About
  PDF
Full Text
(618 K)

Water and Nitrogen Source Interaction with Cotton Growth and Development

J.P. Morgan and D.R. Krieg


ABSTRACT

On the Southern High Plains of Texas, there are approximately 1.5 million hectares of cotton (Gossypium hirsutum L.) planted annually. This semi-arid region has an annual rainfall average of 475-mm and an average growing season rainfall of 350-mm or 2- mm day-1 from May through September. The average summer potential evapotranspiration (PET) is 1000-mm or 6-mm day-1, which makes it necessary to have supplemental irrigation if maximum yields are expected. Approximately 45% of the total acreage in the area is amenable to supplemental irrigation. Application of irrigation water is limited in most production systems and cannot replace losses due to evapotranspiration throughout the growing season. Low energy precision application (LEPA), rather than spray application of irrigation water is becoming more widely used. LEPA provides increased application efficiency and reduction of evaporation. When water supply can be managed through irrigation, the nitrogen supply becomes the next limiting factor. Most of the nitrogen in the soil system is in the nitrate form (NO3-). Nitrate must be reduced in the growing plant before it can be incorporated into amino acids for protein synthesis or incorporated into other organic-N compounds. Uptake and reduction of NO3- is an expensive process in terms of carbon energy requirements. The reduction process requires 8- electrons for each NO3- molecule, the equivalent of half a mole of glucose or three reduced carbons. It requires only 2 to 5% of plants reduced carbon energy to incorporate NH4+ into organic-N compounds vs. 10 to 15% for NO3-. Ideally, NH4+ is the preferred nitrogen source since energy is saved and crop growth is often improved when crops are provided with both NH4+ and NO3- nutrition Ammonical nitrogen (NH4+-N) is an efficient source to plants. However, it is rapidly oxidized into NO3- by the bacterial system. Extensive research for the past 25 years has been directed towards controlling populations of nitrifying bacteria by nitrification inhibitors, but this effort has been unsuccessful for season long control. Fertigation offers the opportunity to provide the crop with a constant supply and readily available source of nitrogen. This study compared the growth, development and yield components of cotton as a response to NH4+ and NO3- ratios at a constant nitrogen supply across variable water supplies. Results of this study indicate that water use efficiency is increased by providing nitrogen through the water. Data indicate a direct response to water supply across all treatments. Within each water treatment, lint yield was found to be responsive to the nitrogen source. This response is most evident within the 75:25 (NH4+:NO3-) ratio. The 75:25 (NH4+:NO3-) a higher ammonical source out yielded the 100% NO3- source due. Lint yield increase was due to an increase in boll number rather than an increase in boll size. The major variability of cotton yields is 80% due to boll number/unit area, while boll size accounts for only 12-15% of yield variability in cotton. LEPA fertigation offers the opportunity to provide cotton with a season-long uniform supply of both NH4+ and NO3- nitrogen that will maximize the potential for optimum production.





[Main TOC] | [TOC] | [TOC by Section] | [Search] | [Help]
Previous Page [Previous] [Next] Next Page

Document last modified May 20, 2002