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Effect of [CaSO.sub.4] (Gypsum) on cotton lint yields, soil fertility, and physical soil properties of heavy clay soils in Missouri.

Abstract: Cotton production on clay soils in Missouri is often limited by poor internal soil water drainage. A two year study was conducted at the University of Missouri Delta Center at Portageville, Missouri to determine whether gypsum ([CaSO.sub.4]) soil amendments may improve soil physical properties and increase cotton yields on a Sharkey clay soil (very fine, montmorillonite, thermic Vertic Haplaquept). Gypsum treatments were applied on small plots at 1.68 and 3.36 Mg [ha.sup.-1] rates. Gypsum improved soil drainage in the seedbeds as indicated by saturated conductivity measurements. Saturated hydrologic conductivity averaged 6.0 E-5 cm [sec.sup.-1] on untreated plots are compared to 1.3 E-4 cm [sec.sup.-1] on plots with 3.36 Mg [ha.sup.-1] gypsum. Gypsum additions decreased soil pH from 6.5 (untreated check) to 6.3 (both gypsum treatments). Soil compaction as measured by bulk density and penetrometer resistance was not significantly effected by gypsum. There was a slight trend towards increased yields f rom gypsum. However, cotton yields and fiber properties were not increased significantly by gypsum applications. Two year average cotton lint yields were 961 kg [ha.sup.-1] for the untreated check, 999 kg [ha.sup.-1] for 1.68 Mg [ha.sup.-1] gypsum, and 995 kg [ha.sup.-1] for 3.36 Mg [ha.sup.-1] gypsum.


Cotton (Gossypium hirsutum) is an important agronomic crop in Southeast Missouri. The Sharkey clay soil association, commonly referred to as "gumbo", comprises about one fourth of the six county area where cotton is grown in Southeast Missouri. It was formed on old slack-water areas along the former course of the Mississippi River (Scrivner et al., 1966). Compared to other soil associations the Sharkey has a limited potential for cotton production. Garrett et al. (1978) lists the average cotton lint yield under irrigated conditions for the Sharkey series as 560 kg [ha.sup.-1], compared to the Maiden series with 784 kg [ha.sup.-1].

Excessive water is a limitation to the use of this soil because surface runoff is slow, and internal drainage is poor. Cotton requires good drainage as low soil oxygen levels limit root growth (Huck, 1970). Saturated hydraulic conductivity is generally less than 4.2 [E.sup.-5] cm [s.sup.-1] compared to 4.2 [E.sup.-3] cm [s.sup.-1] or more for the Maiden soils (Garrett et al., 1978). The soil is firm and plastic and has a very high shrink-swell potential because of a high montmorillonite content. Consequentially, the soils are difficult to till and seedbeds are difficult to prepare. In most years cracks form as the soil is depleted of available water by the growing crops. Furrow irrigation is difficult to manage on Sharkey soils. These properties contribute to low productivity by limiting root growth and reducing plant available soil moisture.

Gypsum ([CaSO.sub.4]) has long been used as an amendment to condition clay soils (McCray et al., 1991). Benefits of gypsum applications can include increased water infiltration, increased root penetration, increased soil aeration, and decreasing the shrinkswell of clay rich soils (Walace, 1994). Gypsum works to decrease bulk soil density by allowing the calcium ion ([Ca.sup.+2]) to infiltrate between the structural layers that make up the clay mineral lattice. This allows montmorillonite to expand making room for additional water. The individual clay particles are not as tightly bound to each other (Ritchey et al., 1995). One potential problem with gypsum applications may be the soil acidification resulting from the sulfate it contains (Sumner et al., 1990).

The purpose of this investigation was to determine if applications of gypsum will increase cotton lint yields on heavy clay soils in Southeast Missouri. The secondary objective was to determine the effect of gypsum on the chemical and physical aspects of Sharkey soils.

