Regulating Effects Of Low Planting Density And Pruning Methods On Cotton (Gossypium Hirsutum L.) Growth Under High Nitrogen Amount

With Jimian 668 (Gossypium hirsutum L.) as the tested cultivar, this study was conducted to investigate the effects of pruning methods on nutrient absorption of cotton plants grown under the conditions of low planting densities (18000,22500, and 27000 plants·hm-2) and high nitrogen applied amount (450 kg·hm-2). The pruning methods included conventional pruning (the removal of vegetative branch, abbreviated as CP hereinafter), no-pruning (with both vegetative branches and fruiting branches retained, as NP hereinafter), and only vegetative branch retention (as OVSR hereinafter). The mian results were as follows.1. Effects of low planting densities and pruning method on growth characteristics and yield of cotton plants under high nitrogen applied amountsAt the planting density of 18000 plants hm-2, the yield of the OVSR treatment was higher than that of the treatments of CP and NP. At the planting density of 22500 plants·hm-2, the yield of the treatments of OVSR and NP was higher than that CP treatment. At the planting density of 27000 plants hm"2, the yield of the treatments of OVSR and NP was lower than that CP treatment. Compared with the CP treatment, the number of boll per plant was higher in the treatments of both OVSR and NP. The highest boll number per plant and average boll weight were recorded when the planting density was 18000 plants hm-2 and only vegetative branches were maintained. Compared with the treatments of CP and OVSR, the number of fruiting node and the number of branch were lower than NP treatment. The highest seed cotton yield was recorded at the density of 27000 plants hm-2 and conventional pruning, reaching a level of 2676.08 kg·hm-2, primarily due to the ideal weight and distribution of biomass. The second highest yield was obtained when the planting density was 18000 plants hm-2 and only vegetative branches were retained.2. Effects of low planting densities and pruning method on plant morphological structure of cotton plants under high nitrogen applied amountsLeaf area index (hereinafter as LAI) was significantly affected by planting density, pruning method, and their combination, all at the probability level of 0.01. At the planting density of 27000 plants·hm-2, there was no significant difference in LAI between NP and OVSR, but the LAI of NP and OVSR was significantly higher than that of CP at the stages of initial flowering, peak flowering, and peak boll-setting. Planting density didn’t have significant effects on light transmittance percentage under most circumstances. Pruning methods had significant effects on light transmittance percentage, the length and diameter of internodes. At the stages of initial flowering, peak flowering, and peak boll-setting, the light transmittance percentage at the planting density level of 18000 plants·hm-2 was significantly higher than that at the planting density levels of 22500 and 27000 plants hm-2. At the same planting density level, the light transmittance percentage of CP was significantly higher than NP and OVSR. The length of internodes of NP was longer than that of CP and OVSR. The diameter of internodes of OVSR was bigger than that of CP and NP. The angle between the main stem and branches of CP and NP was significantly greater than that of OVSR.3. Effects of low planting densities and pruning method on nutrient absorption of cotton plants under high nitrogen applied amountsNitrogen absorption in cotton leaves was significantly affected by planting density, pruning method, and their combination at the stages of initial flowering, peak flowering, and peak boll-setting. Nitrogen absorption of the stem and reproductive organ at initial flowering stage was significantly affected by planting density, pruning methods, and their combination. The highest absorption amount of nitrogen, phosphorus, and potassium was found in the OVSR than that of in CP and NP. The higher the absorption amount of nitrogen, phosphorus, and potassium in the reproductive organs, the higher seed cotton yield was. The highest yield was obtained at the planting density of 27000 plants·hm-2 and nitrogen applied amount of 450 kg·hm-2 when vegetative branches were removed.Our study suggests that the vegetative branches can be retained when the planting density ranges from 18000 to 27000 plants·hm-2; the vegetative branches should be removed at the density higher than 27000 plants·hm-2. In this treatment, the accumulation of nutrients in cotton plants were maintained at suitable levels.