Scientific registration n : 2619 Symposium n : 41 Presentation : poster Claying of Water Repellent Soils: Effects on hydrophobicity, organic matter and nutrient uptake. Apport d'argile en sols sableux imperméables : effets sur l'hydrophobicité, la matière organique et le prélèvement d'éléments nutritifs CARTER D.J. 1, GILKES R.J. 2, WALKER E. 2 1 Agriculture Western Australia, 444 Albany Highway, Albany, Western Australia 6330 2 Department of Soil Science and Plant Nutrition, Faculty of Agriculture, University of Western Australia, Nedlands, WA, Australia 6009. Introduction In Western Australia, water repellent soils are very common on the sandplains of the west and south coastal soils. Over one million hectares have been identified as water repellent on the south coast alone (Summers, 1987). The non-wetting soils aggravate the seriousness of land degradation by increasing run-off, delaying germination, encouraging undesirable pasture species and prolonging the susceptibility of these soils to wind erosion. On a production basis, the non-wetting soils delay seeding and therefore shortens the effective growing season. This can occur one in three seasons in southern Australia (Wetherby, 1984). One solution to the problem has been demonstrated in South Australia with clay incorporation into the topsoil (Obst, 1994). The addition of up to 200 t/ha of dispersible clay to water repellent sand dunes has been effective in reducing the repellency and improving pasture production for at least thirty years. These soils are not suitable for cropping and therefore the benefits to crops have not been demonstrated. The Western Australian work was to investigate the possibility of using the South Australian technique of claying with crops and determine the efficiency of clay rates on yields. Methods A non-wetting soil was selected in 1991 for a randomised block experiment to investigate the effectiveness of clay, wetting agents and lime on overcoming water repellency. The site, about 70 km north of the south coastal town of Albany at Woogenellup, was in an aeolian dune system 10 km south of the Stirling Ranges. The average annual rainfall is about 500 mm. 1
The soil was a deep siliceous sand of the Kojaneerup series (Stoneman, 1990) with greater than one metre depth of sand overlying gravel and with clay at greater depth. The soil was classified as Uc2.21 (Northcote et al., 1975). The water repellency has a MED (Molarity of Ethanol Droplet test) value of four and rated as severe repellency (King, 1981). The site originally had a mixed woodland and heath plant community before clearing in 1972. The native vegetation was a mixture of banksias, depaupurate eucalypts and other myrtaceous plants. Since clearing, the site has been rotated between cropping and annual pastures, in a 1:4 rotation. The site was covered with a poor growth of capeweed (Arctotheca calendula) and grasses prior to the 1991 start of the experiment. From 1991 to 1994 inclusively, the treatments were applications of 100 t/ha dispersible yellow clay, 2.5 t/ha "A" grade agricultural limesand, 50 l/ha Wettasoil (Wettachem Pty Ltd) blanket sprayed, 8 l/ha Wettasoil banded in seeding furrows (equivalent to 50 l/ha but only in the furrows) and a nil treatment. A sub-plot treatment of 2.5 t/ha limesand was applied to each treatment. All treatments were applied once in 1991. The experimental design was plots of 20x6 m in four blocks, the five treatments randomised within each block. The sub-plot treatment was randomised on the left or right half of the plot. In the summer of, the lime and two wetting agent plots were changed to either 100, 50 or 25 t/ha clay treatment, using the same clay as the original 1991 clay. The two cropping sites were used in this change of treatments. The pasture site remained true to the original (Carter and Hetherington, 1994). The crops on the two cropping trials were rotated alternatively as in the past, so that the species were both represented in each year of the experiment. Full stubble retention and direct drilling with a tyned or disced combine were the cultivation practices used. The clay was spread by hand to obtain a uniform distribution. The incorporation details and clay description are included in the previous paper (Carter and Hetherington, 1994; Dellar et al.; 1994) as is the details of crop and soil measurements. Tissue samples of were taken in from lupin and barley crops to determine the nutrient uptake efficiency from the various treatments. Results The yields of crops from 1991 through to 1996 are presented in Table 1. The years up to 1994 include the wetting agent and lime results, after which the clay rates are shown. The comparison of nil and 100t/ha clay addition (1991 application) are shown in Figure 1. On average the yield increase in barley over the six cropping years is 71%. In 1996, the yields of barley were higher in the clay applied plots compared to the 1991 application. The lesser amounts of clay (50 and 25t/ha) increased barley yields but had greater influence on the lupin yields. Neither were as good as 100t/ha. The one crop of canola in 1994 coincided with a poor year and rabbit damage, but the clay treatment was significantly better than the other amelioratives. After 1994 rabbits were excluded from the plots and it was then possible to get lupins through to maturity and harvesting. Table 1. The yields of grain crops (kg/ha) on various treatments to ameliorate water repellency of a Woogenellup non-wetting sand. (Wetta = wetting agent 50l/ha blanket 2
