Texture-contrast Soils Research Articles

Nitrate leaching loss under annual and perennial pastures with and without lime on a duplex (texture contrast) soil in humid southeastern Australia

SummaryMineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl2) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO3– concentrations.The soil contained more mineral N in autumn (64–133 kg N ha−1 to 120 cm) than in spring (51–96 kg N ha−1), with NO3– comprising 70–77%. No NO3– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l−1 as NO3– initially but < 1 mg N l−1 by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l−1 during winter. Losses of NO3– were small in surface runoff (0–2 kg N ha−1 year−1). In 1995, 9–19 kg N ha−1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha−1 in 1995 and 4–10 kg N ha−1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha−1 year−1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha−1 year−1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha−1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.

Chemical concentrations of overland flow and throughflow from pastures on sloping texture-contrast soils

Shallow drains are increasingly being installed to allow cropping and improve pastures in soils prone to waterlogging. Concentrations and loads of a range of chemicals including nitrate, dissolved organic carbon, and phosphorus were measured in overland flow and throughflow (drainage) from grazed standard and improved pastures in a region of the Adelaide Hills, South Australia, with 544 mm annual rainfall. In low to average rainfall years, nitrate losses from standard pastures were up to 21 times higher in throughflow (up to 0.3 kg/ha.year) than in overland flow. Dissolved organic carbon losses from standard pastures were also highest in throughflow (up to 3.5 kg/ha.year) as were loads of Na, Cl, Al, Fe, K, and Mg. Total P loads were higher in throughflow (0.15 kg/ha.year) than in overland flow. However, P concentrations in throughflow were similar to overland flow (up to 0.5 mg/L). Chemical loads from improved pastures were higher in throughflow than in overland flow. Nitrate, dissolved organic carbon, and P losses from improved pastures were up to 0.8, 8.5, and 0.1 kg/ha.year, respectively. Improved pastures had higher dissolved organic carbon concentrations (14 mg/L) and nitrate concentrations than either the standard pastures or those reported off some dairy pastures in the region. Nitrate concentrations were highest in throughflow in subsurface tube drains below the improved pastures (up to 67 mg/L).

Water quality of gully drainage from texture-contrast soils in the Adelaide Hills in low rainfall years

The volume and quality of drainage water in a gully cutting through a series of waterlogged, saline, sodic, and sulfidic Xeralfs in the Adelaide Hills, South Australia, was studied over 3 years. This was done to gain a better perspective of the relative quantities of contaminants being exported from agricultural catchments in low rainfall agricultural environments. It was found that in low rainfall years, when little overland flow occurs and gully flow is predominantly groundwater discharge and throughflow, loads in the drainage gully were up to 41 kg/ha.year of sodium and 2 kg/ha.year of sulfur. Losses of sulfur, magnesium, and calcium followed a similar trend to sodium losses and could be predicted with significant accuracy. The losses of phosphorus (5–7 g/ha.year) and nitrate (<2 g/ha.year) were less predictable. Phosphorus concentrations were of environmental concern each year whereas nitrate concentrations were only above environmental guidelines in the driest year. All phosphorus in the gully drainage was transported in the dissolved form. Dissolved organic carbon concentrations were usually >26 mg/L and will be costly to treat if used for public water supply.

Decreases in Colwell bicarbonate soil test P in the years after addition of superphosphate, and the residual value of superphosphate measured using plant yield and soil test P

