Cotton varieties have been developed with less determinacy and improved fruiting pattern and pest management. These improved characteristics and additional agronomic inputs have translated to an operation that can be very productive with lower rates of N fertilizer.
A reduction of fertilizer inputs is desired to minimize the effects on the environment and improve growth management of cotton crops grown for lint, particularly in years where late-season growth is excessive.
This study was conducted to evaluate the yield and growth potential of Deltapine® cotton varieties to a range of N fertility applications.
|Location||Scott, MS||Planting Date||5/29/19|
|Soil Type||Highly variable clay loam - mixed||Harvest Date||10/20/19
Eight Deltapine® cotton varieties were used in this study.
The experiment was planted in strip plots (12 rows x 1100 feet long) in 38-inch row spacing, on raised beds, and each plot was approximately 1.0 acre. Six middle rows were harvested for yield.
Nitrogen was knife applied in one application as 28% liquid UAN at pin head square (5 to 6 weeks after planting). Five different N rates were used: 0, 30, 60, 90, and 120 lb N/acre.
The plant growth regulator (PGR) mepiquat chloride (4.2% formulation) was applied several times to all 8 varieties during the season as indicated by plant mapping. PGR treatments were as follows:
Across all cotton varieties, both the 0 and 30 lb N/acre treatments had substantially reduced yield compared to the greater N rate treatments.
The 0 lb N/acre treatment had average yields of 450 lb lint/acre (note that these plots were overlaid on a similar study from the previous year and this section of the field received 0 lb of N fertilizer for two years in a row. This is an indication of both the scavenging ability of cotton plants to take in nutrients and the productivity and depth of Delta soils.)
At the 60 lb N/acre treatment, lint yield across all varieties showed an increase with average yields of 1,083 lb lint/acre across all varieties.
Yield in most cases appeared to be optimized between 60 and 120 lb N/acre. The 90 lb N/acre treatment had the greatest average yield in the trial at 1,128 lb lint/acre.
In the 120 lb N/acre treatment, lint yield averaged across all varieties (1,070 lb lint/acre) was lower than either the 60 lb N/acre treatment (1,083 lb lint/acre) or the 90 lb N/acre treatment (1,128 lb lint/acre).
Some varietal responses to N rates were observed and these are likely an interaction with the production season, soil type (variable to mixed), and growth habit of the tested varieties.
The PGR approach managed growth across the range of N fertilizer applied in the test.
The earliest maturity varieties (DP 1614 and DP 1916) had optimal yield at 60 lb N/acre.
Varieties with maturity from 18 to 35 had optimal yield with 90 lb N/acre.
Varieties with maturity above 45 had optimal yield with 120 lb N/acre.
Some varietal responses to N fertilizer were observed in this study. However, this data indicates that acceptable and often higher yield potential is possible with N fertility rates between 60 and 120 lb N/acre.
These results are unique to a cotton-on-cotton production system and should be viewed in that context (i.e. with cotton-on-corn production, these N rates could likely be reduced further; however, reducing N rates should not be done without further testing and careful consideration of the factors involved).
Applied N fertilizer is a primary input to consider in the complex of fertility, growth management, and yield potential. This would be true in fields with historically excessive and unmanageable growth patterns which have lead to boll rot, excessive fruit shed, and reduced yield in those cases.
Farmers should consult their Deltapine agronomist to discuss cotton variety selection and management of each field they intend to plant.