The Problem

Winter wheat established after legumes using conventional tillage systems can leave the soil vulnerable to erosion. About 65-75% of annual precipitation falls after wheat seeding when plants are small and can occur during freeze-thaw cycles. Erosion can be reduced with greater residue cover and soil roughness, and improved water infiltration. Residue cover is usually most effective. Growers have reduced tillage before planting winter wheat after legumes, but fragile legume residues and low residue production often leave little soil cover overwinter. Surface residue levels going into winter wheat could be increased by carrying over spring cereal residue grown before the legume crop. However, spring cultivations are often indicated for incorporation of many legume herbicides. After fall and spring tillage, little cereal crop residue remains to carry through winter wheat planting. Conventional tillage practices for legume production can also increase soil compaction in wet spring condition, reducing water infiltration and increasing erosion potential. This problem is of greatest interest in the higher precipitation Palouse region of Idaho and Washington.

Experimental Results and Interpretation - Tillage Trials

A farm equipment scale trial to evaluate dry pea and lentil residue production and durability across cultivars and tillage intensity is completed for the first year of legume crop and into winter wheat seeding. It was conducted at the UI Kambitsch Research Farm near Genesee, ID. Legume yields, residue production, and residue ground cover after fall tillage and wheat seeding appear in Table 1. Winter wheat was seeded with a 'Haybuster' no-till drill that banded dry fertilizer between rows at the equivalent rate of 'ripper-shooter' applications in the tilled plots.

Results show that Pro-2100 produced the highest seed yield and lentils yielded about as much as the Columbia pea. Crop residue production was highest for Pro-2100, about twice that of lentil. Each additional tillage operation reduced residue groundcover. Planting using this no-till drill reduced residue groundcover from 44 to 27% averaged across tillages and crops and from 75 to 40% in the no-till plots. Using a conventional double-disc opener drill to seed the tilled plots would not have decreased the surface residue as much. This no-till drill with its shank fertilizer application is roughly equivalent to the ripper-shooter in reducing residue groundcover.

Table 1. Legume residue production and maintenance through winter wheat seeding under different tillage practices at UI Kambitsch Research Farm, Genesee, Id, 1997

A spring cereal trial to evaluate wheat and barley residue carryover through pea seeding into winter wheat establishment was started in 1996 at the UI Kambitsch Research Farm as spring wheat and barley strips. Four fall tillage treatments were applied after harvest. The 1996 Cereal crops did not yield as well as desired due to poor seeding conditions followed by dry weather (Table 2). Residue groundcover was consequently lower than desired due to the poor performance of the spring cereal crops, but barley did give higher groundcover levels than spring wheat. The tillage plots were cultivated twice before seeding was with a JD455 drill. Pea establishment was highest in the paratill and lowest in the no-till, mostly due to limited opener penetration under these dry conditions. Many of the plants established in the no-till after spring rain, but did not contribute as much to yield making the no-till lower yielding than the other fall tillage treatments.

Following fall tillages, groundcover was followed through the winter and pea seeding in the spring (Table 3). Residue levels remained nearly constant through the winter with a tendency to decline slightly in the spring. Lowest residue levels were following plowing that gave a 'black soil'. Residue groundcover following chisel and paratill treatments were not different at any sample date and the no-till give the highest levels. Residue levels declined due to preparation for and seeding of pea as shown in the 20-May levels. After pea harvest, the ground was cultivated and winter wheat seeded with a double-disc drill. Residue levels were low and limited cereal residue from the 1996 cereal crop provided limited groundcover.

A repeat of the previous Kambitsch Farm study was started in 1997 and spring barley yielded 83 bu/A while spring wheat yielded 40 bu/A after an extensive Hessian Fly infestation. This indicates that pests can be an increasing factor in reduced tillage systems. Groundcover residue was over 97% after spring crops and fall tillages were done in good soil conditions.

A crop residue management study comparing 1995 fall plow - spring cultivate - seed, fall chisel - spring direct seed, and fall flail-chisel - spring direct seed treatments after 90 bu/A spring wheat was conducted with Wayne Jensen near Genesee, ID. Soil moisture and temperature were not different before seeding of the pea crop. Residue was higher in the chisel treatments throughout the study (Table 4). Peas were planted in 1996 and did not yield differently due to tillage. In the chisel treatments, over 35% of the residue after the pea crop came from spring wheat. Residue groundcover varied little overwinter after planting wheat and wheat yields were not different among tillage treatments. This trial shows the benefit of reducing the tillage on cereal residue before a pea crop to carry some of that residue forward to protect the soil after winter wheat seeding without impact on pea or wheat yield.

Table 4. Tillage comparisons following 1995 spring wheat through 1996 pea and 1997 winter wheat crops, Wayne Jensen Farm, Genesee, ID

A repeat of the previous study was started in fall 1996 using the plow and chisel treatments after a 70 bu/A spring wheat crop. Residue groundcover was always higher in the chisel treatment than in the plow (Table 5). Pea plant population and yield were not affected by previous tillage treatment and greater groundcover is available during winter wheat establishment because of more crop residue when tillage is reduced.

