Evaluation of Calcium Soil Conditioners In an Irrigated Cotton Production System, 1997

J.R. Griffin, Soil, Water, and Evironmental Science Department
J.C. Silvertooth, Plant Sciences Department
E.R. Norton, Plant Sciences Department


A single field experiment was conducted at Paloma Ranch, west of Gila Bend in Maricopa County Arizona in 1996 and 1997. NuCotn™ 33B was dry planted and watered-up on 15 April and 1 April in 1996 and 1997. Various rates and times of application of nitrogen (N) and calcium (Ca) from two sources [N-Cal™ (CO(NH2)2·CaCl2) and CAN-17 (CaNO3)] as well as a standard N source, UAN-32 [NH4NO3·CO(NH2)2] were used to evaluate the check. In 1996 treatments 1, 2,and 3 each received a total of 280 lbs. N/acre, treatment 4 received a total of 210 lbs. N/acre, while treatment 5 received a total of 301 lbs. N/acre. Treatment 1 received only farm standard applications of UAN-32. Treatments 2 and 4 each received a total of 72 lbs. of Ca/acre. Treatment 5 received a total of 79 lbs. Ca/acre from N-Cal™ while treatment 3 received a total of 301 lbs. Ca/acre from CAN-17. Treatment 4 used a conservative N approach (U A guidelines). 1997 was similar to 1996 in the general nature of the experimental design, but different in its actual treatments. Treatments 2, 3, 4, and 5 each used N-Cal™ for the first two irrigation applications then UAN-32 for continued crop N needs. Treatment 4 used a conservative N approach (U A guidelines). Treatments 3 and 5 each received two foliar applications of N-CalÔ. Foliar applications consisted of N-Cal™ mixed with urea for a 15-0-0-8 formula and applied on 22 July and 29 July via a high cycle applicator at a 5 gal/acre rate of N-Cal™ (carrier rate = 40 gal/acre). No significant differences were found among the various treatments in terms of plant growth, soil water content, ECe values, and sodium absorption ratios in 1996 or 1997. Lint yields were not significantly different in 1996 (P<0.05) or 1997 (P<0.05).


Soils in the desert Southwest have long been associated with saline and/or sodic conditions that can cause difficulties in water penetration as well as nutrient relationships. These soils have long been the focus of specific management techniques to control and manage sodium (Na) problems.

Sodic soils are by definition are those soils which contain an exchangeable sodium percentage (ESP) of 15% or more. They can also be characterized as having a Na absorption ratio (SARe) from a saturated soil extract of 13 or greater. Soils high in Na are inclined to have water penetration and infiltration problems due to the dispersion of clay particles within the soil (Yousaf et.al. 1987; Amezketa and Aragues, 1995). Dispersion of clay particles allows them to be transported into pore spaces that were previously available for water penetration and infiltration. Sealing of soil pores can produce a crusting problem that can inhibit seedling emergence and growth. Sodic conditions cannot be corrected with additional irrigation (leaching) applications alone, in fact, the problem may be exacerbated by applying additional water, particularly if it is high in Na. Leaching of a sodic soil can remove the divalent cations calcium (Ca2+) and magnesium (Mg2+) from the soil profile and root zone leaving the monovalent cation Na+. Calcium and Mg are the primary elements that contribute to soil flocculation while Na causing dispersion in a soil. Sodium (Na+) causes dispersion of a soil because of its large hydrated radius, as compared to Ca2+, Mg2+ and potassium (K+). The large hydrated radius of Na+ forces the clay particles apart creating a dispersed soil condition.

Saline soils are defined as a non-sodic soil that contain sufficient soluble salts to impair plant growth and productivity (Brady, 1974). Saline soils generally are found to have an electrical conductivity (ECe) of 4 mmhos/cm or greater from a saturated extract. Saline conditions are generally easier to correct as compared to sodic or saline-sodic soils were leaching can be an effective treatment.

A further problem associated with irrigation is the increase in pH of the soil as a result of the introduction of anhydrous ammonia nitrogen fertilizer into the irrigation water. The increase in pH can cause the flocculating elements, Ca2+ and Mg2+, to precipitate with bicarbonate (HCO3-) and carbonate (CO32-) leaving soluble Na+ in the irrigation water. The application of this type of water has the potential to effectively raise the ESP and the SAR of the soil. This, in turn, can cause a sodic condition that can be difficult to manage.

