Summer field crop status in Kansas
At this point in the 2017 growing season, all summer field crops around the state are in 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 (61% of the corn in Kansas is mature). In some areas such as SE Kansas, 50% of the corn has been harvested (>90% in the south part and >20% in the north section of the SE-EC regions of the state). Soybean and grain sorghum will be ending the grain filling stage and reaching maturity in the coming weeks. Grain fill duration will be connected to temperature, radiation (sunny days), 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 was reduced.
At the national level, the most recent USDA crop progress report estimated total corn production at about 14 billion bushels, 6% lower than in 2016. The average yield is predicted to be close to 170 bu/acre, 5.1 bushels lower than in 2016. Soybean is forecast at a record close to 4.4 billion bushels, 3% higher than in 2016. Sorghum yield per acre was projected on September 1 to be close to 70 bu/acre, 6 bushels lower than in 2016, and an estimated overall production of 370.7 million bushels.
The most recent Kansas Agricultural Statistics Service crop progress report estimates that 91% of the corn crop in Kansas has reached at least the dent stage, more than 60% of the crop is mature, and 19% has been harvested. Overall, 55% of the corn crop in Kansas was classified by the USDA as being in good or excellent condition (down 11% from 2016). For the early-planted corn, pollination was not placed under great moisture conditions (but this varied across the state), but grain-fill period was more favorable for corn yields in some areas of the state.
The dent stage (R5) takes place 40 days after silking, which varies with weather conditions. Kernels are drying down in the dent stage; grain moisture declines to 55% as the starch content increases. Past experience has shown that when corn is reaching the dent stage, biotic or abiotic stress conditions (i.e. high temperatures, drought, pests, hailstorm, etc.) may exert some impact on final kernel weight by shortening the dry matter accumulation period. From dent to the formation of black layer (maturity), corn will lose moisture and total dry weight will increase until filling ceases (Table 1).
Table 1. Growth stages, moisture content, and total dry matter progression for corn from late to physiological maturity. Extracted from K-State Research and Extension publication MF3305.
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).
Further details related to changes in growth and development for corn can be found at: https://www.bookstore.ksre.ksu.edu/pubs/MF3305.pdf
Figure 1. Corn at dent stage and at black layer growth stages. Photos 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 harvest accordingly -- prioritizing cornfields with weak or broken stalks.
In most of the areas of the state the soybean crop (full season soybean) is reaching the final stages of the reproductive phase, ranging from R5 (beginning seed) to R7 (beginning maturity) stages.
The most recent Kansas Agricultural Statistics crop conditions report noted that 38% of the state’s soybean crop is dropping leaves, ahead of the last three growing seasons. At present, 45% of the soybean crop condition has been rated good or excellent. Soybean has been fairly drought stressed up until this last weekend when some areas of KS received much needed rainfall. Seed number has been set on many fields in KS but the remaining yield component is seed size. With the recent rainfall, seed size will see improvement and add soybean yield. The senescence process, detected as yellowing in soybean fields, is progressing quickly with the dry conditions experienced in many areas of the state.
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 yield potential,” eUpdate #648), drought and heat conditions at this point in the season could severely impact seed size. Large changes (i.e. 10-20%) in yield could result from changes in the final seed weight.
Continue to scout your soybean fields for crop production issues. Lodging, effect of late-season diseases on leaf canopy and severe defoliation (primarily caused by insects) 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 size and yield. In addition, green stem syndrome, a condition in which the stem remains green while the seeds are mature, can be an important problem when harvesting. More information on this topic will be in the next issue of the Agronomy eUpdate.
Detailed information about soybean growth and development can be found at: https://www.bookstore.ksre.ksu.edu/pubs/MF3339.pdf
Figure 2. Soybean at full seed stage and final development stages extracted from the Soybean Growth and Development chart (K-State, United Soybean Board, and Kansas Soybeans). Photo and infographic prepared by Ignacio Ciampitti, K-State Research and Extension.
Kansas Agricultural Statistics projected that 81% of the sorghum crop in Kansas is currently at or beyond the coloring stage (Figure 3), 10% behind of last year’s pace. Close to one fourth of the entire sorghum acreage in Kansas was reported at full maturity, 7% behind of last year. Harvested acreage was 2% based on the most recent report , similar to that at this time last season. 65% of the sorghum crop was classified as being in good or excellent condition; with a 9% 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. Early planting was difficult to accomplish in the challenging wet spring of 2017.
Another challenge for sorghum farmers is the presence of sugarcane aphids. Timely scouting for the presence of the aphids and taking appropriate action if the economic threshold is achieved is critical. Update on the current status on sugarcane aphids and other pests can be found at: https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=1520
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 preharvest desiccant products and waiting periods can be found at: http://www.bookstore.ksre.ksu.edu/pubs/MF3046.pdf
Check your crop to see if it is mature before harvest, and for black layer formation. Differences in black layer formation, or maturity, can be present at the same time in different positions of the head. Usually, grain sorghum is mature when grain moisture content is the range of 25-35% (Figure 3).
Further details related to changes in growth and development for sorghum can be found at: https://www.bookstore.ksre.ksu.edu/pubs/MF3234.pdf
Figure 3. Sorghum at the coloring stage and mature/not mature seeds at different positions in the sorghum head. Photos and infographic prepared by Ignacio Ciampitti, K-State Research and Extension.
Further information on corn, soybean, and sorghum growth and development can be found at:
Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist
Doug Shoup, Southeast Area Crops and Soils Agronomist