Legume Green Fallow Effect on Soil Water Content at Wheat Planting and Wheat Yield

a system has been referred to as green fallow (Gardner et al., 1993). These systems have sometimes been sucGrowing a legume cover crop in place of fallow in a winter wheat cessful in the cooler regions of the northern Great Plains (Triticum aestivum L.)–fallow system can provide protection against (Zentner et al., 2001). Zentner et al. (2004) reported that erosion while adding N to the soil. However, water use by legumes early legume planting and termination dates as well as may reduce subsequent wheat yield. This study was conducted to quantify the effect of varying legume termination dates on available effective snow catch before spring wheat planting were soil water content at wheat planting and subsequent wheat yield in essential for success with a legume green fallow system the central Great Plains. Four legumes [Austrian winter pea, Pisum in southwestern Saskatchewan. In Montana, lentils grown sativum L. subsp. sativum var. arvense (L.) Poir.; spring field pea, to full bloom did not reduce subsequent spring profile P. sativum L.; black lentil, Lens culinaris Medikus; hairy vetch, Vicia water compared with tilled or chemical fallow. Howvillosa Roth.) were grown at Akron, CO, as spring crops from 1994 ever, wheat yields in the lentil–spring wheat system were to 1999. Legumes were planted in early April and terminated at 2-wk lower than in the wheat–fallow system during the first intervals (four termination dates), generally starting in early June. three cycles of the system due to lower available N folWheat was planted in September in the terminated legume plots, lowing lentil (Cochran and Kolberg, 2002). In some and yields were compared with wheat yields from conventional till other studies wheat yields following the green fallow wheat–fallow. Generally there were no significant differences in available soil water at wheat planting due to legume type. Soil water at period have been decreased due to lower soil water wheat planting was reduced by 55 mm when legumes were terminated content at wheat planting (Zentner et al., 1996; Schlegel early and by 104 mm when legumes were terminated late, compared and Havlin, 1997) or due to N deficiency (Pikul et al., with soil water in fallowed plots that were conventionally tilled. Aver1997). Under the higher temperature, higher evaporaage wheat yield was linearly correlated with average available soil tive demand environmental conditions of the central water at wheat planting, with the relationship varying from year to Great Plains, the positive economic trade-off between year depending on evaporative demand and precipitation in April, water used by the legumes and their favorable rotation May, and June. The cost in water use by legumes and subsequent and N fixing effects have not been observed (Vigil and decrease in wheat yield may be too great to justify use of legumes as Nielsen, 1998). The objectives of this study were (i) to fallow cover crops in wheat–fallow systems in semiarid environments. determine the effect of legume termination date (using four legume species) on available soil water content at winter wheat planting and subsequent wheat yield in a T limited and highly variable precipitation of the central Great Plains environment, and (ii) to verify the semiarid central Great Plains resulted in the tradiconclusions of Vigil and Nielsen (1998) using a longer tional winter wheat–fallow crop production system used study period (6 vs. 2 yr). to stabilize yields (Haas et al., 1974; Hinze and Smika, 1983). That system, especially with the use of tillage to MATERIALS AND METHODS control weeds during the fallow period, leaves the soil surface vulnerable to soil loss and degradation by wind This study was conducted at the USDA Central Great Plains erosion and has very low precipitation storage efficiency Research Station, 6.4 km east of Akron, CO (40 09 N lat, 103 09 W long, 1384 m). The soil type was a Weld silt loam (fine, (Tanaka and Aase, 1987; Black and Bauer, 1988; Steiner, smectitic, mesic Aridic Argiustols). The experiment was estab1988; Farahani et al., 1998). The introduction of no-till, lished in 1994 on a site that had been in a dryland winter chemical fallow has reduced the potential for wind erowheat–corn (Zea mays L.)–summer fallow rotation the prevision and organic matter loss (Bowman et al., 1999), and ous 3 yr. Before planting the first legume crop, the corn stalks increased stored soil water available for crop production from the 1993 crop were mowed with a flail mower, raked, (Peterson et al., 1996; Nielsen et al., 2002), but has inand removed as bales. troduced the potential for development of herbicideThe experiment was arranged in a randomized split-block resistant weeds when the same herbicide is continually design with each block replicated four times. Two adjacent areas used in the system (Westra, 2004). were alternated each year between legume green fallow/conA possible solution is the use of legume cover crops ventional fallow plots and the following winter wheat plots (i.e., both the fallow phase and the wheat phase of the experiduring the fallow period, which could protect the soil ment appeared each year). A replication consisted of four from erosion while providing organic matter and fixing main plots, 9.1 m wide and 19.5 m long. The four main-plot N to maintain soil quality (Biederbeck et al., 1998). Such treatments consisted of three legume species and a traditional summer fallow treatment. Four legume species were investigated in this study, but only three were tested in any given USDA-ARS, Central Great Plains Res. Stn., 40335 County Road GG, year (Table 1). In preliminary work (Vigil and Nielsen, 1998), Akron, CO 80720. Received 18 Mar. 2004. Wheat. *Corresponding author ([email protected]). lentil was found to produce less biomass for the same amount of water use as the other legumes, and was therefore replaced Published in Agron. J. 97:684–689 (2005). doi:10.2134/agronj2004.0071 © American Society of Agronomy Abbreviations: AWP, Austrian winter pea; FP, field pea; HV, hairy vetch; IHL, Indianhead lentil. 677 S. Segoe Rd., Madison, WI 53711 USA 684 Published online April 27, 2005