Seed Size and Cool Germination Effects on Cotton Stand, Early Growth, and Yield
Growers often ask if small seeds are as capable of producing good stands as larger seeds. The study shown below was conducted by Sandy Stewart to see if that was the case in Louisiana. He included an early April planting date which would be similar to what we often encounter in North Carolina. The take home message is the last paragraph which is in bold. The message is that larger seed are more likely to be important for stand establishment when cool germination values are low. Both sizes of seed worked well when cool germination values were high. The stresses the importance of knowing your cool germination values when planting under less than ideal conditions, especially with varieties that have smaller seed.
SEED SIZE AND COOL GERMINATION EFFECTS ON COTTON STAND, EARLY GROWTH, AND YIELD
Prior to 2005, cotton seed was sold commercially on weight basis such as in 50 lb bags. Growers typically desired a smaller seed, provided it had acceptable germination levels, because of the increased number of seed per pound. In 2006, most cotton seed was sold on a per seed basis in containers with a specified seed count. In response, it is generally believed that larger seed are desirable because of perceived increases in seed vigor that accompany larger seed sizes. Previous research has addressed the effects of seed size and germination test values on cotton stand establishment, growth, and yield. It has been found that larger seed sizes and higher cool germination values generally result in greater plant stands and larger plants than smaller seed and low cool germination values, although the effect on yield has seldom been significant. Few studies, however, have investigated the effects of divergent seed sizes and germination test values. The objective of this research was to determine the effect of various combinations of seed size and cool germination values on cotton stand establishment, growth, and yield. Four seed lots of two varieties, Deltapine DP 555 BG/RR and Deltapine DP 449 BG/RR, were obtained from Delta and Pine Land Company. These lots could be categorized as having the following combinations: 1) large seed and high cool germination, 2) large seed and low cool germination, 3) small seed and high cool germination, and 4) small seed and low cool germination. These eight combinations were planted in a factorial treatment arrangement on two different planting dates in 2005 and 2006 in Alexandria, LA. Experimental design was a split block design with variety and seed quality categories randomized in a factorial arrangement within planting date. Plant stand and a subjective judgment of seedling vigor was recorded 7 and 35 days after emergence, plant height was measured at early bloom and end-of-season, and yield data were collected. Data were subjected to analysis of variance using PROC GLM procedures in the SAS statistical software package.
Analysis of variance revealed no year interactions, therefore data were pooled over years. Moreover, no interactions of planting date, seed quality, or variety were observed for any of the measured parameters. Planting date was found to influence plant stand, seedling vigor, and yield with an early April planting date resulting in greater plant stand, seedling vigor, and yield than a late May planting date. Typically, early April planting dates are more challenging for stand establishment due to cooler temperatures and wetter conditions. However, in 2005 and 2006 the late May planting date proved more challenging and it is believed that this was due to dry conditions in both years following planting. Variety was found to influence plant height with DP 555 BG/RR obtaining a taller plant height be season’s end than DP 449 BG/RR. Seed quality effects were observed on plant stand and seedling vigor, but not for plant height or yield. For plant stand and seedling vigor, the combinations of large seed and high cool germination, large seed and low cool germination, and small seed and high cool germination all resulted in significantly greater plant stand and higher rated seedling vigor than the combination of small seed and low cool germination.
The results suggests that the perceived negative effects of a low cool germination value can be overcome by a larger seed size, presumably due to greater stored energy reserves for emergence within the seed. Similarly, results suggest that the perceived negative effects of a small seed could be overcome by a high cool germination value in stand establishment. The lack of interactions among the treatment factors suggests that these findings should be consistent across varieties as well as environmental conditions. Growers do appear to be justified in seeking larger seed lots or higher cool germination lots for planting. However, the results from this study indicate that the combination of a small seed and a low cool germination is more detrimental to stand establishment than either factor alone. Smaller seeded lots should be handled with care, but may tolerate more challenging conditions than previously thought as long as the cool germination is high. Similarly, a low cool germination lot may emerge satisfactorily in challenging conditions as long as it also has a large seed size.