May 1999


Each year the Potash & Phosphate Institute (PPI) and the Foundation for Agronomic Research (FAR) help support research projects across North America. These projects involve crop production in the field… research to develop efficient high-yielding systems. They are designed to answer current production questions and related environmental concerns.

PPI will be assisting with 11 FAR-supported research projects in the western U.S. in 1999. Eight are continuing from last year and three are new. Nine projects were completed at the end of 1998. Following is a brief summary of each project. Please understand that for projects still in progress the release of detailed results is strictly up to the researcher. If any project is of special interest, you might want to contact the researcher to get a first-hand update.


Alfalfa Response to Forms of Phosphorus in the Irrigated Southwest

Project Leader: Dr. Michael J. Ottman, Plant Sciences Department, University of Arizona, Tucson, AZ 85721. Phone: (520) 621-1583, fax: (520) 621-7186, e-mail:

This project evaluates the relative benefits of different phosphorus (P) sources (liquid and dry) and best management practices for alfalfa production in the irrigated desert climate of Arizona. It was initiated in the fall of 1996 and will conclude at the end of the 1999 growing season.

Results of the first 2 years show that both 10-34-0 and 11-52-0 can be effectively topdressed to produce high yield alfalfa. The topdressd 11-52-0 produced somewhat higher yields in the initial season and seemed to move deeper into the soil than did the water-run 10-34-0. Soil tests from the second season are not yet available. Adequately fertilized treatments with either source produced over 11 tons/A in 1997 and over 12 tons/A in 1998.

Response of Valencia Oranges to Potassium Fertilizer on a Sandy Soil

Project Leader: Dr. Charles A. Sanchez, Department of Soil, Water and Environmental Sciences, Yuma Agricultural Research Center, University of Arizona, Yuma, AZ 85364. Phone: (520) 782-3836, fax: (520) 782-1940, e-mail:

This project evaluates the effectiveness of different rates and sources of potassium (K) fertilizer applied directly to the soil (Superstition sand), to the foliage, or in combination for oranges grown on two different rootstocks in western Arizona. It was initiated in 1997. Following the second harvest (Spring 1999), the orange study will be terminated and a similar study on lemons will be initiated.

In the first year there were large differences in fruit yield and quality between oranges produced on different rootstocks, where ‘Macrophylla’ consistently out-produced ‘Troyer’. There were no significant effects of the fertilizer treatments for potassium chloride (KCl), potassium sulfate (K2SO4), potassium nitrate (KNO3) or monopotassium phosphate (MKP), except for foliar applied MKP that reduced yield of oranges grown on the ‘Troyer’ rootstock. Overall, differences in juice quality were inconsistent and small in magnitude.

Effects of Fluid Phosphorus Fertigation on Growth and Yield of Microsprinkler Irrigated Citrus in the Desert Southwest

Project Leaders: Dr. Thomas L. Thompson, Department of Soil, Water, and Environmental Science, University of Arizona, Tucson, AZ 85721. Phone: (520) 621-3670, fax: (520) 621-1647, e-mail:; and Dr. Michael Maurer.

The objectives of this project are to evaluate P fertigation through microsprinklers for yield and quality of grapefruit and to update P tissue test guidelines for use in desert climates such as in central Arizona. This 3-year project was initiated in the spring of 1998.

The experiment, being conducted at the University of Arizona Citrus Agricultural Center, consists of phosphoric acid (0, 41, 82, 124 lb P2O5/A) split in monthly injections into the microsprinkler irrigation system. The first grapefruit harvest took place in February 1999. There were no fruit yield or quality differences among treatments. However, leaf P levels were marginal during the season, suggesting a fertilizer response may occur in the next season or two.

Evaluation of Balanced Cotton Nutrition Management

Project Leader: Dr. Jeffrey C. Silvertooth, Dept. of Plant Sciences and Dept. of Soil, Water, and Environmental Sciences, University of Arizona, Tucson, AZ 85721. Phone: (520) 621-7616, fax: (520) 621-7186, e-mail:

This project is in its initial year of support by PPI, although it actually began in 1998. The purpose is to evaluate various commercial cotton fertilization regimes involving nitrogen (N), P, K, and micronutrients in relation to the University of Arizona fertilizer guidelines. Six to eight fields will be studied in 1999. Individual plots, replicated 4 times, will extend the length of the irrigation run and will be large enough to harvest into separate modules. Both yield and lint quality will be evaluated.


