Plant growth regulators (PGRs) are frequently used to adjust cotton growth and development.  The objectives of this study were to determine how PGRs affect plant morphology, light distribution and the spatial distribution of leaves and bolls within the cotton canopy.  The field experiments were carried out at Shihezi (Xinjiang Uyghur Autonomous Region, China) in 2014 and 2015.  The experiment included two PGR treatments: (i) flumetralin (active ingredient (a.i.), N-N-ethyl-2,6-dinitro-4-aniline) and (ii) mepiquat chloride (a.i., 1-dimethyl-piperidiniuchloride) plus flumetralin.  No PGR (manual topping) was applied in the control treatment.  The chemically-topped plants were taller and had more main stem internodes than the manually-topped plants.  Furthermore, the PGRs significantly reduced the length of fruiting branches in the upper canopy, resulting in a more compact canopy.  The maximum leaf area index was significantly greater in the chemically-topped treatments than that in the control.  In particular, the PGRs increased leaf area index by 25% in the upper canopy.  The leaf area duration was also longer in the chemically-topped treatments than in the control.  Compared with the control, the chemically-topped treatments increased canopy diffuse non-interceptance by 35.75% in the upper canopy layer, while reducing the fraction of intercepted photosynthetically active radiation by 14.45% in the upper canopy layer.  Light transmittance in the upper and middle canopy layers was greater in the chemically-topped treatments than in the control, which increased boll numbers in both the upper canopy and the middle canopy.  However, the chemically-topped treatments resulted in less light-leakage through the lower canopy layer during the late growth stages, which had a tendency to increase boll numbers in the whole canopy.  In summary, the PGRs optimized canopy shape, light distribution and the spatial distribution of bolls and leaves.

 

Understanding the influence of farming practices on carbon (C) cycling is important for maintaining soil quality and mitigating climate change, especially in arid regions where soil infertility, water deficiency, and climate change had significantly influenced on agroecosystem.  A field experiment was set up in 2009 to examine the influence of residue management and fertilizer application on the C cycle in a cotton field in the Xinjiang Uygur Autonomous Region of Northwest China.  The study included two residue management practices (residue incorporation (S) and residue removal (NS)) and four fertilizer treatments (no fertilizer (CK), organic manure (OM), chemical fertilizer (NPK), chemical fertilizer plus organic manure (NPK+OM)).  Soil organic carbon (SOC) and some of its labile fractions, soil CO₂ flux, and canopy apparent photosynthesis were measured during the cotton growing seasons in 2015 and 2016.  The results showed that SOC, labile SOC fractions, canopy apparent photosynthesis, and soil CO₂ emission were significantly greater in S+NPK+OM (residue incorporation+chemical fertilizer) than in the other treatments.  Analysis of all data showed that canopy apparent photosynthesis and soil CO₂ emission increased as SOC increased.  The S+OM (residue incorporation+organic manure) and S+NPK+OM treatments were greater for soil C sequestration, whereas the other treatments resulted in soil C loss.  The S+NPK treatment is currently the standard management practice in Xinjiang.  The results of this study indicate that S+NPK cannot offset soil C losses due to organic matter decomposition and autotrophic respiration.  Residue return combined with NPK fertilizer and organic manure application is the preferred strategy in arid regions for increasing soil C sequestration.