Effects of gypsum and stubble retention on the chemical and physical properties of a sodic grey Vertosol in western Victoria.
Alkaline sodic soils, defined as having an exchangeable sodium percentage (ESP) [greater than or equal to] 6% (Isbell 1996), and a pH >8 (Rengasamy and Olsson 1991), encompass approximately 73% of agricultural land in Victoria (Ford et al. 1993). This level of exchangeable sodium combined with high soil pH makes these soils prone to swelling and dispersion when the soil is wet, causing soil structural problems such as water logging and poor infiltration. When dry, these soils suffer from crusting and hardsetting, which can limit crop establishment, and ultimately cause yield decline (Greene et al. 2002).
Gypsum is commonly used to ameliorate structural problems on sodic soils in Victoria, but most of the reported results have been based on Red-brown Earths (Greene and Ford 1985; Greene et al. 1988; Ford et al. 1993; Rengasamy et al. 1984). Few studies have investigated the processes involved in the gypsum reclamation of alkaline sodic Vertosols. In addition to gypsum application, stubble management on soils is also important. Studies in New South Wales showed that the retention of stubble prevented soil erosion and had long-term benefits for soil structure (Packer et al. 1984). Valzano et al. (1997) showed that stubble burning caused a deterioration in soil physical properties.
We examined the effects of gypsum and two stubble management practices [stubble burning (SB) and stubble retention (SR)] on the properties of a sodic grey Vertosol in western Victoria.
Experimental site and design
The study site was situated near the Victorian town of Natimuk, 324 km north-west of Melbourne and 25 km west of Horsham (36.45 [degrees] S, 142.15 [degrees] E) (Fig. 1). The area has a semi-arid climate with a mean annual rainfall of 451 mm (Bureau of Meteorology, Canberra). Rainfall predominantly falls during winter to late spring, peaking in July-September. The region is used extensively for the production of winter cereal and oilseed crops.
[FIGURE 1 OMITTED]
The soil was described as (i) a sodic grey/brown Vertosol (Isbell 1996), (ii) Ug6.2 (Northcote 1979), (iii) a grey clay (Stace et. al 1968), or (iv) a Vertisol (Soil Survey Staff 1992). Soil textures ranged from light clay/clay loam at the surface to light--medium clay subsoils. This soil had a neutral to alkaline pH due to the presence of soil carbonates throughout most of the B horizon (Table 1). X-ray diffraction results (Moore and Reynolds 1997) indicated that the soil mineral fraction at Natimuk had considerable amounts of smectite, with lesser quantities of kaolinite and illite. Quartz and muscovite were also found throughout the profile. Calcite was only found in the B horizon of the soil (Valzano 2000).
A randomised plot design was used, with 3 replicates of each stubble-gypsum combination, giving a total of 12 plots (2 stubble treatments x 2 gypsum treatments x 3 replicates). Treatments commenced in May 1995, when plots receiving gypsum (called G10) were treated with 10 t/ha of phosphogypsum (90% purity) spread with a mechanical spreader. Control plots (G0) received no gypsum. SB and SR were the stubble treatments imposed on the G10 and G0 plots. In SB plots, crop residue was burnt on an annual basis in the autumn prior to sowing. Reduced tillage was practised when plots were fertilised and sown, using a modified Horsham drill with 25-cm row spacings. Winter crops were grown for 3 years using the following rotation: wheat-safflower-canola.
The Natimuk site had a mean annual rainfall of 451 mm during the study period. In 1997 rainfall was below the mean, with a total of 338 mm.
In November 1997, 2 replicate disturbed soil samples were removed from the 0-75 and 150-225 mm depths from all treatments, air dried, and sieved to <2 mm. These samples were then used for laboratory determinations of exchangeable and soluble cations and Emerson aggregate tests. Two replicate undisturbed core samples (75 mm length by 40 mm radius) were also removed from 2 depths (0-75 and 150-225 mm) for moisture characteristic and penetrometer resistance measurements.
Exchangeable cations ([cmol.sub.c]/kg) were determined using 1 M ammonium acetate (pH adjusted to match soil pH) as described by Rayment and Higginson (1992). The effective cation exchange capacity (ECEC) ([cmol.sub.c]/kg) was calculated from the sum of the exchangeable cations [Ca.sup.2+], [Mg.sup.2+], [K.sup.+], and [Na.sup.+], as it was found to give comparable results to the CEC (Valzano 2000). The ESP (%) was calculated from the ratio of exchangeable [Na.sup.+] to ECEC:
(1) ESP = ([Na.sup.+.sub.ex]/ECEC) x 100
where the subscript `ex' denotes exchangeable.
