L.) + clover (Trifolium pratense L.)-grain sorghum [Sorghum bicolor (L.) Moench]-soybean [Glycine max (L.) Merr.] cropping sequence at a fertilization rate of 90 kg N ha 1 } management systems. The simplicity, inclusiveness, and inherent flexibility of the indexing procedure can be considered benefits and drawbacks, depending on the point of view taken. Data requirements of the approach, however, are stringent. Consequently, its most appropriate use may be with data from long-term agroecosystem experiments.

In July of 1993 and 1994, southern Nebraska experienced devastating windstorms, with winds estimated to exceed 45 m s -1 . These storms resulted in severe brittle-snap of corn (Zea mays L.), with stalks breaking near the primary ear node in the basal portion of an elongating internode. In the storm path were several experiments established on a Hord silt loam (Cumulic Haplustolls) to determine the effect of selected management practices (crop rotation, hybrid selection, planting date, and N fertilization) on nitrate leaching to ground water from irrigated cropland. After the storms, the number of broken plants was determined in these experiments to evaluate how management practices influenced severity of the damage. In 1993. crop rotation, hybrid, planting date, and N fertilization, and their interactions, all affected the amount of brittle-snap. Treatments that resulted in more rapid growth (optimum to excess N rates, corn rotated with soybean [Glycine max (L.) Merr.], and early planting) increased the severity of damage. In continuous corn, 7% of the plants broke, compared with 33for rotated corn; damage ranged from 4 to 33 among hybrids; and percent broken plants increased quadratically. from 8for the 0 kg N ha 1 treatment to 24at N rates equal to or greater than 80 kg N ha -1 . Only the hybrid factor was significant in 1994. Amount of brittle-snap was related to stage of development (r = 0.55, n = 160, P < 0.001). The great difference in severity of damage among hybrids indicates that the current best management strategy to limit brittle-snap losses is to plant hybrids less prone to breakage. Alternative management strategies, such as late planting, suboptimal N rates, and continuous cropping of corn, all are known to limit yield regardless of windstorms, There is a need for greater knowledge of cell and tissue characteristics that render hybrids susceptible or resistant to brittle-snap. Also, methods for simulating brittle-snap are needed to foster effective selection for resistant lines in breeding programs.

A field soil quality test kit was developed to permit rapid assessment of numerous soil characteristics recognized as basic indicators of soil quality. This study was conducted to determine the accuracy and precision of indicator measurements with the field soil quality test kit. Data collected with the test kit were compared with that from standard laboratory analyses using soils from grassland and cropland on two farms in Stutsman County, North Dakota. Results obtained with the test kit for electrical conductivity, soil pH, soil nitrate, and gravimetric water content compared well with those found by standard laboratory analyses. Significant differences in soil respiration between the field and laboratory methods were attributed to the inclusion of root respiration in the test kit measurement and to differences in sampling time, disturbance, and soil depth. Repeated test kit measurements were, for the most part, no more variable than standard laboratory analyses except when the water status of soils neared saturation. This preliminary evaluation demonstrated the field test kit to be an effective screening tool for point-scale assessment of soil quality by providing accurate and precise data over a range of soil conditions.

Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997-2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

Agricultural sustainability is enhanced by management practices that optimize the performance of multiple agroecosystem functions. The performance of western Corn Belt cropping systems was evaluated based on four agroecosystem functions: food production, raw materials production, nutrient cyding, and greenhouse gas regulation. A simple multiattribute ranking procedure was used to quantify agroecosystem performance using data from a long-term cropping systems experiment near Mead, NE. Treatments included in the procedure were continuous corn (Zea mays L.) (CC), corn-soybean [Glycine max (L.) Merr.] (C-SB), corn-oat (Avena sativa L.) + clover [80% sweet dover (Melilotus officinalis L.) and 20% red clover (Trifolium pratense L.)]-sorghum [Sorghum bicolor (L.) Moench]-soybean (C-OCL-SG-SB), and corn-soybean-sorghum-oat + clover (C-SB-SG-OCL) each at three N fertilization levels (ZERO, LOW, and HIGH). Based on treatment averages of soil and crop indicators from 1983 to 1998, agroecosystem performance scores ranged from 66.6 to 77.3, with a least significant difference (LSD) between treatments of 2.2 (P < 0.05). Treatments with the highest scores included C-OCL-SG-SBILOW (77.3), C-SB/LOW (76.9), CC/LOW (76.7), CC/HIGH (76.6), and C-SB-SG-OCL/LOW (75.3). Among these treatments, those fertilized at the LOW N rate attained high scores through moderate performance in all four agroecosystem functions. The CC/ HIGH treatment, however, attained a high score solely through its superior capacity to be highly productive, as its scores for the two environmental quality-related functions were the lowest among all treatments. Correlations between production- and environmental protection-related functions were negative, emphasizing the importance of employing management practices that are productive yet minimize deleterious environmental impacts.