At this point in the 2015 growing season, all summer field crops around the state are entering into their final reproductive stages. Corn has already gone through the dent stage (R5) on most fields and, depending on the weather conditions, could take from a few days to weeks to become fully mature -- 25-35% moisture content, formation of black layer. For both the soybean and sorghum crops, the coming weeks will be critical in shaping the final yield. Grain fill duration will be connected to temperature and precipitation conditions and the source:sink balance within the plant, which involves the leaf to grain relationship. A lack of functional green canopy will result in a short grain fill period; and a similar situation will occur if the grain number is reduced.
At the national level, the most recent USDA crop progress report estimated total corn production at about 13.7 billion bushels, which is 4% less than the 2014 crop production. The average yield is predicted to be close to 169 bu/acre, 2 bu/acre down from 2014. Soybean follows a similar trend, with overall yield per acre down 1% compared with 2014. Sorghum yield per acre was projected to increase by 7 bu/acre, from 68 to 75 bu/acre, and an overall production of 572 million bushels.
The most recent Kansas Agricultural Statistics Service crop progress report estimates that 91% of all Kansas’ corn crop is at the dent stage, more than 50% of the crop is mature, and 11% has been harvested. Overall, 56% of the corn crop in Kansas was classified by the USDA as being in good or excellent condition. As compared with last year, the pollination time and grain-fill period was much more favorable for corn yields this year.
The dent stage (R5) takes place 40 days after silking, which varies with weather conditions. Grains are drying down in the dent stage, with a moisture content level around 50-60%. Past experience has shown that when corn is reaching the dent stage, biotic or abiotic stress conditions – such as high temperature stress, drought, pests, hailstorm, etc. -- may exert some impact on final kernel weight by shortening the dry matter accumulation period. Currently, most of the corn is approaching maturity; thus, the influence of stress conditions on yield would be small. Final kernel weight is determined as the crop reaches full physiological maturity, or maximum dry mass accumulation. This can be identified as the formation of the black layer, the black line formed at the bottom of the grain (Figure 1).
Figure 1. Corn at dent stage and at black layer growth stages. Photo and infographic prepared by Ignacio
Ciampitti, K-State Research and Extension.
The most important task from this point on is to scout the fields for the presence of weak stalks and plan the harvesting procedure -- prioritizing corn fields with weak or broken stems.
In most of the areas of the state the soybean crop is reaching the final stages of the reproductive phase, ranging from R5 (beginning seed) to R7 (beginning maturity) stages. More information about soybean growth and development can be found at: bit.ly/IDBeanStage
Kansas Agricultural Statistics reported 96% of the state’s soybean crop is setting pods. At present, 55% of the soybean crop condition has been rated good or excellent. The senescence process, detected as yellowing in soybean fields, is progressing quickly now with the warm temperatures and dry conditions experienced in recent weeks. Kansas Agricultural Statistics reported that 19% of leaves had dropped, similar to this point in 2014.
A considerable portion of the potential soybean yield will be determined in the upcoming weeks, between full seed stage (R6; Figure 2) and the beginning of maturity (R7). The beginning of maturity is recognized when only one pod on the main stem has reached mature color (e.g. brown color). At this point of the season, any biotic or abiotic stress can still impact seed size. As discussed in a previous eUpdate article (“Estimating soybean yields,” eUpdate #525), drought and heat conditions at this point in the season can severely impact seed size. Large changes (e.g. 10-20%) in yield could result from changes in the final seed weight.
Continue to scout your soybean fields for crop production issues. Lodging can be an issue for soybeans. Lodging can affect harvesting, as well as the late-season photosynthetic efficiency of soybeans – which can accelerate senescence and cause reductions in seed weight and yield.
Figure 2. Soybean at full seed stage. Photo and infographic prepared by Ignacio Ciampitti, K-State Research and Extension.
Kansas Agricultural Statistics projected that 83% of the sorghum crop in Kansas is at or beyond the coloring stage, 18% ahead of last year’s pace. Almost a quarter of the entire sorghum acreage in Kansas was reported at full maturity, 13% ahead of last year. More than 60% of the sorghum crop was classified as being in good or excellent condition; with 7% projected as a very poor or poor. Similar to soybean, a portion of the potential sorghum yield remains to be determined in the next coming weeks.
One of the main late-season factors that can affect sorghum yields in Kansas is the possibility of a killing freeze before maturity. An early freeze will reduce the final seed weight due to a cessation in the dry matter allocation to the grain. The only management practice to avoid this phenomenon is to use shorter-season hybrids and earlier planting dates in environments prone to early freezes. This was difficult to accomplish in the challenging wet spring in 2015.
Another challenge for sorghum farmers is the presence of sugarcane aphids. The occurrence of the aphids across the state continues to expand. Timely scouting for the presence of the aphids and taking appropriate action if the economic threshold is achieved is critical. More information on the sugarcane aphid can be found at:
Continue to scout your sorghum fields for crop production issues, including lodging or bird feeding. Often the utilization of pre-harvest desiccation will help reduce the moisture content and will promote a more uniform maturation and an earlier harvest time. Utilization of pre-harvest desiccants is recommended when the crop is fully mature (25-35% moisture content), which is the stage at which a desiccant will not affect yields. Applications before maturity could compromise the final yield. Information related to different products and waiting period can be found at: http://www.ksre.ksu.edu/bookstore/pubs/MF3046.pdf
Figure 3. Sorghum at the coloring stage. Photo and infographic prepared by Ignacio Ciampitti, K-State Research and Extension.
Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist