Illinois
Fertilizer Conference Proceedings
January 27-29, 1992
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John E. Sawyer and Stephen A. Ebelhar1
Winter wheat (Triticum aestivum L.) occupies large acreage and is important in the crop rotations of southern Illinois. With potential for high production levels, adequate supply of nutrients must be available for optimum plant growth and production. This study was conducted to determine if sulfur nutrition (an essential element not routinely applied for crop production) was limiting winter wheat production in southern Illinois. The effects of S rate, tillage system, and variety on wheat growth and production were investigated at two sites in southern Illinois, Brownstown -- Cisne silt loam soil (Fine, Montmorillonitic, mesic Mollic Albaqualf) and Dixon Springs -- Grantsburg silt loam soil (Fine-silty, mixed, mesic Typic Fragiudalf). Results from the first year of this study, 1990, can be found in the 1991 Illinois Fertilizer and Chemical Association Proceedings and are not duplicated here. In 1991, results were quite similar to those found in 1990. Grain yield was not increased with S application. Increasing S rates from 0 to 30 lb S/acre resulted in increases in flag leaf and whole plant S concentrations (especially at Dixon Springs), but did not increase yield. Lack of response to S application was again consistent in 1991, and was consistent across all varieties and both tillage systems. Also, equal yields were produced with conventional-till and no-till at Brownstown, but a slight reduction in yield occurred at Dixon Springs with no-till. Plant and soil parameters measured in 1991 to determine wheat response to S application indicated that sufficient levels of S were available from sources other than fertilizer S. Based on these two years of study, routine application of S fertilizer for wheat production in southern Illinois does not appear warranted.
Winter wheat has historically been an important crop in the rotations of southern Illinois. In recent years the acreage of winter wheat has increased substantially. According to the January 24, 1990 Illinois Farm Report published by the Illinois Agricultural Statistics Service (USDA, 1990), a total of 1.78 million acres of winter wheat were harvested for grain in 1989, an increase of 42 percent from 1988 and an increase of 87% from 1987. In addition, yield production was at record levels in 1987 and 1989.
With the current large acreage of winter wheat, especially in southern Illinois, and with the potential for record levels of production, increased demand on the soil to supply nutrients required for adequate growth and production of wheat may be creating deficiencies of nutrients not currently being applied for crop production, such as sulfur.
In the past, S deficiencies have been recognized in the midwest United States, but have not been widespread (Alway, 1940; Hoeft and Walsh, 1970; Thorup and Leitch, 1975; Rehm, 1976; Hoeft, 1980). However, as a result of several factors, increased likelihood of S deficiencies may occur. These factors include increased crop production level, less application of S as impurities in fertilizers (such as phosphatic fertilizers) and pesticides, less contribution of S from the atmosphere (either from precipitation, dry deposition, or direct absorption of atmospheric compounds), use of minimum tillage systems which may reduce S mineralization from crop residues and soil organic matter, and fewer crop-livestock operations and increased acreage that receives no manure applications.
As crop demands for S increase, deficiencies are more likely to occur on soils that inherently supply less available S or can retain less available S within the rooting zone; those that have low organic matter content, have a coarse texture, and have low or physically unavailable sources of S in the subsoil. Many of the soils in southern Illinois could fit into this category. However, soils with acidic and high clay content (free iron and aluminum oxides) subsoils accumulate more profile sulfate-S (Kamprath et al., 1956). Most reported wheat responses to applied S have occurred on coarse textured - low organic matter soils with low capacity to retain sulfate in the subsoil (Oates and Kamprath, 1985; Mahler and Maples, 1986; Wells et al., 1986; Mahler and Maples, 1987).
