Project Summaries

11-847AZ  Project Manager: E. M. Barnes

NEW AND NARROWER RANGE OF RECOMMENDED COTTON PLANTING DENSITY IN ARIZONA

Guangyao (Sam) Wang and Randy Norton, University of Arizona

Currently the recommended cotton planting density is in the range of 25-50K/A. Growers have asked us to narrow down the range for specific locations in Arizona. There are three major reasons for the need: 1) seed cost has increased significantly along with a technology charge in the past decade. Cost for 10 lbs of cotton seed was $7 in 1996 which increased to $70 or so in 2010, a 10-fold increase. Reducing planting rate while maintaining cotton yield is desirable to growers to reduce their input and increase their profitability. 2) Cotton varieties have changed significantly in the last 10 years. These new varieties might require different optimal planting density. 3) Growth habit differences should be accounted for in recommending planting density. Varieties with a bush-type growth pattern versus more of a cluster-type growth pattern will likely have different optimal planting densities.

Planting density experiments were conducted at three locations in Arizona (Maricopa, Marana, and Safford) in 2011 and two locations (Maricopa and Safford) in 2012. A bush-type (ST4498 B2RF) and a columnar-type (DP0949 B2RF in Maricopa and PHY565 WRF in Safford) variety were used in the study, while the experiment in Marana included three fields with different varieties. Nine planting densities were used at Maricopa Ag Center (6,000 to 84,000 seeds per acre), and six planting densities at Safford Ag Center (10,000 to 110,000 seeds per acre), and three planting densities at Marana (20,000 to 40,000 plants per acre). Cotton was planted in April at Maricopa and in May at Safford and managed according to common local practices. Actual plant population at each density was counted at late growing season or final harvest. Lint yield and quality were measured at the end of the season to find the optimal density for cotton production in each location.

Cotton seeds of six commonly used varieties in Arizona were planted from March 21 to May 2 at Maricopa Ag Center and four times from April 6 to May 26 at Safford Ag Center with four replications at each location.

Plant population below 15,000 plants per acre reduced cotton lint yield at both Maricopa and Safford. When plant populations were over 20,000 plants per acre, lint yield of all three varieties did not change significantly. Based on the data from 2011 and 2012, it seemed that a final plant population of 30,000 to 35,000 plants per acre should be used in all three locations. It should be noted that cotton was planted on 4/20/2011 and 4/16/2012 at Maricopa and on 5/23/2011 at Safford for this study. The recommended plant population might change with planting dates that are significantly earlier or later.

Highest yields at Maricopa came from the early planting dates, and cotton lint yield started to decrease after mid-April.  When planted early at Safford (April 18 or before), lint yields were significantly lower compared to later planting dates (May 6 and later). The main reasons for lower yield were not plant population, but stunted plant growth under cooler temperature that resulted in reduced vegetative growth.

Planting density studies at Maricopa and Safford suggest that it is possible to recommend a narrower planting density for growers in Arizona. While planting early could lead to stunted plant growth under cooler temperature and reduced lint yield, delayed planting in Maricopa could result in reduced yield, mainly due to heat stress in July and August at peak bloom stage for these planting dates.

 

Project Year: 2012
 

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