Decreases in Colwell bicarbonate soil test P in the years after applying single (ordinary) superphosphate, and the residual value of superphosphate, was measured in a long-term field experiment on a duplex (texture contrast) soil (sand over lateritic ironstone gravel clay sand at 10–15 cm), at Wongan Hills, Western Australia, typical of many soils used to grow crops in Western Australia. Ten levels of P (0–91 kg P ha-1) were applied once only in late May to different plots in different years from 1988 to 1993. Wheat (Triticum aestivum), or lupin ( Lupinus angustifolius)) were sown in late May of each year, when the P treatments applied that year were banded (drilled) with the seed. Soil samples were collected each June to measure soil test P. Seed (grain) yields of the crops were measured each December. The residual value (RV) of P applied in previous years was calculated relative to P applied in the current year, using grain yields (RVyield) and soil test P (RVsoil). Soil test P measured on soil samples collected in June was related to yields measured in December that year to provide soil P test calibrations. Relative to P applied in the current year, soil test P decreased by between 15 to 30% for P applied one year previously, by 25 to 30% for P applied three years previously, and by 60 to 70% for P applied six years previously. Soil test P was affected by spatial variation, and it also varied in the different years, for P applied in the current year, one year previously, two years previously, etc. Compared with P applied in the current year, mean RVyield determined in the different years decreased by about 40% one year after P application, followed by a further 20% decrease for P applied two years previously, followed by a further 20% decrease for P applied three to five years previously. Relative to current P, RVsoil decreased by about 25% one year after P application, followed by a further 20% for P applied two years previously, followed by a further 10% for P applied three years ago, and followed by a further 6% for P applied four and five years ago. As measured in the different years, the soil P test calibration varied between years for P applied one, two etc. years previously. This was so even when the same cultivar of wheat was grown at the same site in different years.

The Deterioration of Tall Wheatgrass Pastures on Saline Sodic Soils

The deterioration of sown tall wheatgrass (Elytrigia elongata) growing on 3 sodic saline soils was investigated in the Laprida basin, in the center of the Buenos Aires province of Argentina. These soils are known to have poor drainage and high saline levels and support different species associations. On each soil type the native grassland was compared to sown wheatgrass, in terms of plant density and cover and soil physical and chemical characteristics. The 3 soil types reacted differently to tillage. Tillage had little impact on soil type A (typic Natraquoll), a poorly drained soil with a loamy A horizon (14 cm) overlying a silty clay loam. Soil type B (typic Natraquaf), a wet texture contrast soil with bleached horizons has characteristics that are likely to severely limit plant growth. The sowing of wheatgrass increased ground cover by live vegetation on this soil type. This contrasted with soil type C (typic Natralboll), a saline soil with an organic matter-rich but thin (8 cm) A horizon. In this soil, the plant density declined and other components such as pasture cover also declined with time. This pasture deterioration was attributed to several soil factors including decreased organic matter content and increased soil bulk density. It was concluded that the varied performance of wheatgrass sown pastures was a function of the different inherent characteristics of the soils.

Fate of nitrogen-15-labelled urea applied to wheat on a waterlogged texture-contrast soil

Fertilizer N losses on waterlogged texture-contrast soils (sand over clay) are usually attributed to denitrification and leaching. In this experiment, waterlogging events were imposed on 25-cm-diameter, 75-cm-long columns of texture-contrast soil planted to wheat (Triticum aestivum L.). Treatments included 6, 12, and 18 d of aerobic conditions between fertilization using 15N-labelled urea (5.0 g m-2) and 3-d waterlogging events. Denitrification, measured by 15N-chamber methods, was the largest loss mechanism identified during waterlogging. Dinitrogen was the main product of denitrification. Longer aerobic periods prior to waterlogging increased denitrification losses from 3.1 to 9.4% of the urea-N added. Leaching losses of 15NO3 (3.1 – 5.3%) between 20 and 70 cm were less than denitrification fluxes. Total15 N recovery in the wheat plants and soil was 87.9% before waterlogging and decreased to 72.3% after waterlogging. The balance of added fertilizer N was reasonably well reconstructed if it is assumed that NH3 volatilization accounted for the early loss of 12% of the urea-N, and that in addition to the measured surface fluxes of N2 + N2O, some of these gases remained entrapped in the soil. This study confirms that texture-contrast soils cropped to wheat have a high potential for N losses through denitrification and leaching during waterlogging events.

