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.

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.