Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 29, 2008
Publication Date: N/A
Interpretive Summary: Tillage in most crop rotations is used to prepare seed-beds, control weeds and other pests, manage crop residues, reduce soil compaction, and incorporate fertilizer and pesticides. Adopting conservation tillage to reduce erosion, increase N use efficiency, and build organic matter would improve soil and environmental quality under irrigated farming systems. A reduced tillage system for potato based rotations was developed using existing commercial field equipment with minor modifications. Compared to conventional tilled systems that leave little crop residue on the soil surface, our system maximizes residue retention and requires fewer trips across the field thereby saving time, labor, capital, and energy. This strategy reduced the total number of passes in potato rotations from nine to six and soil disturbance operations from seven to four, compared to those used in conventional tilled treatments. For sweet corn, field operations were reduced 50%. After four years of reduced tillage little change has been observed in microbial communities or activities. Populations of several plant pathogenic fungi tended to increase with higher fertilization rates under both tillage regimes. Pythium and V. dahliae populations within the conventional tilled potato treatment were greater than the reduced tillage treatment. Fusarium populations were greater under reduced tillage for potato as well as the two corn treatments. There were no significant differences found in potato, sweet corn or field corn yields between treatments receiving variable fertilizer rates or timing of fertilizer applications under center pivot irrigation.
Technical Abstract: Potato production in irrigated regions typically occurs on soils low in organic matter that are highly susceptible to agri-chemical leaching under poor irrigation scheduling, and wind erosion when soils are left bare. Reduced tillage has had limited testing in potato production. The objective of this research was to determine the effects of reduced tillage (RT) and conventional tillage (CT) on soil chemical, biological and physical properties of an irrigated sweet corn/sweet corn/potato (Zea mays-Zea mays-Solanum tuberosum) rotation. The RT strategy used reduced the total number of passes from nine to six and soil disturbance operations from seven to four, including harvest, compared to those used in the conventional tilled treatments. For sweet corn, field operations were reduced 100% during corn years as corn was seeded directly into the previous year’s residue. Reducing tillage did not adversely affect potato yields, averaging 74.0 and 73.7 Mg/ha for the conventional and reduced tillage treatments respectively. Compared to CT, RT-second year sweet corn yields declined an average of 8% from first year sweet corn and 15% in the reduced tillage compared to CT treatment. Potato vine biomass averaged 2700 kg/ha among both CT and RT treatments over the 4-year period. First year sweet corn stover biomass averaged ~ 5450 and ~ 4900 kg/ha for the CT and RT treatments respectively, and declined 300 – 500 kg/ha for second year sweet corn. Stover C:N in RT treatments were 4-10 units higher than CT. Soil bulk density increased from 1.20 to 1.48 Mg/m in a year. Total soil organic C, microbial biomass, and C and N mineralization potentials showed no significant increase after four years of reduced tillage. Extended laboratory incubations of soil with measurements of CO2 were used to differentiate the size and turnover of the Ca and Cs functional C pools. We used a three pool model to describe the turnover of soil organic matter as a function of tillage. The Ca pool comprised less than 5% of the total C and had an average field MRT of <25d. The slow pool (Cs) contained 47-52% of the total C and had field MRT’s ranging from 5-10y . Pythium, Fusarium and V. dahliae populations declined by the 4th year under reduced tillage. Use of reduced tillage in this rotation did not adversely affect yields and showed a positive although minor influence on soil properties.