Materials and Methods

A cotton study was conducted at the University of Missouri-Delta Center Lee Farm (36[degrees]N, 89[degrees]W) in Pemiscot County, Missouri in 1999 and 2000. Cotton was planted on a Sharkey series (very fine, montmorillonitic, thermic Vertic Haplaquept) soil. The texture was determined by hydrometer and was found to be 68% clay, 36% sand and 2% silt. This classifies as clay on the USDA Textural Triangle. The clay mineralogy of the research area was identified using X ray diffraction and it was found to be composed of almost entirely montmorillonite with trace to minor amounts of kaolinite.

In 1998 the research area was limed with 3.32 Mg [ha.sup.-1] of calcitic lime. The experimental design was a randomized complete block with four replications. Three Gypsum treatments were applied to raised seedbeds with a spacing of 95-cm in early May of 1999. These gypsum applications were immediately incorporated and the cotton variety Stoneville 474 was planted the following day. In early May of 2000 the cotton variety Stoneville 474 was planted on the same raised seed beds used in 1999. Each plot was 3.8 m wide and 9.5 m long. Gypsum treatments were 0,1.68, and 3.36 Mg [ha.sup.-1] pelletized gypsum was applied using a 3.8 m "Gandy box applicator". Soil samples of the study area were collected from the 0 to 15 cm depth before planting in 1999 and mid July 1999 and 2000. Soil fertility analysis consisted of pH (water), neutralizable acidity, exchangeable cations (Ca, Mg, K. Na), loss on ignition (LOI), Bray 1 extractable phosphorus, and [SO.sub.4]-S. Cation exchange capacity was calculated from measured va lues for Ca, Mg, K, and Na. Penetrometer readings were collected for the 7.5, 15 and 22.5 cm soil depth twice during 2000 on July 10 and August 28. These readings were collected from five positions relative to the beds and tractor wheel tracks. Following harvest in 2000 in situ bulk density and saturated hydraulic conductivity measurements were determined for each plot using the ring method for bulk density and enplaned cylinders having 7.5 cm of soil for the saturated hydraulic conductivity (Carter, 1993).

For both years nitrogen fertilization consisted of 45 kg [ha.sup.-1] N as urea ammonium nitrate 32% (UAN 32) pre-plant and 67 kg [ha.sup.-1] N as UAN 32 in mid June. The standard methods of weed and insect control were used for cultivating cotton in Southeast Missouri. The crop was furrow irrigated five times during each growing season with approximately one inch of water each time.

In early October of each year the two middle rows of each strip were mechanically harvested and the seed cotton weighed and recorded. The seed cotton was ginned using a 20 saw Continental gin stand preceded by an inclined cleaner and feeder extractor. The gin stand was followed by one stage of lint cleaning. Lint samples from each plot were sent to the International Textile Research Center for fiber quality analysis using a high volume instrument.

Statistical analysis of the data were preformed with SAS (1990) using General Linear Modeling procedures. Fisher's Protected Least Significant Difference (LSD) was calculated at the 0.05 probability level for making treatment mean comparisons.

Results and Discussion

In 1999 and 2000 cotton lint yields for gypsum treatments were statistically equivalent to the control (Table 1). In 1999 the high rate of gypsum application numerically increased cotton lint yields (687 vs. 646 kg [ha.sup.-1]) while the low rate decreased yields (636 vs. 464 kg [ha.sup.-1]) The two-year mean lint yield was calculated for each treatment and the rate of 1.68 Mg [ha.sup.-1] Gypsum was found to be the highest with 999 kg [ha.sup.-1] lint. In 2000 both rates of gypsum application raised cotton lint yields. Gypsum applications in 1999 or 2000 (Tables 2a and b) did not affect gin turnout. Lint quality was also not affected by gypsum applications in either year (Tables 2a and b). Gypsum applications lowered soil pH and raised the amount of neutralizable acidity (NA) in the soil. The amount of pH decrease was not related to rate of gypsum application. [SO.sub.4]-S and Ca levels were also increased by gypsum applications and the increase was related to the rate of gypsum application. Cation exchange capacity (CEC) was calculated from soil test values. The calculated CEC was greater for gypsum treatments; this is accounted for by the increases in Ca and NA levels for gypsum treatments. All other chemical soil fertility parameters were not affected by gypsum applications (Table 3).

