There is a lack of data on conservation tillage under field conditions characteristic of a dairy operation. Thus, simulated rainfall was used to compare total P (TP), algal-available P (AAP), and dissolved molybdate-reactive P (DMRP) losses from the conventional, chisel, and no-till systems for corn both with and without surface-applied manure prior to tillage. Rainfall was applied at several times during the growing season of 1978 and 1979. A portion of the previous year's residue was removed in 1978 and all the residue was left in 1979. Concentrations and losses of TP and AAP among unmanured tillage treatments were similar to trends observed for sediment concentrations and losses. In 1978, the chisel and notill systems were ineffective in reducing TP and AAP losses relative to the conventional system. In contrast in 1979, lower TP and AAP losses occurred from unmanured chisel and no-till sites relative to unmanured conventional sites. In both years of the experiment, surface spread manure increased DMRP concentrations where the manure was not completely incorporated by tillage. In contrast, little difference was observed in DMRP concentrations among unmanured treatments. Manure also increased AAP concentrations for no-till but had only a slight effect and no effect for the chisel and conventional systems, respectively. AAP concentrations from manured sites followed the order no-till > conventional = chisel. Differences in runoff volumes among treatments influenced P losses. Runoff losses were relatively high for no-till, particularly after planting, and losses of DMRP and AAP were very high where manure was surface applied. Often, runoff was reduced for the chisel system relative to other tillage systems, and consequently these reductions increased the effectiveness of this system in reducing P losses.

Little data are available on P losses in runoff from land under conservation tillage (CT) where the surface‐applied fertilizer variable has been eliminated. Thus, simulated rainfall was used to evaluate the comparative effects of four tillage systems on the losses of total P, dissolved molybdate‐reactive P (DMRP) and algal‐available P (AAP) where fertilizer was subsurface banded at planting. Tillage treatments included conventional (CN) and three CT systems: chisel plow (CH), till‐plant (TP) and no‐till (NT). Above‐ground portions of corn (Zea mays L.) plants were removed prior to simulation. Trials were conducted over a 4‐yr period, with individual trials being performed in June and July, September, or October of various years. The NT, CH, and TP treatments reduced total P losses by an average of 81, 70, and 59%, respectively, relative to CN. Concentrations and losses of total P among tillage treatments followed those for sediment concentrations and losses. Concentrations of DMRP were, in most cases, lowest for CN, although differences among treatments were generally small and not significant. With the exception of the first simulated rainfall trial (September 1980), no significant correlation was observed between DMRP concentrations and residue cover. Losses of DMRP for the CT treatments were similar to, or significantly lower than those for CN. Differences in AAP concentrations varied among treatments and sampling periods, although concentrations were usually lowest for NT. The relative percentage of AAP concentrations to total P concentrations increased over the course of this study. This increase was 6, 8, 26% higher for CH, TP, and NT, respectively, relative to CN. Relative to CN, the NT, CH, and TP treatments reduced AAP losses by an average of 63, 58, and 27%, respectively. These results indicate that CT systems can effectively reduce AAP losses in runoff relative to CN, especially at times when high sediment concentrations and losses occur from conventionally tilled land.

Little data are available on conservation tillage under field conditions characteristic of a dairy operation. Thus, simulated rainfall was used to compare soil and water losses among conventional, chisel, and no‐till systems for corn both with and without surface‐applied manure prior to tillage. Rainfall was applied at several times during the growing season of 1978 and 1979. A portion of the previous year's crop residue was removed in 1978 and all the residue was left in 1979. A tillage × date interaction was observed for runoff losses in both years of the experiment. Significantly lower runoff occurred for the conventional and chisel systems relative to the no‐till system immediately after planting. At later sampling periods, runoff significantly increased for the conventional system and runoff losses approached that from no‐till. In contrast, lower runoff losses occurred for the chisel system relative to the other tillage systems. This was most apparent in 1979 when more residue was partially incorporated or left on the soil surface. Surface spread manure decreased runoff for all tillage treatments at the September 1978 sampling period and at both sampling periods in 1979. The results indicated the greatest response with the chisel system. In 1978 and 1979, a tillage × manure interaction was observed for soil loss. In 1978, little difference in soil loss was observed among unmanured tillage treatments. However, the application of manure reduced soil losses for chisel and no‐till systems relative to the conventional system. In 1979, soil losses were lower from unmanured chisel and unmanured no‐till treatments than from the unmanured conventional treatment. Soil losses were significantly lower from the manured chisel treatment than all other treatments.

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Time of data collection relative to recent tillage may influence results of studies comparing water and soil losses among tillage systems. In this study a rainfall simulator was used at various times during the growing season over a 4‐yr period: (i) to compare water and soil losses from conventional (moldboard plow; CN) and three conservation tillage (CT) treatments: chisel plow (CH), till‐plant (TP), and no‐till (NT) and (ii) to observe major trends in runoff volumes as a function of rainfall simulation date. Above‐ground portions of corn (Zea mays L.) plants were removed prior to rainfall simulation. Trials were conducted in September 1980, June and July 1981, October 1982, and June and July 1983. Runoff volumes for CT treatments were consistently less than those observed for CN. For CT treatments, the volume of runoff (per unit rainfall) averaged 11, 20, and 52% lower than that observed for CN for the June 1983, July 1981 and 1983, and October 1982 sampling periods, respectively. Only the CH treatment significantly reduced runoff relative to CN soon after planting. Among CT treatments, CH was significantly more effective in reducing runoff in September 1980. For the remaining sampling periods, differences among CT treatments were not significant. An increase in residue cover consistently resulted in a decrease in sediment concentrations and, most often, a decrease in soil loss. Across all sampling periods, the NT treatment consistently decreased soil loss by 80 to 90% relative to CN, while soil losses for the CH and TP treatments varied, ranging from about 45 to 90% less than those for CN. Only in September 1980 did low runoff for CH result in soil loss which was less than that observed for NT.