Soil Disturbance-Residue Management Effect on Winter Wheat Growth and Yield

The need to reduce soil erosion, maximize soil water conservation, and optimize grain production in dryland cropping systems in the Central Great Plains has culminated in development of nontilled fallow systems. These systems have greatly reduced the degree of soil disturbance, and the amount and degree of residue incorporation. The objectives of this study were to evaluate the influence of soil disturbance and residue management on soil temperature, soil water, and winter wheat (Triticum mstivum L.) growth. Two field studies were established in 1981 and 1982 on an Alliance silt loam (Fine-silty, mixed, mesic Aridic Argiustoll) with treatments consisting of various degrees of soil disturbance (moldboard plow, tandem disk, and no tillage), residue incorporation (on the soil surface or incorporated), and amount of residue applied (0.0,O.S, and 1.0 of that produced by the previous crop). Decreased soil disturbance (tillage) and increased residue application decreased maximum, and increased minimum, soil temperatures. In all tillage treatments, soil water content showed a significant positive linear relationship to residue application rate. Grain yield was similar for all treatment factors, except tillage within the 19831984 season when tilled (3.48 Mg ha-') treatments produced more grain than the nontilled (3.20 Mg ha-') treatment. Early development and growth of winter wheat was slowed by the presence of residues (surface or incorporated) or the absence of tillage. However, by completion of heading, phenology and yield were similar for all treatments. Cooler soil temperatures slowed development and growth during those stages when the meristem temperature was influenced most by soil temperature. However, after jointing, when air temperature and photoperiod were controlling development and growth, differences among treatments disappeared. Interaction of wheat development with soil temperature, air temperature, and daylength may contribute to the crop's inability to consistently capitalize, in terms of grain yield, on the greater amount of water stored in nontilled and mulched systems. W.W. Wilhelm and J.F. Power, Agric. Res. Sew., USDA, Keim Hall, East Campus, and H. Bouzerzour, Dep. of Agronomy, Univ. ofNebraska-Lincoln, Lincoln NE 68583. Contnbution from USDAARS in cooperation w t h the Agric. Res. Div., Univ. of NebraskaLincoln, Lincoln NE. Published as Paper no. 8610 Journal Senes, Agric. Res. Div. Received 11 April 1988. *Corresponding author. Published in Agron. J. 81:581-588 (1989). S OIL EROSION and drought are among the major problems associated with grain production in the Central Great Plains. The need to reduce soil erosion and to maximize soil water conservation for optimum grain production culminated in the development of nontilled fallow systems (Duley, 1960; Fenster and Peterson, 1979; McCalla and Army, 1964). These systems of wheat production have become increasingly important in the Great Plains since the 1950s. Tillage practice effects on soil temperature, soil water, and crop growth have been widely studied (Adams, 1965, 1966; Adams et al., 1976; Allmaras et al., 1964; Army et al., 1961; Black, 1970; Burns et al., 1971; Ciha, 1982). Reduced soil temperatures in mulched versus nonmulched soil, particularly during the time of the season when soils are warming and canopy cover is not established, have been reported frequently (Allmaras et al., 1964; Anderson and Russell, 1964; Burrows and Larson, 1962; Greb, 1966; Hillel et al., 1975). Anderson and Russell (1964) found that each 1.1 Mg ha-' of straw mulch depressed morning temperature in the 100and 200-mm soil depth an average of 3°C during early spring, compared with bare soil. Crop growth is usually depressed under nontilled conditions in early spring (Allmaras et al., 1964; Anderson and Russell, 1964; Burrows and Larson, 1962). This may be caused by the influence of surface residues on soil temperature. Soil water content is greater in mulched than in bare soils as a result of reduced evaporation (Adams et al., 1976; Anderson and Russell, 1964; Army et al., 196 1; Burns et al., 1971; Hillel et al., 1975; Papendick et al., 1973). Mulches can reduce evaporation via one or more of following mechanisms: (i) reducing soil temperature, (ii) impeding vapor diffision, (iii) acting as periodic focal points for temporary vapor condensation and absorption into mulch tissue, and (iv) reducing wind velocity at the soil interface (Greb, 1966). 582 AGRONOMY JOURNAL, VOL. 8 1, JULY-AUGUST 1989 Table 1. Analysis of variance outline and explanation of single-degree-of-freedom comparisons used to evaluate data. Source of variation df Explanation Total Blocks Error Treatments Nontilled vs. tilled Within nontilled residue linear residue quadratic Within tilled disk vs. plow in vs. on