Gypsum applications decreased in situ bulk density slightly in the seedbeds (1.1 vs. 1.2 g [cm.sup.-3]). The differences were found to be not significant at the alpha = .05 level (Table 4). These values are within the range given as typical for the Sharkey series by Pettry and Switzer, 1996. Gypsum applications significantly increased the saturated hydrologic conductivity of the seedbeds. For the high gypsum rate this number was more than doubled (1.1E-4 cm [sec.sup.-1] vs. 4.5E-5 cm [sec.sup.-1]). This increase in hydraulic conductivity for the seedbeds is not great enough to cause a decrease in the time needed to drain the field.

When all five penetrometer readings from each treatment area were averaged for each date the application of gypsum decreased penetrometer resistance at the 7.5 cm depth. Average penetrometer readings for the 15 and 22.5 cm depths showed no consistent trend (Table 5). Gypsum applications decreased penetrometer resistance readings more in furrows than in seedbeds.


Gypsum additions did not significantly increase cotton lint for the Sharkey series soils. There was however a numerical increase in the two year average lint yield for both rates of gypsum application. This increase was approximately 34 kg [ha.sup.-1] for both years and both rates. Gypsum applications did increase exchangeable Ca and [SO.sub.4] S levels in the soil. Currently pelletized gypsum sells for $37.95 per Mg in Southeast Missouri. The cost to producers for the 1.68 and 3.36 Mg [ha.sup.-1] rates are $63.75 and $127.50 respectively. At lint price of $1.34 per kg lint gypsum application would not be a profitable practice for Missouri cotton producers. At times gypsum in the form of waste dry wall is available to cotton producers at lower prices. This waste product may be economical for cotton producers to use.
Table 1.

Average cotton lint yields for gypsum treatments 1999 and 2000.

Treatment Lint yield 1999 Lint yield 2000 2 year mean
 kg [ha.sup.-1] kg [ha.sup.-1] lint yield
 kg [ha.sup.-1]

Control 646 a 1275 a 961 a

1.68 Mg [ha.sup.-1] 636 a 1362 a 999 a

3.36 Mg [ha.sup.-1] 687 a 1302 a 995 a

Lint yields with the same letter indicate non-significance at the alpha
= 0.05 level.
Table 2a.

Average gin turnout and cotton fiber quality measurements for gypsum

Treatment % turnout micronaire length uniformity strength

Control 34 4.6 1.12 82.7 27.4

1.68 Mg [ha.sup.-1] 34 4.5 1.11 82.5 27.3

3.36 Mg [ha.sup.-1] 34 4.6 1.11 82.7 26.4

Treatment elongation leaf

Control 5.6 1.0

1.68 Mg [ha.sup.-1] 5.2 1.0

3.36 Mg [ha.sup.-1] 5.2 1.0
Table 2b.

Average gin turnout and cotton fiber quality measurements for gypsum
treatments 2000

Treatment % turnout micronaire length uniformity strength

Control 40 5.1 1.14 84.6 27.1

1.68 Mg [ha.sup.-1] 41 5.2 1.13 84.8 27.3

3.36 Mg [ha.sup.-1] 40 5.1 1.12 84.6 26.8

Treatment elongation leaf

Control 6.2 1.8

1.68 Mg [ha.sup.-1] 6.1 2.0

3.36 Mg [ha.sup.-1] 6.1 1.8
Table 3.

Average soil fertility levels for gypsum treatments for soil samples
collected June 27, 2000.

