No-Till and Conventional-Till Effects on Spring Wheat in the Palouse

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Stephen O. Guy and Mary A. Lauver, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83844-2339

Abstract

Erosion is a major problem in the Palouse region of Idaho. While high residue tillage systems can reduce erosion, crop productivity is a concern. An experiment was conducted near Genesee, ID to assess the effects of no-till and conventional-till on spring wheat (Triticum aestivum L. emend. Thell.) from 2001 to 2004. Tillage treatments had no effect on spring wheat plant stand, plant height, grain yield, grain hardness, biomass, heads per square foot, or harvest index. Weight of 200 seeds was significantly higher by 0.37 g in no-till treatment, and test weight was 1.2 lb/bu higher in no-till, while grain protein was 0.5% less than in conventional-till. These effects were possibly due to more available soil water retained in the NT areas that were not disturbed by cultivation. These results indicate that well managed no-till systems with adequate nitrogen fertilization could help reduce erosion without detrimental effects on spring wheat yield, quality, and biomass.

Introduction

The Palouse is a 3.4-million-acre dryland farming region in northern Idaho and eastern Washington where erosion is a problem due to the steep slopes, with some slopes up to 60% or greater (19). Erosion can result in an annual soil loss of 9 to 35 tons/acre in this area (16), where the loessial soils are vulnerable to erosion especially over winter when most precipitation falls (4). No-till and reduced-tillage production systems have potential for improving soil conservation and reducing input costs such as fuel and labor (5).

Numerous studies have been conducted to evaluate the effects of reduced- and no-till systems on crop production, and to address grower concerns regarding crop yield, pest problems, and effects on soil structure and crop quality. Curtin et al. (3) reported that yield of continuous spring wheat was not significantly affected by tillage, nor did tillage have an effect on biomass production. In Spain, Lopez-Bellido et al. (10) reported that no-till and reduced-tillage improved soil water content and reduced soil erosion but may not always result in increased grain yield. Hammel (6,7) reported decreased winter wheat yield in no-till systems in clay soils due to increased bulk density of the soil. However, crop residues will accumulate over time in NT systems reducing soil erosion and improving the physical, chemical, and biological properties of dryland soils (1,8). In Spain, Lopez-Bellido (11) observed that hard red spring wheat grain quality was better under conventional tillage than no-till. The objective of the following study was to examine the effects of two tillage systems, conventional-till (CT) and no-till (NT), on the agronomic performance and grain quality of eight spring wheat cultivars on a silt-loam soil in the Palouse cropping region of Idaho.

Tillage Comparison Design

A four-year tillage trial was established at the University of Idaho Kambitsch Research Farm near Genesee, Idaho, where annual precipitation averages nearly 27 inches. The three-year crop rotation for spring wheat was winter wheat (Triticum aestivum L. emend. Thell.)-spring wheat-dry pea (Pisum sativum L. subsp. sativum), a common rotation used in both CT and NT systems in the region. The trial was established on a Palouse silt loam (USDA: Pachic Ultic Haploxeroll; FAO: Siltic Kastanozem) soil.

Treatments were arranged in four replications as a two-factor randomized complete-block split-plot design, with two tillage treatments as main plots and eight spring wheat cultivars as sub-plots. Conventional tillage consisted of chisel plowing to an 8-inch depth in the fall and two spring cultivations with a field cultivator with harrow attachment, a common tillage regime in the region. The chisel plow was 13 ft wide with straight coulter disks running in front of each shank. Each shank was 3 inches wide with 4-inch wide twisted shovels attached and shanks were spaced 12 inches apart. The cultivator was 36 ft wide with 1-inch wide shanks tipped with 5-inch wide shovels spaced 7 inches apart, and had a tine harrow following with tines spaced 3 inches apart. The depth of the cultivations was 3 to 3.5 inches. No-till areas were not disturbed except during planting operations. Tillage treatments were established for the 2000 crop year. In 2001 and 2002, experimental plots were seeded with a Great Plains (Great Plains Manufacturing, Inc., KS) no-till drill with a turbo coulter ahead of each of five double-disk openers spaced 9 inches apart. In 2003 and 2004, plots were seeded with a Flexi-coil (CNH America LLC) small-plot no-till drill with hoe type openers. Each of the five openers seeded a paired row with 3-inch spacing and openers were spaced 10 inches from center to center of pairs. Plots were 20 ft long.

The spring wheat cultivars were: ‘Penawawa,’ ‘Wawawai,’ and ‘Zak’ soft whites; ‘IDO 377s’ hard white; and ‘Hank,’ ‘Jefferson,’ ‘Westbred 926’ (WB 926), and ‘Westbred 936’ (WB 936) hard reds. The spring wheat cultivars were managed using cultural methods recommended in Northern Idaho Grower Guide (13). All management practices, including fertilizer, weed control, and pest control were uniformly applied across cultivars and tillage treatments to eliminate any confounding of the tillage and variety treatments with other management input effects. Planting dates were 24 April 2001, 24 April 2002, 16 May 2003, and 27 April 2004. Harvest dates were 17 August 2001, 16 August 2002, 25 August 2003, and 1 September 2004.

All plots were harvested with a small plot combine to determine grain yield. Seedling populations were determined by counting plants along 3.3-ft lengths of two rows at the two leaf stage. Plant height was measured from ground level to the tip of the terminal spikelet at two locations in each plot. Test weight, 200-seed weight, whole grain protein at 12% moisture, and kernel hardness were determined on sub-samples of harvested grain. Whole grain protein and kernel hardness were determined at the University of Idaho Wheat Quality Lab in Aberdeen, ID using Near Infrared Spectometry technology. Crop biomass, heads per square foot, and harvest index were determined from plants cut at soil level from 5.5 ft² of the physiologically mature plots prior to harvest. Harvest index was calculated as a ratio of the grain weight in the biomass sample to total biomass weight.