Soluble cation levels were determined using a method described by Craze et al. (1993); 1: 5 soil :water extracts were prepared and then analysed for soluble [Ca.sup.2+.sub.s], [Mg.sup.2+.sub.s], [K.sup.+.sub.s] and [Na.sup.+.sub.s]. The total cation concentration (TCC) ([mmol.sub.c]/L) was calculated from the sum of the soluble cations [Ca.sup.2+], [Mg.sup.2+], [K.sup.+] and [Na.sup.+]. The sodium adsorption ratio (SAR) of the soil was calculated as follows:
(2) SAR = [[Na.sup.+.sub.s]]/[([[Ca.sup.2+.sub.s]+[Mg.sup.2+.sub.s]]).sup.1/2]
where the subscript `s' denotes soluble.
Electrical conductivity and pH
Soil solution electrical conductivity (EC) and pH were determined from 1:5 soil:water extracts following end-over-end shaking for 1 h. The EC measurements (dS/m) were then made on an Activon 301 conductivity meter. The pH of the soil was recorded on an ANAX bench-top pH meter.
Percentage organic carbon for all depths and treatments was determined using the Walkley-Black chromic acid method (McLeod 1973).
The soil dispersion index was determined from the Emerson aggregate class and Loveday and Pyle subdivision using a similar method to that described by Murphy (1995). The Emerson aggregate class was determined on air-dried aggregates (>2 mm) and remoulded soil balls (5 mm diameter), made from the air-dried soil (Emerson 1967). Classes 2 and 3 were subdivided as per Loveday and Pyle (1973). A period of 2 h was allowed for dispersion to occur, ensuring that all soils with dispersive properties were likely to be identified.
Penetrometer resistance measurements (0.06 MPa suction)
A handheld penetrometer (1.2 mm point) was used to measure soil resistance (MPa) from core samples (all plots and depths) brought to a suction of 0.06 MPa. Six randomly positioned replicate measurements were made to a depth of 7 mm at a range of depths in each core. The depths were 0-7 and 68-75 mm in the 0-75 mm sample and 150-157 and 218-225 mm in the 150-225 mm sample.
Volumetric moisture characteristic determinations were made at a number of suctions [0.003 (field capacity), 0.01, 0.06, 0.1, 0.5, and 1.5 MPa (permanent wilting point)] using methods described by Loveday (1974). The available water holding capacity was determined by subtracting the permanent wilting point water content from the field capacity water content.
Samples for micromorphological examination were taken by slowly pushing tins (160 by 90 by 50 mm) into wet soil and excavating soil from around the sides of the tin as it was pushed in. Samples were taken from the surface of the A horizon and the 150-200 mm depth. After drying at 40 [degrees] C, the samples were impregnated with CR 64 polyester resin. Duplicate, vertically oriented thin sections (75 by 50 mm) were then produced from the impregnated soil samples with the longer dimension parallel to the surface. The thin sections were then described qualitatively according to the terminology of Brewer and Sleeman (1988) and Bullock et al. (1985).
The significance of treatment effects was determined by analysis of variance using GENSTAT[R] 5.3.1. Statistical analysis was carded out on all treatments for all depths. Skewed data were transformed to the natural logarithm. Comparisons between all depths and treatments were based on least significant differences at P = 0.05.
Effect of gypsum and stubble management on soil chemical properties
A combined stubble-gypsum effect was present in 1997 (Table 2), resulting in lower rates of [Na.sup.+.sub.ex] displacement at 0-75 mm in SR plots than in SB plots. The opposite effect occurred at 150-225 mm, where there were higher levels of [Na.sup.+.sub.ex] displacement in SR plots than in SB plots. The results indicated that G10 significantly (P < 0.01) decreased exchangeable sodium ([Na.sup.+.sub.ex]) compared with G0 at both 0-75 and 150-225 mm depths of the soil (SR and SB).
There was a significant (P < 0.05) increase in exchangeable calcium ([Ca.sup.2+.sub.ex]) in the G10 plots at both 0-75 and 150-225 mm depths of the stubble treatments (SR and SB). Stubble treatment did not affect [Ca.sup.2+.sub.ex] (Table 2).