Treatment pH NA OM P K
 Units Meq/100gr % mgkg-1

Control 6.5 0.8 2.3 62 260

1.68 Mg [ha.sup.-1] 6.3 2.3 2.3 63 272

3.36 Mg [ha.sup.-1] 6.3 1.8 2.4 60 261

Treatment Ca Mg Na SO4-S CEC

Control 3141 659 57 14.2 22.2

1.68 Mg [ha.sup.-1] 3419 638 54 25.9 25.0

3.36 Mg [ha.sup.-1] 3452 644 51 40.0 24.7
Table 4.

Average bulk density and saturated hydraulic conductivity for 7.5-cm
depth soil samples collected in seedbeds following harvest in 2000.

Treatment Bulk density Hydraulic conductivity
 gr. [cm.sup.-3] cm [sec.sup.-1]

Control 1.2a 4.5 E-5a
1.68 Mg [ha.sup.-1] Gypsum 1.1a 9.1 E-5b
3.36 Mg [ha.sup.-1] Gypsum 1.1 E-4b
Table 5.

Average penetrometer readings for gypsum treatments 7-10-2000 and

Treatment July 10 ,2000 August 28, 2000

 6 inch 12 inch 18 inch 6 inch 12 inch
 K Pa

Control 152 313 383 219 400

1.68 Mg [ha.sup.-1] 144 399 384 157 346

3.36 Mg [ha.sup.-1] 154 261 418 208 368

Treatment August 28,

 18 inch
 K Pa

Control 418

1.68 Mg [ha.sup.-1] 533

3.36 Mg [ha.sup.-1] 418


This work was made possible by the generous support of Cotton Inc. and the Missouri State Support Committee.

Literature Cited

Carter, Martin R. 1993. Soil Sampling and Methods of Analysis. Lewis Publishers, Boca Raton, Florida.

Garrett, J., F. Allgood, B. Brown, R. Grossman, and C. Scrivner. 1978. Soils of the Southeast Missouri Lowlands-major types, fertility, and yield information for soils found in the low lands of the Bootheel area. Univ. of Missouri - extension circular 922

Huck, M.G. 1970. Variation in taproot elongation rate as influenced by composition of the soil air. Agron. J. 62:815-818.

McCray, J.M., Sumner, M.E., Radcliffe, D.E., and Clark, R.L. 1991. Soil Ca, Al, acidity and penetration resistance with subsoiling, lime, and Gypsum treatments; Soil Use and Management. Vol. 7 p. 193-200.

Pettry, D. E., and Switzer, R. E. 1996. Sharkey soils in Mississippi. Miss. Agri. & Forestry Exp. Station Bull. No 1057.

Ritchey, K.D., Feldhake, C.M., Clark, R.B., Sousa, D.M.G. de, 1995. Improved water and nutrient uptake from subsurface layers of gypsum-amended soils; Agricultural utilization of urban and industrial by-products: Proceedings of a Symposium of Soil Science Society of America.

SAS Institute. 1990. SAS/STAT guide for personal computers. Version 6.0. SAS Inst. Cary, N.C.

Scrivner, C.L., Baker, J.C. and Miller, B. J., 1966. "Soils of Missouri,", Univ. of Missouri Agri. Expt. Station. Circular 823.

Sumner, M. E. Radcliffe, D. E. McCray, Carter, M. E., and Clark, R. L. 1990. Gypsum as a ameliorate for subsoil hardpans. Soil Technology v 3 p. 253-258.

Walace, A. 1994. Use of gypsum on soil where needed can make agriculture more sustainable. Communications in Soil Science and Plant Analysis. Vol. 25 p. 109-116.
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Author:Phillips, Andrea
Publication:Transactions of the Missouri Academy of Science
Article Type:Statistical Data Included
Geographic Code:1USA
Date:Jan 1, 2001
Previous Article:Collegiate Division 2000.
Next Article:The first distributional record of the least weasel, Mustela nivalis, in Northeastern Missouri.

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