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Univ. of Georgia, Coastal Plain Exp. Stn., P.O. Box 748, Tifton, GA 31793-0748
* Corresponding author (gascho{at}tifton.cpes.peachnet.edu)
Received for publication October 9, 2000.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The quantities of lime required for neutralizing acidic N applications can be calculated. Theoretical calculations of the acidity provided by ammonium nitrate (NH4NO3) indicate that 3.6 kg of CaCO3 equivalents are needed to neutralize the acidity from 1 kg of N (Boswell et al., 1985). In practice, the amount of lime varies widely, from values as low as 0.4 (Pearson and Hoveland, 1992) to 4.7 kg (Morris et al., 1992). Lime applications of 2.3 to 4.7 kg were required for each kilogram of N applied as NH4NO3 to a double-crop of ryegrass (Lolium multiflorum L.) and sorghum [Sorghum bicolor (L.) Moench] in a 5-yr study on a Coastal Plain silt loam in Louisiana (Morris et al., 1992). Soil type greatly affects lime requirement, but crops, acidic fertilizers, and nutrient removal are factors.
Subsoil acidity and infertility and their effects on plant growth, development, and yield have been researched in numerous studies, which are well reviewed (Adams, 1984; Sumner, 1994). Detrimental plant effects from subsoil acidity vary with crop, rooting depth, and tolerance of high concentrations of soluble Al or Mn. Adams et al. (1967) found that cotton yields were reduced by about one-third when roots were restricted to the Ap horizon of a Greenville fine sandy loam (Rhodic Paleudult) because of strongly acid subsoil. However, peanut yields and rooting depth were not affected by the same subsoil acidity that limited cotton yield and rooting depth.
Studies have been conducted to incorporate lime at various depths to modify subsoils. Pearson et al. (1973) greatly increased cotton root elongation and mass in a growth chamber experiment when subsoils were mixed with lime. Doss et al. (1979), in a field study, concluded that incorporating lime to a 30-cm depth was sufficient to obtain a satisfactory root system for high-yielding cotton and corn. In their study, soil pH, over periods of 1 and 2 yr, was affected little below where the lime was placed in acid soil. In conservation tillage systems, very limited incorporation of agrochemicals can be accomplished; therefore, chemical changes in the subsoil must be from surface-applied materials. Brown and Munsell (1938) surfaced-applied lime at rates up to 22.4 Mg ha-1 to alfalfa (Medicago sativa L.) plots from 1914 to 1919, and in 1937, they found that the pH on a fine sandy loam had been modified to a depth of 91 cm by 15.7 to 22.4 Mg ha-1. Later, Brown et al. (1956) initiated a lime study in 1930 on a permanent grass sod that had not been disturbed since the 1890s. Nine years later, the pH in the profile of this fine sandy loam had increased to depths of 15, 30, 38, and 45 cm for rates of 4.5, 9, 18, and 36 Mg ha-1 lime, respectively. By 1953, 18 Mg ha-1 lime had increased the pH to a depth of 61 cm, and 35 Mg ha-1 lime had increased the pH to a depth of 76 cm. The authors stated that for a given soil and climate, rates and final depths of penetration depend on the amount of lime and lapse of time.
Sumner (1994) summarized many experiments where lime and gypsum had been surface-applied. The review indicated that both materials were effective in moving Ca into subsoils and alleviating Al toxicity. However, changes in the subsoil were slow with lime additions when no or little acidic N was applied.
Results from lime experiments conducted several decades ago may have limited value in the modern era because production systems have changed substantially. These changes include both deeper plowing (1980s) and a shift to conservation tillage (present), use of greater amounts of fertilizer nutrients, higher analysis fertilizers, increased use of acid-forming fertilizers, increased irrigation, improved cultivars, and greater removal of Ca and Mg by increased crop yields. The literature reveals very little information on long-term lime studies in recent years, and no long-term data were found for the sandy soils of the southern Coastal Plain.
