2000 Table of Contents

2000 STEEP III Progress Report

RESEARCH PROJECT TITLE: Impact of direct seeding on crop water use efficiency, soil physical and microbial
properties and quality of soil organic matter.

INVESTIGATORS: David Bezdicek, WSU; Steve Albrecht, ARS, Pendleton; Mary Fauci,
WSU, Pullman; Marcus Flury, WSU, Pullman; John Hammel U of ID.

INTERIM REPORT:

PROJECT OBJECTIVES: 1) Determine crop water use efficiency, seed zone temperature, soil profile winter water storage, and N use efficiency under DS and conventional systems. 2) Evaluate the transitional soil physical and biological interactions under DS systems and the influence from different crop rotations. 3) Evaluate the quantity and quality of SOM changes under DS systems and the significance in sequestering atmospheric carbon dioxide.

KEY WORDS: direct seed, soil quality, carbon sequestration, crop rotation

STATEMENT OF PROBLEM:
Many growers are asking about costs and benefits from DS systems in the long term and in the transitional period. Long-term benefits are best understood, but short-term benefits are less certain given the current depressed commodity prices and the cost of getting into DS. One short-term benefit is increased soil water storage and water use efficiency under DS. Another is the change in soil pore size distribution from old root and earthworm channels under DS. In spite of greater compaction under DS systems, water infiltration seems to be increasing. Soil organic matter (SOM) increases at the surface of DS and is the property most talked about by growers and researchers alike because it holds the key to so many vital functions in soil. Total SOM tells us little about the quality of SOM, but the POM and light fractions of SOM accumulate quickly under DS and can be used as indicators of soil quality in the transition period. Increasing SOM under DS means carbon is being sequestered. Sequestering C interests grower hoping to participate in trading C credits.

ZONE OF INTEREST: Studies will take place in high, intermediate, and low rainfall zones.

ABSTRACT OF RESEARCH FINDINGS: In the Pacific Northwest, the concern for loss of soil organic matter with tillage and the potential to sequester C by eliminating it has stimulated interest in direct seeding or no-till. Soil water, nitrogen behavior, and seed zone temperature in long-term conventional (CT) and direct seed (DS) sites were measured to evaluate if DS increases soil water storage and water use efficiency. At one location under DS, there was better accumulation and distribution of soil water. Long-term simulations with the CropSyst model indicate optimization of water conservation is a primary goal to enhance yield. Sites were also evaluated for total soil C, soil respiration, particulate organic matter (POM) C, and POM supported respiration. Reducing tillage and eliminating fallow increased carbon sequestration in soils as indicated by the various soil C measurements.

RESULTS AND INTERPRETATION: Research sites for our studies are grouped by rainfall zone below.

High rainfall zone: Palouse, WA - These plots are located at a private farm with a winter wheat-barley-lentil rotation. The farm has not been tilled for more than 25 years. In 1996 the grower began farming an adjacent field that previously had been managed with conventional tillage. Soil samples were taken in 1996 and 1998 at four paired locations within the long-term NT (WA25NT) and the adjacent new NT (WA1NT or WA3NT) fields, respectively.

Intermediate rainfall zone: Pendleton, OR - Soil samples were collected from the following long-term plots located on the Columbia Basin Agricultural Research Center in spring 1998. Pasture (OR pasture) - permanent pasture since 1931, grazed until 1985, and since then has been clipped once or twice a year. Conventional tillage (OR68CT) - established in 1931, the rotation is winter wheat/fallow, the tillage is moldboard plow and residue is burned in the spring. No-till or direct seed (OR16NT) - started in 1982, there is no tillage, since 1988 the rotation is winter wheat/fallow and wheat stubble is flailed and left on the field. Whitman and Garfield counties, WA - Seven sites in the Northwest Crop Project comparing three and four year DS rotations.

Low rainfall zone, Touchet, WA -14 years continuous DS spring wheat compared to conventional wheat-fallow.

Soil water and nitrogen behavior, seed zone temperature, as well as other soil characteristics under DS and conventional systems (CT) were analyzed during two years at Palouse and Touchet as part of Juan- Pablo Fuentes's M.S. work. Under DS, there was better accumulation and distribution of soil water at Palouse. Soil temperatures under CT at Palouse tended to be higher in summer and lower in winter as compared with DS due the insulating effects of crop residue. Thus, the potential for a reduction in soil water evaporation during the drier season was created under DS. At the drier location (Touchet), soil moisture followed the same trend under DS and CT, which could indicate no real benefits of fallow in water storage.

No differences in water uptake efficiencies were found between DS and CT. Water supply (Ws) significantly increased evapotranspiration (ET). Additionally Ws and ET were significantly and positively correlated with grain yield and above ground biomass. Water utilization efficiency of the winter crops at Palouse was higher under DS than under CT. In contrast, water utilization efficiency of spring cereals was higher under CT. Comparisons in utilization efficiencies between DS and CT at Touchet were not possible to verify.

Nitrogen use efficiency for grain and above ground biomass, as well as N uptake efficiency was linearly correlated with the amount of water supplied and evapotranspiration. Therefore, the water balance mainly controlled the N uptake and N use efficiency.

After the appropriate calibration of the CropSyst model, long-term simulations of DS and CT for both locations showed the higher sensitivity of the drier area in terms of yield. Under abnormal dry conditions, cereal grain yields can be affected by more than 60%. Therefore, optimization of water conservation must constitute a primary goal.

