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.   Specific objectives are to determine the effects of reduced tillage on 1) weed dynamics, 2) soil organisms and their activities (i. microflora, ii. plant pathogens, and iii. nematodes), 3) carbon and nitrogen cycling and trace gas (CO2, N2O, CH4) fluxes, and 4) changes in nitrogen use efficiency. 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 trended 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.