Chemical losses off dairy catchments located on a texture-contrast soil: carbon, phosphorus, sulfur, and other chemicals

Runoff (overland flow and A/B horizon interflow) from 2 grazed dairy pastures at Flaxley, South Australia, accounted for <15% of April{October rainfall in 1996; 88{96% of runoff was overland flow. A range of chemicals, including carbon (C), phosphorus (P), and sulfur (S), was measured in runoff As much as 2·3 kg P/ha, 10·7 kg/ha of total dissolved C, and 1·8 kg S/ha was lost from the catchments in that year. Loads of other chemicals ranged from 0·6 g/ha (boron) to 39·8 kg/ha (aluminium). Over 92% of P, 76% of total dissolved C, and 93% of S was lost in overland flow. Between 50% and 60% of P, and 60% and 85% of S, was in the dissolved form; 64-96% of total dissolved C was dissolved organic C. Other chemicals varied from 0% (aluminium) to 97% (sodium) as the dissolved form. Relatively high losses of P and dissolved organic C are important to a dairy industry which is under increasing pressure to demonstrate minimal environmental impact from farming practices.

Phosphorus movement down a toposequence from a landscape with texture contrast soils

Pedological processes culminating in physical and chemical differences to the soil profile down a toposequence also changed the migrating potential of phosphorus (P) within the landscape. Considerable erosion had occurred resulting in a large movement of soil from the upper to the lower slopes. This, in turn, had led to a decrease in profile depths on the upper slopes and an increase on the lower slopes. We found that in the upper parts of the toposequence there was enhanced macropore or bypassing flow resulting in a greater and deeper leaching of P compared with the lower slopes. The P that moved was almost entirely in the dissolved form and clearly originated from commercial phosphate fertiliser that had been added to the soil surface immediately prior to the start of irrigation. We could find no evidence to support the commonly held view that P often moves through soil in association with very fine clay-sized particles. When considering land management options for reducing phosphate movement in catchment areas, our results suggest that the upper parts of the landscape need to be given special consideration.

Earthworms in some Tasmanian forest soils in relation to bioturbation and soil texture profile

Soil properties and earthworm population density were examined for 5 forest soils derived from Silurian-Devonian sandstones (Mathinna Beds) in north-eastern Tasmania. The soils occur along gradients of altitude, rainfall, and forest type; they include 2 with texture-contrast and 3 with gradational soil profile types. The density and biomass of the most abundant earthworm species Megascolex montisarthuri, and of all earthworm species combined, were found to be greater in gradational than in texture-contrast soils. A greater proportion of the earthworms in gradational soils than in texture-contrast soils was found to occur at soil depths exceeding 10 cm. The contrast was most pronounced between the 2 texture-contrast soils and the single gradational soil that occur under dry eucalypt forest. This paper explores the hypothesis that bioturbation of surface and subsurface layers by earthworms is an important mixing process that in gradational soils outweighs the counter tendency for soil particles to sort and thus form texture-contrast profiles.

Fallow management, soil water, plant-available soil nitrogen and grain sorghum production in south west Queensland

The effects of tillage frequency (conventional, reduced and zero), primary tillage implement (disc, blade and chisel plough), stubble management (retention and removal), gypsum application, and paraplowing were examined with respect to soil water storage, soil nitrate accumulation, crop establishment, crop growth, grain yield and grain nitrogen content for 4 successive sorghum crops on a sodic, texture-contrast soil in south west Queensland. Retention of sorghum stubble (v. removal) produced an increase in mean yield of sorghum grain of 393 kg/ha, due to increased soil water extraction and increased water use efficiency by the following crop. The highest mean yield occurred after reduced blade tillage with stubble retained. Zero tillage with stubble removed gave the lowest mean grain yield. Zero tillage always had the lowest quantity of soil nitrate-nitrogen at sowing. In one fallow, increased aggressiveness of primary tillage (disc v. blade plough) increased the quantity of nitrate-nitrogen in the top 60 cm of soil at sowing. These effects on available soil nitrogen did not result in corresponding differences in grain nitrogen content. Results indicate that for optimum fallow management on this texture-contrast soil in south west Queensland, sorghum residues should be retained, tillage frequency should be reduced, but not to zero, blade ploughing should be preferred to discing, and gypsum application should not be practised.

