A field study was conducted to investigate the effects of population density and nitrogen rate on yield, growth, and fiber response of ultra narrow row (UNR) cotton. Stand loss occurred at densities greater than 22 plants
Ultra narrow row (UNR) cotton production has been proposed as an economical means to increase cotton production efficiency (Atwell et al. [
Nitrogen management is an important aspect of UNR cotton production because excessive nitrogen may lead to rank growth and defoliation difficulties whereas insufficient nitrogen may decrease yields (Rinehardt et al. [
Selection of a population density sufficient to produce an even canopy has also received attention in UNR research. Atwell et al. [
Few studies have examined the interaction between population densities and nitrogen rate in UNR cotton. Boquet et al. [
The objective of this research was to examine the effects of population densities and nitrogen rates on seed cotton yields and plant architecture in UNR cotton in order to determine the most cost effective management strategies in the Mid-South.
Research was conducted from 2000 to 2002 at the USDA-ARS Southern Weed Science Research Farm, Stoneville, MS (33°N latitude) on a Bosket silt loam (fine-silty, mixed thermic Aeric Ochraqualf). The soil had a pH 6.7, 1% organic matter, a CEC of 15 me/100 g, and soil textural fractions of 26% sand, 56% silt, and 18% clay. Field preparation in the fall consisted of disking, subsoiling, and bedding. In the spring, beds were reduced to approximately 8 cm with a reel and harrow conditioner. These low beds were suitable for irrigation and planting. In the year prior to test initiation, the test area was planted in UNR cotton but not fertilized to deplete soil nitrogen. Nitrogen rate recommendations based on soil analyses on this field (Pettiet Agricultural Services, Leland, MS) were 134 kg N ha-1. Test plots were 13 m long and 4 m wide which allowed 16 rows spaced 25 cm apart.
Fertilizer application and insect control programs were standard for cotton production (Reddy [
Herbicide and growth regulator treatments were applied with a tractor-mounted sprayer with fan nozzles delivering 187 L ha-1 water at 179 kPa. Weed control consisted of paraquat (1.1 kg ai ha-1) applied preplant, followed by fluometuron and pendimethalin (1.1 and 0.8 kg ha-1) at planting, followed by glyphosate (1.1 kg ai ha-1) at the one and four-leaf stages of cotton growth. Subsequent weed control was accomplished by hoeing. Plant height was managed with mepiquat chloride (30.7 g ai ha-1) applied at first matchhead square and two weeks thereafter. Harvest preparation consisted of defoliation by two applications of thidiazuron and diuron at 1 kg ai ha-1 and 0.5 kg ai ha-1, respectively, followed by boll opening with ethephon at 1.1 kg ai ha-1.
Field plots were harvested with a John Deere 1755 Finger stripper harvested modified with a bagging attachment to determine seed cotton yields, lint percentage, and lint yield. Burrs, leaves, and stalks were removed by hand prior to weighing. Boll counts, boll weight, bolls per plant, stand counts, and height and nodes were determined by hand picking a 2 m2 plot perpendicular to the direction of planting on the center eight rows. Seed cotton was ginned with a Continental Eagle laboratory gin, and fiber properties were determined by the USDA-Agricultural Marketing Service, Dumas, AR. Plant height and node measurements and bolls by node position were taken on ten randomly selected plants per plot.
The experimental design for each year was a randomized complete block with factorial treatment structure of four plant populations and four nitrogen rates with four replications and repeated for three years. Nitrogen treatments were reapplied in the same plot and populations were randomly reassigned to nitrogen plots. Therefore, in an analysis combined over years the experimental design is a split plot where nitrogen is the main unit and population is a subunit. The design changes to a split plot because year is a repeated measure for the nitrogen main unit treatment and an additional level of replication for the population subunit treatment. Data were subjected to analysis of variance in PROC MIXED (Statistical Analysis Systems, 2005, Software version 9.1., Cary, NC) to determine the significance among main effects. Treatments were separated at the 5% level of significance using an LSD test.
For traits in which there was a significant interaction between year and population density or nitrogen rate, the results were presented by year. In cases where the year by population density, year by nitrogen rate, or population density by nitrogen rate interactions were not significant, data were averaged across years, population densities were averaged across nitrogen rates, and nitrogen rates were averaged across population densities.
Population densities determined at 3 weeks after planting indicated the initial densities were within 90% of the target populations, and there were no differences in population densities across nitrogen rates (data not shown). Population densities determined at harvest were within 90% of the target population for all nitrogen rates for the target population of 22 (Table
Effect of plant population and nitrogen rate on the stand count as a percentage of the target population at harvest averaged over three years.
Population density (% of target population) | ||||
Target population density (plants m-2) | ||||
Nitrogen (kg ha-1) | 22 | 30 | 37 | 44 |
0 | 95.0 | 87.6 | 86.7 | 84.0 |
56 | 98.9 | 86.9 | 82.9 | 78.4 |
112 | 92.9 | 85.4 | 74.0 | 73.0 |
168 | 93.3 | 86.0 | 79.4 | 74.3 |
The LSD for comparing stand count as a percentage of the target population (same nitrogen rate) at harvest is 5.4. The LSD for comparing nitrogen rate (same target population) at harvest is 5.0.
Jost and Cothren [
The reduced stands at the higher populations may have resulted from intraplant competition. Molin et al. [
There were no significant differences in seed cotton yield, lint percentage, and lint yield between population densities (Table
Effect of plant population density and nitrogen rate on seed cotton yield, lint percentage, lint yield, bolls plant-1, bolls number, and boll weight averaged over years.