Exchangeable magnesium ([Mg.sup.2+.sub.ex]) levels decreased (P = 0.02) in 1997 in plots treated with gypsum (Table 2). This decrease in [Mg.sup.2+.sub.ex] was evident at both 0-75 and 150-225 mm depths. A stubble-induced effect was also present. At 0-75 mm, [Mg.sup.2+.sub.ex] was reduced to a lower value in SR plots than in equivalent SB plots. These surface effects corresponded with higher [Mg.sup.2+.sub.ex] levels at a depth of 150-225 mm in the SR plots than SB plots.
Stubble treatments influenced gypsum movement and its effect, resulting in greater levels of leaching of sodium from the B horizon of SR plots than from SB plots (Table 3). The G10 treatment significantly decreased (P < 0.05) [Na.sup.+.sub.s] under SB at a depth of 0-75 mm. This decrease was accompanied by a small increase in [Na.sup.+.sub.s] at 150-225 mm depth. By contrast, when the G10 treatment was combined with SR, there was no decrease in [Na.sup.+.sub.s] at 0-75 mm, compared with a significant 30% decrease at 150-225 mm.
Levels of [Ca.sup.2+.sub.s] increased from approximately 0.1 [mmol.sub.c]/L in G0 plots to 0.7 [mmol.sub.c]/L in gypsum-treated plots in both SB and SR treatments (0-75 mm depth) (Table 3). However, in the deeper subsoil (150-225 mm), a combined stubble-gypsum effect occurred. At this depth, [Ca.sup.2+.sub.s] levels only increased when the G10 treatment was combined with SR. In SB G10 plots, [Ca.sup.2+.sub.s] levels were similar to those in equivalent G0 plots. These results correspond inversely with the previously mentioned changes in soluble sodium. However, they differ from the results obtained for [Ca.sup.2+.sub.ex] levels, which were found to increase at all measured depths in the G10 SB and G10 SR plots.
Soluble magnesium was not significantly affected by the gypsum or stubble treatments in 1997.
The G10 treatment significantly (P < 0.05) increased soil solution EC (Table 3) compared with G0. At the start of the growing season in 1996, the EC was 0.14 dS/m in G0, compared with 1.3 dS/m in G10 plots (A. Smith pers. comm.). This difference between G0 and G10 plots was still present in 1997, but to a lesser extent. A stubble management effect was also present at a depth of 150-225 mm, resulting in a significantly higher EC in SR G10 plots than in SB G10 plots. The elevated EC results generally corresponded with increases in soluble cations except for the SR G10 treatment at 150-225 mm, where TTC was lower than for the SR G0 treatment.
Soil pH declined significantly (P < 0.05) with gypsum application in 1996 (A. Smith unpublished data), but not in 1997 (Table 3). Although the effect in 1997 was not statistically significant, trends indicate that soil pH in both the A and B horizons was lower in G10 than in G0 plots (except SB G10 in the B horizon). These findings correspond with the previously mentioned EC results (i.e. a high EC was associated with a low pH) and are due to the displacement of [H.sup.+] ions from the double layer as a result of [Ca.sup.2+] ions.
There were no significant differences between treatments; however, SR tended to result in higher levels of organic carbon than SB (Table 3). In addition, G10 tended to result in higher organic carbon levels than G0 (this latter effect being related to improved crop yields in the gypsum treatments).
Effects of treatments on soil physical properties
The results show that changes in soil chemistry influenced the physical attributes and behavioural characteristics of the soils. The stubble treatments affected some soil physical properties, thereby altering the leaching regime of some of the cations mentioned in the previous section.