Our previous STEEP III research had found increased SOM under DS compared to conventional tillage. The greatest increase in SOM of 50% was noted at Palouse, with a slight increase noted at the wheat-fallow site at Touchet. Many of the above measurements were highest for direct seed compared to conventional at the soil surface 0-5 cm (0-2 inches), but were lower at the 5-20 cm depth due to the lack of surface soil inversion. At the Palouse site we are able to follow a transitional period as an adjacent parcel has been under DS for three years now. However, the Palouse site is unreplicated and may be unique. Therefore we sampled replicated tillage plots from the Pendleton Research Station for additional soil C measurements. Soil from long-term conventional and direct seed sites in Oregon and Washington was evaluated for soil C, C respiration, particulate organic matter (POM) C, and POM supported respiration. Light fraction C and a stable C pools are being analyzed.

Soil C decreased with depth in soils that are not tilled and was evenly distributed in the tilled system (Figure 1). Carbon under NT was the highest at the surface where residues accumulate, but C under CT was similar at all depths because tillage mixes residues resulting in even distribution of C in the profile. Reducing tillage and eliminating fallow increased carbon sequestration in soils as measured by soil C. Baseline soil organic matter determinations were also made at the seven sites in the Northwest Crop Project. After a complete crop rotation the site will be resampled to evaluate the accumulation of SOM under DS with various crop rotations.

Figure 1. Soil C from Oregon and Washington sites. n=4. Error bar represents standard deviation of the mean.

Soil respiration (SR) was monitored in the laboratory. High respiration indicates an accumulation of C that under ideal conditions is easily mineralized. Highest SR rates were in the 0-5 cm depth in direct seed systems and in permanent pasture (Table 1). Soil respiration under conventional tillage systems (i.e. moldboard plow) was similar at all depths. When expressed on a C basis, soil C at the soil surface is more labile under a no-till system than under conventional management and it is also less reactive at lower depths. Under CT, soil C is equally reactive at all depths due to distribution of fresh residues with tillage (Table 1). This observation suggests conventional tillage accelerates carbon loss from soil, while DS and pasture sequester atmospheric carbon. The accumulation of C at the surface under DS is rapid. Within three years C was sequestered at the surface as indicated by the increased respiration in the 0-5cm (Table 2) in the WA03 compared to WA01.

Table 1. Cumulative CO₂-C respired in 365 days on soil basis and on a soil C basis (adjusted for the amount of C).

Table 2. Years into DS and its effect on accumulation of soil C as indicated by soil respiration measurements. Cumulative CO₂-C respired in 80 days.

The particulate organic matter POM is a labile pool of SOM between 53 and 2000 micrometers. Measuring POM C allows us to detect changes in soil C before changes in total soil C are measurable. The POM C accumulated at the surface in the pasture and NT soil and tillage created an even distribution of POM C throughout the profile (Figure 2). Within three years, the accumulation of POM C at the soil surface is evident.

Figure 2. Particulate organic matter C from Oregon and Washington sites. n=4. Error bar represents standard deviation of the mean.

The amount of C respired from the POM fraction reflected the amount of POM C in the soil. Under conventional tillage, POM is similar at all depths within the tillage zone and POM respiration is intermediate between that of the surface and lower depths of DS systems (data not shown). When POM C respiration was expressed on a POM C basis, we found surface POM of the WA03 site was more labile than the POM remaining at the surface for 25 years or more. A similar trend occurs at lower depths, where POM C from WA03 is still more labile than POM C from WA25. How C passes from fresh residues into the POM fraction, light fraction and ultimately into the recalcitrant C pools will aid our understanding of a soil's potential to store soil C.

Table 3. Respiration of the POM C expressed on a soil basis and adjusted for the amount of POM C present. Cumulative CO₂-C respired in 365 days.

Our preliminary survey of worms in Eastem WA and Northem ID in the spring of 1999 found worms throughout the intermediate and high rainfall zones. Tunneling activity of worms forms macropores that can improve water infiltration. Canadian research has shown increased earthworm populations after a broadleaf crop in rotation, such as canola, mustard, flax, pea, and lentil. We are following earthworm populations at the Ruark's plots near Pomeroy, WA. These plots are part of the Northwest Crop Project, a crop rotation study. We place 8-inch diameter rings in plots representing each of the residues from the four-year rotation. We sampled twice in spring 1999 and three times in spring 2000. We plan to continue sampling over the next two seasons to follow the crop effect on earthworms.

INTERACTION (COOPERATION) WITH OTHER SCIENTISTS CONDUCTING RELATED ACTIVITY: We work with Dennis Roe, NRCS, Colfax on the Northwest Crop Project. David Huggins, ARS, Pullman has collaborated on the water use efficiency, seed zone temperature, water storage, N use efficiency and crop modeling portion of this research. Stewart Wuest and Dale Wilkins, ARS, Pendleton, are involved with the earthworms and soil C modeling, respectively.

PUBLICATIONS AND PRESENTATIONS:
Albrecht, S. L., D. F. Bezdicek, M. F. Fauci, K. W. Skirvin, and R. W. Rickman. 2000. Effects of tillage on soil carbon in semiarid cropland. In Patterson, L., D. Singh, and P Frank (eds) 2000 Columbia Basin Agricultural Research Center Annual Report. Ag. Exp. Stat., Oregon State Univ. Special Report 1012. pp 14-18.

Albrecht, S. L., M. F. Fauci, D. F. Bezdicek, and K. W. Skirvin. 2000. Organic matter fractions from Pacific Northwest soils: Depth and tillage effects. In Patterson, L., D. Singh, and P Frank (eds) 2000 Columbia Basin Agricultural Research Center Annual Report. Ag. Exp. Stat., Oregon State Univ. Special Report 1012. pp 19-23.

Bezdicek, D. F., M. F. Fauci, and R. D Roe. 1999. Earthworm dynamics and soil biology. Seedsman Northwest. Sept/Oct.

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