There are several traditional treatments used to correct sodicity problems in soils. One approach involves the use of gypsum (CaSO4·2H2O). Gypsum (CaSO4·2H2O) tends to increase the levels of Ca2+ in the soil that can then exchange with the Na+ creating sodium sulfate (Na2SO4), which can be leached from the soil. This addition of Ca2+ lowers the SAR and contributes to the exchange and leaching of soil Na+.

Another common treatment of sodic soils is the addition of elemental sulfur (S). Elemental S, when oxidized by soil microbes and combined with water, reacts to form sulfuric acid (H2SO4), which reacts with naturally occurring calcium carbonate (CaCO3), releasing "free" Ca2+. This Ca2+ in the soil solution can then exchange for Na+ in the form of Na2SO4, which can be leached from the soil. Sulfuric Acid (H2SO4) can also be added to the irrigation water directly. When adding elemental S or H2SO4, not only can Na be converted to a leachable form but the pH of the soil is also lowed via the release of hydrogen (H+) into the soil.

Considering the Na levels that are often accumulating in desert soils, there has been an increase in the number of soil amendments to combat the problem. Extensive studies conducted worldwide on arid soils have shown that there is a consistent relationship between the effects of SAR, pH and electrolyte concentration on relative hydraulic conductivity (Ks) and clay dispersion (Suarez et al., 1984). It has also been demonstrated that the plant available Ca2+ is highly independent of the amount of calcium carbonate (CaCO3) naturally present in the soil (Flocker and Fuller, 1956).

Along with the conventional methods of treating sodic and saline conditions, there has been an increasing emergence of numerous synthetic water-soluble polymers (WSP's). The WSP's include polyacrylamide (PAM), polyvinyl alcohol (PVA), polymaleic anhydride (PMA), and polysaccharides. Research studies have shown that these synthetic polymers have reduced soil surface crusting (Helalia and Letey, 1989; Wood and Oster, 1985; Terry and Nelson, 1986), improved water holding capacity (Nimah et al., 1983; Shanmugananathan and Oades, 1982; Woodhouse and Johnson, 1991), improved aggregation and reduced clay dispersion (Aly and Letey, 1988), enhanced nutrient uptake by crops (Fuller et al., 1953) and enhanced ability for reclamation of saline and sodic soils (Wallace et al. 1986a). However, they do not impart an exchange for Na+ on the soil adsorption complex.

N-Cal™ (18-0-0-6) was introduced as an alternative to synthetic polymers, gypsum and elemental sulfur for use as a soil conditioner. N-Cal™ supplies a plant available form of nitrogen (N) as urea [CO(NH2)2], as well as Ca as calcium chloride (CaCl2), to the soil-plant system. N-Cal™ provides Ca2+ ion from CaCl2 as a means to decrease the SAR and ESP of the soil system, while could improve flocculation and reduce clay dispersion of the soil system. By creating a better flocculated soil system, water infiltration can be improved and soil crusting reduced.

Improved soil flocculation can also enhance seedling emergence when applied before seedling germination.

Materials and Methods

The field experiment was planted with an Upland (Gossypium hirsutum L.) cotton variety (NuCotn 33B) on a Wellton sandy loam soil at Paloma Ranch, AZ (field 24D2) on 14 April 1996 and (field 18A3) on 31 March 1997. Both experiments were dry planted then watered-up on 15 April 1996 and 1 April 1997. The experimental design of the project for both years was a five treatment, randomized complete block with four replications. Plots were eight 36-inch rows wide, extending the full length of the irrigation run approximately 1250 feet from head to tail. Pre-season and post-season soil samples were collected for each treatment on 12 April 1996 and 20 December 1996 respectively (Table 1 and 2). In 1997 pre-season and post-season soil samples were collected for each treatment on 31 March and 23 December (Table 3 and 4). A surface soil sample (approx. top 5cm) was also obtained on 16 June 1996 (Figures 1 and 2). Five irrigation water quality samples were taken at varied intervals for 1997 (Table 5).