Boron Nutrition of Nut Crops

Project Leader: Dr. Patrick Brown, Department of Pomology, University of California, Davis, CA 95616. Phone: (530) 752-0929, fax: (530) 752-8502; e-mail:

This project studies the benefits of foliar boron (B) sprays applied at different rates and time on yield and quality of almond and walnut nut crops. The project was initiated in 1994 and completed at the end of the 1998 growing season.

Almond research evaluated the effect of B nutrition on flowering, fruit set, and yield following a similar (and very successful) study with pistachio. Spraying B at a rate of 1 to 2 lb Solubor/100 gal on B deficient almond trees significantly increased fruit set and yields in 1995 and 1996. Of special note is the fact that often almond trees responded positively to supplemental B sprays without showing visible B deficiency symptoms. Results in 1997 suggest an optimal application is to mix 3 lb Solubor with compatible insecticides and fungicides to reduce application costs and to spray postharvest.

Walnut research was initiated in 1997. Foliar B treatments dramatically increased walnut set and retention, reduced or totally eliminated pistillate flower abortion (PFA) and increased ultimate nut yield. Results in 1998 were variable across three sites and strongly affected by prevailing weather conditions. At sites where PFA was not as severe, the application of B had no effect on reducing PFA. At a site with the most prevalent PFA of around 58 percent, B sprayed two weeks after nut set reduced PFA by around 16 percent and increased yield by 20 percent.

Establishing Updated Guidelines for Cotton Nutrition

Project Leader: Dr. Bill Weir, University of California Cooperative Extension Service, 2145 Wardrobe Ave., Merced, CA 95340. Phone: (209) 385-7403, fax: (209) 722-8856; e-mail:

This project studied various aspects of K fertilization of cotton in the San Joaquin Valley of California. It was initiated in 1994 and concluded following the 1998 growing season.

The 1996-98 studies emphasized in-season K applications to supplement a well-managed preplant program (previously studied) aimed at producing high yields. Initial results substantiated that foliar K (4.5 lb K2O/A) applied twice at one to three weeks after first bloom produced the greatest yield increases compared to that applied earlier or later in the season. Studies in 1997 showed that additional yield may be obtained by increasing rates up to 13.5 lb K2O/A, also applied twice. Foliar applications were not beneficial in the weather-shortened 1998 season where yields were only slightly above 2 bales per acre. Overall, results indicate that foliar applications of K should be recommended on potentially high yielding fields regardless of soil test or previous fertilizer applications.

Potassium Nutrition of Processing Tomatoes in the Sacramento Valley

Project Leader: Dr. Tim Hartz, Department of Vegetable Crops, University of California, Davis, CA 95616.
Phone: (530) 752-1738, fax: (530) 752-9659, e-mail:

Preliminary survey information gathered prior to the beginning of this study indicated that K deficiency of processing tomatoes may be relatively widespread in California. Conducted from 1995 through 1998, this project studied the effect of sidedress, foliar, and water-run K applications on processing tomato yield, fruit quality, and severity of premature decline of tomato vines.

Survey results in 1996 suggested that soil cation balance, specifically the relative amounts of extractable K and magnesium (Mg), are correlated to the incidence of yellow eye and white core, important factors for peeled and diced products. Applying gypsum or K decreased these color disorders in a field with moderate cation imbalance in 1997; the combination of materials was especially effective. However, in fields of severe cation imbalance, a positive response is less probable. Due to substantial levels of K fixation in these soils, it is difficult to alter their K availability or K/Mg balance. In 3 of 4 commercial fields studied in 1998, K applications reduced the incidence of yellow eye and /or improved the color of peeled fruit. It was also observed that maximizing peeled fruit quality requires a higher level of K nutrition than is required for maximum yield, percent soluble solids or comminuted color.

Determining Potassium Fertility Needs of Celery and Peppers

Project Leader: Richard Smith, University of California Cooperative Extension Service, 1432 Abbott St., Salinas, CA 93901. Phone: (831) 759-7357, fax: (831) 758-3018, e-mail:

Intensively produced vegetable crops have high nutritional requirements. This project evaluated the K nutritional needs of peppers and celery growing on the central coast of California and the diagnostic techniques to sustain high yield and quality. It was initiated in 1997 and terminated at the end of 1998.