The objectives were to determine the effects of surface soil liming on long-term chemical changes in two acid soils of the southern Coastal Plain to determine optimum liming rates needed for providing high yields in a modern cropping system and if yield suppression in cotton grown at low pH can be corrected by Ca or Mg fertilization.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Surface soil samples (0–15 cm) were collected in each subplot before fertilization and spring planting, but they were not obtained from the Tifton soil in 1988 and 1999 and from the Pelham soil in 1988, 1998, and 1999. In the first year on the Pelham soil, 1977, they were collected in the summer, following the initial application of lime in the spring. Each sample consisted of ten 2.5-cm-diam. cores mixed together. Depth samples (0–15, 15–30, 30–45, 45–60, 60–75, and 75–90 cm) were collected in February of 1978 and 1998 on the Tifton soil and 1980 and 1997 on the Pelham soil. For each depth, soil from three 7.6-cm-diam. probes was composited from a specific subplot within each lime plot, and this subplot received recommended rates of all nutrients (Plank, 1989), except Ca and Mg. Depth samples on both soils were collected in June 2000 and were a composite of three 15-cm increments (0- to 45-cm depth) from each subplot that did not receive Ca or Mg. Soil pH was determined in a 1:2 soil/water suspension after an equilibration period of 30 min. Soil Ca, K, P, and Mg were extracted by the Mehlich-1 method and determined according to procedures used in laboratories of southern states (Donohue et al., 1983), but P and K values are not presented because lime applications did not significantly (P = 0.05) affect their concentrations or distributions in the soil profile. Soil from depth samples collected in 2000 was extracted with 1 M KCl for determination of exchangeable soil Al, H, Ca, and Mg. Total acidity, Al, and H were determined by titration (Lin and Coleman, 1960). Calcium and Mg were determined by atomic absorption spectroscopy. Cation exchange capacity and Al saturation were calculated.
Yields were determined from mechanical harvests of the center one-third of the same subplots where the depth samples were collected. Grains, peanut seeds and pods, and cotton lint and seeds were then harvested and removed from the remainder of the plot area. Harvested pearl millet [Pennisetum glaucum (L.) R. Br.] forage and other crop residues were returned to plots.
Field-spread lime costs and gross value of crops, except canola (Brassica napus L.), were calculated from yearly prices reported in Georgia Agricultural Facts (Georgia Agric. Stat. Serv., 1970–2000). Canola prices were derived from the Canadian market (P.L. Raymer, personal communication, 2001).
Data from surface soil analyses and crop yields were statistically analyzed by ANOVA as a randomized complete block design (SAS, 1998). Data from depth samples were analyzed by the method of Cochran and Cox (1955), using a split-plot arrangement with subunits (depths) in strips. Differences in soil profile pH, Ca, and Mg from the earlier to later sampling were analyzed by the t-test (SAS, 1998). Cotton yield data were analyzed in 2000 using the split-plot analysis, with lime rates as the main plots and Ca and Mg fertilization as the subplots. Means were separated by LSD (P = 0.05).
Tifton Soil
Tifton soils are well drained, occurring on ridgetops and uplands of the southern Coastal Plain (Calhoun, 1983). The lower part of the profile, below 89 cm, is composed of plinthite, and many nodules of ironstone occur on the surface and upper part of the profile. In their natural state, Tifton soils are low in fertility and organic matter and strongly acid throughout the profile. They are moderately permeable and medium in available water capacity. They are well suited for row crops, small grains, and sod crops.
The experimental site is one of the most productive in the Coastal Plain. It had been in row crops and forages for approximately 50 yr before the initiation of this study. During that period, it had likely been limed and fertilized uniformly, as gauged by the initial pH and soil analyses. Crops in the study were irrigated each year but at a greater frequency since 1995 due to the installation of a permanent lateral-move sprinkler irrigation system that includes these plots.
Pelham Soil
Pelham soils were once considered unsuitable for crop production due to poor drainage. In their native state, vegetation is softwood trees and water-tolerant shrubs, but crops can be grown successfully if these soils are drained, limed, and fertilized. The series is extensive in the Atlantic Coast Flatwoods region of southeastern USA (Anonymous, 1981). It is nearly level (0–2% slopes) and well suited to tillage because of sandy texture to a depth of 60 cm (Stevens, 1973). Corn, cotton, peanut, soybean, tobacco (Nicotiana tabacum L.), and bahiagrass (Paspalum notatum L.) are now grown extensively on drained Pelham soils. Calhoun (1983) describes the soil as moderately permeable and without drainage. The water table is 15 to 45 cm below the surface from midwinter to midspring. Pelham soils are of marine origin, occurring in flat areas of the region. In their native state, they are low in fertility and organic matter and are strongly acid throughout the profile.
Since the plot area was cleared of pine (Pinus palustris L. and P. elliotti L.) trees in 1957, tobacco has been the primary crop and has received small amounts of lime. Crops received supplemental irrigation after the first 5 yr.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Lime requirement for the medium lime rate was 5.25 kg for each kilogram of NH4NO3 applied. That requirement was considerably greater than the theoretical acidity produced by ammoniacal N application (Boswell et al., 1985). Our data are similar to those by Morris et al. (1992) for a double-crop study of 5 yr on a Coastal Plain soil. A wide range of ratios of lime needed to N applied have been suggested in the literature. However, that is not unexpected as factors including soil, cropping systems, and leaching of bases are all involved in pH management.
