|1||W. of Miller Rd., N. of RID canal / severely affected|
|2||W. of Miller Rd., S. of RID canal / severely/moderately affected|
|3||W. of Miller Rd., N. side of Broadway , moderately affected|
|4||W. of Miller Rd., S. side of Broadway, moderately affected|
|5||Buckeye Upland Variety Test|
|6||Tonopah area, very severely affected|
|7||Tonopah area, non-affected|
Soils were sampled from all fields to a depth of about six to 10 inches according to Figure 2, primarily to address salinity and sodium (Na) gradients. Results from a complete / full spectrum set of analyses are presented in Table 1.
Tissue samples were also collected (leaf blades and petioles) from each field. Results from the complete tissue analyses are presented in Table 2.
Soil samples were also collected from several representative locations in each field and composited by one foot depth increments, to a total depth of four feet (Table 3).
Figure 3 and Table 4 provide outlines of salinity (ECe ,dS/m) and exchangeable Na percentages (ESP) for the surface samples at Buckeye and Tonopah. Figure 4 and Table 5 offer similar results for the Paloma field, followed by Table 6 with a complete set of soil analyses.
There is certainly evidence for some rather saline and/or sodic conditions revealed from these results. However, none of the results indicate anything unusual, particularly in the context of what is "normal" for the areas in question and in terms of relative comparisons. We definitely need to be conscious of these conditions and they can impact several aspects of field / crop management. Soil salinity and / or Na do not appear to be the critical features associated with the crop response patterns experienced. It is interesting to note an increase in soil salinity (ECe) levels at about the three foot depth in the Tonopah soils (Figure 6), that coincide with a gravel layer at that depth and the probable restriction in drainage that would occur under those conditions. All other ECe values indicate good leaching conditions and overall salt management.
Vertical lines are present on many of the nutrient figures (Fe, Zn, K, and P) indicating where current (UA) soil test "critical levels" exist for cotton. The only factor that presents potential concern in the review of this information are the soil K levels (Figures 11 and 12, ammonium acetate extractions). Using a soil test critical level of 150 ppm K, several of the fields are low and some are borderline. It is also interesting to note low soil K values throughout the profile in those cases. This is significant considering cotton root development patterns, and the probability that K uptake is taking place at depths two to four feet below the surface late in the season. However, these results do not offer any clear indication that the problems in question are due strictly or primarily to poor K nutrition. The plant symptoms match K deficiency symptoms to some extent, but they also look a lot like Verticillium wilt.
Potassium nutrition may be contributing to the problems encountered, but Verticillium wilt is probably a factor as well. There are very likely a number of factors contributing to the overall symptoms that were expressed. Verticillium wilt was common in many parts of Arizona in 1997, most of which have soils that are relatively high in extractable K. An important factor to consider relative to these and similar fields, is that poor and/or weak root development is also very likely contributing to the problems. Although this is hard to identify in an absolute manner, symptoms did indicate root system problems.
Speculation could propel a rather lengthy discourse on the problems we encountered late in the 1997 in much of central Arizona. The purpose of this report is to provide an outline of the data obtained from the samples that were collected in a systematic fashion in response to the occurrence of the symptoms and the many questions that were posed as a result. We can offer a good characterization of these fields as a result of the samples and analyses. However, this type of experience demonstrates the fact that field diagnostics are not always simple and clear-cut. Some of the relationships considered in this project have been studied extensively elsewhere, such as the K nutrition/Verticillium wilt interactions. Plant nutrition studies involving K, micronutrients, and possible Verticillium wilt interactions are needed to address the relationships associated with cotton production systems in Arizona and premature late-season senescence.