Evaluating Site-Specific Soybean Management within the Mississippi Soybean Verification Program (SMART – Soybean Management through Application of Research and Technology)
Project Leader: Dr. Alan Blaine
Cooperating Scientist: Jim Thomas, Mitt Wardlaw and Brian Ward
Summary:
Thirty-four fields were involved in the project in 2002. Using GPS technology, grid soil samples were collected and field boundaries were determined and true field acreage was calculated. All fields were scouted weekly or biweekly for weeds, insects, and diseases. Irrigated fields were scouted twice a week to determine irrigation needs. Also some fields were utilized for in-season foliar insecticide/fungicide tests. Two scouting methods were utilized when data was available for comparison.
Statement of project objectives:
Objective 1 – To continue to improve mid-south soybean production efficiency (profit potential) through unbiased evaluation and incorporation of “precision agriculture” technology into existing actual on-farm soybean production systems via multi-state and statewide soybean research verification programs.
Objective 2 – Evaluate the potential for more profitable soybean production by implementing Extension recommendations more precisely utilizing Global Positioning Systems (GPS) and other precision agriculture technology including remote sensing.
Objective 3 – Identify and quantify factors that are major contributors to in-field yield differences or variances as determined by yield monitors, remote sensing and their generated maps, field scouting, and any other technology.
One field in the program located in the central part of the Delta has been a long time problem field for a participating producer. Areas of plant stress were first identified with the use of remotely sensed images (Figure 1). The lighter colored areas in the image indicate the weaker areas in the field as opposed to the darker areas which represent healthy areas. This field has weak areas that consistently show up year after year in the same locations regardless of cropping pattern/history. With the use of a GPS, stressed areas were mapped in order to monitor plant growth and development throughout the growing season. The small red dots on the image show the areas that were mapped (Figure 1). Soil and plant tissue samples were collected in the stressed areas, as well as in areas of normal plant growth for comparison, and a complete nutrient analysis was conducted. The soil samples showed a distinct difference between samples taken from affected and unaffected areas. The difference here was only slight being medium P and K levels in the stressed areas versus high levels in the unaffected areas. The plant tissue samples however, indicated that within the plant insufficient levels of N, P, K and S were present (Table 1). This observation verified that soybeans are an excellent forager for residual nutrients. If comparative samples had not been taken (soil vs. tissue) this problem might have gone undetected.
Table 1: Soil and Plant Tissue sample analysis
Although there was a notable difference in plant canopy between the normal and stressed areas across the field, plants appeared to be healthy. The pictures in figure 1 show the difference in canopy development in the stressed areas compared to non-stressed areas. Plants in the most severely stressed areas exhibited chlorotic leaf tissue much later in the growing season (Figure 1).
Figure 1: Remotely sensed image showing stressed vs. normal soybean growth
A producer field located on the Yazoo river near Satartia, MS experienced mid June flooding from the Mississippi River back waters on a portion of the field. As the water receded, the producer replanted the flooded area at three different dates over a four week period. The three planting dates were GPS mapped, and monitored for weed and insect infestations as separate fields for needed management as each area progressed. An infestation of grasshoppers was found in the second and third plantings at the V-4 to V-5 growth stage. Insecticide applications were only necessary in these two areas.
Topographic contour maps were developed in selected fields using a RTK (Real Time Kinematics) GPS unit. This data was used in identifying high and low elevation areas within in the field. It was observed that these areas correlated with stressed areas during the growing season. In an above average rainfall year higher elevations exhibit less stress than lower elevations. The exact opposite has been observed in below average rainfall years. Over the past couple of seasons we observed some differences in growth and development that were not easily explained. However, when elevation was measured the problem was identified as drainage. This could be compounded due to planting method, soil texture, soil tilth, and stage of growth.
The field in the North Mississippi Hill region was planted in late May. A remotely sensed image was taken on June 7, which was approximately two weeks after emergence. The variability seen in figure 2 is soil variability instead of plant growth variability because the soybeans were only in the V-1 to V-2 stage. The contour map indicates the high and low areas within the field (Figure 2). According to the yield map (Figure 3), the lowest yielding areas were the highest elevation areas within the field, except for a drainage area where the crop drowned out from early rainfall (Figure 2). However, during the growing season of 2002 this field experienced below average rainfall, lower flatter areas produced higher yields than the high elevations.
Figure 2: Early season remotely sensed image with elevation contours
Figure 3: Yield map
Another field in the North Mississippi Hill region indicated stressed areas within the field by remotely sensed imagery. These areas were scouted and assessed to be an area where a weed control application was missed. We also observed a drainage /glyphosate injury area that affected plant growth and development (Figure 4). Due to the drainage problems these areas failed to fully canopy throughout the entire growing season. The producer sprayed these areas twice with one quart of glyphosate (2X = 2lbs.) for weed control. Consequently, the soybean injury shown in the bottom picture of figure 4 was the result.
Figure 4: Yield and remotely sensed imagery
Based on preliminary research, management practices need to be refined to maintain profitability. Practices such as: evaluation of new materials, timely application of insecticides/fungicides, low use rates, and method of application and volume are examples of a few management practices that are currently being used and evaluated in the Mississippi verification program (SMART). Many voids exist in the evaluation of new management options and Mississippi’s verification program is a major avenue for evaluation.
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