Donald L. Tanaka

Fallow method influences on soil water and precipitation storage efficiency

Abstract Summer fallowing is practiced in the Great Plains of the U.S.A. in order to store soil water, control weeds, make nutrients available and stabilize crop yields. Soil water storage and precipitation storage efficiencies on chemical and stubble-mulch fallow plots were compared for three 14-month fallow periods for a winter-wheat-fallow rotation (Triticum aestivum L.) and three 21-month fallow periods for spring-wheat-fallow rotation in the northern Great Plains to determine during which seasonal segment the fallow method might influence soil water storage. The experiment was conducted on a glacial till Williams loam (fine-loamy mixed, Typic Argiboroll) from July 1981 to April 1985. Soil water contents to a depth of 1.70 m were measured, using the neutron scatter technique, for seasonal segments during the fallow period. Soil water storage was similar from harvest to spring on chemical and stubble-mulch fallow plots. The over-winter to spring segment resulted in the most consistent precipitation storage efficiencies (33.3–71.1%). Soil water storage differences as a result of a fallow method are most likely to occur during summer fallow for 14-month winter-wheat-fallow rotations and during the second overwinter for 21-month spring-wheat-fallow rotations. Soil water storage for the entire fallow period was greater on chemical fallow than on stubble-mulch fallow in two out of three 14-month winter-wheat fallow periods and in one out of three 21-month spring-wheat fallow periods.

Fertilizer Application Timing Influences Greenhouse Gas Fluxes Over a Growing Season

Microbial production and consumption of greenhouse gases (GHG) is influenced by temperature and nutrients, especially during the first few weeks after agricultural fertilization. The effect of fertilization on GHG fluxes should occur during and shortly after application, yet data indicating how application timing affects both GHG fluxes and crop yields during a growing season are lacking. We designed a replicated (n = 5) field experiment to test for the short-term effect of fertilizer application timing on fluxes of methane (CH(4)), carbon dioxide (CO(2)), and nitrous oxide (N(2)O) over a growing season in the northern Great Plains. Each 0.30-ha plot was planted to maize (Zea mays L.) and treated similarly with the exception of fertilizer timing: five plots were fertilized with urea in early spring (1 April) and five plots were fertilized with urea in late spring (13 May). We hypothesized time-integrated fluxes over a growing season would be greater for the late-spring treatment, resulting in a greater net GHG flux, as compared to the early-spring treatment. Data collected on 59 dates and integrated over a 5-mo time course indicated CO(2) fluxes were greater (P < 0.0001) and CH(4) fluxes were lower (P < 0.05) for soils fertilized in late spring. Net GHG flux was also significantly affected by treatment, with 0.84 +/- 0.11 kg CO(2) equivalents m(-2) for early spring and 1.04 +/- 0.13 kg CO(2) equivalents m(-2) for late spring. Nitrous oxide fluxes, however, were similar for both treatments. Results indicate fertilizer application timing influences net GHG emissions in dryland cropping systems.

Yield and water use of broadleaf crops in a semiarid climate

Abstract The predominate crops grown in the northern Great Plains of the United States are cereal grains, which are well adapted to the region’s semiarid climate and short growing season. However, rotations are changing because minimum- and no-till production systems improve precipitation-use-efficiency. Therefore, producers are seeking diversity in crop choices to improve the design of their rotations. Our objective with this study was to examine water relations and agronomic performance of seven broadleaf crops that may be suitable for a semiarid climate. Dry pea (Pisum sativum L.), dry bean (Phaseolus vulgaris L.), and sunflower (Helianthus annuus L.) were the most favorable for this region considering crop yield and water-use-efficiency (WUE). Soybean (Glycine max L.), crambe (Crambe abyssinica Hochst), canola (Brassica rapa L.), and safflower (Carthamus tinctorius L.) were less successful. Water use for grain production ranged from 23 to 37xa0cm among crops whereas water-use-efficiency varied three-fold. Soil water extraction patterns differed between sunflower and dry pea, with sunflower extracting more water as well as accessing water deeper in the soil profile. Integrating oilseed and legume crops with cereal grains in a cycle-of-four rotation will aid producers in managing diseases and weeds, as well as improve grain yield due to the rotation effect.

Economic evaluation of topsoil loss in spring wheat production in the northern Great Plains, USA☆

Abstract Relationships among topsoil removal treatments and additions of nitrogen and phosphorus fertilizer on dryland spring wheat yields in a wheat-fallow rotation were used to determine the on-site effects of topsoil loss and fertilizer applications on net returns and to estimate the value of soil. Yields estimated from a production function and corresponding net returns for spring wheat under alternative soil loss levels and fertilization rates were examined. A numerical optimization routine was used to determine the most efficient levels of fertilizer applications for farm managers at various levels of soil loss. The value of soil in spring wheat production was derived by estimating the accumulated discounted values of production from land without soil loss versus land with soil loss over various planning horizons. Production function estimates indicated that, when all variables were at their mean values and soil loss was varied, the first centimeter of soil loss reduced wheat yeild from 1719 kg ha −1 to 1709 kg ha −1 , whereas the last centimeter of loss reduced yield from 1362 kg ha −1 to 1331 kg ha −1 . Each additional centimeter of soil loss increased the yield loss. The economic analysis indicates that the optimum amount of N and P that should be applied increases with each increment of soil loss. Fertilizer reduces yield loss to some extent, but net returns continue to decline as soil loss increases. This result confirms that N and P fertilizers are imperfect economic substitutes for soil. Estimated soil values are a function of the farm managers planning horizon and the natural soil erosion rate. If erosion is occurring at a rate of 44.8 Mg ha −1 year −1 , the value of soil ranges from

Long-term effects of topsoil removal on soil productivity factors, wheat yield and protein content

59.33 ha −1 for a planning horizon of 20 years to

Substitutability of Fertilizer and Rainfall for Erosion in Spring Wheat Production

305.48 ha −1 for a planning horizon of 68 years. The equivalent level annuity values of these estimates are

Comparison of soil quality and productivity at two sites differing in profile structure and topsoil properties

3.99 ha −1 year −1 and

Crop sequence influences on sustainable spring wheat production in the northern Great Plains.

10.58 ha −1 year −1 , respectively.

FARM VALUE OF TOPSOIL IN SPRING WHEAT PRODUCTION

Quantifying long-term effects of soil erosion on plant production and soil quality can aid in restoring degraded soils. The objectives of this study were to determine the long-term effects of topsoil removal on spring wheat (Triticum aestivum L.) yield and soil productivity factors. In 1982, the surface 0, 6, 12, and 18 cm of topsoil was mechanically removed from a Williams loam (fine-loamy, mixed, superactive, frigid Typic Argiustoll) and subsequently cropped. Soil samples were collected in 1998. There was no difference in soil organic matter (SOM), particulate organic matter (POM), mineralizable N, or water stable soil aggregates (WSA) in the surface 15 cm. Though not significant, there was an average increase of 1.2 g SOM kg−1 soil from the surface 15 cm since 1982, but fungal and bacterial biomass was reduced. The SOM and POM increased in the surface 15 cm of soil where grass was planted in strips between plots. Topsoil removal did not affect soil water at planting nor wheat yields from 1998–2001. The use of commercial fertilizer maintained crop yields, but SOM remained unchanged indicating that, restoring erosion damage is unlikely with a conventionally tilled wheat-fallow rotation in semi-arid regions.