Clay dispersion, as determined by a clay dispersion index (DI), was significantly (P < 0.001) affected by the gypsum and stubble treatments at all measured depths in 1997 (Table 4). The G10 plots had lower dispersion values than their equivalent G0 plots. In addition, plots treated with SR had lower dispersion values than equivalent SB plots (except for G0 subsoil). The SR G10 plots had the lowest DI values (and hence the lowest dispersion) in both the A and B horizons. By contrast, the SB G0 (0-75 and 150-225 mm depths) and SR G0 (0-75 mm depth) plots showed the highest levels of clay dispersion. These dispersion effects corresponded with sodium levels in the soil as represented by the ESP and SAR results. For example, regressions between DI and ESP and DI and SAR give the following relationships:
(3) DI = 0.5 ESP + 2.1 ([r.sup.2] = 0.55, P < 0.05)
(4) DI = 2 ln(SA[R.sub.1:5]) + 4.0 ([r.sup.2] = 0.64, P < 0.05)
Penetrometer resistance (0.06 MPa suction)
At or below 75 mm, the gypsum and the stubble treatments had significant (P < 0.05) effects on the penetrometer resistance of the soil (Fig. 2). For example, at a depth of 75-82 mm, SR G10 plots clearly showed the highest resistance values compared with all the other plots and treatments. By contrast, at greater depths (150-157 and 218-225 mm), the SR G0 plots resulted in the highest penetrometer resistance values, while the SR G10 plots gave the lowest values. At the depth of 218-225 mm, SR G10 treatment resulted in a lower penetrometer resistance than the SB G0 treatment (not significant). This change in effect may be due to the accumulation of both exchangeable and soluble sodium in the SB G10 treatment at this depth.
[FIGURE 2 OMITTED]
Soil bulk density
As with the chemistry of the soil, soil bulk density (Table 4) was significantly (P < 0.05) affected by treatment. Results indicate that by 1997, bulk density was slightly lower in G10 plots than in G0 plots. Stubble treatment did not have a significant effect on the bulk density of the G10 plots. However, there was a significant stubble effect at G0, with bulk density in SB G0 (150-225 mm layer) plots being much higher than in equivalent SR plots.
The soil moisture characteristic curves indicated that at 0-75 mm depth and a suction of 0.003 MPa (field capacity, FC), SR G10 retained approximately 39% moisture, which was greater than (P < 0.05) 36% in SR G0, 35% in SB G10, and 32% in SB G0 (Fig. 3). At 150-225 mm depth, the SB G0 treatment again gave the lowest moisture content (FC); however, unlike 0-75 mm depth, the remaining treatments resulted in similar moisture contents of approximately 39.5%.
[FIGURE 3 OMITTED]
At a suction of 1.5 MPa (permanent wilting point, PWP), SR G0 (0-75 mm depth) resulted in the highest soil water content, followed by SB G0, SR G10, and SB G10. Treatment effects on the PWP moisture content were different at 150-225 mm, where SB G10 had a moisture content (~27%) similar to SR G0. This result corresponded with the accumulation of sodium in SB G10 plots (150-225 mm depth). By contrast, SR G10 had the lowest PWP water content, approximately 21.5%. This result reflected the accumulation of [Ca.sup.2+.sub.s], an increase in EC, and a decrease in SAR for SR G10 treatments at this depth.
The available water holding capacity (AWHC) of the soil was determined by difference in soil moisture retained at FC and PWP. The results (Table 4) indicated that the AWHC at both depths was significantly (P < 0.05) affected by the gypsum and stubble treatments. Under SR, the AWHC increased in G10 plots at both depths compared with G0 plots. In the SB plots, by contrast, the AWHC only increased significantly in G10 plots at 0-75 mm relative to G0 plots (Table 4), indicating that a lot of the gypsum in SB plots had not moved out of the layer at this stage. This was also evidenced by the larger decrease in ESP in SB G10 than SRG10. These findings contrast with the short-term 1996 results, which did not show significant differences in the AWHC between treatments (A. Smith pers. comm.).
Effects of treatments on soil micromorphology
The micromorphological thin sections indicated that there was a gypsum and stubble management effect on soil porosity, biological activity, and major associated structures. The effects of the treatments on surface soil micromorphology are presented in Fig. 4. As the micromorphological properties of the subsoil were only slightly affected by the treatments, subsoil slides are not shown.
[FIGURE 4 OMITTED]
Soil porosity. Gypsum and stubble were found to alter the pore space of the soil in the surface 0-75 mm. The treatment effect was not as pronounced in the B horizon of the soil. At a macro (1:1) scale (0-75 mm depth), the SR plots had greater pore space than the equivalent SB plots (compare Fig. 4b and d with a and c). This result correlates with the low bulk density measurements for the SR treatments discussed earlier.
