Nutrient uptake in cotton in relation to plant architecture
SummaryThe studies on uptake of nitrogen, phosphorus and potassium by two morphologically contrasting varieties of cotton MCU-1 and PRS-72 (bothGossypium hirsutum L.) at weekly intervals, showed that till the bursting of early formed bolls, the former type accumulated these nutrients in larger quantities in leaves and stem than in the fruiting parts unlike the latter type where differences in nutrient contents of these organs were very narrow till the active bolling phase. From flowering onwards, the fruiting parts of PRS-72 contained more phosphorus. Because of its bushy habit more dry matter accumulated and more nutrients remained unutilised in leaves and stem of MCU-1 at harvest compared with the short-branch variety PRS-72. Though both the varieties gave the same yield of seed cotton per unit area, PRS-72 removed considerably less quantities of nitrogen, phosphorus and pottassium. The short fruiting branch character in cotton therefore appears to contribute substantially towards balanced and economic utilization of nutrients.
Relation of Growth and Development to Mineral Nutrition
Plants are unique organisms that have the capacity to absorb inorganic elements and water through their root systems and carbon dioxide from the atmosphere and combine these into cellular constituents using energy from sunlight. Managing the supply of inorganic elements (nutrients) is a fundamental component of all plant production systems. If nutrient deficiencies are occurring, achievement of optimal yields requires a producer to supply fertilizer nutrients to supplement the pool of available nutrients in the soil to meet the nutritional needs of the specific plant. In addition, the timing of fertilizer applications should ensure that high availability of the applied nutrient(s) corresponds to the peak nutrient requirements of the developing root system. A basic understanding of the growth pattern and nutrient uptake with time by the cotton plant is essential in making wise nutrient management decisions, especially in production systems where nutrients may be deficient (Gerik et al., 1998). This chapter will focus on the elements considered essential for cotton plants, and their uptake and distribution within the plant.
Physiology of the Cotton Plant
A measure of distinction is attached to the physiology of the cotton plant by reason of the dimorphism of its branches, its indeterminate growth habit, and the shedding of small floral buds and young bolls. According to environ­ mental conditions, the branches produced by the cotton plant may be either vegetative or fruiting; the Upland cottons of the South produce variable proportions of the two. Customarily, one or more vegetative branches are developed from the lower sixth to ninth main-stalk nodes after which fruiting branches appear at the successively higher nodes. The interval between the appearance of new fruiting branches is about three days and between the successive nodes of the fruiting branches (each with a floral bud) there is an interval of about six days. Flowering is thus progressive and for a time it becomes more rapid as the plant grows. After flowering and boll setting have continued fot a number of weeks, however, both the growth of the plant and the production of flowers are checked and may stop. Also, many, if not most, of the floral buds abort before anthesis. The flowering and fruiting behavior of American Upland cotton, Gossypium hirsutum L., is day-length neutral; however, there are short-day cottons which develop only vegetative branches during long days. Without the advantage of suitably high temperatures, the day-length neutral cottons behave like short-day cottons under long days and produce only vegetative branches.