Data were analyzed using ANOVA with tillage treatments as main plots and cultivars as sub-plots (14). Year was considered random, and tillage and cultivar were considered fixed effects.

Effects of Cultivars, Tillage Treatment, and Years

As expected, there were significant differences among years and cultivars for all traits studied (Table 1). Furthermore the year and cultivar, or genotype, interaction was highly significant (P < 0.01) for all traits studied except seedling population (P = 0.073) and plant height (P = 0.135). Carr et al. (2) demonstrated in other spring wheat studies where genotype × environment, including years, were significant for all tested parameters. Navabi et al. (15) observed that the genotype × environment patterns were inconsistent over years and Ma et al. (12) reported that year × genotype, site × genotype, and year × site × genotype interactions were significant for spring wheat yields. Because the emphasis of this paper is on tillage effects on spring wheat, the data for the well demonstrated cultivar, year and cultivar × year interactions are not further reported.

Year had a significant effect on all traits studied (Table 1). Yield, test weight, seed weight, and harvest index were all significantly higher in 2001 than the other three years. In a study by Johnston et al. (9), environmental conditions prevailing from May to July explained 67% of yield variability observed in spring wheat. Much of the difference among years can be explained by weather. There was lower than normal June and July precipitation (30-year mean = 3.06 inches) in 2003 by 2.43 inches and in 2004 by 1.93 inches. Temperatures were also higher than normal in June and July of 2003 and 2004, reducing the grain-filling period and crop yields, as noted by Rao et al. (17). Furthermore, planting was delayed in 2003, and yield was nearly 20 bu/acre lower compared to 2002 at 61 bu/acre and 2004 at 60 bu/acre, and more than 30 bu/acre lower than in 2001 at 73 bu/acre. Despite the effects of year on crop performance, the year × tillage and the year × tillage × cultivar interactions were not significant for any evaluated parameter. This shows that years had a greater influence on cultivar performance differences than tillage.

Tillage influenced test weight (P = 0.014), 200-seed weight (P = 0.053), and grain protein (P = 0.074) (Table 1). Test weight was 1.2 lb/bu higher in NT than CT (Table 2), and as expected, the 200-seed weight was also higher in the NT than CT by 0.37 g. Under NT conditions, the soil temperatures tend to be cooler earlier in the growing season, resulting in slower growth observed and more conservation of soil water for the grain filling period (1). This is visually illustrated in Figure 1 in a photo taken on 25 July 2001, when crops were nearing maturity and changing color. This photo shows the experimental design with the three crops, dry pea, barley, and spring wheat planted left to right, and tillage strips running horizontally across the slope. Plots in some NT strips have remained green longer in the season than plots in the adjacent CT strips, presumably indicating more late-season soil water available in NT. Although soil water was not quantified in 2001, in 2004 soil water was two to five percent higher in NT than CT at crop physiological maturity (J. L. Johnson-Maynard, 2005, personal communication). Grain protein averaged 11.1% for the three soft white varieties, 13.1% for the four hard red varieties, and 12.2% for the hard white variety under uniform nitrogen fertility management. Grain protein was 12.0% in NT, lower by 0.5% (P = 0.074) than the CT treatment and all varieties had lower protein in NT than in CT. Higher test weight and seed size in NT than CT would indicate a better grain filling period in NT with more soil water, but a better grain filling period might also lower protein in NT and thus indicate a need for higher N availability to reach desired protein for hard varieties.

Fig. 1. Photo taken 25 July 2001 of tillage experiment at the Kambitsch Farm near Genesee, ID. CT and NT strips run horizontally across slope and crops. Visual color differences between tillage strips started about one week prior to this photo and lasted through crop maturity.

All other measured traits, including yield, were not significant between NT and CT (Table 1). In a lower rainfall area, Schillinger (18) measured lower yields in NT than CT in four of five years, reduced head number and straw weight in two of five years in NT, fewer kernels per head in NT three of five years, but no tillage effect on seed weight. This suggests that when moisture is severely limited, the variable grain quality differences between NT and CT that both we and Lopez-Bellido (11) observed may not be a factor in NT spring wheat production when moisture is not as severely limiting. There were no significant interactions between cultivars and tillage treatments except for harvest index (Table 1), where all cultivars had a greater harvest index in NT than CT except for IDO 377s, which was greater in CT.

Conclusions

This study shows that many spring wheat agronomic, quality, and biomass characteristics were not affected by no-till. The no-till treatment did not decrease yield nor adversely affect quality and increased test weight and seed weight. This benefit was possibly due to more available soil water conserved by not disturbing the soil with cultivation and preserving the residue layer, thus allowing for a longer grain filling period. However, delayed early growth with cooler soil conditions in NT and better grain filling in NT could have contributed to lower grain protein. The variation from year to year, due to precipitation and temperature differences, had the most significant effect on the characteristics studied.

No-till production systems can be economically attractive because of reduced fuel consumption and labor needs, but growers are concerned about decreased crop yield with no-till practices. This study showed that with proper management in these environments, yields can equal those obtained under conventional tillage practices and some grain quality factors can be improved. No-till systems can also benefit from improved soil quality factors, such as higher earthworm populations (8), and more crop residue remaining on the surface that retains soil water and reduces soil erosion.

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