Table 6 lists application dates and rates for all treatments in 1996. For treatments 2, 4 and 5, N-Cal™ was used as the primary N source until approximately 72 lbs. Ca/acre had been applied. UAN-32 (urea, ammonium nitrate 32-0-0) was used thereafter to meet crop N demands. Treatment 5 received an application of N-Cal™ with the water-up irrigation that resulted in an additional 21 and 7 lbs of N and Ca/acre respectively. For treatment 3, CAN-17 (17-0-0-24) was used as the initial N and Ca source. In order to meet initial N rates approximately 301 lbs. Ca/acre was applied. Treatment 1 received no Ca and was fertilized only with UAN-32. Treatment 4 followed a more conservative N management approach (U A guidelines) where no N was applied after peak bloom (9 August 1996 and 17 August 1996). All fertilization applications were water-run in the irrigation stream in both seasons.

In 1997 a slightly different set of treatments were used. Table 7 lists application dates and rates for all treatments in 1997. Treatment 1 received no Ca and was treated only with UAN-32, similar to 1996. Treatments 2, 3, 4, and 5 used N-Cal™ as the primary N source until approximately 58 lbs. Ca/acre had been applied; UAN-32 was used thereafter to meet crop N demands. Treatment 4 followed a more conservative N approach similar to 1996. Treatments 2, 3, 4, and 5 all used N-Cal™ in the first two irrigation applications.

Two foliar applications of N-Cal™ were applied at approximately first bloom and peak bloom to treatments 3 and 5 on 22 July 1997and 29 July 1997 (Table 7). N-Cal™ was combined with urea to create a 15-0-0-8 material that was used for the foliar applications. This material was applied at a rate of 5 gallons/acre/application. The carrier rate used was 40 gallons/acre. The N-Cal™ foliar mixture has a density of 11 lbs./gallon. The foliar applications applied approximately 8 lbs. N/acre and 4 lbs. Ca/acre at each application. All foliar applications were applied with a "high cycle" mechanical sprayer.

Routine plant measurements for each experimental plot were performed on a regular basis at approximately 14-day intervals throughout the 1996 and 1997 seasons. Plant measurements taken included: plant height, number of mainstem nodes, number of flowers per 50 feet of row, percentage canopy closure and the number of nodes from the top fresh flower to the terminal (NAWF). Petioles were also obtained for nitrate nitrogen (NO3-N) analysis. The petioles were collected at the same time as plant measurements were made.

Soil water measurements were also taken routinely directly preceding and directly following an irrigation event. Soil water measurements were taken from all plots with a neutron probe at 1-foot intervals from the surface to a depth of 5 feet.

Surface soil samples were taken to a depth of approximately 5 centimeters on 19 June 1996. These surface soil samples were evaluated on the water side, seed row and dry sides of the beds for exchangeable Na percentage and ECe (Figures 1 and 2).

Yields for each treatment were determined by harvesting the entire center four rows of each plot and weighing the seedcotton with large portable electronic scales at the end of the field. Lint turnout was determined from each plot by ginning an approximately 15-lb. subsample of seedcotton.

The crop was irrigated until 1 October and 8 October in 1996 and 1997 respectively. The entire area of study was defoliated on 1 November 1996 and 17 November 1997. All the plots were harvested with a mechanical picker on 11 December 1996 and 16 December 1997. Lint yields were obtained for each treatment by harvesting the entire center four rows of each plot with a two row mechanical picker. Seedcotton subsamples were collected for ginning, from which lint turnout estimates were made (35% both years). Results were analyzed statistically in accordance to procedures outlined by Steel and Torrie (1980) and the SAS Institute (SAS, 1988).

Results and Discussion

Plant growth and development patterns for all treatments are shown in Figure 3 (A, B, C, and D) for 1996. The center line in all figures represents an optimal baseline for cotton in Arizona with the upper and lower lines representing the upper and lower 95% confidence interval thresholds (Silvertooth et al., 1996). Low height to node ratio (HNR) and nodes above white flower (NAWF), indicating low plant vigor, were observed throughout the entire season in all treatments (Figure 3 B, and D). However, fruit retention (FR) patterns remained near optimum levels throughout most of the season (Figure 3 A). Petiole NO3--N levels were very similar among the different treatments over then entire season (Figure 3 C). All of the NO3--N levels dropped early in the season possibly coinciding with the plants entering an early cut-out period. The NO3--N levels then returned to normal levels as the plants moved into a top-crop stage of plant development.