Pelham Soil
Soil samples in 1977 were collected 3 mo following the first lime application, accounting for the initial difference in soil pH, Ca, and Mg for lime rates (Fig. 2)
. The sharp dips in pH, especially for no- and low-lime plots, occurred when 
200 kg N ha-1 was applied to crops in 1991 and 1995. Soil pH on no-lime plots, based on a 9-yr average, declined from 5.2 in the first period to 4.9 in the last period. Even though there were notable fluctuations in pH over the years on low- and high-lime plots, the average pH did not change much for either rate between the early 9-yr period and the late 9-yr period, but soil pH was slightly elevated for all lime rates midway through the study. Generally, the pH was maintained above 5.5 for the low rate and above 6.0 for the high rate.
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Initially, soil Mg for the no-lime plots was below the sufficiency level of 15 mg kg-1 (Fig. 2c), but levels did not decline below the initial level until the 1990 season because 24 kg Mg ha-1 (mean) was applied annually as fertilizer from 1977 until 1986 (Table 3). During the last 10 yr, the annual application of 176 kg N ha-1 (mean) was likely responsible for the declines in Mg observed in those years. Dolomitic lime applied in 1977, 1978, and 1983 (Table 3) maintained soil Mg >15 mg kg-1 for the low lime rate, but concentrations in the last 10 yr were insufficient, with the exception of 1 yr following lime application in 1993. Initial lime application for the high-lime plots increased soil Mg to double that of the no-lime plots, and the concentration has been maintained at well above sufficiency throughout the study.
The Pelham soil is inherently low in bases, including Ca and Mg. This study indicates that maintaining pH at 6.0 assured sufficient availability of Ca and Mg. The high rates of N applied in the final 9 yr greatly reduced Ca and Mg reserves. The loss of available Ca and Mg suggest that they should be monitored, by soil testing, to ensure adequate availability in such a sandy soil.
Subsoil Effects
Treatments that received lime were compared with the no-lime treatment to determine depth of liming effects over years (Table 4). Also, the same lime treatment could be compared statistically over years for the Tifton soil but not for the Pelham soil because only mean data are available for samples taken in 1980. Liming increased soil pH and Mehlich-1 Ca and Mg in both subsoils over the period of the study. The data indicate that applications of gypsum or phosphogypsum, which supply no Mg and enhance leaching of K and Mg from the surface soil (Alva et al., 1991), are unnecessary unless a more rapid increase in soil Ca is desired.
Tifton Soil
In 1978, 8 yr after the study began, soil pH, Ca, and Mg levels at the 30- to 45-cm depth (below the plow layer) were increased by limestone applications, indicating movement over time (Table 4). However, depths below 45 cm were not affected by treatments. Twenty years later, soil pH, Ca, and Mg levels were increased to the 75- to 90-cm depth by limestone applications. Levels in the profile were related to rate of limestone application. Movement during the latter period may have been enhanced by the large amounts of ammoniacal N applied during the latter part of the study (Table 2). Calcium and Mg in the soil profile decreased from 1978 to 1998 for the no-lime treatment (P = 0.05; data not shown). Soil Ca also decreased for the low lime rate. Soil pH and Mg increased over 20 yr for the high lime rate, and Mg increased for the medium lime rate. By 1998, soil pH was >5.6, Ca was >150 mg kg-1, and Mg was >25 mg kg-1 at all depths for the medium lime rate, and levels of each measurement were greater for the high lime rate. After 20 yr, the evidence is clear that reserves of Ca and Mg are being depleted below plow depth for the no-lime treatment.
Pelham Soil
In 1980, 3 yr after the study began, the high rate of lime increased soil pH in the 30- to 45-cm depth (below plow layer), but there was no evidence of Ca and Mg movement at this depth (Table 4). Seventeen years later, soil pH, Ca, and Mg levels had been increased by lime application at each depth sampled. Without lime application, soil Ca and Mg were depleted from the profile and especially from the upper layers sampled. In 1997, soil pH was >5.6 and Ca >100 mg kg-1 for the low lime rate at depths to 60 cm, but Mg was <15 mg kg-1 for all depths with this rate. At the latter sampling, soil pH was >6.0 for depths above 75 to 90 cm for the high lime rate, and Ca was >100 mg kg-1 and Mg >15 mg kg-1 at all depths.
Crop Effects
Tifton Soil
Generally, crop response to lime (Table 5) occurred only when substantial amounts of N were applied (Table 2). Lime increased corn yields in 2 of 3 yr, 1979 to 1981, and cotton, canola, and millet yields during the last 9 yr, 1991 to 1999, of the study. Leguminous crops were grown in 17 of the first 21 yr, and the average relative yield for unlimed plots was 101%, indicating no beneficial effect from lime (Table 5). Neither the no-lime nor the low-lime treatments was sufficient during the last 10 yr when relative yields averaged 80 and 90%, respectively. There was only 1 yr, 1991, when crop yield (cotton) was greater for the high lime rate than for the medium rate. Surface soil pH was 6.0 each year except 1992 for the high lime rate and >5.5 for the entire period for the medium rate (Fig. 1a). Surface soil for the medium and high lime rates always contained >200 mg Ca kg-1 and 20 mg Mg kg-1, except in 1992 for the medium rate (Fig. 1b and 1c).
