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The article focuses on the benefits of variable rate nitrogen applications for California cotton production. It develops a practical method for creating variable rate fertilizer nitrogen application maps based on existing yield maps, remotely sensed NDVI images, and/or soil bulk electrical conductivity maps and soil nitrate N levels obtained through directed pie-season sampling. It conducts replicated experiments in large commercial fields in which the treatments are variable rate fertilizer application, fixed rate fertilizer application, and control. The use of yields monitors, global positioning systems, remote sensing, and other attributes of site-specific crop management is increasing in California. California farmers who have adopted yield monitoring and mapping technology have frequently observed a high level of yield variability in their fields. In some cases growers have been able to interpret these yield maps on their knowledge of the field and use this interpretation to improve their management and enhance profitability. One of the most promising site-specific management practices is variable rate input application.

Plant Growth Regulator (PGR) is commonly used in cotton plant management. When applied to the crop, it redirects plant growth from the vegetative leaves to boll production and as a result can increase yield. In the 2000 and 2001 growing seasons experiments were performed in Mississippi to study the effect of PGR application across different Normalized Difference Vegetation Index (NDVI) regions of a field. NDVI measurements were extracted from remotely sensed data acquired over the field. In the 2000 experiment, the field was segmented into two types of treatment strips. One type received blanket applications of PGR according to traditional methods. The other treatment strips received no PGR. The treatment strips contained three different NDVI groupings to research if plants with different NDVI measurements respond differently to PGR. The 2001 experiment replicated the 2000 experiment, but added treatment strips as Spatially Variable plant Growth Regulator (SVPGR) applications to the design. The intent of this study was to determine if SVPGR application methods could be used as a technique to reduce PGR application costs and at the same time maintain or increase yields over the traditional (100%) method of applying PGR. The results of this research indicated that a cost savings of approximately 24% was realized in using the SVPGR method as compared to the traditional method. [ABSTRACT FROM AUTHOR]

Application of chemical harvest aids is necessary to improve harvestability and lint quality of the cotton crop. When applied properly to the crop, these chemicals stimulate leaf loss and promote boll opening. Traditionally, harvest aids have been applied at a constant rate across a field, resulting in over-application to areas that may have matured faster than others due to soil type, insect pressure, or disease. In 2003, a project was conducted in the San Joaquin Valley of California to evaluate the use of remotely sensed imagery for site-specific applications of cotton harvest aids in both Acala and Pima cotton. Remotely sensed imagery from airborne and satellite sources was obtained over the study area and analyzed to determine the most appropriate method for harvest aid prescription generation. Variable rate applications were applied via a commercial aerial applicator and compared to traditional blanket aerial applications. Seed cotton yield and harvest aid performance were not significantly decreased through the use of variable application technologies. [ABSTRACT FROM AUTHOR]

Organic cotton production requires alternatives to harvest aid chemicals for crop termination and fiber quality preservation. In these trials a self-propelled two-row thermal defoliation apparatus was tested in spindle picked and stripper harvested cotton. HVI classing data for thermal, chemical, and untreated control plots were compared. Fiber property data from similar trials in 2002 were presented where data from 2003 trials were not available. Leaf and color grades were improved; thereby increasing fiber value as compared to untreated and chemically defoliated controls. Other fiber properties were not greatly affected. Spinning and yarn properties were mostly unchanged. Rapid desiccation following thermal treatment makes it possible to harvest two days after defoliating. Foreign matter content of seed cotton did not decrease significantly after seven days, indicating completion of plant response. Insect mortality and the possibility of early harvest were additional benefits observed with thermal defoliation. [ABSTRACT FROM AUTHOR]

Cotton producers increasingly are under pressure to reduce chemical use, control stickiness, avoid weather damage and make a profit in the face of the lowest cotton prices in history. Organic producers are called upon to produce a high quality fiber without using any chemicals at all. The thermal defoliation research reported here is an attempt to provide producers with additional tools to meet these objectives. Thermal defoliation gives organic producers a way to terminate their crop. Other producers may appreciate being able to eliminate insects that cause stickiness, to defoliate during bad weather and to harvest shortly after treatment. Thermal defoliation was shown to work in three states (and over three years in New Mexico) in Pima, Acala and upland cotton varieties. While defoliation (leaf drop) is not as great as that attained with chemical treatment, desiccation (leaf withering) is usually more pronounced, and almost instantaneous. Two weeks after heat treating at 300 F for 8 seconds (burning 13 gallons of propane per acre) plants were 60% defoliated and 80% desiccated. [ABSTRACT FROM AUTHOR]

Given the results of the 2000 and 2001 image-based PGR application experiments in Mississippi, ITD wished to attempt to replicate these results in a PGR experiment conducted in a different cotton production region. The San Joaquin Valley of California was chosen as the site to conduct a PGR experiment for 2002. The San Joaquin Valley was chosen because of its different growing conditions from Mississippi, as well as the availability of a cooperating producer (Ted Sheely) and concurrent collaborative research on-going by USDA and University of California researchers at the farm. [ABSTRACT FROM AUTHOR]

Mapping the location of K-fixing soils in the San Joaquin Valley continues. In 2001 and 2002, 33 soil profiles were sampled. They fall into three categories: Sierra Nevada coarse-textured alluvium, Coast Range coarse-textured alluvium, and fine-textured alluvium. So far, complete mineralogical assays have been made on 5 profiles. Sierra Nevada alluvium soils have high amounts of vermiculite and >60% K fixation, and fixation increases with depth; Coast Range alluvium has more chlorite and <60% K fixation. On the samples characterized so far, K measured by the sodium tetraphenyl boron method (hypothesized to extract exchangeable K and a portion of fixed K) was not consistently related to conventional soil test K, or to the source of parent material. On the other hand, K fixation measured by amount of K removed from an 18 mmol solution in a 7-day incubation was related to source of parent material. [ABSTRACT FROM AUTHOR]

Acala cotton fields in several production regions of California in 2002 experienced a range of symptoms, including early cessation of main stem and sympodial branch growth, foliar red or bronze coloration followed often by leaf necrosis, and in some limited cases, observable leaf wilting. Most University of CA Advisors and private consultants we met with felt the range and severity of these occurrences were considerably worse than experienced in the same areas in any recent years in Upland / Acala cotton. Variations on these symptoms were observed in widespread locations in several San Joaquin Valley counties in 2002, and field symptoms that were similar in some respects and different in other respects were also observed in the Imperial Valley region in southern California. In most fields, the first observations of problems began about mid-bloom, with the first observable symptoms differing somewhat across locations. In many cases, more severe than normal red and purple coloration in upper canopy stem and petiole tissue, or dark red or bronze coloration in upper canopy leaf blades were among the first plant symptoms observed. In most cases analyzed, plants developed moderate to severe nutrient deficiencies after mid- to late-fruiting. Soil and plant tissue tests available from many, but not all affected fields indicate that although plant tissue levels were low in several nutrients, including nitrogen and potassium, corresponding soil nutrient levels were generally within University of CA recommended levels. The worst-affected fields in the San Joaquin Valley generally had low to moderate yields, but the fruit loads were quite high given the smaller size and reduced vigor of the plants. Observations and soil and plant tissue tests available indicate that this problem was noted in numerous varieties, but foliar symptoms developed earlier and were worse in some varieties than in others. Yield data in these fields is inadequate to determine clearly if varietal differences in timing of symptoms resulted in yield differences. Although definitive causes of observed problems have not been identified based on these field observations, some generalizations are described that may prove useful if problems recur in other years. [ABSTRACT FROM AUTHOR]