Crop production on duplex soils: an introduction

Duplex or texture-contrast soils occur over about 60% of the agricultural areas of south-west Western Australia. Annual crops of wheat, barley, oats, and lupins predominate on these soils, grown in rotation with annual pastures. The climate is characterised by cool, wet winters and hot, dry summers. Crop production is restricted to the winter and spring and is limited by waterlogging in the wet winter months and by water shortage during grain filling in spring. Research on crop production on duplex soils has been undertaken for the past 8 years by a collaborative team from the CSIRO Dryland Crops andyoils Program and the Western Australian Department of Agriculture. This research has been focussed on 3 sites at which processes limiting crop production on duplex soils have been highlighted. This special issue was initiated to summarise that research and to put it in its regional and national perspective. Additionally, opportunity was taken to compare and contrast experiences both within Western Australia and throughout Australia, and to draw out management options for crop production on duplex soils.

Subsoil macropore space of a transitional red-brown earth after either deep tillage, gypsum or both .II. Chemical effects and long term changes

The management of sodic texture-contrast soils of the riverine plains of S.E. Australia for crops other than rice is difficult because improved subsoil structure often deteriorates after a few seasons of irrigated cropping. This research aimed to improve understanding of the processess which cause deterioration of macropore space (volume and permeability of air-filled soil at -10 kPa matric potential) as well as providing some guidelines for improved management. A transitional red-brown earth was ameliorated by eight different treatments and compared with an unameliorated control treatment in a field experiment. The treatments included surface gypsum application, deep ripping after gypsum application, five designs of gypsum-enriched slots and traffic-free beds after addition of gypsum and deep ripping. The macropore space of the subsoil after initial winter cropping and summer fallow is described from measurements on soil cores collected from the experiment. An index of electrochemical stability (EC/ESP) is proposed which explains the loss of macroporosity of cultivated subsoil in the absence of significant soil stressing by wheels. Considerable loss of macropore volume and permeability after the first summer crop could be associated with loss of soluble gypsum, some increases of exchangeable sodium and compression by lateral swelling of the uncultivated soil from between the slots. These changes were compensated by an increase in the number of vertical fissures, directly observed and deduced from measurements of water entry into whole plots. Thus, management of the balance of soluble salts is essential for the long-term productivity and profitability of such systems of amelioration using deep tillage zones and gypsum application. This is in the absence of significant compaction under wheels or opportunities for addition or organic matter and formation of biopores by roots and soil animals. The relief of lateral swelling of the uncultivated B horizon by the loose slots and formation of extra vertical fissures is a process which may provide long-term benefits and deserves further research.

Modeling and Field Measurements of the Effect of Nitrogen Source on Nitrification

AbstractThe movement of N in relation to water movement and plant uptake is, in part, determined by the rate of nitrification. Nitrifying bacteria are known to be inhibited by low pH. A laboratory incubation and a field experiment were conducted to study nitrification of NH4 supplied by ammonium sulfate (AS), diammonium phosphate (DAP), and urea, N sources that produce environments with different pH, particularly when applied to moderately acidic, poorly pH‐buffered soil. The field site was located on a texture contrast soil (sandy, thermic Natric Durixeralf) at Merredin, Western Australia. The incubations were performed on a sample of the surface 100 mm of this soil. The initial pH and the pH‐buffer capacity of the sample were 5.4 and 4 mmol kg−1 (pH unit)−1, respectively. Nitrification rates were found to vary with the inherent alkalinity of the N source, viz., urea > DAP > AS. The nitrification process was modeled taking into account the effect of pH on nitrifier growth and activity. A linear relation in the model between pH, and both the specific growth rate and activity of the nitrifiers accounted for most of the variability between N sources. In the field experiment, 15N remained largely in nonnitrate form for the first month after application, presumably because of low temperatures, but after 53 d production of NO3 was greater with urea than AS. With the slow rate of nitrification, the leaching of NO3 was minimal.

