Climate factors affect cotton production

In talking with many people in the last few weeks, I realize how fortunate that we have been in Missouri during this planting season. According to the Missouri Crop Progress and Condition Report for the week ending June 6, our percentage of fields with squares is six percent which is 16 days ahead of last year and 3 days ahead of the 5-year average. Cotton condition was rated 8 percent poor, 18 percent fair, 71 percent good, and 3 percent excellent, virtually unchanged from a week earlier. For the previous four weeks, Dunklin county rainfall has been at 3.33 inches, with lesser amounts in surrounding counties. If you look at the state wide rainfall patterns, we are blessed by not having the excess moisture experienced by many of the districts. Our Southeast District shows only 1 percent surplus compared with 64 percent in the North Central and 56 percent in the Northeast. Statewide surplus soil moisture is 20 percent.

There were several problems last season which delayed the maturity of our cotton. The first was the wet, cool conditions early in the season. It was difficult to get the cotton planted due to the wet conditions. Also the temperatures were cooler for the first part of the season which resulted in delayed maturity. So our cotton was behind schedule and didn?t really catch up until late August. This has not been a problem this year and in my opinion, the cotton looks good.

Cotton is a crop that is grown on every continent except Antarctica. It is grown in over 60

Countries in the world. Thus, it is grown under a wide range of climatic conditions. For our purposes, sunlight, precipitation, and temperature are the factors that most affect our cotton production.

With our weather patterns this year, we had a low maximum temperature on May 10 at Glennonville of 58.3, Cardwell at 58.0 and Clarkton at 57.9. Since then, the highs have been mostly in the 80?s and 90?s. So this year, when it warmed up, it warmed up quickly.

As I have mentioned in past columns, the temperature (heat units) is what drives the growth and development of the plant. The optimum range for photosynthesis is 74 to 90 degrees. Cotton can cool itself by opening stomates in the leaves to allow water to evaporate. Another key to high yield in cotton is having plenty of moisture available. It has been shown that well watered plants are often 10 degrees cooler than the air temperature. In 1990 in Arizona it was shown that with air temperatures of 121 were reached, the plant canopy only reached 88 degrees in well watered cotton. Under the same temperature, non-irrigated cotton canopies reached 104 degrees which affected the carbohydrate and eventually fiber production. Most of the water used by the cotton plant is used to cool the plant which helps with maximizing fiber production. The evaporative cooling in one acre of July cotton provides the same cooling as 50 to 100 typical home air conditioners.

I have an opportunity each year to observe the lack of moisture on cotton in SE Missouri. In most years, this cotton is earlier in maturity and on average; the non-irrigated cotton is much shorter in height. According to irrigation surveys, the non-irrigated cotton averages over 200 pounds per acre less yield. During dry years, I have seen many nutrient deficiency symptoms such as potassium and nitrogen because the root system cannot take them from the dry soil.

While we have been fortunate to have had the rainfall this year, we also have some non-irrigated cotton wilting under the hot dry conditions. This cotton needs rain. While we have experiences some rainfall this week, more will be needed to keep the plants growing normally.

One concern that we will see on occasion is the high night temperatures. This can have a harmful effect on cotton if the low temperature stays in the upper 70?s or gets to 80 degrees. Under these conditions, the plants are not able to recover at night and use more respiration as the plant attempts to cool itself. The prolonged high night temperatures can impact yield and fiber quality. High night temperatures increase plant temperature because the cotton closes its stomates and ceases evaporative cooling when the sun sets. At night the only source of evaporative cooling is from a moist soil surface or free water on the plant from a recent rain or sprinkle irrigation.

Research at the University of Arkansas has shown that high night temperatures caused an increase in respiration which impacted the sugar content which is needed to make the cellulose in the cotton fiber. We are fortunate that this does not occur very often in Missouri. One advantage in growing cotton in the extreme northern end of the cotton belt is that we generally have better cotton fiber. According to cotton classing office data, cotton grown in Southeast Missouri generally has higher strength and longer fibers than the same varieties grown further south.

Some years we experience a shorter growing season due to lower temperatures. But we generally have enough temperature to produce above average yields. Our yield record in Missouri is 1,106 pounds per acre harvested in 2008. Our previous best was 1,054 pounds per acre harvested in 2004. Last year, the projected 1,132 was not realized due to poor harvest conditions. Although our yield was only 927, we were better than many states in the Mid-South which have far more heat units than we do.

While we are off to a good start, there are a lot of things that can happen during the remainder of the season. In talking with others, we have not had major insect outbreaks. We usually get the first projection of cotton yields in the August Cotton and Wool Outlook Report. We are eagerly awaiting this report since the crops looks so good at this point of the season.

University of Missouri Extension programs are open to all.

Dr. Michael R. Milam is an agronomy specialist and county program director with University of Missouri Extension in Dunklin County.