In a statewide survey of soils in Illinois, Hoeft et al. (1985) found little
corn (Zga mavs L.) response to S application in the field; a total of only 5
of 82 sites responded, but in the greenhouse 60%, of the soils (surface samples)
responded to S application. This was an indication that many soils in Illinois
have a limited ability to supply adequate available S for crop production and
that contributions from sources other than the soil were major factors in supplying
S for crop uptake in the field. They did measure an average growing season rainfall
deposition of 9.71b S/acre in 1978 at sites in southern Illinois. Also, they
found no relationship between extractable soil S level, Ca(H2PO4)2 HOAc extractant,
and corn yield response to S application,.
It has been approximately 10 years since the survey by Hoeft et al. (1985) was
conducted and it may be possible that atmospheric contributions have declined
to the point that little S is applied to soils from that source. Recent measured
annual average sulfate-S deposition from precipitation (1978-1987) in southern
Illinois was 8.2 lb S/acre and winter plus spring deposition was 3.91b S/acre
(NADP/NTN, 1990).
Today, possible S deficiencies will occur most readily on soils that have low S supplying power. In the survey by Hoeft et al. (1985), two of the five responding sites were in southern Illinois on low organic matter soils. Also, the only crop studied was corn. Little if any S research has been conducted on winter wheat in Illinois.
The general goal of this project was to determine if sulfur nutrition is currently
limiting winter wheat production in southern Illinois. Specific objectives were
to: (i) measure plant nutrient composition and grain yield response of several
adapted wheat varieties on two tillage systems to the spring topdress application
of S fertilizer, (ii) determine plant nutrient composition and wheat grain yield
response to rate of spring topdress S application.
Field studies were conducted in 1990 - 1991 at two sites in southern Illinois, the Brownstown Agronomy Research Center located in south central Illinois and the Dixon Springs Agricultural Center located in extreme southern Illinois. This is a continuation of the study which was initiated in 1989 - 1990. For each experiment, winter wheat was grown after a preceding soybean Gl cine max(L.) Merr.] crop.
Experiment 1
A randomized complete block experimental design with three replicates was used at each location with a split-split plot arrangement of treatments: main plot-- tillage system, no-till (NT) and conventional-till (CT); sub plot-- spring topdress S application, either no S or 251b S/acre as ammonium sulfate; and sub-sub plot-- winter wheat variety, Becker, Cardinal, Caldwell, and Pioneer' variety 2555 (Pioneer® variety 2548 at Dixon Springs). Individual sub-sub plot dimensions were 12 by 70 ft at Brownstown and 10 by 40 ft at Dixon Springs. Chemical characteristics of the surface 8 in. of soil at Brownstown were pH 6.4, P1 110 lb P/acre, 220 K lb/acre and organic matter content 2.4% and at Dixon Springs they were pH 6.5, P1 37 lb P/acre, 150 lb K/acre and organic matter content 2.7%.
Conventional-tillage was performed with one pass of a tandem disk and one pass with a field cultivator. Individual varieties were planted in 7 in. rows at a rate of 90 lb seed/acre on 15 Oct. 1990 at Brownstown and on 18 Oct. 1990 at Dixon Springs. At Brownstown, both the NT and CT was planted with a conventional double disk opener drill. It was not fitted with notill coulters. At Dixon Springs, the drill was fitted with no-till coulters. Nitrogen rate was uniform on all plots (total of 1101b N/acre) with 40 lb N/acre applied as diammonium phosphate in the fall before tillage and planting and the remainder (70 lb N/ acre) applied either as ammonium nitrate or a combination of ammonium sulfate and ammonium nitrate as a topdress application in early spring (7 Mar. 1991 at Brownstown and 6 March 1991 at Dixon Springs). Harmony Extra, 0.5 fl. oz. /acre, plus surfactant, 0.25% v/v, was applied on 21 Mar. 1991 at Brownstown to control chickweed.
Soil samples, 5 cores/sample, were collected by 8 in. depths to 24 inches four times throughout the growing period from the non-S treated sub plots. Flag leaf samples, 100/plot, and whole above ground plant samples, 20/plot, were collected at Feekes' stage 10.1 (head emergence), 6 May 1991 at Brownstown and 3 May 1991 at Dixon Springs, and grain samples were collected at harvest. The number of wheat heads/ft2 and the plant height to the top of the wheat head were measured on 21 May 1991 at Brownstown and 3 June 1991 at Dixon Springs. At Brownstown, each entire plot was harvested on 17 June 1991, and at Dixon Springs, a 5 ft pass was harvested from each plot on 20 June 1991.
Experiment 2
Four rates of spring topdress S (0, 5, 15, and 30 lb S/acre as ammonium sulfate applied 7 Mar. 1991 at Brownstown and 6 Mar. 1991 at Dixon Springs) were arranged in a randomized complete block design with four replicates. Winter wheat variety Cardinal had been conventionally planted on 16 Oct. 1990 at Brownstown and 12 Oct. 1990 at Dixon Springs. The N rate was a uniform 110 lb N/acre at each location, applied at 40 lb N/acre as diammonium phosphate in the fall before tillage and as a combination of ammonium sulfate and ammonium nitrate as a spring topdress. Plot size was 20 by 45 ft at Brownstown and 10 by 40 ft at Dixon Springs. A 5 ft wide pass was harvested for grain yield at Dixon Springs and a 12.5 ft wide pass was harvested from each plot at Brownstown.
Chemical characteristics of the surface 6 in. of soil at Brownstown were pH 6.5, P1 90 lb P/acre, 2901b K/acre and organic matter content 2.2% and at Dixon Springs were pH 6.5, P, 44 lb P/acre, 1501b K/acre and organic matter content 2.8%. Potassium was applied at 25 lb K/acre at Dixon Springs and diammonium phosphate at 45 lb P/acre at both locations.
Flag leaf samples, 100/plot, and whole plant samples, 20/plot, were collected at Feekes' stage 10.1, 6 May 1991 at Brownstown and 3 May 1991 at Dixon Springs. Grain samples at harvest were collected at Brownstown only. Soil samples, 5 cores/sample, were collected by 8 in. depths to 24 inches from the zero S rate plots four times during the growing period.
Analysis
Grain weight and moisture content were determined from each plot and grain yield was adjusted to 13.5% moisture. Plant samples were dried at 140°F, ground in a Wiley mill to pass a 0.0394 in. screen, and analyzed for total N and S. Total N, including NO3, was determined using a Leco (St. Joseph, MI) model FP-428 N analyzer. Total S was determined by digestion with nitric-perchloric acid (Blanchar et al., 1965) and analysis of the digestate by inductively coupled plasma spectrometry (ICP). Soil samples were analyzed for S by extraction with Ca(H2PO4)2 HOAc (Hoeft et al., 1973) and S in the extract determined by ICP. Analysis of variance for all measured parameters were carried out using the Statistical Analysis System (SAS Institute, 1988) using the General Linear Models (GLM) procedure. Orthogonal coefficients were utilized to determine significant S rate effects and to determine which regression equations to fit.
Precipitation was collected at each site and analyzed for SO4-S.
Collection started on 12 Mar. 1990 at Brownstown, with SO4 determined by the
turbidimetric method (Standard Methods, 1980). Dixon Springs is a collection
site of the ongoing National Atmospheric Deposition
Program, IR-7, National Trends Network (NADP/NTN), Fort Collins Colorado. The
concentrations were used to calculate S deposited in precipitation at each site.
Results of the first year of this study, 1989 - 1990, can be found in the 1991 Illinois Fertilizer and Chemical Association Proceedings. Those results and discussion will not be repeated in this report.
Experiment 1
Brownstown - Plant Growth
Wheat plant heights at Brownstown were significantly different for the main effect of variety and for the interaction of variety and S application in 1991 (Table la). Height differences due to variety (Table 2) would be expected because of differing growth habits of the varieties. A reduction in height of Caldwell with S application (2 in.) resulted in the significant interaction between varieties (Table 2).
