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Packing Summer Fallow Before Seeding Wheat: Agronomic Benefits and Environmental Concerns

Bill Schillinger and Harry Schafer, WSU Ritzville
with Grant Miller and Ron Jirava

Objective

To determine the effects of compressing the dry surface soil mulch of summer fallow with a coil packer on seedzone water content, soil bulk density, winter wheat emergence, and soil susceptibility to wind erosion.

  1993 1994
Location: Ritzville, WA Lind, WA
Annual precipitation: 11 inches 9 inches
Soil: Ritzville silt loam Shano sandy loam
Cropping System: Wheat-Fallow Wheat-Fallow

Treatments

Check - no packing
Coil packed

Field Operations

1993: Coil packing was conducted on August 25. Plots were seeded to Lewjain at 35 lb/ac on August 27 with HZ split-packer drills (16" row spacing). Plots were seeded at two depths: shallow - approximately 4" and; deep - approximately 6". There were six replications.

1994: Plots were coil packed on August 29 and seeded to Lewjain at 35 lb/acre on August 30 with International split-packer drills (18" row spacing). Seeding conditions were marginal. The drills were set to place seed as deep as possible. Plots were replicated six times.

Results

Soil Bulk Density. In 1993, coil packing significantly increased soil bulk density (i.e. the weight of dry soil per unit volume) between the 2.5 and 5" soil depths (Fig. 1). In 1994, the dry surface soil mulch layer was thin, overlying a high bulk density layer. Because the loose surface layer was so thin, coil packing had no effect on soil bulk density (Fig. 2).

Wheat Seedling Emergence 1993: With shallow seeding, there were significant differences in the number of plants emerged between 7 and 9 days after planting (DAP) (Table 1). This would have been important, for example, if a crusting rain had occurred between 7 and 9 DAP. For 10 DAP onwards there were no differences in seedling emergence nor final stand establishment between treatments. With deep seeding, coil packing resulted in significantly better seedling emergence on all sampling dates as well as the best final stand establishment (Table 2). The reason for these differences in not clear, although roll-back of large soil clods into the furrow may have hindered seedling emergence in control plots. Note: Because of the excellent seeding conditions in 1993, deep seeding was somewhat of an "artificial" treatment.

1994: Coil packing had no effect on wheat seedling emergence in 1994 (Fig. 3). The hard tillage pan impeded penetration of the grain drill points into the soil, and seed placement averaged only 1.8" below the pan created by the rodweeder in both packed and control plots.

Soil Clods and Residue. Coil packing reduced the number and weight of clods in all size groups both years (Fig. 4 and Fig. 5) The proportion of clod reduction with coil packing was similar for both the Ritzville and Shano soil types. Clods are especially difficult to maintain on the coarse-textured Shano soil due to lack of soil structure and low (<1%) organic matter. There was a large quantity of surface residue remaining on the Shano soil at the end of the fallow cycle at Lind in 1994. Coil packing significantly reduced surface residue from 1124 lb/acre to 722 lb/acre.

Yield Components and Crop Characteristics. In the 1993-94 crop year, packing increased grain yield about 5 bu/acre over the control treatment in both deep seeded and shallow seeded plots (Table 2). The yield difference was primarily due to more heads per unit length of row in packed plots (Table 2). Of interest, grain yield with deep seeding exceeded that of shallow seeded plots for both packed and control treatments.

Summary

In 1993, coil packing a thick, low-bulk density soil mulch significantly increased wheat seedling emergence and benefited grain yield. In 1994, on a soil with a thin mulch layer overlying a high-bulk density tillage layer, there were no effects of coil packing on soil bulk density nor wheat seedling emergence. Packing rendered the soil more vulnerable to wind erosion at both locations by burying residue and reducing clod mass. In our opinion, the coil packer should: 1) always be used judiciously, and 2) not used when the soil surface is already deficient in clods and/or residue.

Table 1. Wheat seedling emergence (plants per 3 ft of row) on several sampling dates as affected by coil packing prior to fall seeding in 1993.

Shallow Seeding Deep Seeding
DAP1 Control Coil Packed Sig. DAP Control Coil Packed Sig.
7 0.2 1.8 ** 8 0.2 1.4 *
8 10.8 18.9 *** 9 6.2 13.1 **
9 26.0 31.8 * 10 20.7 30.0 **
10 35.5 38.3 NS 11 24.8 32.1 **
11 37.1 39.5 NS 12 26.4 33.6 **
12 36.9 39.8 NS 18 26.7 33.2 *
18 36.1 38.9 NS        

    1Days after planting
    *, **, *** Significant emergence differences at the 0.05, 0.01, and 0.001 probability levels, respectively, for each sampling depth.
    NS Not significant

Table 2. Yield components and crop characteristics of Lewjain winter wheat in the 1993-94 season.

COMPONENT Packed-Deep Seeded Control-Deep Seeded Packed-Shallow Seeded Control-Shallow Seeded Sig. CV (%) LSD
Grain Yield (bu/acre) 58.4 53.0 53.6 48.6 * 4.9 7.9
Kernels per head 30.1 31.5 28.0 29.2 NS 9.2  
1000 grain weight (g) 36.6 37.0 34.6 33.7 *** 5.2 2.3
Heads per 3 ft of row 145.3 125.3 151.8 134.8 ** 11.9 20.5
Residue (lb/acre) 4578 4036 4302 3891 NS 5.2  
Harvest index (HI) 43.4 44.0 42.9 42.8 NS 1.8  

    NS = no significant differences
    * = significant at 10% level
    ** = significant at 5% level
    *** = significant at 1% level
    HI = (grain yield/total above-ground dry matter) x 100

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Chart 2
     
 

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Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA Redesigned by Leila Styer, CAHE Computer Resource Unit; Maintained by Debbie Marsh, Dept. of Crop & Soil Sciences, WSU