A survey of 12 commercial pepper fields in 1997 in the Hollister-Gilroy area revealed that 10 were capable of significant fixation of soil K; pepper tissue K was also low in 10 of the crops. A similar survey of 15 celery fields in the SalinasValley indicated that all but one field was adequately fertilized with K. Fresh sap K levels utilizing the Cardy meter for both pepper and celery tissue were highly correlated with standard laboratory measurements. One field experiment was conducted in 1998 to evaluate different rates of K2O (0, 20, 45, and 90 lb/A) for pepper production. However, residual soil K was sufficiently high so that no yield response was observed in this case.

Potassium Nutrition of Pistachio: Development of Fertilizer Recommendations and Diagnostic Procedures

Project Leader: Dr. Patrick Brown, Department of Pomology, University of California, Davis, CA 95616. Phone: (530) 752-0929, fax: (530) 752-8502; e-mail:

The primary objectives of this study were to determine the response of pistachio to K application and to develop optimal K fertilizer programs. The study was initiated in 1996 and terminated at the end of 1998.

The study was conducted on mature ‘Kerman" pistachio trees in three commercial orchards. Treatments consisted of four annual fertilizer rates (0, 120, 240 and 360 lb K2O/A), three K fertilizers (K2SO4, KCl and KNO3), and two application methods (micro-sprinklers vs. soil banding). Potassium application, regardless of K source, application rate, and method, significantly increased nut yield and quality, soil K availability, and leaf K level. The economic effects of K use were evaluated using net return and value to cost ratio (VCR, the ratio of the value of increased yield from K used to the cost of K used). Potassium application was shown to be highly profitable to growers, with net returns for K use in the range of $378 to $1,648 per acre and VCRs of 3.5 to 30.5. Based on both agronomic and economic results of this study, it is recommended to apply K fertilizers via fertigation systems at the rate of 120 to 240 lb K2O/A (at least for low and medium testing soils), using either K2SO4 or KCl.

Reassessment of Leaf Potassium Critical Values in Almond

Project Leaders: Dr. Patrick Brown, Department of Pomology, University of California, Davis, CA 95616. Phone: (530) 752-0929, fax: (530) 752-8502; e-mail:; and Dr. Steven Weinbaum.

Almond yields have increased substantially since the University of California guidelines for leaf K were first published in the early 1960s. Increasing numbers of growers and analytical laboratories are concerned that the current UC guidelines for leaf K are inadequate. This project was initiated in 1998 and will continue for three years to evaluate and update these guidelines.

A vigorous almond orchard with low leaf K levels was chosen as the study site. Baseline yields for individual trees were determined in this initial year, and K2SO4 was applied at 0, 120, 240, and 360 lb K2O/A to begin establishing a broad range of tree K status. Whole tree excavations were conducted at a separate location (Delta College’s Regional Almond Variety Trial).The data obtained indicate that K accumulation by almond is substantial and continuous during fruit development, beginning immediately following fruit set. Potassium removal for a 4,335 meat pounds per acre "Nonpareil" crop is estimated to be about 350 lb/A K2O equivalent.

Predicting Potassium Availability in Rice Fields under Alternative Rice Straw Management Practices

Project Leader: Dr. Chris van Kessel, Department of Agronomy and Range Science, University of California, Davis, CA 95616. Phone: (530) 752-4377, fax: (530) 752-4361. e-mail:

This project is in its initial year; the first field harvest will be taken in the fall of 1999. The purpose is to re-evaluate the accuracy of soil K tests for predicting K fertilizer needs for rice production. The K supplying power of flooded rice soils will also be studied as affected by alternative (to burning) rice straw management practices. The work is in support of a larger K rice project being funded with fertilizer check-off funds administered through the Fertilizer Research & Education Program (FREP).


Chloride’s Role in Maximizing Wheat Performance (Multi-Regional Project)

Project Leader: Dr. Brad Brown, University of Idaho SW Idaho Research & Extension Center, 29603 U of I Lane, Parma, ID 83660. Phone: (208) 722-6701, fax: (208) 722-6708, e-mail:

This project was initiated as part of a multi-regional project begun several years earlier. It was initiated in the fall of 1997 and will terminate (tentatively) in 2000.

An irrigated winter wheat trial involving 16 varieties (mostly soft white, some hard red) was planted in the fall of 1997 on a location with a history of leaf spotting (physiologic leaf spot). However, there was little physiologic leaf spotting among the varieties studied despite low soil and plant chloride (Cl) levels. Chloride fertilization (0 vs. 40 lb/A) did not increase yield that averaged about 96 bu/A. It was observed that yields may have been limited by moisture stress during stem extension. There was a highly significant interaction for whole plant Cl, as varieties differed appreciably in this parameter, with applied Cl. Kernel weights of 200 seed (38.0 vs. 39.4 g), test weights (58.8 vs. 59.3 lb/bu), and plant height (34.9 vs. 35.3 inches) were all increased with Cl when averaged across varieties. The experiment has been moved to a nearby field for the 1998/99 growing season.

