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 mid-September 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.