Carolina Cotton Notes - Planting Date and Yield

All the wet weather has us way behind on cotton planting. The paragraph below is an excerpt from Cotton Information:

Planting date trials have been conducted in North Carolina for a number of years. The results indicate that optimum yields are harvested when cotton is planted before May 5. Yields decline approximately 12 pounds per day after May 5. Avoid planting after May 20 if possible. Cotton planted after May 20 yields substantially less, may require more insecticide applications, and is more difficult to prepare for harvest.

This is a simplified explanation for a more complex relationship. For simplicity the relationship described above is based on a linear fit of planting date data collected over several years. Figure 1 shows what really happens in most years. There usually is very little decline in yields with planting date until a certain point where you get a sudden drop off in yields beyond that point. Where that drop off occurs depends on where you are in the State and most importantly what type of fall we have. The red line in figure one illustrates that point. The yellow lines shows what happens when you take the data and force a linear regression of the data. In this case yields decline by 10 pounds of lint per day of delay, similar to the statement in the paragraph above. If you look at the red line forced to fit through the actual data you see that from May 13 through June 17 yields declined only about a ½ a pound per day, but declined by about 64 pounds of lint from June 17 to June 25.

Figure 1. The influence of planting date on lint yields per acre in Rocky Mount in 1998.

This response is typical of what happens in most years although the rapid drop off that normally occurs usually happens earlier. We had a great fall in 1998 that delayed the drop off and the drop off could happen in late may or early June depending on fall weather. For example in one year yields may decline dramatically after May 20 and in another year after June 10. In most years there is no large decline in yields until sometime in late May or early June.

Figure 2 shows how planting date influenced yield in the hurricane plagued year of 1999. Here the response is more linear. Yields declined by 11 pounds per day based on the linear regression; however, notice there was a plateau from late May to early June.

Figure 2. The influence of planting date on lint yields per acre in Rocky Mount in 1999.