Agriculture & Natural Resources: AgentThin grass stands
Source: Drs. Chris Teutsch, Ray Smith, & Jimmy Henning; UK Forage Extension Specialists
Our forage extension team has had a number of calls on hay stands and pastures that appear to be thinner than normal this spring. There are a number of reasons that stands are thin. We have had many here in Woodford County with many potential causes.
Low carbohydrate reserves going into fall is one likely cause. What we did last summer and fall can sometimes come back to haunt us the following spring. Close, frequent, and late fall cutting or grazing can result in low energy reserves in the plant. This can cause stands to regrow slower and become thinner over time. When you combine this with a long and cold winter, grass stands can struggle to get started in the spring.
Hayfields and pastures need adequate soil fertility to remain strong and vigorous. Soil fertility programs need to be based on a current soil test and all required nutrients including lime need to be applied in a timely manner. In hayfields, potassium is often deficient. This is due to the removal of relatively large quantities of potassium compared to phosphorus. Potassium is involved in water regulation in the plant, translocation of sugars produced during photosynthesis, disease tolerance, and winter survival. So poor potassium fertility, combined with a hard winter, can weaken forage stands.
In some years, we just can’t seem to warm up in the spring. Cold springs can limit early vegetative growth. Since reproductive growth in cool-season grasses is a function of both day length and temperature, the result is that grass plants will tend to produce a seed head about the same time each year. In cold springs, this results in a higher seed head to leaf ratio and ultimately lower yields that have more stem and less leaf.
To manage for thin stands, soil test and apply needed nutrients. Applications of lime and fertilizer should be based on a recent soil test. Woodford County residents may be eligible to receive up to 20 free soil samples. Maintaining adequate soil fertility at all times allows for the development of strong and vigorous sods. It is important to remember that fertility programs need to be balanced according to soil test results and end use. So if you are making hay, you will need to add back more phosphorus and potassium because it is being removed in the forage tissue. In contrast, nutrient removal from pastures that are being grazed is minimal.
It is also very tempting to delay harvest and allow stands to “thicken up” before the first harvest. The presence of the seed head can actually delay the development of vegetative tillers at the base of the plant by acting as sync for sugars made during photosynthesis and shading vegetative tillers. This can actually slow vegetative regrowth in pastures. In addition, the presence of the seed head and stem also decreases forage quality. By clipping or harvesting the seed head and stem, regrowth from the base of the plant can be stimulated and forage quality can be increased.
Apply nitrogen after clipping or harvesting seed heads. Combined with a timely first harvest, application of 40-60 lb. N/A immediately after harvest can stimulate regrowth of pastures resulting a leafy second cutting. It also can help to thicken stands and exclude summer weed pressure.
After the second hay cutting, or as we get into June in our pastures, rest cool-season grass stands and allow them to go into summer with about six inches of regrowth. This will allow pasture plants to accumulate stored carbohydrates that will be used to adapt to the hot and often dry conditions of summer, and at the same time, buffer the temperatures that plant crowns are exposed to through shading. The best way to rest cool-season pastures during the summer months is to incorporate warm-season grasses into your grazing system. This will provide grazing during summer, the months when cool-season pasture growth is limited by high temperatures.