1989 Annual Report for LNC89-024
Crop Rotation, Legume Intercropping, and Cultural Pest Control as Substitutes for Purchased Inputs in a Cash Grain Cropping System
Summary
Rationale:
Production research in recent years has focused primarily on the development of individual
technologies. Evaluation procedures of the research have primarily focused on production per
acre, productivity per unit input or return to the investment in the technology. Little work has
been done to compare the relative advantage or disadvantage of alternative technologies or
production systems.
Objectives:
1) Determine the effect of crop rotation, at different levels of purchased chemical and fertilizer
input, on the productivity and profitability of each cropping system.
2) Determine the effect of the crop rotation, legume intercropping and varying levels of
purchased fertilizer inputs on the fertility of the soil over time.
3) Determine the influence of crop rotation and varying levels of chemical and mechanical weed
control on weed populations and species shifts over time.
4) Determine the long-term effects of cropping systems and level of purchased inputs on soil
productivity.
Methods:
The specific cropping systems used in the study were: continuous corn, corn/soybeans,
corn/soybeans/wheat, and corn/oats/canola. Within each rotation, four management strategies
were employed: 1) standard extension recommendations with a corn yield goal of 150 bushel per
acre; 2) a maximum yield system designed to use all the best currently available technology with
a corn yield goal of 180 bushel per acre; 3) a reduced input system with the goal of producing
reasonable yields (>80 percent) of normal while reducing the use of purchased fertilizer and
pesticide inputs by 40 percent; and 4) a true organic production system using no purchased
fertilizers or pesticides. Animal manure or sludge was not used as nutrient sources in any system.
Rather, legumes were interseeded in rotations where possible as nitrogen sources. The study was
conducted for two years (1989-1990) at the Throckmorton Purdue Agriculture Center near
Lafayette, Indiana.
Results:
In the low input system, corn yields for the rotational production strategies were higher than
continuous corn. However, as additional N was added, even in the minimal input system, the
"rotation effect" was much less pronounced. In the minimal or reduced input system and at the
standard and high input levels, yields of corn were essentially equal in all rotations. As inputs
were reduced below the standards set by the Extension service, reductions in yields resulted.
Only in the continuous corn rotation was a yield increase noted at the highest levels of inputs.
The extent of yield differences between input systems was much smaller with soybeans as
compared to corn. This was most likely due to the ability of soybeans to fix their own nitrogen
and the relatively high initial fertility levels of this site. Weed control was the critical factor
effecting yields in this study. When compared to the other three, weed pressure was found to be
much greater and more limiting at the lowest management level. Substitutions of cultural for
chemical weed control in soybeans was more successful than in corn.
Wheat yields showed no significant differences among the minimal, standard, and high input
levels. This indicates that the current recommendations of fertility are adequate or might be too
high. Data collected from both oats and canola reveal the same conclusions as for wheat.
Potential Contributions and Practical Applications:
The data presented in this report is preliminary and represents only short term effects from a
long-term study. However, some conclusions can be drawn. At this point the data clearly
suggests that the current input recommendations made by the Extension Service are adequate,
though there is obviously room for improvement.