Treatments | Seed cotton yield (kg ha-1) | Lint (%) | Lint Yield (kg ha-1) | Bolls Plant-1 | Boll number (boll m-2) | Boll weight (g) |
---|---|---|---|---|---|---|
Target Population (plant m-2) | ||||||
22 | 2695 | 37.9 | 1015 | 3.7 | 81.1 | 3.4 |
30 | 2634 | 37.6 | 981 | 3.2 | 81.0 | 3.3 |
37 | 2586 | 37.5 | 963 | 2.9 | 83.3 | 3.1 |
44 | 2590 | 38.3 | 985 | 2.4 | 81.3 | 3.3 |
LSD ( | ns | ns | ns | 0.2 | ns | ns |
.55 | .35 | .97 | .01 | .77 | .16 | |
Nitrogen (kg ha-1) | ||||||
0 | 1736 | 38.7 | 661 | 2.1 | 59.3 | 3.0 |
56 | 2991 | 38.2 | 1133 | 3.2 | 89.8 | 3.4 |
112 | 2921 | 37.2 | 1087 | 3.4 | 88.4 | 3.4 |
168 | 2859 | 37.2 | 1066 | 3.4 | 89.1 | 3.2 |
LSD ( | 184 | 1.0 | 97 | 0.2 | 5.1 | 0.3 |
.01 | .01 | .01 | .01 | .01 | .03 |
Boll numbers (bolls m-2) and boll weight were not significantly different across populations (Table
Seed cotton yields, bolls plant-1, boll weight, and bolls m-2 increased as nitrogen rate increased from 0 to 56 kg ha-1, but there were no further increases at rates greater than 56 kg ha-1. These results are consistent with those of Clawson et al. [
Plant height increased in response to increase in nitrogen rate, but the population density effect on height was not significant (Table
Effect of plant population density and nitrogen rate on height for each year and number of nodes at harvest averaged over years.
Height (cm) | Nodes | |||
Treatments | 2000 | 2001 | 2002 | |
Target population (plant m-2) | ||||
22 | 77.3 | 64.2 | 69.7 | 16.5 |
30 | 75.1 | 59.4 | 70.0 | 16.1 |
37 | 77.1 | 63.8 | 69.6 | 15.9 |
44 | 77.1 | 62.1 | 68.8 | 15.5 |
LSD ( | ns | ns | ns | 0.6 |
.44 | .40 | .95 | .01 | |
Nitrogen (kg ha-1) | ||||
0 | 56.8 | 41.5 | 44.7 | 13.9 |
56 | 73.6 | 59.0 | 65.4 | 15.8 |
112 | 83.6 | 73.0 | 80.8 | 16.9 |
168 | 92.5 | 76.0 | 87.3 | 17.8 |
LSD ( | 3.1 | 4.1 | 4.3 | 0.6 |
.01 | .01 | .01 | .01 |
Nodes decreased in response to increases in population density but increased in response to increasing nitrogen. The difference in height and nodes between 56 and 168 kg ha-1 nitrogen was approximately 18 cm and 2 nodes, respectively, with no yield advantage between these rates.
There were no significant differences between population densities for percentage bolls by node position. The mean percentages were 23, 41, and 39 for nodes 4 to 8, and 9 to 12, and greater than 12, respectively. Jost and Cothren [
The percentage of bolls for nodes 4 to 8 increased with nitrogen rate to 112 kg ha-1 (Table
Effect of plant population density and nitrogen rate on percentage of bolls found at nodes 4 through 8, 9 through 12, and greater than 12.
Percentage of bolls by node positions | |||||||||
Variable | Nodes 4 to 8 | Nodes 9 to12 | Nodes | ||||||
2000 | 2001 | 2002 | 2000 | 2001 | 2002 | 2000 | 2001 | 2002 | |
Nitrogen (kg ha-1) | |||||||||
0 | 10.7 | 4.4 | 6.8 | 43.2 | 28.6 | 29.4 | 46.1 | 67.0 | 63.8 |
56 | 22.6 | 8.1 | 12.6 | 45.8 | 40.5 | 43.1 | 31.4 | 51.4 | 44.3 |
112 | 28.9 | 19.8 | 34.5 | 41.8 | 48.9 | 41.5 | 29.3 | 31.4 | 23.9 |
168 | 32.7 | 24.5 | 37.6 | 42.9 | 49.6 | 36.3 | 24.4 | 25.9 | 26.1 |
LSD ( | 7.1 | 6.6 | 8.6 | ||||||
Micronaire, fiber length, strength, and uniformity were not affected by increasing population density (Table
Effect of plant population and nitrogen rate on fiber micronaire, strength, length, and uniformity averaged over years.
Treatment | Micronaire | Strength (kN kg-1) | Length (cm fiber-1) | Uniformity (%) |
---|---|---|---|---|
Nitrogen (kg ha-1) | ||||
0 | 4.03 | 254 | 2.72 | 82.4 |
56 | 3.93 | 260 | 2.75 | 82.5 |
112 | 3.87 | 259 | 2.75 | 82.1 |
168 | 3.89 | 263 | 2.78 | 82.1 |
LSD ( | 0.14 | 5 | 0.03 | ns |
.01 | .03 | .01 | .09 |
Taken together, these data indicate that little can be gained by exceeding populations of 22 plants m-2 or nitrogen rates of 56 kg ha-1. Plant mortality increased in response to the increase in population density. Stand counts as a percentage of the target population were the highest at 22 plants m-2 at 3 WAP and at harvest indicating a greater economy in seed usage. Yields and boll numbers were equivalent across all populations, and there was little change in fiber properties in response to population or nitrogen rate increases. In addition, the increased height at the higher nitrogen rates may be detrimental to stripper harvesting because a greater stalk biomass would pass through the stripper without achieving greater yield.
The authors wish to thank Ms. Debbie Boykin, Statistician, USDA-ARS, for assistance with the experimental design and data analysis.