Table 5. Tillage comparisons following 1996 spring wheat through 1997 pea and 1998 winter wheat crops, Wayne Jensen Farm, Genesee, ID

Near Colton, WA, in cooperation with Art Schultheis, a comparison of direct spring seeding of lentils after harrow versus cultivation after harrow and before seeding was started in spring 1997. The stubble of the spring barley was disced in early fall and chiseled/harrowed in late fall. Residue levels and lentil crop performance were not different for the two spring treatments (Table 6). This study shows that tillage before seeding lentils can be reduced with no adverse effects on lentil performance and reduces potential for soil compaction. Under many conditions this may increase the previous crop residue on the lentil fields.

In addition to the on-going trials above, there are eight new on-farm trials started in the fall of 1997 to evaluate residue management systems in reduced tillage for legume cropping to increase residue through winter wheat seeding. These sites are:

1. Nathan and Steve Riggers west of Nezperce, ID following 65 bu/a spring wheat with a) fall plow - conventional seed, b) fall disc - direct seed, c) spring burn - direct seed, d) direct seed

2. Eric Hasselstrom near Winchester, ID following winter wheat with a) fall flail - direct seed, b) spring burn - direct seed, c) fall disc - direct seed, d) direct seed

3. Randy and Larry Keatts south of Lewiston, ID following spring wheat with a) fall disc - direct seed, b) fall subsoil/disc - direct seed, c) fall chisel/harrow - direct seed, d) spring burn - direct seed, e) direct seed

4. Art Schultheis near Colton, WA following winter wheat with a) fall disc/subsoil - direct seed b) direct seed

5. Richard Druffel south of Pullman, WA following spring wheat with a) fall disc/subsoil - direct seed b) direct seed

6. Larry Cochran near Colfax, WA following spring barley with a) fall chisel and fall cultivate/harrow - direct seed, b) direct seed

7. Bob Garrett near Endicott, WA following spring wheat with a) fall chisel/harrow - direct seed, b) direct seed

8. Bob Garrett near Endicott, WA following winter wheat with a) fall chisel/harrow - direct seed, b) direct seed

Planned for several of the trials are additional weed control option studies, soil physical properties studies, and fertility response studies in conjunction with tillage variables.

Weed Control

In 1997, weed control options for legumes under reduced tillage or high residue situations were investigated. Herbicides were applied across the tillage strips on the trial with Wayne Jensen near Genesee, ID and to a lentil field with carryover residue south of Genesee. Imazethapyr (Pursuit) and imazethapyr/pendimethalin (Prowl) were applied before planting and spring tillage operations. Metribuzin (Lexone/Sencor) was applied after planting and before emergence. Quizalofop (Assure), bentazon (Basagran) and imazamox were applied at the 7-8 node growth stage of pea and bud stage of lentil.

Weed control could not be evaluated due to low weed population at both sites. Lentil was injured severely with imazamox and was too green to harvest (Table 7). Lentil yield did not differ among the harvested treatments. Pea was not injured with any treatment and pea yield was not different among herbicide or tillage treatments (Table 8).

Soil Physical Properties

Soil physical properties were measured to evaluate effects of tillage. Soil impedance (SI) and bulk density were measured in the spring of 1997 at two sites, the spring cereal residue carryover trial at the UI Kambitsch Farm near Genesee and the 1996-1997 trial with Wayne Jensen. Soil impedance was measured with a soil penetrometer to a depth of 20 inches. Bulk density of the soil surface layer (0-4") was measured with a surface density gauge.

At the Jensen site, SI and bulk density of the chisel treatment was greater than the plow treatment (Figure 1). This is due primarily to the greater soil disturbance achieved with the moldboard plow compared to the shallower, less inversive chisel treatment. These differences in SI and bulk density, however were not significant.

At the Kambitsch site, soil physical properties reflected the depth and type of tillage (Figure 2). No-till had the highest levels of SI within the soil surface zone affected by tillage (0-8"). Values of SI in the no-till treatment were approximately two times greater than SI values within the other tillage treatments. No substantial differences in SI were found among plow, chisel and paratill treatments. Bulk densities of the soil surface layer (0-4") were not significantly different among tillage treatments, although no-till had the highest bulk density.

Fig. 2. Soil impedance and surface layer bulk density results comparing plow, no-till, paratill and chiesel tillage treatments.

Publications

Veseth, R.J., S.O. Guy, D. Thill, J. Hammel, T. Fiez, J. Yenish. 1997. New minimum tillage systems for legume-winter wheat cropping sequence. PNW Conservation Tillage Handbook Series No. 20, Chap.2. PNW Extension publication in Idaho, Oregon and Washington. (Distributed through the May 1997 PNW STEEP III Extension conservation Tillage Update)

Veseth, R.J. June 1997. Direct seed pea/lentil tour. The Growers' Guide. Colfax, WA

Veseth, R.J., S.O. Guy, D. Thill, J. Hammel, T. Fiez, J. Yenish. 1997. New minimum tillage systems for legume-winter wheat cropping sequence. June 1997 Field day proceedings: Highlights of Research Progress. Washington State Univ. Dept. of Crop and Soil Sciences Technical Rpt. 97-1

Veseth, R.J., S.O. Guy, D. Thill, J. Hammel, T. Fiez, J. Yenish. 1997. New minimum tillage systems for legume-winter wheat cropping sequence. June 1997 Field Day Research and Extension Report. Univ. of Idaho, Dept. of Plant, Soil and Entomological Sci.

Veseth, R.J., S.O. Guy, D. Thill, J. Hammel, T. Fiez, J. Yenish. October 1997. New minimum tillage systems for legume-winter wheat cropping sequence. The Growers' Guide, Colfax, WA