ISSUE 5 June 10, 2010
SATURATED SOILS AND SOYBEAN RESPONSE
Recent heavy rains in North Dakota and northwestern Minnesota counties have caused crop damage. Extended periods of excess soil moisture have a negative effect on crop growth and yield. In early growth stages, soybean plants can survive for only two to four days under water in anaerobic conditions. Moderate water movement can reduce flood damage by allowing some oxygen to get to the plants, keeping them respiring and alive. Drainage of the water within one to two days increases the chance of plant survival.
Research indicates that the oxygen concentration approaches zero after 24-hours in a flooded soil. Without oxygen, the plant cannot perform critical functions. Nutrient and water uptake is impaired and root growth is inhibited. Even if flooding doesn’t kill the plant, it may have a long term negative impact on crop performance. Excess moisture in the early vegetative stages retards root development. These stressed plants may be subject to greater injury during a dry summer because the root system is not sufficiently developed to access available subsoil water.
The magnitude of injury to seedlings is determined by several factors including which plant development stage it is in during the ponding of water, the duration of flooding, the air and soil temperatures as well as the number of auxiliary buds present on damaged plants. If the sun is shining and air temperatures are warm during flooding (greater than 77 F), plants may not survive more than 24 hours. Cool temperatures may increase the plant survival rate. On the other hand cold and wet weather favors disease development. Previous applied seed treatments might help in the protection of the seedling roots. If seedling development is slow and takes more than three weeks soil borne pathogens have an opportunity to cause damage to the roots. Delayed soybean growth allows diseases such as Fusarium root rot, Phytophthora rot and Pythium rot to establish and weaken or destroy seedlings. There are varietal differences in tolerance to excess moisture conditions, and this tolerance is related to Phytophthora resistance. One strategy to manage Phytophthora is to use ‘major gene’ resistance (the use of genes like Rps1k or Rps6, which NDSU currently recommends against Phytophthora). Varieties with these major genes tend to have fewer effects of excess moisture conditions compared with varieties without the genes.
After the water stress is removed favorable growing conditions are important to help plants recover from the stress. Soybean plants are amazingly resilient and can grow out of severe stress conditions. Soybean planted in wide rows may benefit from cultivation, once soils are dry enough, to open and aerate surface soil and promote root growth. Be careful working wet soil as this may cause compaction. Maintain a good weed control strategy so that crop plants are not robbed of nutrients and moisture later in the season.
Soybean plants under severe stress conditions.
Extension Agronomist broadleaf crops
LATE PLANTING WHEAT AND CORN
In several regions of the state, excessive moisture has caused planting to be delayed. We are currently beyond what we would consider the "last planting dates" for wheat and corn. Nevertheless, those with significant acreage yet to plant have been asking about the impact of very late planting on the development and yield of these crops. Unfortunately we do not have a large recent research database to draw on when attempting to answer this question.
Depending on the location in the state, the last planting last date that is recommended for wheat is between the first week in May (southern ND) and the first week in June (northern tier of ND), with the optimum planting dates being about a month earlier. Research has shown that the yield of wheat decreases about 1% per day in delay beyond the optimum planting date. Furthermore, planting after the last planting date increases the risk of even greater losses in yield and test weight due to the likelihood that the crop will be exposed to high temperatures during flowering and grain filling. Spring wheat requires in excess of 2800 growing degree days from planting to maturity. In most years and regions of the state, the likelihood that wheat planted before June 20th will receive 2800 growing degrees and reach maturity before the middle of September, is quite high. In abnormally cool summers, like last year, maturity may actually be pushed into October if planting occurs in mid-June. Yield losses are less with late planted crops in cooler than normal summers, but in cool summers late planting may push maturity late enough in the fall that other critical farm operations are impacted by a late harvest. The benefits of having a crop in the field, rather than going with the prevent plant option, includes the utilization of excessive soil moisture, and more effective weed control.
For corn, yield losses for delays beyond May 20 are in the 1.5 to 2.0 bu/acre per day depending on the weather during the summer (in cool summers the losses are even greater). Coupled with the yield loss is the fact grain moisture content may increase by about a third of a percent per day delay in planting. Earlier maturing hybrids can be used to partially offset the undesirable gains in grain moisture, but there are limits to the availability of ultra-early hybrids for a given zone. For example, if planting is delayed until mid-June, Hicks at the University of Minnesota (http://www.soybeans.umn.edu/pdfs/CornGuide.pdf) recommends hybrids that are 15 or more relative maturity (RM) units earlier than what is recommended for early planting. For most zones of the state, there simply are no hybrids available commercially that are 15 RM units earlier than what is normally recommended.
In summary, the probability of producing a profitable crop of wheat or corn declines rapidly as planting is delayed beyond the middle of June. Growers should carefully assess the risks associated with a late planted crop with some of the longer term benefits of having a crop in the field during the summer.
Extension Agronomist for Cereal Crops