Tillage and variety significantly influenced the number of heads/ft2 measured in late May. No interactions were significant (Table la). The mean head count was significantly lower for no-till than conventional-till (Table 2) and may have been a reflection of competition with chickweed Stellaria media in the fall with no-till or just a reaction to the no-till system. Chickweed was controlled by spring application of Harmony Extra, but competition earlier in the fall may have reduced tillering. As was found in 1990, differences in the head number were measured between varieties (Table 2), with Cardinal having the lowest head count.
Brownstown - Flag Leaf
Flag leaves collected from the non-S treated plots (Feekes' growth stage 10.1 -- initial heading) had S concentrations (Table 3) above the level (0.20 % S) considered sufficient (Reneau et al., 1986). Flag leaf S concentration was not significantly affected by S application (Tables la and 3), however, the trend was for higher S concentration when fertilizer S was applied. Sulfur concentration differed between varieties (Tables la and 3), 0.05 % difference between the highest and lowest concentration. Also, S concentration varied differentially with variety between tillage system. In general, the flag leaf S concentration was lower with NT.
Flag leaf N concentrations (Table 3) were within the range considered sufficient (Vaughan et al., 1990). Nitrogen concentration was significantly different between varieties (Tables la and 3), significantly higher with CT, and varied somewhat between varieties on each of the tillage systems (Tables la and 3). Application of S had no effect on flag leaf N concentration (Tables la and 3).
All measured flag leaf N/S ratios (Ntotal/Stotal) were lower than the level of 18 or below considered sufficient (Reneau et al., 1986). Overall, S application lowered the flag leaf N/S ratio (Tables la and 3). With the N/S ratio already in the sufficient range with no S application, further decrease with S application indicates that accumulation of inorganic S above plant requirements was taking place in the leaf tissue (Stewart and Porter, 1969; Rasmussen et al., 1975). Also, a significant difference between varieties, and varieties between tillage system was measured (Tables la and 3). Becker and Cardinal consistently had higher N/S ratios than Caldwell and Pioneer 2555.
Brownstown - Whole Plant
No significant differences were found for whole plant (Feekes' growth stage 10.1) S concentration (Tables lb and 4). Overall, the concentrations measured, with or without applied S, were slightly below the critical level of 0.15 % (Ward et al., 1973). The average 0.01 % increase in S concentration (from 0.13 to 0.14 % S) due to S application was not deemed statistically significant (Tables lb and 4)).
Only the main effect of tillage resulted in a significant difference in whole plant N concentration (Tables lb and 4). All N concentrations measured were above the critical level of 1.25 % N (Ward et al., 1973) (Table 4).
The whole plant N/S ratio was significantly lower when S was applied (Tables lb and 4), and significantly lower for Pioneer 2555 than the other three varieties (Tables lb and 4). Again, as was found for the flag leaf N/S ratio, the lower N/S ratios with S application indicates the accumulation of inorganic S above plant requirements (Roberts and Koehler, 1965; Stewart and Porter, 1969; Rasmussen et al., 19'15). All whole plant ratios (Table 4) were well within the critical range of 15 to 16 or less (Stewart and Porter, 1969; Rasmussen et al., 1975, 1977; Spencer and Freney, 1980; Mahler and Maples, 1986).
Brownstown - Grain
Wheat grain yield, S concentration, and N/S ratio were significantly different only for the main effect of variety in 1991 (Tables la and 5). Yield was highest for the variety Cardinal and lowest for Pioneer® 2555. Some differences were probably due to varying resistance to diseases present in 1991 -- Powdery mildew (Erysiphe graminis f. sp. tritici, Glume blotch (Seproria nodorum), and Leaf blotch (Septoria tritici) -- or differences in timing of flowering and infestation of Scab (Fusarium spp.). The diseases present in 1991 were the same as those present in 1990, and resulted in the low overall grain production, 39 bu/acre.