At 0-75 mm depth, slides of both the SR G0 and SR G10 soils showed some accommodated structural pores (fissures) and some channels leading to small chambers or vughs. By contrast, the SB G0 and SB G10 slides showed some fissures, but channels, chambers, and vughs were lacking. Vesicles or crusting usually indicate raindrop impact. The vegetative cover from the canola crop at the time of sampling may have prevented these features from occurring. Alternatively, evidence of such features may have been lost due to the stripping of material from slides during their preparation.
At 150-225 mm depth (data not presented), the thin sections did not have the macropores that were present in the surface horizon. However, at this depth, SB G0 plots had some small fissures and one infilled channel, while SR G0 plots had small to medium sized fissures that were related to the vertic (shrink-swell) properties of the subsoil.
In the B horizon, the SB G10 treatment had some very small fissures near the surface and also gave a slightly more porous appearance than the SB G0 plot. The SR G10 thin section gave a more porous appearance than the SB G10, SB G0 and SR G0 thin sections.
Biological activity. Significant biological activity, as evidenced by small faecal pellets and roots (which are only visible at high magnification), was found at 0-75 mm in the SR G0, SB G10 and SR G10 plots and also at 150-225 mm in the SR G10 and SR G0 plots. (Data not shown in Fig. 4.) Biological activity was more pronounced in the SR than the SB plots (in particular the B horizon). These biological sources may have contributed to the macropores in the SR G0 and G10 plots.
Major associated structures (cutans and nodules). There was some evidence of void argans (clay coatings indicative of clay dispersion and deposition processes) surrounding fissures and channels. The coatings were less prevalent in the G10 than in the G0 plots. Furthermore, these clay coatings were more pronounced at 150-225 mm than 0-75 mm. A large sesquioxide concretion (8.6 mm diameter) with undifferentiated fabric (Fig. 4b) was seen in the SR G0 thin section (0-75 mm depth), while smaller concretions were present in the other thin sections. Although there was some mottling near the soil surface, mottles were more pronounced in the B horizon of all plots, in particular SB G0.
The high sodium levels in the soil profile of the G0 plots at Natimuk caused the soil aggregates to break down from dispersion, causing other soil management problems such as poor infiltration, water logging, and compaction. These problems could also be inferred from the micromorphological, bulk density, and penetrometer resistance data. The current study aimed to modify the composition of the exchangeable and soluble cations in the soil (with gypsum) and thus reduce levels of clay dispersion over the short and longer terms. The use of stubble management, along with different crop rotations (Jarwal and Rengasamy 1998), was also important, as this was shown to directly alter certain soil physical properties and interact with the gypsum treatments.
After approximately 2.5 years, the gypsum treatments and, to a lesser extent, the stubble treatments, had a significant effect on the composition of the exchangeable and soluble cations and on soil physical properties. The results also indicated interactions between the gypsum and the stubble treatments. Stubble management related changes in soil hydrology (as inferred from micromorphological changes in meso/macroporosity) were also found to have a significant effect on the composition of cations in the A and B horizons of the soil, which in turn affected soil physical properties. Work by Jarwal and Rengasamy (1998) indicated that crop type might also effect the efficiency of the gypsum/stubble treatments.
The rate of gypsum used in this experiment affected both surface and subsurface layers. In both layers the gypsum decreased the levels of exchangeable and soluble sodium, thereby decreasing dispersion (Eqns 3 and 4) and hence improving the stability of clay microaggregates. This led to an increase in the available water holding capacity in G10 plots (0-75 mm SB; 0-225 mm SR) and higher crop yields than on G0 plots (Jarwal and Rengasamy 1998).
The higher crop yields resulted in more plant residue being returned to the soil (Jarwal and Rengasamy 1998); this would result in small increases in organic carbon. This increase in organic carbon further stabilised the soil and thereby increased the AWHC (Fig. 5). If plant residues are not removed, burnt, or oxidised they will aid in building up organic matter, which further improves the soil structure (Tisdell and Oades 1982).
[FIGURE 5 OMITTED]
The improved surface cover under stubble retention has a biological (soil organic matter/faunal activity) and a mechanical effect on the soil (Fig. 6). Soil organic matter was marginally increased by stubble retention (Table 3). This increase may have assisted with soil stabilisation by decreasing clay dispersion. The micromorphological investigations indicated greater soil faunal activity under SR than SB (Fig. 4). This improvement in faunal activity, particularly by meso/macro invertebrates (evidenced by their faecal pellets), may have contributed to increased macroporosity within the surface horizon and at depth. Consequently improved water acceptance (as seen after heavy rain) and the AWHC of the soil were increased. The mechanical effect of stubble occurs via increased surface protection from raindrop impact and hence reduced chance of surface crusting. Thus, infiltration rates are maintained, and the AWHC is improved. Both the biological and mechanical effects improve crop yields, which, in turn, promote through-flow of [Ca.sup.2+.sub.s] into the subsoil.