Precision Fertilization of Irrigated Potatoes in Southern Idaho

Project Leader: Dr. Jeff Stark, Univ. of Idaho Aberdeen Research & Extension Center, P.O. Box AA, Aberdeen, ID 83210. Phone: (208) 397-4181, fax: (208) 397-4311, e-mail:

This study is in its initial year of support from PPI, although it was initiated in 1998. The purpose is to evaluate P and K fertilization of commercial potato fields based on (1) soil sampling of 1.5 acre grids (precision management), (2) utilizing soil maps plus aerial photos (zone management), and (3) composite field sampling (conventional management). Three fields will be studied in 1999, with 10 to 15 acre replicated strips representing the different fertilizer programs. Tuber yield and quality will be determined, and an economic analysis will be conducted comparing the three management systems.


Chloride Nutrition Website

Project Leader: Dr. Richard Engel, Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717-3120. Phone: (406) 994-5295, fax: (406) 994-3933, e-mail:

This is a non-conventional research project involving the summarization of Cl research, literature, and field photos on PPI’s web site. This project was initiated in 1997 and completed in early1998. This website will assist researchers, Extension personnel, industry representatives, and farmers rapidly "come up to speed" relative to this significant new market for KCl in the Great Plains and western North America.

The URL for the web site is

Effect of Boron Fertilization on Alfalfa Production

Project leader: Dr. Grant Jackson, Western Triangle Research Center, Montana State University, P.O. Box 1474, Conrad, MT 59425. Phone: (406) 278-7707, fax: (406) 278-7797, e-mail:

This research in northwestern Montana evaluated the potential benefits to B applied across different P fertility levels for intensively managed irrigated alfalfa. It was initiated in 1997 and terminated at the end of 1998.

Annual rates of B at 0, 1, and 2 lb/A were applied across P2O5 rates of 0, 40, and 80 lb/A. First year yields (3 cuttings) averaged above 6 tons/A, but there was no response to either nutrient applied. There also was no response to the fertilizer treatments the second year, although yields increased to an average of 8.6 t/A.


Phosphorus and Potassium Soil Test Relationships and Nutrition for Irrigated Alfalfa Production in Utah

Project leader: Dr. Richard T. Koenig, Department of Plants, Soils and Biometeorology, Utah State University, Logan, UT 84322-4822. Phone: (435) 797-2278, fax: (435) 797-3376, e-mail:

This project evaluates P and K fertilizer recommendations for irrigated alfalfa production on calcareous soils and re-calibrates the sodium bicarbonate soil test for both P and K. It was initiated in 1996 and is scheduled to terminate at the end of 1999.

Thus far, yield and soil test responses to P have been evaluated on a total of six sites over two years, and responses to K have been evaluated on four sites. Annual yields among sites have ranged from 4 to 8 t/A, while responses to P and K fertilizer have ranged from 0.5 to 2 t/A. The previous soil test cutoff for P fertilization was 10 parts per million (ppm), and the cutoff for K was 100 ppm. Rates of P fertilizer required to achieve the critical soil test P level have varied substantially, especially for very low testing sites (< 5 ppm). Soil test responses to K fertilizer have been difficult to define. On low testing K sites (<100 ppm), relatively high rates of K fertilizer (>300 lb K2O/A) have been required just to maintain soil test K values. Based on relationships between soil test P and K and percent maximum yield developed using these data, the soil test P cutoff has been increased to 15 ppm and the K cutoff to 150 ppm. Fertilizer recommendations based on soil test P and K levels have also been raised. Due to the variability in soil test response to both P and K fertilization, it is recommended that alfalfa growers soil test more frequently until deficiencies are corrected, especially on very low testing sites. Based on information from this study, a new Utah State University alfalfa guide will be published in 1999.

Fertilizer Requirements for Long-Term Sustainability of High Yielding Crops

Project Leaders: Dr. Richard T. Koenig, Department of Plants, Soils and Biometeorology, Utah State University, Logan, UT 84322-4822. Phone: (435) 797-2278, FAX: (435) 797-3376, e-mail:; and Dr. Von D. Jolley, Brigham Young University.