Readjusting the water balance to combat dryland salting in southern Australia: Changing the hydrology of a texture contrast soil by deep ripping

Dryland salting is one of the biggest problems in dryland agriculture in southern Australia. It has been caused by the replacement of the original, deep-rooted, perennial trees and shrubs with shallow-rooted, annual crops and pastures. The accompanying decrease in evapotranspiration has caused an increase in deep infiltration to the groundwater. The rising groundwater has in many areas been salinised through mobilisation of salts previously stored in the regolith above the groundwater table. The effect on agriculture where such saline groundwater rises to or close to the surface is disastrous. To remedy the problem deep infiltration must be reduced again, preferably by increasing plant water use and at the same time increasing agricultural production. In this paper details are presented of a study in western Victoria of the relative effects of conventional tilling and deep ripping on water movement under, and yield of, phalaris and lucerne pastures on a texture contrast soil. Deep ripping reduced water logging and thus increased lucerne survival. Deep ripping increased penetrability to roots. It appeared to increase yield of both lucerne and phalaris significantly, and thus their water use. Deep ripping appeared, however, to decrease run-off and increase lateral flow to preferential flow channels leading downward; thus deep ripping appears to also increase deep infiltration. In addition it was observed that on this particular texture contrast soil the first major throttle to downward flow of water is not at the top of the B horizon but near the top of the C horizon. This would have considerable ramifications in terms of soil management.

Influence of working depth of a curved rigid tine on the mixture of fragments produced by deep ripping a texture-contrast soil

A curved, rigid tine with a 50 mm wide point was used to deep rip a texture-contrast soil at different depths of working. The soil had a sandy clay loam A horizon, about 90 mm deep, over a dense clay B horizon; both horizons were drier than their lower plastic limit when ripped. The depth of working varied from 100 to 500 mm and the analysis was done on the loose soil from the lower part of the trough formed by the tine, below the lower boundary of the A horizon. The size and horizon-of-origin of the fragments were measured and their volume recorded as a proportion of the total volume at the water content when ripped. The smaller (0·5 to 2 mm) fragments from the A horizon moved more easily towards the bottom of the trough, but their proportion declined as working depth increased. Fragments from the B horizon with diameter less than a tenth of the point width declined with working depth, whereas soil from the same horizon with more than a tenth of the point width increased with working depth. These different size classes of fragments may have been produced by different soil failure processes induced by the tine. Below a depth of 300 mm the mixture had a relatively constant composition; this depth seemed to correspond to the “critical depth” of working of the tine. The amount of mixing of soil from the two horizons was more than was anticipated from initial visual inspection of the contents of the trough.

CHARACTERIZATION OF WATER ENTRY INTO A SOIL WITH A CONTRASTING TEXTURAL CLASS

Parameters characterizing water entry into a texture contrast soil (loamy sand over clay) were obtained from measurements along a transect. Spatial variability of selected infiltration parameters was studied using geostatistics and frequency distribution statistics. The occurrence of transmission macropores, stained with methylene blue, was recorded and their influence on measured parameters assessed. Sorptivity measured at a small suction (−100 mm potential), which is not influenced by macropores >0.3 mm equivalent diameter, exhibited slight spatial dependence, whereas in situ steady-state ponded infiltration rates had no spatial dependence. Cylindrical transmission macropores with measured diameters greater than 2 mm strongly affected the magnitude and frequency distribution of “detached” Ksat values, but did not affect in situ ponded sorptivity, presumably because the surface area available for adsorption was not increased significantly by pores of this size. Excluding all pores greater than 0.3 mm equivalent diameter, however, reduced sorptivity by 40%. The results indicate that in modeling runoff processes there is a need to discriminate between macropore and matrix contributions to the variability of infiltration parameters in the field.

