Soil Evaluation and Management Planning

by Jeffrey C. Silvertooth,
Extension Agronomist - Cotton

As we progress into the harvest season many farms in Arizona are anticipating decent or near average yields. Following the many challenges that have confronted the 1999 Arizona cotton crop it has actually progressed rather well. Challenges encountered by growers have included a wet, cold spring, late plantings, winds in the spring that contributed to early square loss, locally-heavy Lygus infestations, late pink bollworm pressure, a record long monsoon season, and even damaging hailstorms locally; just to name a few. Probably the greatest challenge that anyone growing cotton faces is trying to make a profit with the current cotton market conditions. However, despite the dismal market, I continue to be impressed and somewhat amazed by the resilience, flexibility, and optimism that many cotton farmers are able to maintain.

Basically, there are two general strategies that have been commonly considered in an effort to realize a profit with cotton production (or in agriculture in general right now). One is to generate tremendous increases in yield and the second is to maintain (or improve) yields with a reduction in the cost of production. It is the second general option that I commonly see being addressed on many farms around the state and region. In an attempt to reduce the costs of production and maintain yield, many innovations and creative practices are being developed and employed. Some of these changes include reductions in tillage and field cultivations (often involving the use of herbicide tolerant transgenic varieties), improvements in irrigation efficiencies, modifications and refinements of plant growth regulator use, fertilization programs, or pest management techniques. As a good example, ultra narrow row production systems have been developed and tested on several farms around the state. It is important to scrutinize every production system and each input that is provided to a crop in terms of the cost/benefit relationship. If a given input is adding to the cost of production it must be considered in relation to the benefit it provides, particularly to the bottom line (yield, quality, and system efficiency). It is very important to identify those inputs and practices that are beneficial and those that are not. Accordingly, it is also important to not discontinue the use of any given input or practice unless there is clear evidence that it is not providing a direct benefit to the crop production process.

This is an excellent time of year to review production inputs such as plant nutrients (fertilizers) and soil amendments in terms of crop performance. This is an area of crop production that we need to consider with care, both in terms of short- and long-term management of a field or farm. I suggest that farmers and crop managers review production records for this and previous years for all fields in relation to their fertility management program. If there is an inclination to reduce fertilization in response to the depressed cotton markets and an effort to reduce the cost of production, this decision needs to be made with appropriate information at hand. I recommend that a fertilization program should begin with a good soil sample from the field in question, followed by a series of appropriate soil tests in a good laboratory. The general guidelines for cotton fertility management in Table 1 are based on work done in Arizona and this region. These values represent the "critical levels" for soil test results and proper fertilization. In general, our field research projects have shown that if the soil test results from a field are above the critical levels in Table 1, the probability for a positive crop response to fertilization with that nutrient is low and decreases with higher soil test values. Soil test results below the critical levels have a good probability for crop response from fertilization for that nutrient. We have the most information and the most confidence in the guidelines for P and K. The information in Table 1 seems to be accurate and generally acceptable for the other nutrients listed. More work in this area is needed and a current project designed to address the calibration of these soil tests to cotton fertilization in Arizona continues with the support of funding from the Arizona Cotton Growers Association and members of the Arizona fertilizer industry and laboratories.

Therefore, if there are questions concerning the need and appropriate rates of fertilizer applications for optimum yields in Arizona cotton, I first recommend the collection of a good soil sample and submission to a lab for the appropriate analyses. Review the results in relation to the information presented in Table 1. Also, review carefully the fertilization program, crop rotation (and fertilization of those crops), and yield histories associated with each field when evaluating and developing a fertility program for next year. It is not good to indiscriminately withdraw or add fertilizers to a production plan without proper evidence and justification.

All crop inputs need to be considered in relation to production efficiencies (e.g. yield/acre vs. cost/acre). This is true for all crop production inputs and practices and it is particularly critical during periods of severe economic stress.

Table 1. Soil fertility and soil testing guidelines for Arizona cotton.

* Pertains to samples collected after a pre-plant irrigation and is used primarily for pre-plant or very early season applications of fertilizer N only.

Full Disclaimers

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

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