Influence of Nitrogen and Boron Interaction on Cotton Production

ABSTRACT
Studies across the cotton (Gossypium hirsutum L.) growing regions of the United States have shown boron and nitrogen to be essential nutrients for profitable cotton production. Four levels of nitrogen (N) (0, 34, 67, and 101 kg/ha for 1996 and 0, 67, 101, and 135 kg/ha for 1997) and four levels of boron (B) (0, 0.56, 1.12, and 2.24 kg/ha) were used on DPL-50 in a split-plot design with B subplot treatments randomly assigned within N whole plot treatments. The treatments were replicated four times. Nitrogen as sodium nitrate and ammonium nitrate for 1996 and 1997, respectively, were side-dressed and boron was foliarly applied as solubor. Yield parameters were measured for each treatment. There was no N X B interaction so data were averaged over N and B rates, respectively. In both years, increased N rate up to 101 kg/ha N increased lint yield (P < 0.01). The increase in lint yield for 1996 was 96, 369 and 455 kg/ha for 34, 67, and 101 kg/ha N over the untreated control, respectively. In 1997, however, the only significant yield increase was observed for the 101 kg/ha N rate. For both years, the maximum yield was achieved with 101 kg/ha N and 0.56 kg/ha B rates. Adding foliar boron at 2.24 kg/ha, however, decreased lint yield over the untreated control. Leaf blade tissue level increased with increasing B rates compared with the initial B level. Additional research is needed to fully understand the benefit of B in N utilization.

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Assessing the Salinity Threat to Sustainable Irrigated Cotton Production in the Lower Gwydir and Macintyre Valleys

ABSTRACT
Worldwide, the incidence of soil and water salinisation is increasing. This is particularly the case in irrigated agricultural regions and potentially in Australia’s intensively irrigated cotton-growing areas. This paper describes a broad scale approach to estimate this threat in the cotton growing areas of the lower Gwydir and Macintyre valleys using baseline soil and water information and a steady-state soil and water balance model. Results suggest with the current water quality and soil types, irrigated cotton production appears to be sustainable. Using the geostatistical method of indicator kriging and several ‘worst case’ scenarios in the model, areas that are at risk if saline water is used for irrigated agriculture are identified.

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Optimization of Cotton Irrigation using Evolutionary Algorithm and Simulation Model

ABSTRACT
The optimal management of irrigation is a principal constraint facing agriculture worldwide. The potential number of combinations of irrigation schedules over a growing season is enormous when the variables involved are considered. Theoretically, on any given day during a cropping season, a decision can be made to irrigate or not. This associated with specific irrigation amounts and methods. The outcome of a decision and the nature of future decisions is a function of the status of the crop at any given decision point. Thus, there are an extremely large number of potential irrigation schedules for any given crop season. Evolutionary algorithms are computer based optimization and search techniques that mimic natural selection to efficiently search very large solution spaces. They are based on the biological concepts of evolution through mechanisms such as selection, crossover and mutation. Cotton irrigation scheduling (timing and amount of water) can be approached as an adaptation problem. In this study a cotton simulation model (GOSSYM) was integrated with an evolutionary algorithm to provide irrigation recommendations to farmers. The results show that this approach to irrigation scheduling is an improvement over the expert system currently associated with the model. This evolutionary algorithm consistently derived irrigation itineraries that resulted in higher economic return. More interesting, this new approach is also generic and it is applicable to other cultural practices and to any cropping situation.

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Influence of Irrigation and Plant Density on Cotton Yield in Southern Italy

ABSTRACT
The effects of irrigation timing and plant density on the main morphological and agronomic characters of cotton were investigated over five years from 1987 to 1991 in Southern Italy. Five irrigation levels were combined with four plant densities (6, 9, 12 and 15 plants per m2). Times and volumes of irrigation were determined by thermopluviometric patterns and the phenological plant phase. The highest seedcotton yields wee obtained with high plant densities and irrigation at each phenological stage. These results confirm the importance of optimum water management in southern Italy. Irrigation increased the open bolls per plant markedly while the boll weight number per plant decreased in correlation with plant density.

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Economization of Nitrogen Requirement of Summer Irrigated Cotton through Use of Biofertilizers

ABSTRACT
An experiment was conducted on G. hirsutum variety LRA 5166 under summer irrigated conditions in Western Maharashtra to assess the possibility of reducing rates of N fertilizer through the use of bio-fertilizers. The experiment was on a medium deep, black soil, low in N, medium in P2O5 and high in K2O. Experiments were repeated over three years from 1995 to 1887 in split plots with three replications Sixteen treatment combinations consisted of the use of bio-fertilizers Azotobacter and Azospirillium through seed treatment and soil application with four levels of N, 0kg, 40kg, 60kg and 80kg per hectare. P2O5 and K2O were applied as basal dressings of 40 kg/ha. Pooled data indicated no significant differences between Azotobacter and Azospitillium or the method of application. However, bio-fertilizer seed treatment reduced inorganic N requirements by about 25%.

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Effects of Meteorological Parameters and Irrigation on Cotton Phenology in Greece

ABSTRACT
The influence of temperature, relative humidity, rainfall and irrigation on the duration of cotton phenological stages was studied in the cotton producing zone of Greece during a 10 year period (1986-1994). Influence was found to be parameter and stage dependent. Temperature was the most time affecting parameter. More specifically, the minimum temperature in the early stages and the maximum temperature in the late stages played the most significant (negative) role. Within the temperature range encountered, the variability between temperature (Ta) and time to a certain phenological stage (N) was explained only slightly better by an exponential than a linear function. By fitting a linear regression between 1/N and Ta, the thermal time required above a threshold temperature (To) was estimated for each developmental stage between sowing and harvesting and for the whole cotton cultivation zone. Rain lengthened cotton developmental stages, particularly when falling between sowing and anthesis or boll opening and harvest. Addition of irrigation water to rainfall, weakened regressions. The role of the relative humidity in regulating cotton phenology was insignificant, except occasionally after squaring. Multiple regression analysis, taking into account together all parameters studied, was justified as the coefficient of variation was usually increased. However, in many cases one or more parameters, apart from temperature, could be omitted as non-significant. Predictability of the relations established is discussed.

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Irrigation Withdrawal Time, Nitrogen Fertilization, and Cultivar Maturity Interactions in Upland Cotton

ABSTRACT
Normal cotton management practices in South Texas terminate irrigation as early as first open boll (about 6 weeks after first bloom) and use N fertilization rates ranging from 135 to 200 kg/ha. Experiments were conducted at the Texas A&M University Agricultural Research and Extension Centre in Uvalde, TX during the 1995, 1996, and 1997 seasons. This study evaluated growth and yield responses of very early, early, medium, and medium late maturing upland cultivars to early termination of irrigation and reduced level of N fertilization. Termination of irrigation three wk after early bloom did not decrease yields. High rates of N fertilization do not increase yields. Very early and early cultivars showed superior yield performance when soil moisture availability is plentiful during early season. DP5409 showed superior yield performance in all three years, including the droughty 1996. Medium-late DP90 produced superior yield under early-season droughty conditions and heavy early boll set. Earlier than normal termination of furrow irrigation and lower than normal nitrogen fertilization rates appear to be feasible practices leading to reduced-input production. Selection of appropriate cultivars is key for superior yield performance.

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