[FIGURE 6 OMITTED]
Under the reduced surface cover with stubble burning (Fig. 6), there are detrimental effects on soil biological and mechanical properties. Biological activity, as evidenced in the micromorphological investigation, is reduced, which reduces macroporosity. As macroporosity has a major influence on yields (Jayawardane and Chan 1995), yields are concomitantly reduced and hence there is less through-flow of [Ca.sup.2+.sub.s] into the subsoil. Also, without the stubble to protect the soil surface, crusting is greater and the impeding surface layer contributes to reduced water movement into the subsoil (Greene and Ringrose-Voase 1994; Valzano et al. 1997). As a result yields are further lowered and again there is less though-flow of [Ca.sup.2+.sub.s] in the subsoil.
Crop type and sequence
Other studies at the Natimuk site indicated that certain crop types could significantly influence soil properties through a process of biological reclamation (Jarwal and Rengasamy 1998). For example, the roots of certain `break' crops such as legumes and canola may facilitate the leaching of gypsum through the profile (a process known as `biological drilling') (Fig. 7). However, Cresswell and Kirkegaard (1995) concluded that the benefits of biological drilling have not been demonstrated on Australian soils. Alternatively, by reducing the pH of the soil, the break crops may have assisted with the dissolution of calcite and subsequent release of calcium into the soil.
[FIGURE 7 OMITTED]
Combined effects of gypsum, stubble management, and crop type on soil properties
From the above discussion, the successful management of sodic Vertosols in the medium to longer term will generally require the addition of gypsum (at similar rates to that used in the present study), stubble retention, and crop rotations (for biological reclamation to be facilitated). The effects of the gypsum treatments on soil properties in relation to the stubble management practices are illustrated in Fig. 8. The previous sections have demonstrated that there is a significant interaction between the application of 10 t/ha of gypsum, the management of the stubble from the previous crop, and the type of crop used in the rotation (Rengasamy and Jarwal 1998). In general, stubble retention, compared with stubble burning, enhanced the depth of effect of the gypsum treatments on the soil profile. Stubble retention, by protecting macropores at the soil surface and allowing them to connect with other macropores in the subsoil (that resulted from biological drilling and/or biological activity), enhanced the movement of gypsum throughout the profile. Due to potential raindrop impact and less biological activity on the SB plots, there is less opportunity for connectivity between surface and subsurface pores, and hence the movement of calcium from the gypsum is impeded.
[FIGURE 8 OMITTED]
Table 1. Soil profile description from Natimuk Depth (mm) Horizon Description 0-100 A1 10YR2/1w; fine sandy clay loam-light clay; weak subangular blocky structure; peds break with some effort; no effervescence to HCl; few fine roots (1-2 mm); pH 6.5; diffuse boundary to B1 100-160 B1 10YR5/3w; light clay; subangular blocky; peds break with considerable effort; slight effervescence to HCL; few fine roots (<1 mm); pH 7.2; sharp boundary to B21 160-440 B21 10YR6/3w; light-medium clay; subangular blocky structure; peds break considerable effort; strong effervescence to HCl; few fine roots (<1 mm); pH 8.4; sharp boundary to B22 440+ B22 10YR4/4w; light-medium clay; subangular blocky