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Data by which we can quantify effects of soil depth upon productivity from controlled experiments are essentially lacking for semiarid regions. In connection with mined land-reclamation research in North Dakota, an experiment was established in which soil was reconstructed by building a wedge with productive subsoil (B and upper C horizon) on top of leveled sodic mine spoils derived from shale. Thickness of the subsoil wedge ranged from 0 to 210 cm. Topsoil (A horizon) was then spread over the subsoil wedge to provide a topsoil either 0, 20, or 60 cm thick. A fourth treatment consisted of mixing subsoil and topsoil within the wedge in a 3:1 ratio (no topsoil on the surface). Four crops-alfalfa (Medicago saliva L.), crested wheatgrass (Agropyron desertorum), native warm-season grasses (Souteloua gracilis and Bouteloua curtipendtda), and spring wheat (Triticum aestivum L.)-were grown each year on these plots from 1975 through 1979. Yields of all crops increased as total soil thickness (topsoil plus subsoil) increased to the 90-to 150-cm range. Highest yields equaled or exceeded yields that would be expected in these years on similar undisturbed soil types under good management in the same county. In most instances, over 90% of the maximum yields observed was obtained when 70 cm of subsoil plus 20 cm of topsoil covered the sodic spoils (SAR = 25, clay = 38%). Yields from 60 cm of topsoil were similar to those from 20 cm of topsoil. With no topsoil, only native grama grasses produced over 75% of maximum, but all crops except wheat produced at least 90% of maximum with at least 90 cm of the mixed subsoil-topsoil spread over spoils (wheat yields were only about 80% of maximum). Water was extracted from the upper 30 to 90 cm of spoils when the soil-spoil interface was within 90 cm of the soil surface. Thickness of topsoil had no influence on depth of water extraction. Alfalfa extracted water to about 135 cm if sodic spoils were within 90 cm of the surface and to about 175 cm where spoils were covered with at least 150 cm of soil materials. Depth of water extraction by crested wheatgrass under these two situations was about 120 and 150 cm; by native grasses about 80 and 120 cm; and by spring wheat about 75 and 90 cm, respectively. There was no evidence of any accumulation of soil water just above the soil-spoil interface under any situation.

Root growth of a plant species has a potential pattern set by genetics, but there is a variable plastic component Quantifying the dynamics of root growth is necessary for knowledge of root growth that responds to conditions of the soil about development of rhizoplane and rhizosphere structure, and will indicate potentials for soil C sequestration and for water and nutrient environment and climatic demands placed on the whole usage. Root growth was measured during 3 yr in spring wheat (Triti-plant (Zobel, 1992). Brouwer and deWit (1969) emphacum aestivum L.) on fallow and in seven crops in spring wheat-winter size the dynamic balance between root and abovewheat-alternative crop rotation under minimum tillage on Wilton silt ground growth for plant growth modeling: deficiencies loam (fine silty, mixed, superactive, frigid Pachic Haplustolls). Two in water and nutrient supply can result in greater betypes of minirhizotrons (standard [Stand MR] and pressurized-wall lowground allocation of physiological resources and in-[P-wall MR]) were read with a microvideo camera. Average maximum creased root growth. Different patterns of root growth rooting depths fell into agronomic groups: oilseeds safflower (Cartharesponses to water regimes in semiarid zones are remus tinctoris L.), 1.64 m, and sunflower (Helianthus annuus L.), ported in the literature. In one pattern, more frequent 1.45 m; spring wheat, 1.31 m; mustard family crops crambe (Crambe irrigation or rainfall results in more shallow depths of abysinnica Hochst. ex R. E. Fr.), 1.17 m, and canola (Brassica rapa), 1.13 m; and legumes dry bean (Phaseolus vulgaris L.), 1.00 m, soybean root growth (Hoogenboom et al., 1987, with soybean; [Glycine max (L.) Merr.], 0.99 m, and dry pea (Pisum sativum L.), Merrill and Rawlins, 1979, with sorghum [Sorghum bi-0.99 m. Median depths of root length growth ranged from 0.92 m for color (L.) Moench]). Another response is the tendency safflower to 0.46 m for dry bean, and ratios of median to maximum for root growth to penetrate less deeply in the profile depths averaged 0.51. Six out of eight crops showed greatest rooting as drought lowers the water content of subsoil (Merrill depths in relatively wet 1995, likely because of wetter subsoil. Greatest et al., 1996, with spring wheat). total root length in safflower, crambe, canola, soybean and dry bean Root growth systems are hierarchical, and each loweroccurred in drier-than-average 1997, which is interpreted as a response ordered class of root members has lower diameter, less to soil water deficit. Results indicate that diverse crop rotations have mass per length unit, shorter length, and less life span the potential to utilize water and nutrients and input C over different than higher-ordered roots. Thus, much of a plant's root soil profile positions than spring wheat-based monocropping.

