Site Specific Outline

TITLE: Developing Sustainable Field Cropping Systems in Semi-arid Eastern Oregon

Site-Specific Farming

Traditional farming practices in eastern Oregon ignore the inherent spatial variability found in most farm fields. Managing fields uniformly has led to over fertilization in areas with high residual nutrients and unnecessary applications of insecticides and herbicides in areas not affected by insects and weeds. The extensive variability in soil properties (texture, depth, slope, and aspect) and crop productivity, coupled with concerns about water and soil quality, and narrow profit margins justify farming based on the needs of specific areas within a field. Site-specific farming (SSF) has the potential to increase efficiency in farm decision-making, improve profit margins, and reduce environmental pollution. Furthermore, SSF has the potential to reduce insecticide and herbicide resistance that may occur when whole fields are frequently and uniformly sprayed. Research is needed to improve the efficiency of inputs through SSF.

PREVIOUS WORK AND PRESENT OUTLOOK

Site-Specific Farming

The extensive variability in soil properties and crop productivity (Mulla and Schepers, 1997) and the need to increase profit margins (Wollenhaupt et al., 1994) support the introduction of SSF. Concerns of excessive environmental pollution when fields are treated uniformly as in traditional farming practices also justify SSF. These practices have led to over fertilization in areas with high residual nutrients and unnecessary applications of insecticides and herbicides in areas that do not need treatment (Mulla and Schepers, 1997; Wollenhaupt et al., 1994). Furthermore, insecticide and herbicide resistance may occur when whole fields are sprayed uniformly with insecticides. Evaluation and implementation of SSF has been made possible by advancements in remote sensing, global positioning systems (GPS), geographical information systems (GIS), variable rate technology (VRT), and grain yield monitors. These technologies made it possible to identify and treat specific areas within a field differently from others. SSF has the potential to revolutionize crop production by increasing profit margins through improved efficiency in the management of field variability.

Farm profits in eastern Oregon are decreasing because of stagnant wheat prices and ever increasing input costs. Managing inputs more efficiently is one way to increase profit margins. Site-specific farming provides this opportunity. There is considerable variation in wheat yields within fields in eastern Oregon. Figure 1 shows wheat yields in Wasco County in 2001 in a relatively flat field. Although uniform fertilizer and herbicides were applied to the whole field, wheat yields varied from about 5 to 70 bu/acre.



Fig. 1. Wheat grain yields in field 'Paulson' at Mr. John McElheran in Wasco County in 2001.


Given that the field is relatively flat, more variations could be expected on the hilly and sloping fields that characterize >50% of eastern Oregon landscape. Many factors influence the spatial variability of crop yields. Soil depth appears to have caused the variability of wheat yields observed in the farm shown in Fig. 1. If this field had been managed based on the yield potential of different areas, the farmer would have saved on fertilizer and would have increased his profit margin. More fertilizer could have been applied in areas with high yield potential and less in areas with less yield potential. The profit margin could be further increased if insecticides and herbicides were spot applied to target only affected areas. Information obtained from yield maps as in Fig. 1 is valuable for fertilizer management. Areas that were low yielding may have high residual nutrients and may require reduced fertilizer rates in the following season. In other fields in eastern Oregon, slope and aspect influence plant growth and grain yield. For example, north-facing slopes are usually cooler and wetter than south facing slopes and produce higher yields than south facing slopes particularly in drier years. Under such situations farming the two slopes uniformly is inefficient use of inputs. Kent Madison, an Oregon grower, estimates a $10 per acre increase in returns through soil mapping and precision fertilizer application on his wheat fields and in Washington wheat farms, an increase of $3.39 to $14.80 more per acre return has been observed with site specific farming.^[1]

Despite the advancement in technology, adoption of SSF is lagging primarily because it has not proven to be more profitable than traditional farming practices (Lowenberg-DeBoer and Swinton, 1997, Lowenberg-DeBoer and Boehlje, 1996). A review of economic analyses shows that SSF was profitable only in some situations (Lowenberg-DeBoer and Swinton, 1997). However, all of these studies provided partial budgets based on inadequate input and output information and therefore cannot be reliably used to evaluate the viability of SSF. As illustrated in recent precision agriculture conferences such as Robert et al. (1996, 1998), early research on SSF has been dominated by the development and evaluation of instrumentation and VRT of fertilizers. Likewise studies on economic returns to SSF have been based on fertilizer or single factor responses. Fertilizer alone or single factors, however, have not explained the observed spatial and temporal variation in grain yields (Everett and Pierce, 1996; Solohub et al., 1996; Mulla and Schepers, 1997; Braum et al., 1998; Machado et al., 2000). To successfully evaluate and implement SSF, more information on factors affecting variability of grain yields is required.

The observed spatial and temporal variation (season to season) in crop growth is the result of the interactions between biotic and abiotic factors experienced during a growing season (Mulla and Schepers, 1997; Braum et al., 1998; Machado et al., 2000). I hypothesize that implementation and adoption of SSF will be successful when biotic and abiotic factors, limiting grain yields and profitability, can be identified and managed at different locations and for different plant growth stages in integrated systems.