Guozheng Yang

Effects of Plant Density on Yield and Canopy Micro Environment in Hybrid Cotton

A rational plant population is an important attribute to high yield of cotton, because it can provide a beneficial micro environment within the canopy for plant growth and development as well as yield formation. A 2-yr field experiment was conducted to determine the optimal plant density based on cotton yield in relation to the canopy micro environment (canopy temperature, relative humidity and light transmittance). Six plant densities (1.2–5.7 plants m−2) were arranged with a completely randomized block design. The highest cotton yield (1 507 kg ha−1) was obtained at 3.0 plants m−2 due to more bolls per unit ground area (79 bolls m−2), while the lowest yield (1 091 kg ha−1) was obtained at 1.2 plants m−2. Under the moderate plant density (3.0 plants m−2), there was a lower mean daily temperature (MDT, 27.1°C) attributing to medium daily minimum temperature (Tmin, 21.9°C) and the lowest daily maximum temperature (Tmax, 35.8°C), a moderate mean canopy light transmittance of 0.51, and lower mean daily relative humidity (MRH) of 79.7% from June to October. The results suggest that 3.0 plants m−2 would be the optimal plant density because it provides a better canopy micro environment.

Fertilizer 15N Accumulation, Recovery and Distribution in Cotton Plant as Affected by N Rate and Split

Abstract N fertilization of 300 kg N ha−1 is normally applied to cotton crops in three splits: pre-plant application (PPA, 30%), first bloom application (FBA, 40%) and peak bloom application (PBA, 30%) in the Yangtze River Valley China. However, low fertilizer N plant recovery (NPR) (30-35%) causes problems such as cotton yield stagnation even in higher N rate, low profit margin of cotton production and fertilizer release to the environment. Therefore, it is questioned: Are these three splits the same significance to cotton N uptake and distribution? An outdoor pot trial was conducted with five N rates and 15N labeled urea to determine the recovery and distribution of 15N from different splits in cotton (Gossypium hirsutum L. cv. Huazamian H318) plant. The results showed that, cotton plant absorbed fertilizer 15N during the whole growing period, the majority during flowering for 18-20 d regardless of N rates (150-600 kg ha−1). Fertilizer 15N proportion to the total N accumulated in cotton plant increased with N rates, and it was the highest in reproductive organs (88% averaged across N rates) among all the plant parts. FBA had the highest NPR (70%), the lowest fertilizer N lose (FNL, 19%), and the highest contribution to the fertilizer 15N proportion to the total N (46%) in cotton plant, whereas PPA had the reverse effect. It suggests that FBA should be the most important split for N absorption and yield formation comparatively and allocating more fertilizer N for late application from PPA should improve the benefit from fertilizer.

Effect of Potassium Application Rate on Cotton (Gossypium hirsutum L.) Biomass and Yield

Cotton production in China is recently confronted with either yield loss by plant early senescence resulted from potassium (K) deficit, or cost rise and nutrients leaching by K excess use. However, the optimal K rate in term of cotton biomass production and yield remains uncertain to make a recommendation for the farmers. Both field with random block design and outdoor pot trials were carried out to determine how cotton (Gossypium hirsutum L. vs. Huazamian H318) biomass and yield were affected by K rates. The result showed that K2 (225 kg ha–1) harvested the highest yield (1 341 kg ha–1) and bore the most bolls (74 bolls per square meter) in the field trial, with a similar trend for the pot trial. As expected, cotton biomass of K2 was the highest at each of the sampling stages, especially for reproductive organs. Cotton biomass initiated simultaneously the fast accumulation period (FAP), but terminated the period differently among five K rates (0–450 kg ha–1). During the period, K2 had the highest biomass accumulation rate both on an average and in the maximum, and for vegetative and reproductive organs. It suggests that K rate of 225 kg ha–1 be optimal to produce a favorable yield in the field of medium fertility when N 300 kg ha–1 and P2O5 90 kg ha–1 are applied in the Middle Reaches of Yangtze River, in which condition cotton plants accumulate greater amount of biomass with a higher accumulating rate.