The mean grain yield and grain S concentration with and without S application was exactly the same, 39 bu/acre and 0.15 % S. Significant differences in grain S concentration and N/S ratio between varieties were small, and both indicators of S status were in the sufficiency range, above 0.12 % S (Rasmussen et al., 1975; Randall et al., 1981) and below a N/S ratio of 17 (Randall et al., 1981; Mahler and Maples, 1987).
Grain N concentration was significantly different between varieties
(Tables la and 5) and the
interaction between variety and tillage was significant. The grain N concentration
for each variety was lower with NT, with the largest decrease found with Pioneer®
2555 and the smallest decrease with Cardinal and Caldwell (Table
5).
Dixon Springs - Plant Growth
Differences in wheat plant heights were significant between varieties and S application (Table 6a). The measured increase in height from S application was minimal, overall one inch taller with S application and 2 inches taller with S, application on NT (Table 7). As was found at Brownstown, height differences due to variety would be expected because of differing growth habits of the varieties.
Head count was significantly different between variety and the interaction between tillage and S application was significant (Table 6a). Head count was lowest for Cardinal and PioneerO 2548, and was highest for NT when no S was applied (Table 7).
Plant heights and head counts were similar for both locations in 1991. Cardinal had the lowest head count at both locations.
Dixon Springs - Flag Leaf
Wheat flag leaf S and N concentration, and N/S ratio, were all significantly different for the main effects of variety and S application (Table 6a). Also, a significant interaction between S application and variety occurred for N concentration.
Although S application increased flag leaf S concentration and
decreased N concentration and N/S ratio, all measured concentrations without
applied S were in the sufficient ranges (Table 8).
Significant differences in nutrient concentrations were measured between varieties.
These differences were similar to those found at Brownstown
Dixon Springs - Whole Plant
Application of S resulted in significantly higher plant S concentration and lower N/S ratio (Tables 6b and 9). Differences in plant S and N concentration were found between varieties, and the N concentration was significantly higher with CT than NT (Tables 6b and 9).
Again, as was found with the flag leaf analysis, the levels of
S and N measured in the whole plant without S application were in the sufficient
range. Also, the N/S ratio was well below the critical level. This again reflects
the accumulation of inorganic S in the plant tissue. This was the same trend
as found at Brownstown. Also, the levels of N and S measured in the flag leaves
and whole plants were quite similar at each location in 1991.
Dixon Springs - Grain
Wheat grain yield was significantly different between varieties and tillage system (Table 6a). Also, there was a significant interaction between variety and tillage system. In general, the yield was lower for all varieties with NT, except Caldwell, which was higher (Table 10). Differences in yield between varieties would be expected because of their differing yield potentials. Sulfur application had no effect on yield (29 bu/acre with no S application and 27 bu/acre with S) (Tables 6a and 10). The overall yield level was quite low in 1991 at Dixon Springs. This is a reflection of the same diseases being present as those at Brownstown, except that the pressure was more severe at Dixon Springs.
Application of S had no effect on grain S or N concentration (Tables 6a and 10). The S concentrations were above the critical level of 0.12% S. Differences in S concentration were present between varieties, ranging from 0.13 % for Pioneer'32548 to 0.15 % S for Caldwell.
Grain N concentrations were significantly different between varieties, with highest N concentration for Caldwell. Also, the interaction between tillage system and S application was significant (Tables 6a and 10). For an unknown reason the N concentration was lower with S application on CT but was higher with S application on NT.
Soil (Brownstown and Dixon Springs)
Extractable SO4-S in the surface soil was constant throughout the growing season at Brownstown (Table 11), but was lower in the spring than in the fall at Dixon Springs (Table 12). Although the S soil test has not been reliable for predicting past crop responses to S application in Illinois (Hoeft et al., 1985), these test levels would predict that no response would occur to S application -- a test level greater than 10 ppm S (Hoeft et al., 1973).