Results from 1997 exhibited similar plant growth and development patters as those obtained in 1996 (Figure 4 A, B, C, and D). Low plant vigor (HNR and NAWF) was observed throughout the entire season for all the treatments (Figure 4 B, and D). Fruit retention (FR) levels, for all the treatments, were above optimum levels throughout most of the season (Figure 4 A).

Soil samples taken in 1996 revealed lowered Na levels from pre-season to post-season as indicated by a lowered ECe and ESP (Table 1 and 2). Treatment 5 showed the greatest reduction in both ECe and ESP. All treatments had lowered ECe values. The pre-season sample in 1997 was very similar to the 1996 pre-season, however the post-season sample in 1997 was very dissimilar (Table 3 and 4). In 1997 all treatments revealed an increase in the ECe and the ESP from pre-season to post-season, and Na levels also increased for all the treatments.

Figures 5 - 12 presents volumetric soil water data for four sample dates immediately following irrigation events in 1996 and 1997. Analysis of variance performed on this data did not reveal any significant differences among treatments with regard to soil water content at any depth or date of sampling. This would generally indicate that there were no differences among the treatments in terms of total water penetration. Another interesting observation from these data is the apparent linear increase in soil water content from the surface to the lower portions of the profile. This indicates sufficient drainage from the surface portions of the profile but that there might be some type of impedance to drainage leading to the observed accumulation of water in the lower portions of the profile. The impedance to drainage is most likely a CaCO3 layer, which is very prevalent in these arid soils. This observation appears to be independent of treatment and is apparently due to natural soil conditions.

A distinct gradient of increasing yields was observed across the study area from east to west in 1996. This is most likely due to a high degree of inherent soil variability. Yields were higher for treatments 4 and 5 relative to 1 and 3 (P=0.07) in 1996 (Table 8). In general, ECe and ESP values were slightly lower at the end of the season relative to the pre-season (Tables 1 and 2) samples. Treatment 5 showed the greatest change in ECe and ESP and the highest yields. This is apparently due to the water-up treatment of N-CalÔ that moved Na+ away from the emerging seedling, thus increasing water movement, and early plant vigor. However, the effect in the plants is not directly apparent based upon the plant data obtained. In general, ECe and ESP values were slightly lower at the end of the season relative to the pre-season (Tables 1 and 2) samples for all treatments.

Results from 1997 also showed a gradient of increasing yields from east to west in the study area. Yields tended to be higher for treatments 1 and 4 relative to 3 and 5 (P=0.11) in 1997 (Table 9). All of the treatments showed increases in the ECe and the ESP (Table 3 and 4). This is most likely attributable to the highly sodic and saline irrigation water that was applied (Table 5) and the perched water around the 5-foot level in the soil profile (Figures 9-12). The perched water contributed to the increased ECe and ESP with capillary action moving soil water to the soil surface. An increase of salts at the soil surface was observed for all the treatments in 1997.

Treatments 3 and 5 received the two foliar applications of N-Cal™. The foliar applications of the material caused some leaf "burn" in the upper levels of the plant and the terminal area.

Treatment 1 showed the highest yields in 1997. However, in both years, treatment 4 was closely related to the top yielding treatment, using a conservative N approach and N-Cal™ in its management regime. Based on these results, it is difficult to determine the absolute effectiveness of N-Cal™ due to the high degree of variability from year to year.

Yields for 1997 were considerably higher that those obtained in 1996 (Figures 8 and 9). In 1997, results revealed an average yield among all treatments of 1780 lbs. of lint/acre (3.7 bale/acre). In 1996 an average yield of 1570 lbs. of lint/acre (3.3 bale/acre) was realized. A difference in yield between years is due to growing season differences.


The financial, resource, and technical assistance provided by PFI Corporation, J.S. Stephens and Sons, Everardo Vasaldua, and the University of Arizona Cotton Research Assistants is greatly appreciated.


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This is a part of publication AZ1006: "Cotton: A College of Agriculture Report," 1998, College of Agriculture, The University of Arizona, Tucson, Arizona, 85721. Any products, services, or organizations that are mentioned, shown, or indirectly implied in this publication do not imply endorsement by The University of Arizona. The University is an Equal Opportunity/Affirmative Action Employer.
This document located at http://ag.arizona.edu/pubs/crops/az1006/az10065c.html
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