spray, 8l/ha banded, lime = 2.5t/ha, clay is subsoil with 35% clay, added at rates indicated in Table). Crop YEAR 100t/ha Clay 50L/ha Wetta 8L/ha Wetta Lime Nil BARLEY 1991 1992 1993 1994** 1857 3472 2583 713 1481 2411 1481 244 1324 2056 1617 80 1481 1617 1933 157 1514 1806 2022 108 100t/ha Clay 1991 100t/ha Clay 50t/ha Clay 25t/ha Clay Nil 1996 2722 3594 2904 4049 1796 2467 1656 2518 1493 1552 100t/ha Clay 50L/ha Wetta 8L/ha Wetta Lime Nil CANOLA 1994** 472 151 109 304 318 100t/ha Clay 1991 100t/ha Clay 50t/ha Clay 25t/ha Clay Nil LUPINS 1996 2561 1776 2414 1767 ** very poor year with extensive rabbit damage 2353 1646 1972 1311 961 1082 The wetting characteristics and organic matter values are shown in Table 2. The clay clearly reduced the water repellency rating (MED King, 1981) with the new application of clay at 100t/ha having the greatest decrease. The MED of the 1991 application showed an increase in MED, which may be anomalous because it was the first significant rise in MED value for this treatment over the six years after the initial application. The increase in MED value in depth was significant for all treatments, but there were differences between treatments. The nil treatment was still higher in water repellency at 100mm than the treated soils. The organic matter levels in the top 50mm were higher in the clay treated soils than the nil treatment. This elevated OM level was also significant at the 50-100mm depth, indicating that the clay supported better plant growth and increased input of organic material into the soil. The microbial activity was measured as biomass carbon by Dr. Margaret Roper (C.S.I.R.O. Perth, Western Australia) and was found to be 198 µg/g soil and 60.9 µg/g soil for the clay and nil treatment respectively. 3
Table 2. Soil measurements of MED (King, 1981) and percentage organic matter (loss on ignition method) in the soil surface after treatment with various rates of clay on a water repellent Woogenellup soil sampled in March 1997. Soil Attribute Treatments Nil 100 t/ha 1991 100t/ha * 50 t/ha* 25 t/ha* sed MED 0-50mm 3.7 2.3** 0.7 2.7 3.2 0.21 (t) MED 50-100 3.2 2.6 2.5 2.9 3.4 OM% 0-50mm 2.0 3.1 3.3 2.6 2.6 0.22 (t) OM% 50-100 1.3 2.8 2.9 2.0 2.1 *clay applied, (t) is treatment standard error (sed) **MED value in 1996 was 1.4 for this treatment, all other treatments had MED values similar to those in the above table. The nutrient status of the crops was investigated in (Table 3). The plants, sampled late in the season at the milky dough stage, show that the total uptake of nutrients (potassium and phosphorus) was greatly influenced by the presence of clay, which had its major influence on total dry matter production. This dry matter increase is shown by the yields in Table 1 and increased plant numbers in Table 3. The potassium concentration in the tops was also influenced by the presence of clay, but phosphorus was not, as indicated by the uniform concentration on all treatments. Critical levels of nutrients could not be determined at the late stage of sampling, but it was thought that the K values on the nil plots were very low and could be deficient. Table 3. The results of nutrient analysis of whole tops (g/sq. m and % dry basis) of barley and lupins grown on Woogenellup water repellent sand with various clay treatments. Plants were sampled at the milky dough stage on 20/10/95. Treatment Potassium Potassium Phosphorus Phosphorus Barley Plants/sq.m g/sq. m %db g/sq. m %db 100 t/ha 1991 219 9.97 0.69 2.63 0.18 100 t/ha* 196 11.66 0.74 2.92 0.19 50 t/ha* 161 4.27 0.52 1.65 0.20 25 t/ha* 141 3.93 0.49 1.76 0.22 0 t/ha 122 2.73 0.47 1.30 0.23 Lupins 100 t/ha 1991 73 7.5 0.80 1.76 0.19 100 t/ha* 64 5.81 0.71 1.34 0.18 50 t/ha* 58 4.4 0.57 1.32 0.18 25 t/ha* 53 2.82 0.54 0.96 0.19 0 t/ha 37 2.87 0.56 0.93 0.2 * clay applied 4
Figure 1. Barley yields (kg/ha) on 1991 clay-amended soil (100t/ha) and nil treatment at the water repellent Woogenellup site (1991 to 1996). Annual rainfall in each year of crop arranged in ascending order. 4000 Yield (kg/ha) 3000 2000 1000 Clay (100 t/ha) Nil 0 294 (94) 320 (91) 352 (96) 415 (95) 464 (93) 520 (92) Rainfall mm and Year The soil was analysed for nutrient status in 1996 (Table 4) prior to seeding. Organic carbon, nitrogen and phosphorus distributions across treatments and with depth were similar in that they reflected the increased levels with the addition of clay to the topsoil. The results of the potassium analysis were different from the above elements. The accumulation in the nil treatments at depth (50-100mm) was most noticeable. The clay treatments were variable, with only the 50t/ha having a depressed level. Figure 2. Moisture retention curve for a clayed Woogenellup soil compared to the water repellent soil. Soil sampled to 50mm and 100mm depth. 14 Moisture (% gravimetric) 12 10 8 6 4 2 Nil 0-50mm Nil 50-100 Clay 0-50 Clay 50-100 0 0 0.25 0.5 0.75 1 1.25 1.5 Matric Potential (MPa) 5
