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Fluid Journal : Fluid Journal 2005-2007
Winter 2005 Fluid Journal 2 Embryo abortion. Although there are about 40 ovules per boll (8 to 10 ovules/compartment; 4 to 5 compart- ments/boll) rarely do we find 40 mature seeds/boll. The typical boll contains 25 to 30 mature seeds and 10 to 15 aborted ovules. Embryo abortion is primarily caused by inadequate nutrition from both organic and inorganic supplies. The lack of adequate reduced N-com- pounds is the primary causal agent for embryo abortion, in my opinion. Cotton produces a large number of floral buds during its life but only a small percentage of the young fruit ever matures and contributes to yield. When viable embryo numbers drop below 20 seeds/boll, the entire fruit usually aborts about 5 to 7 days post anthesis. As the embryo dies, ethylene is produced, and as ethylene concen- trations increase with increasing numbers of dead embryos, the boll aborts. This represents a significant loss of both reduced Carbon (C) and minerals. Boll abortion is quite pronounced in cotton where it ranges from 85 to 90 percent in low-yielding environments to 65 to 80 percent in high-yielding environments. Adequate water. Maintaining an adequate water supply to minimize the risk of plant water stress reducing photosynthesis and N metabolism, and maintaining an adequate supply of N, P, K, and S in the soil solution during the early phase of each fruit's development are very critical to capitalizing on the inherent yield potential of this crop plant. The biology of the cotton plant is basically that of a woody perennial with an indeterminate growth habit. Seed production is insignificant to its survival as a plant species. Any minor disturbance in its supply of environ- mental resources required for growth will result in shedding of small fruit to maintain vegetative tissue for re- growth when the stress is relieved. In today's production systems we emphasize earliness, which means we want to retain a very high percentage of the first three to four weeks of flowering. Water and nutrient supplies during the critical stages of develop- ment of each young fruit determine whether it is retained to maturity or aborts. Sparse root density. One other major problem with cotton that increases the probability of water and nutrient stress is the root system. Cotton is a tap-rooted plant that has the potential to exploit considerable soil depth. However, cotton has an extremely low root length density (root length/soil volume) throughout the depth of the profile, averaging only one cm/cm3 of soil. This sparse density causes significant problems with both water and nutrient acquisi- tion at a sufficient rate to meet the demands of a high-yielding crop, especially in environments with high evaporative demand. Peak water demand Peak water demand occurs from 70 to 110 days after planting and aver- ages about 0.25 inches/day. With average rainfall and 4 gallons/minute/ A of irrigation water supply, we can maximize yield of high-quality fiber within the temperature constraints of our growing season. We have developed management strategies involving plant density (row spacing/ plant population/row length) to minimize the risk of excessive plant water stress during critical develop- mental periods in the life of the plant. We have clearly demonstrated that narrow rows (30-inch) and an in-row population of three plants/foot of drill row are ideal; however, populations from 2 to 4 plants/foot are not yield limiting. Water/N relationships Under irrigated conditions, the amount of N required per acre depends entirely on water supply (Figure 1). We determined that cotton requires 5 pounds N/inch of water Figure 1. Effect of water and N supplied at varying levels on lint yield of cotton
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