Inter-relationships of cotton plant height, canopy width, ground coverand plant nitrogen status indicators

摘要

Petiole-NO3, leaf N and chlorophyll (SPAD) meter readings are good in-season indicators of the N statusof the uppermost part of cotton (Gossypium hirsutum L.) plants. Petiole-NO3, particularly is widely used inthe USA as an in-season plant N test that guides N fertilizer recommendations in cotton. However, theseN status indicators do not take account of plant biomass, canopy width or percent cover. The objectives ofthis study were to assess the effect of N fertilizer rates on the commonly used indicators of plant N status;leaf N, petiole sap NO3and chlorophyll meter (SPAD) readings and the plant growth measurements; plantheight, canopy width, and percent ground cover, and determine to inter-correlations among the them.Irrigated field studies were conducted at Lubbock, TX USA in 2010 and 2011, New Deal, TX in 2010, and atHalfway, TX in 2011. Zero-N and a full N fertilizer rate of 134, 101, and 112 kg N ha−1were used at Lubbock,New Deal, and Halfway, respectively. The 2010 cotton growing season in West Texas was much wetterthan average, and the 2011 season was much drier than normal. As a result, plant height, canopy width,and ground cover were greater in the 2010 sites than in 2011. The effects of N fertilizer were greatest forthe two cultivars in subsurface drip irrigation (SDI) at New Deal in 2010 for all three N status indicators,and for the three plant growth measures compared to the other site-years. Correlation analysis indicatedthat among the three plant N indicators, leaf N was the most sensitive to plant parameters. These effectswere positive in 2010 and negative in the 2011 dry year. Petiole NO3was the plant N indicator that wasthe most insensitive to plant growth, but the marked seasonal decline pattern reduces its usefulness forlate-season N management.