We hypothesized that drought accelerates wind erosion by increasing plant and soil factors of erodibility together, compounding the erosion hazard. Erodibility factors measured in biennial spring wheat–fallow on Pachic and Typic Haploborolls soil were (i) soil‐inherent wind erodibility (SIWE) by rotary sieving, (ii) surface roughness by pin meter and chain methods, (iii) standing residue profile, and (iv) residue coverage photographically. Four tillage treatments ranged from low residue (LR) to no‐till (NT). The erodible fraction of surface soil (a SIWE measure) changed from 53% during a dry period (1989–1990) to a less erodible 26% during a wet period (1992–1994). Median erosion protection values calculated from flat and standing residue measurements made after seeding were, respectively, 16 and 43% in 1989 to 1990, and 80 and 76% in 1992 to 1994. Soil losses estimated by RWEQ model equations were 11 to 6100 times greater during 1989 to 1990, compared with 1992 to 1994. No‐till was protective, and estimated soil losses on LR were up to 3000 times greater than those on NT. However, low residue yields in 1988 (930 vs. 3640 kg/ha avg.) resulted in inadequate protection after seeding in 1990, even in NT; and soil losses in LR and NT were 13 and 8 Mg/ha, respectively. Results indicate biennial small grain–fallow is nonsustainable in the long term from a soil‐erosion perspective.

production (Halvorson, 1990b). Saline-seep areas have been controlled and returned to crop production by Winter wheat (Triticum aestivum L.) can add diversity to dryland growing alfalfa and/or annual-cropping the seep recrop rotations in the northern Great Plains, but it is susceptible to charge area (Halvorson, 1984; Halvorson and Reule, winterkill in low surface residue environments. A 12-year study was conducted to determine the response of two winter wheat cultivars, 1980). Halvorson and Black (1985) reported crop yields Roughrider and Norstar, to tillage system (conventional-till, CT; minithat generally were Ͼ80% of 2-year fallow yields when mum-till, MT: and no-till, NT) and N fertilizer rate (34, 67, and 101 grown in an annual cropping system with adequate N kg N ha Ϫ1 ) in a dryland spring wheat-winter wheat-sunflower (Helianand P fertilization. Aase and Schaefer (1996) reported thus annuus L.) rotation. Grain yields were greater with MT (1968 annually cropping spring wheat with NT was more profkg ha Ϫ1 ) and NT (2022 kg ha Ϫ1 ) than with CT (1801 kg ha Ϫ1 ), but itable and productive than spring wheat-fallow in a 356tillage system effects on grain yield varied among years. Increasing mm precipitation zone in northeast Montana. Peterson N rate from 34 kg N ha Ϫ1 to 67 kg N ha Ϫ1 increased grain production et al. (1996) and McGee et al. (1997) point out that MT from 1844 to 1953 kg ha Ϫ1 , but yield response to N rate varied among and NT fallow systems have a high percentage of the soil years. The greatest overall grain yield (2111 kg ha Ϫ1 ) was obtained profile recharged by the first spring following harvest.with NT and application of 101 kg N ha Ϫ1 . Grain yields were lowest during years when plant-available water (PAW) was Ͻ300 mm. InContinuing the fallow period for 5 to 12 months is very years with Ͼ400 mm PAW, leaf spot disease incidence was greatest, inefficient and costly. Therefore, cropping systems more particularly at the lowest N rate with NT. Application of adequate intensive than crop-fallow are needed to efficiently uti-N reduced the disease incidence in all tillage treatments. Cultivar lize the water stored by NT and MT systems. Black et differences were significant 3 out of 12 years, but not consistent. al. (1981) reported more efficient water use with more Winterkill was a factor for both cultivars in only 1 year in the CT intensive cropping systems. Improved precipitation storand MT plots. Winter wheat performed well as a rotational crop in age efficiency with MT and NT allows producers the this cropping system when using MT and NT systems and adequate N option of cropping more intensively than with cropfertility. Our long-term results indicate that producers in the northern fallow (Halvorson and Reule, 1994; Peterson et al.,

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Sunflower (Helianthus annuus L.) is a warm‐season, intermediate water‐use crop that can add diversity to dryland crop rotations. Reduced tillage systems may enhance sunflower yield in intensive cropping systems. A 12‐year study was conducted to determine how sunflower cultivars of early and medium maturity respond to tillage system (conventional‐till, CT; minimum‐till, MT; no‐till, NT) and N fertilization (34, 67, and 101 kg N ha−1) within a dryland spring wheat (Triticum aestivum L.)–winter wheat–sunflower rotation. Averaged across N rates, cultivars, and years, sunflower seed yields were greater with MT (1550 kg ha−1) than with NT (1460 kg ha−1) and CT (1450 kg ha−1). Increasing N rate above 34 kg N ha−1 generally increased grain yield, but varied from year to year. The tillage × N interaction showed that the highest seed yields were obtained with NT (1638 kg ha−1) and MT (1614 kg ha−1) at 101 kg N ha−1. Total plant‐available water (TPAW) of <350 mm greatly reduced sunflower yield potential, due to water stress, compared with yields for 350 to 500 mm of TPAW. TPAW > 500 mm did not result in increased sunflower yields over those with 350 to 500 mm TPAW. Yield differences between cultivar maturity classes varied from year to year and with tillage and N level. At the lowest N rate, weeds were more problematic in NT than in CT and MT plots. More N fertilizer may be needed with NT to optimize sunflower yields than with CT and MT, because of less residual soil NO3–N with NT. Results indicate that producers in the northern Great Plains can use sunflower successfully in annual cropping systems, particularly if MT and NT are used with adequate N fertilization.