Making the best out of a bad situation: Using that ugly looking crop to assess field spatial variabi

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

When scouting corn and soybeans this year it quickly becomes obvious that the cold wet period experienced in mid-May dramatically exposed the spatial variability within fields. Stands that appeared uniform at emergence now are highly variable in plant size and vigor. The stress of excess water and associated limited root growth magnifies field spatial variability and can reveal problem areas within the field. Some of the soil and field factors revealed by the variable plant stands include the location of tile lines/areas needing tile, areas with soil compaction, slope and surface drainage, and the nutrient status associated with various soil types. Problem areas are easily visible by the presence of plants that are relatively shorter, less vibrant, and paler in color. Some of this variability will be mitigated as the growing season progresses, provided we return to a more “normal” weather pattern. However, the early season conditions experienced this year will likely result in some very colorful yield maps this fall.

Variable rate nitrogen application is an example of how plant variability assessment data can be used within the same season it is acquired. Highly variable corn fields are generally good candidates for variable rate nitrogen applications. Pale to yellow plants in poorly drained heavy soils are often symptomatic of nitrogen loss due to denitrification. The same symptoms on coarser well drained soils can indicate nitrogen loss due to leaching. Variable rate nitrogen application can be accomplished on many levels. On its simplest level, growers can identify deficient areas, selectively sample with a PSNT, and manually adjust N application accordingly. Information on PSNT is available through your local MSUE office. Some agri-business firms offer variable rate technology using hand-held measuring instrumentation or on-the-go plant assessment and rate adjustment. Conditions of restricted root growth associated with wet weather can exacerbate Manganese (Mn) deficiency in soybean. These problems typically appear on high pH soils or muck soils. Several foliar applied products are commercially available to treat Mn deficient soybeans. Please see last week’s article on tank-mixing Mn products with glyphosate.

In many cases, there is not much that can be done this growing season to address the revealed problem areas, but growers can use the information to their advantage to make some long-term changes that will likely have a positive effect on future crops. Several obvious water-related fixes include mapping the location of gullies to identify where grass waterways may be needed and mapping drowned out areas to reveal where extra subsurface drainage may be effective. Areas of the field showing Magnesium deficiencies (striped corn) could be marked out and targeted for an application of dolomitic lime after harvest. Quite often these areas are associated with acidic sand hills and hillsides on relatively higher elevations within fields. Magnesium deficiency can also be addressed in-season by foliar applications of Mg products such as Epsom salt. Soil compaction areas will be revealed due to their inability to rapidly drain water and in severe conditions water may pond in long ribbons across the field associated with wheel traffic patterns. These areas should be identified and targeted for deep tillage when soil conditions allow in the fall to address the compaction.

In addition to scouting fields on foot, aerial imagery can be an effective tool to characterize spatial variability. This can be as simple as going up in your neighbor’s plane and snapping a few pictures. In addition, commercial aviation firms can be procured to take aerial imagery although the costs associated with this service can be significant. On a more sophisticated and expensive level, computer technology can be used in conjunction with digital aerial imagery to quantify spatial variability based on plant and soil light reflectivity. Finally, those colorful yield maps obtained this fall, used in conjunction with scouting reports taken today, can be instrumental in helping identify where specific problem areas exist.

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