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Exchangeable Al in soils (0–45 cm depth) in 2000 was the same for the no-lime plots on both soils (Table 7), but relative cotton yields were 84% on the Tifton soil and only 18% on the Pelham (Tables 5 and 6). Yields were not increased with lime rates above the low lime rate on both soils, indicating that Al concentrations of 0.30 and 0.23 cmolc kg-1 on the Tifton and Pelham soils, respectively, were not toxic to cotton plants. In a survey of Al studies, van Lierop (1990) reported that maximum crop yields were obtained with levels of 0.1 to 0.2 cmolc Al kg-1 or less, but Al-sensitive crops—alfalfa, soybean, and barley—required levels <0.1 cmolc kg-1. Some investigators have used Al saturation to determine Al toxicity for crops. Kamprath (1970) found that optimum growth of cotton and soybean was obtained on Southern Coastal Plain soils when Al saturation was 
20%, but Adams and Pearson (1967) summarized a number of cotton experiments in which Al saturations at optimum growth were 30% for two soils and 5% for another.
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Comparison of Tifton and Pelham Soils
The Tifton soil contained much greater concentrations of Ca and Mg than the Pelham soil in the beginning and throughout the study. The low-lime treatment, which supplied an average of 122 kg Ca ha-1 yr-1 from limestone and fertilizer on the Tifton soil (Table 2) and 182 kg Ca ha-1 yr-1 on the Pelham soil (Table 3), maintained Ca >100 mg kg-1 on both surface soils. This treatment supplied an average of 23 and 50 kg Mg ha-1 yr-1 on the Tifton and Pelham soils, respectively. The low lime rate maintained Mg at levels >15 mg kg-1 in 28 of 31 yr on the Tifton, but levels were <15 mg kg-1 in 8 of the final 9 yr on the Pelham. The medium-lime treatment on the Tifton soil and the high-lime treatment on the Pelham provided Ca concentrations >100 mg kg-1 and Mg concentrations >15 mg kg-1 on both soils. A medium lime rate may have been adequate on the Pelham if this treatment had been included. The high rate of lime was not needed to provide the amount of Ca and Mg considered to be sufficient on the Tifton soil for the 31-yr period.
During the last 10 yr, when greater N rates were applied than in the early years of the study, maintaining soil fertility appeared more critical for the Pelham soil than for the Tifton soil. Yields of the lesser lime rates relative to the high-lime plots were much lower on the Pelham soil than on the Tifton soil. The amount of limestone (CaCO3 equivalent) provided by the low rate (242 and 488 kg ha-1 yr-1 on the Tifton and Pelham soils, respectively; Tables 2 and 3) was insufficient for both soils. Crop yields for the medium and high rates on the Tifton soil were equal, except for cotton in 1991 (Table 5). It appears that the high lime rate resulted in some overliming on both soils. High pH was the cause of Zn deficiency in corn on the Tifton soil (Boswell et al., 1989). Manganese deficiency in corn and soybean was observed by the authors and reported for peanut (Parker and Walker, 1986) on high-lime plots on the Pelham soil.
Our study was not designed to be able to differentiate changes in surface soil from changes in subsoil due to lime effects, but examination of the data for the Tifton soil suggests that complete modification in the subsoil may not be required for greatest yield. Conversely, modification of pH and Ca in upper depths of the Pelham subsoil by the low rate of lime (Table 4) did not result in crop yields comparable to the high rate of lime (Table 6) when high inputs of N were applied. However, Mg may have been a limiting factor in later years because the concentration was <15 mg ha-1 throughout the profile (Table 4). The high lime rate ameliorated the Pelham subsoil by establishing a pH >6.0 to a depth of 75 cm and providing adequate Ca and Mg throughout the profile, but it is not known whether higher yields were the result of the subsoil amelioration.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The data also show that dolomitic lime applied to the surface soil will increase soil pH, Ca, and Mg in subsoils over a period of years.
Data collected in the final year of the study suggest that Al toxicity was a primary factor in suppressing crop yield in the no-lime plots on both soils. Cotton yields in 2000 were low when exchangeable Al in the surface 45 cm of soil exceeded 0.3 cmolc kg-1, and yields were not improved on any plots by application of Ca salts, Mg salts, or both.
Soil acidity appeared to be a greater soil fertility factor on the Pelham soil than on the Tifton soil. More frequent liming at low rates may have resulted in better maintenance of surface soil pH without as much penetration of Ca and Mg to the subsoil. A practical approach appears to be to analyze soil regularly and apply moderate quantities of dolomitic lime to maintain surface pH near 6.0 to ensure nutrient availability.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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