Thesis abstracts

Bioturbation, rainwash and texture contrast soils: An evaluation of transporting processes on soil genesis in the Sydney Basin G. S. HumphreysSome aspects of the role of bioturbation in soil formation in south‐eastern Australia P. B. MitchellPlant water relations and community water use in a Banksia woodland near Perth, Western Australia Jonathan DoddThe pre‐mining assessment of a coal mining lease north of Esperance, Western Australia Paul G. van der Moezel

The size and horizon of origin of fragments produced by deep ripping texture contrast soils

Two texture contrast soils were cultivated by deep ripping when they were drier than their lower plastic limits. The size distribution and soil horizon-of-origin of the resulting fragments were measured. One soil, a transitional red-brown earth, had either been previously uncultivated below the A horizon or had been deep ploughed and gypsum added two years previously. There was much fragmentation and mixing of soil from both of the horizons. Fine soil (<2 mm diam.) from the A horizon reached the lower depths of the trough made by the ripping and coarse soil from the B horizon (>50 mm) was brought to near the surface. The fragment size distributions were characteristically bimodal. Fragments of the fine mode (<2 mm) came mainly from the A horizon, fragments of the coarse mode (11-25 mm or larger) came mainly from the B horizon. In the laboratory, clods from the deep ripped soil were crushed at the same low water potential (air dry). The crushing energy per unit mass (specific crushing energy) was inversely proportional to the normalized geometric mean diameter of the fragments produced. Suggestions are made for modelling the effects of deep ripping.

Residual value of phosphorus from superphosphate for wheat grown on soils of contrasting texture near Esperance, Western Australia.

The residual value for wheat of phosphorus (P) from superphosphate was measured in field experiments on two texture-contrast (duplex) soils near Esperance, Western Australia. Superphosphate was applied to previously untreated plots once only, in 1980, 198 1, 1982 or 1983. The residual value of this P was measured in 1983 relative to P applied in 1983. Results were similar for both soils. Superphosphate applied in previous years did not produce the same yield as superphosphate applied in the current year. As calculated from yield response, relative effectiveness was 65, 42 or 32% after 1, 2 and 3 years, respectively. Yield depended on P content of plant tops, and this relationship was independent of time of P application. As the period of contact of P with the soil increased, less P was taken up by the plants, and this limited yield. As calculated from the P content of plant tops, relative effectiveness was 60, 30 or 23% after 1, 2 and 3 years, respectively. The amount of P extracted from the soil by 0.5M sodium bicarbonate decreased by about 54% from day 210 to day 575 after application of superphosphate, by a further 35% from day 575 to day 940, and by 15% from day 940 to day 1305. Bicarbonate-extractable P determined on soil samples collected mid January 1983 gave a good prediction of yields measured in the spring of that year

Range condition assessment in bladder saltbush (Atriplex vesicaria) communities.

Factors contributing to changes in the condition of saltbush communities (Atriplex vesicaria) in the Riverine Plain and Barrier Range regions of New South Wales were measured under a variety of seasonal situations. Groups of eight plots, representing a range of past grazing intensity, were established at each location and measurements were made of species biomass, canopy cover and frequency, forage availability and soil fertility. In both regions, high grazing intensity was characterized by the elimination of the saltbush (A. vesicaria) and an increase in other species, such as Astrebla (mitchell grass), Sclerolaena spp. (copperburrs), annual Atriplex spp. and a wide range of ephemeral species. These changes were best characterized by canopy cover measurements which gave a quantitative assessment of the vegetation changes (in contrast to frequency) and gave values that were less seasonally variable than biomass. Up to 83 species were recorded, but these were aggregated into approximately 9 groups to simplify the collection and analysis of data, without loss of information. On the Barrier Range site, the A. vesicaria was replaced by palatable species, so that there was little loss of overall forage production. Similarly, there was little evidence of loss of soil fertility, as measured by various measures of soil nitrogen, available phosphorus and organic carbon. There was no erosion on these sites, although this may occur on other saltbush communities that grow on texture contrast soils. On the basis of these results, four separate indices of condition are proposed for saltbush communities. These are based on the measurement in the growing season of the canopy cover of major perennial and biennial species or species groups. They are (i) the relative cover of A. vesicaria (the major observable change in these communities), (ii) the relative total cover of desirable forage species (an index of forage productivity), (iii) percentage similarity (an index of community change for conservation purposes), and (iv) the relative area of eroded soil surface.