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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Water Management and Conservation Research » Research » Publications at this Location » Publication #301852
Title: Inter-relationships of cotton plant height, canopy width, ground cover, and plant nitrogen status indicators

Author
item MUHARAM, F - Universiti Putra Malaysia
item Bronson, Kevin
item MAAS, S - Texas Tech University
item RITCHIE, G - Texas Tech University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2014
Publication Date: 12/5/2014
Citation: Muharam, F.M., Bronson, K.F., Maas, S.J., Ritchie, G.L. 2014. Inter-relationships of cotton plant height, canopy width, ground cover, and plant nitrogen status indicators. Field Crops Research. 169:58-69.

Interpretive Summary: Spectral indices calculated from canopy reflectance are useful for estimating plant growth and health. However, these plant measurements are often not directly compared with plant nutrient status. The objective of this study was to evaluate plant height, plant width, and ground cover as indicators for estimating cotton plant N status. In this two-year field study, plant height, canopy width, and percent ground cover were compared with indicators of N status (leaf N, petiole sap NO3 and chlorophyll meter readings) to identify which growth parameter were most closely related to plant N. Cotton was fertilized at a full rate, half rate, and no N fertilizer in two sites in West Texas. Full rates for the two experiments were 101 and 224 kg ha-1. In Halfway, TX percent ground cover had the highest correlations with leaf N, and chlorophyll meter measurements, compared to plant height or plant width. In Lubbock, plant height, plant width, and percent cover had similarly strong relationships with leaf N or chlorophyll meter readings, suggesting they could be used to estimate plant N status when other growth factors were not limited. Relationships between plant growth parameters and petiole sap NO3 were weak and only present in the early season. In conclusion, percent ground cover can provide useful information in determining N status in cotton. However, a limited number of actual leaf N measurements for ground-truthing the ground cover-leaf N relationship would be required.

Technical Abstract: Petiole-NO3, leaf N and chlorophyll (SPAD) meter readings are good in-season indicators of the N status of the uppermost part of cotton (Gossypium hirsutum L.) plants. Petiole-NO3, particularly is widely used in the USA as an in-season plant N test that guides N fertilizer recommendations in cotton. However, these N status indicators do not take account of plant biomass, canopy width or percent cover. The objectives of this study were to assess the effect of N fertilizer rates on the commonly used indicators of plant N status; leaf N, petiole sap NO3 and chlorophyll meter (SPAD) readings and the plant growth measurements; plant height, 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 in2010, and at Halfway, TX in 2011. Zero-N and a full N fertilizer rate of 134, 101, and 112kg Nha-1 were used at Lubbock, New Deal, and Halfway, respectively. The 2010 cotton growing season in West Texas was much wetter than 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 for the 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 indicated that among the three plant N indicators, leaf N was the most sensitive to plant parameters. These effects were positive in 2010 and negative in the 2011 dry year. Petiole NO3 was the plant N indicator that was the most insensitive to plant growth, but the marked seasonal decline pattern reduces its use fullness for late-season N management.