The purpose of the "Utah Centennial Plots" is to evaluate the long-term sustainability of yield and the effects on soil properties of organic (manure), inorganic (fertilizer), and combined organic and inorganic fertilizer programs on two crop rotations: alfalfa-wheat and alfalfa-corn-wheat. The study was initiated in the fall of 1996 with alfalfa and wheat as the first crops in the rotation and will continue indefinitely.

Averaged over two cropping seasons, wheat yields were 40 bu/A for the unfertilized control, 70 bu/A for the organic treatment, 91 bu/A for the inorganic treatment, and 89 bu/A for the combined organic/inorganic treatment. Alfalfa yields in the first full hay production year (1998) averaged 8.6 t/A for the control, 9.1 t/A for the organic treatment, 8.8 t/A for the inorganic treatment, and 8.8 t/A for the combination. Calculations of plant-available N using USDA/NRCS methods for manure applied to wheat are apparently underestimating N supplied and, therefore, limiting yield with the manure program. Year-to-year variability in manure nutrient content and form, as well as the different methods available for nutrient crediting, makes it difficult to accurately calculate manure application rates. Among treatments for alfalfa, soil test P and K values are changing and more significant yield differences are expected as a result of the fertility program in the future.


Influence of Tillage and Phosphorus Rate and Placement on Corn Yields

Project leader: Dr. Shiou Kuo, Puyallup Research & Extension Center, Washington State University, Puyallup, WA 98371-4998. Phone: (253) 445-4500, fax: (253) 445-4569, e-mail:

This project evaluated P management in conventional and ridge tillage systems for corn production in western Washington. It was initiated in 1996 and terminated at the end of 1998.

Silage yields and total P uptake were not appreciably affected by annually applying P2O5 at 0, 30, 60, and 90 lb/A. However, P uptake tended to be higher in the last two years for the ridge tillage system; this was especially obvious during the early stages of growth. The ridge tillage system allowed repeated banding of P in the same P-enriched zone, which would account for the higher P availability and plant uptake.

Jonagold Apple Fertility Studies in Western Washington

Project Leader: Mr. Gary Moulton, Mt. Vernon Research & Extension Unit, 1468 Memorial Hwy., Mt Vernon, WA 98273-9788. Phone: (360) 848-6131, fax: (360) 848-6159, e-mail:

The objectives of this study were to evaluate K and Mg fertigation of intensively managed semi-dwarf Jonagold apple trees grown in high plant populations under drip irrigation. It was initiated in 1996 and terminated at the end of 1998.

There were no significant differences in yield or quality measurements of the fruit (starch, soluble solids, or fruit pressure) at the off-station location studied during the first two years. Only starch conversion was increased at the Mt. Vernon station in 1996 by K fertilization studied over three years. Little response was initially expected as the beginning soil fertility was very good. However, available soil K and Mg have dropped substantially in the wetted drip-irrigated zone, and the fertilizer treatments should produce significant benefit over the no fertilizer control in subsequent years. Late-season nutrition is of special concern as leaf K dropped significantly from mid-July to harvest. It appears that drip fertigation may need foliar supplementation to maintain K in a proper balance with N.

Evaluating Potassium Sources and Time of Application for Potato Production in the Columbia Basin

Project leader: Dr. Joan R. Davenport, Washington State University Irrigated Agriculture Research and Extension Center, 24106 N. Bunn Rd., Prosser, WA 99350-9687. Phone: (509) 786-9384, fax: 509-786-9370, e-mail:

This program evaluates the benefits of different K sources, forms (liquid vs. dry), and time of application on yield and quality of potato production under center pivot irrigation. The study was initiated in 1997 and will continue through 1999.

Overall, the fertilizer treatments did not significantly impact yield (averaged 24.5 t/A in 1997 and 39.7 t/A in 1998) or percentage of the crop in the US #1 classification. Specific gravity was impacted by treatment, however, in that it was higher than the control treatment when K2SO4 was applied as a granular (100 percent preplant) or liquid with three in-season applications, or where liquid KCl was applied 100 percent preplant. Also, the incidence of black leg disease was reduced by K fertilization. In 1998 specific gravity was low overall and unaffected by treatment. This appears to be related to the extremely hot weather from late July until harvest. Other research indicates that there is a relationship between K fertilization and specific gravity. This study suggests that it is not sufficiently strong to significantly overcome adverse effects caused by weather.


We at PPI/FAR are pleased to be part of research and education programs that advance the cause of efficient production agriculture.