Also, quite high levels of extractable SO4-S were
measured in the subsoils at both locations (Tables 11
and 12), especially the 16 to 24 in. depth. These
high values probably reflect accumulation of SO4 at the depth where
the impedance of water flow occurs in each soil. In conjunction with the high
levels of extractable S in the surface layer, these high subsoil levels give
an explanation as to why plant S concentrations are adequate without application
of fertilizer S and why no response in production has been found from S application.
That is, a more than adequate supply of SO4-S is available within
the rooting depth on both soils and reflects the reason why most reported wheat
responses to applied S have occurred on coarse texture-low organic matter soils
with low capacity to retain sulfate in the subsoil (Oates and Kamprath, 1985;
Mahler and Maples, 1986; Wells et al., 1986; Mahler and Maples, 1987).
Experiment 2
Brownstown - Grain
Sulfur application rate had no consistent effect on wheat grain yield in 1991 (Table 13), with an increase, decrease, and then increase again in yield as S rate increased (significant cubic response). The maximum increase in yield was 5 bu/acre with the 51b S/acre rate, but only 2 bu/acre with the 10 lb S/acre rate. Because of these inconsistencies, it is not clear if this was a true response to application of S.
Grain S concentration and N/S ratio responded significantly to
S application rate (quadratic response) (Table 13).
The differences were quite small, and actually resulted in a lower S concentration
and higher N/S ratio with 15 lb S/acre rate than any of the other rates, including
the zero rate. Both S concentration and N/S ratio were in the range considered
sufficient. Grain N concentration was not affected by S application rate (Table
13).
Brownstown - Flag Leaf
Flag leaf S and N concentrations were not affected by S application rate (Table 14). The N/S ratio varied significantly with increasing S rate (cubic response), with the highest N/S ratio at the 51b S/acre rate, the same rate that produced the highest yield (Table 14). All parameters were within the range considered sufficient.
Brownstown - Whole Plant
Whole plant N concentration was not affected by S rate (Table 14). Whole plant S concentration and N/S ratio responded significantly to S rate (Table 14). The plant S concentration increased with S rate, while the N/S ratio decreased (both significant linear responses). The whole plant S concentration at the zero S rate was just below the 0.15 % S sufficient level of Ward et al. (1973). The first increment of applied S, 5 lb S/acre, brought the S concentration into the sufficient range (Table 14). The N/S ratios for all application rates, including the zero rate, were within the sufficient range.
Dixon Springs - Grain
Wheat grain yield was not significantly affected by S application rate at Dixon Springs (Table 15). The low yields were the result of severe disease pressure at this site. No grain samples were collected in 1991.
Dixon Springs - Flag Leaf
The flag leaf S concentration increased significantly with increasing S rate (linear response) (Table 15) and the N/S ratio decrease significantly with increasing S rate (linear response). Both were in the sufficient range. The N concentration was not affected by S application (Table 15).
Dixon Springs - Whole Plant
The whole plant S concentration increased significantly with increasing
S rate (cubic response) (Table 15) and the N/S ratio
decreased significantly with increasing S rate (linear response). The N/S ratio
at all S rates was well within the sufficient range, however, with no
S applied, the whole plant S concentration was below the 0.15 % S critical level.
The first rate of S, 5 lb/acre, brought the concentration into the sufficient
range. This was similar to the response at Brownstown. The whole plant N concentration
varied as S rate increased (cubic response), being higher at the 5 lb S/acre
rate than at any other rate (Table 15). All N concentrations
were above the critical level of 1.25%.
Soil (Brownstown and Dixon Springs)
Extractable SO4-S in the surface soil increased throughout the growing period at Brownstown, especially the late spring (Table 16), but was lower throughout the spring than in the fall at Dixon Springs (Table 17). Although the S soil test has not been reliable for predicting past crop responses to S application in Illinois (Hoeft et al., 1985), at both locations, the test levels would indicate that no response would be expected from S application, test levels were above the 10 ppm S critical level (Hoeft et al., 1973).