structure; peds break with considerable effort; strong effervescence to HCl; pH 9.2 Table 2. Exchangeable cations, effective cation exchange capacity (ECEC), and exchangeable sodium percentage (ESP) from Natimuk (November 1997) Stubble Treatment Na Ca Mg ECEC ESP (cmol/kg) (%) 0-75 mm SB G0 1.1 5.6 5.5 13.0 8.5 G10 0.1 9.4 3.5 13.7 1.0 SR G0 1.4 5.7 4.8 12.9 10.7 G10 0.7 9.1 3.2 13.8 5.5 150-225 mm SB G0 2.6 7.6 6.6 16.6 14.9 G10 2.2 9.1 5.1 17.0 12.9 SR G0 3.3 6.4 7.4 17.4 18.4 G10 1.2 9.7 6.1 17.9 6.7 l.s.d. (P = 0.05) 0.3 1.6 2.0 5.2 2.4 P < 0.01 P < 0.01 P = 0.02 n.s. P <0.05 n.s., not significant. Table 3. Soluble cations, total cation concentration (TCC), sodium adsorption ratio (SAR), electrical conductivity (EC), pH (water) and organic carbon (OC) from Natimuk, November 1997 TCC, SAR, EC, pH, and soluble cations all measured in 1:5 soil : water; OC, organic carbon Stubble Treatments Na Ca Mg TCC ([mmol.sub.c] /L) 0-75 mm SB G0 0.7 0.1 0.1 0.9 G10 0.2 0.7 0.1 1.0 SR G0 0.5 0.1 0.1 0.8 G10 0.5 0.7 0.1 1.3 150-225 mm SB G0 1.5 0.1 0.2 1.8 G10 1.7 0.1 0.2 2.0 SR G0 1.7 0.1 0.3 2.0 G10 1.2 0.4 0.2 1.8 l.s.d. (P = 0.05) 0.26 0.2 0.12 0.76 P < 0.01 P < 0.05 n.s. n.s. Stubble Treatments SAR EC pH OC [([mmol. (dS/m) (water) (%) sub.c]/ L).sup. 0.5] 0-75 mm SB G0 2.2 0.09 6.3 1.6 G10 0.4 0.17 5.9 1.9 SR G0 1.5 0.09 6.8 1.9 G10 1.1 0.16 6.5 1.9 150-225 mm SB G0 3.6 0.15 7.6 0.3 G10 4.1 0.17 7.6 0.5 SR G0 4.1 0.14 7.5 0.5 G10 2.5 0.22 6.9 0.8 l.s.d. (P = 0.05) 0.6 0.04 0.6 0.24 P < 0.01 P < 0.05 P < 0.01 n.s. n.s., not significant. Table 4. Dispersion index (DI), bulk density (BD), and available water holding capacity (AWHC) from Natimuk, November 1997 Stubble Treatments DI BD AWHC (0-16) (g/[cm. (%) sup.3]) 0-75 mm SB G0 5.5 1.49 17.0 G10 2.3 1.46 22.4 SR G0 4.0 1.48 19.3 G10 1.3 1.42 25.1 150-225 mm SB G0 9.8 1.65 10.4 G10 7.8 1.45 12.7 SR G0 10.8 1.52 12.1 G10 2.5 1.48 18.0 l.s.d. (P = 0.05) 2.0 0.1 3.5 P < 0.001 P < 0.05 P < 0.05
The authors gratefully acknowledge the assistance in statistical analyses of the data by Mr Ross Cunningham and Ms Christine Donnelly. Comments made by two anonymous referees and David Burrow were also appreciated. This project was supported by the Department of Forestry, ANU and the Grains Research Development Corporation. Tim and Janice Sudholz are acknowledged in allowing the use of their land and in carrying out the crop management of the trials and Andrew Smith for use of some data. Assistance with the chemical analysis from John Marsh is acknowledged.
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Manuscript received 17 July 2001, accepted 2 May 2001
F. P. Valzano (ABF), R. S. B. Greene (A), B. W. Murphy (C), P. Rengasamy (D), and S. D. Jarwal (E)
(A) School of Resources, Environment and Society, ANU, Canberra, ACT 0200, Australia.
(B) Current address: Recycled Organics Unit, Building B11b, University of New South wales, NSW 2052, Australia.
(C) Centre for Natural Resources, Department of Land and Water Conservation, Research Centre, Cowra, NSW 2794, Australia.
(D) Department of Soil and Water, University of Adelaide, Glen Osmond, SA 5064, Australia.
(E) Victorian Institute for Dryland Agriculture, Horsham, Vic. 3400, Australia.
(F) Corresponding author; email: Frank. Valzano@unsw.edu.au
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|Author:||Valzano, F.P.; Greene, R.S.B.; Murphy, B.W.; Rengasamy, P.; Jarwal, S.D.|
|Publication:||Australian Journal of Soil Research|
|Article Type:||Statistical Data Included|
|Date:||Nov 1, 2001|
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