Also, as was found for experiment 1, high levels of extractable SO4-S were measured in the subsoils at both locations (Tables 16 and 17). These high levels, as in experiment 1, probably explain the lack of consistent response to rate of fertilizer S in experiment 2.
S Depostition
At Brownstown, rainfall has been collected to determine SO4-S deposition since Mar. 1990. Total SO4-S deposition for the March 1990 through August 1990 period was 10.7 lb S/acre. The total S deposition for the September 1990 through June 1991 period was 13.61b S/acre. This second time frame represents the growing season for the 1990 - 1991 crop year. This is a sizable amount of S, and would represent approximately the entire S requirement of a 55 bu/acre wheat crop (about the level of production in 1990 - 1991).
At Dixon Springs, a NADP/NTN collection site, the Oct. 1989 through
June 1990 deposition of SO4-S in precipitation was 6.4 lb S/acre and the Oct.
1990 through June 1991 precipitation deposition was 6.2 lb S/acre. Also, the
yearly deposition for 1988 was 6.7 lb S/acre, for 1989 was 8.3 lb S/acre, and
for 1990 was 9.21b S/acre. In all time periods, this represents a sizeable amount
of the S requirement for crop production.
Overall results in 1991 were quite similar to those in 1990. Winter wheat grain yield was not increased by spring topdress application of S. The lack of yield response was consistent across all varieties tested and on both tillage systems, no-till and conventional-till. Application of S rates from 0 to 301b S/acre resulted in increases in plant S, but not consistent increases in grain yield. All parameters used to determine possible wheat response to application of S, including plant S concentration and N/S ratio, flag leaf S concentration and N/S ratio, grain S concentration and N/S ratio, and soil test, indicated that sufficient levels were available without application of supplemental fertilizer S.
Most likely, combined input of available S from sources other than fertilizer S -- such as subsoil sulfate, precipitation, dry deposition, atmospheric SO2 absorption by plants, and mineralization of organic matter -- supply more than an adequate amount of available S for wheat production, for example, the total amount taken up by an 80 bu/acre wheat crop, approximately 20 lb S/acre (Beaton and Wagner, 1985).
It is important to remember that most reported wheat responses to application of S have occurred where the soil supply of available S was low -- coarse textured sands with low organic matter and low capacity to retain sulfate in the subsoil. The silt loam soils of southern Illinois have low organic matter, but clay subsoils and fragipans limit the leaching or movement of sulfate out of the profile. In fact, quite high levels of SO4-S were measured at that depth at both experimental locations. Also, it is important to note that most of southern Illinois is in the highest SO4-S precipitation deposition area of the Continental United States -- 1989 and 1990 annual average deposition pattern of 6 to 9 lb S/acre (NADP/NTN, 1990 and 1991).
Some differences in plant growth and plant nutrient concentrations were found
between varieties, tillage systems, and S rates, but, in general, those differences
did not ultimately reflect or result in differences in overall grain production.
This probably results from the fact that most plant parameters measured, such
as number of heads/ftz, S concentrations, and N concentrations always tended
to be in an optimum range for crop production, even when differences existed
between treatment factors. The factor that consistently affected production
level the most was wheat variety itself.
Table 11: Extractable soil SO4-S concentration by depth, Experiment 1 -- Brownstown, 1991
Table 12: Extractable soil SO4-S concentration by depth, Experiment 1 -- Dixon Springs, 1991
Table 13: Effect of S rate on wheat grain yield and S and N concentration-- Brownstown, 1991
Table 16: Extractable soil SO4-S concentration by depth, Experiment 2 -- Brownstown, 1991
Table 17: Extractable soil SO4-S concentration by depth, Experiment 2 -- Dixon Springs, 1991
1John E. Sawyer is Manager, Agronomy Services, GROWMARK®, Inc., 1701 Towanda Ave., P.O. Box 2500, Bloomington, IL 61702 and Stephen A. Ebelhar is Agronomist, University of Illinois, Dixon Springs Agricultural Center, Simpson, IL 62985.
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