The moisture retention characteristics of a clayed soil (100t/ha applied in 1991 and sampled in ) showed no real improvement in water holding capacity due to the clay addition (Figure 2). This would suggest that the addition of clay to the sandy soil has not changed the matric potential of the sand or that it cannot be determined by this method due to the small amount of clay added or the variability of the samples. Table 4. Soil nutrient levels of water repellent Woogenellup grey sand, sampled 29/5/96 at two depths 0-50mm and 50-100mm. LOI is loss on ignition, organic carbon was determined by Walkley Black method and total potassium by XRF. Treatment Depth LIO % Org C % N Total % P Total K Total % (mm) ppm 100t/ha 91 0-50 3.2 1.2 0.065 79.8 0.057 50-100 2.6 1.0 0.051 62.5 0.035 100t/ha 95 0-50 3.5 1.2 0.065 85.0 0.075 50-100 2.7 1.0 0.051 60.0 0.035 50 t/ha 95 0-50 2.8 1.1 0.060 72.3 0.028 50-100 2.5 1.0 0.046 52.5 0.020 25 t/ha 95 0-50 2.6 1.0 0.057 76.0 0.063 50-100 2.4 0.9 0.046 60.5 0.058 0 t/ha 0-50 2.1 0.9 0.042 70.5 0.023 50-100 1.6 0.7 0.030 37.5 0.108 The particle size analysis of clayed soils revealed that some movement of the added clay might have occurred from the top 50mm to the next 50 mm (Table 5). This was noticeable only on the continuously cropped 1991 application and did not occur on the pasture site. Table 5. The proportion of clay in the topsoil (%) of clay amended water repellent sands at Woogenellup, sampled 19/5/97. Clay Treatment Depth 0-50mm 50-100mm 100t/ha 1991 cropped 3.0 3.1 100t/ha 5.0 1.9 50t/ha 1.7 1.2 25t/ha 1.5 1.4 Nil 0.9 0.9 100t/ha 1991 pasture 4.5 1.5 Nil 1.4 1.2 Conclusions The results of this study has shown that the addition of clay to water repellent soils has improved the wettability of these soils and in turn the production from these soils. The mechanism by which this is achieved is multi-faceted with improving the uniform wetting profiles of the soil as the chief contributor. This was previously shown to increase the 6
effectiveness of herbicides and improve establishment of crops (Blackwell et al., 1994; Carter and Hetherington, 1994). Further studies reported here have shown that the clay does not increase the water holding capacity of the soil by changing the matric potential, but allows more of the soil to wet up. This therefore opens up more of the soil volume to root exploitation. This is exemplified by some nutritional benefits of adding clay to the soil, particularly the uptake on potassium. The potassium levels in the soil would suggest that the clay is both holding more K as well as wetting up more of the soil so a greater root volume can be explored. This results in the greater total amounts of K in the plant tops. Improved crop growth has also increased soil organic matter and total nitrogen levels. Anecdotal evidence on this site and other broadacre clay application sites show that the roughness obtained with the addition of clay and also the extra soil strength imparted, greater control of wind and water erosion is obtained. Other field evidence would also suggest this (Harper and Gilkes, ). The eluviation may limit the longevity of the amendment but at this stage it seems to be a problem associated with a continuous cropping system. Long term trials will monitor this possibility. Acknowledgments Rob Hetherington is acknowledged for all his technical assistance to the project on claying soils. The Grains Research and Development Corporation and the Wool Program within Agriculture Western Australia, whose funds are gratefully acknowledged, supported this study. John Cooper and his sons, Grant and Max, who have supplied the site at Woogenellup and supported the concept of claying, have enthusiastically followed the study. References Carter, D.J. and Hetherington, R.E. (1994) Claying of water repellent soils on the South Coast of Western Australia. In «Soils 94» Proc 3 rd Triennial W.A. Soil Science Conf., Broadwater Resort Busselton, Sept. 1994, 193-196. Blackwell, P. S., Morrow, G., Nicholson, D., Wiley, T., Webster, A., Carter, D. J., and Hetherington, R. E. (1994). "Improvements to crop yield and pasture production on water repellent sand by claying in Western Australia, 1991-1993; including comparisons to surfactants and limesand." Proc. 2nd National Water Repellency Workshop, Perth, Western Australia, August 1994. Dellar, G. A., Blackwell, P. S. and Carter, D.J. (1994). "Physical and nutritional aspects of adding clay to water repellent soils." Proc. 2nd National Water Repellency Workshop, Perth, Western Australia, August 1994. Harper, R. J. and Gilkes, R.J. (1994) Hardsetting in the surface horizons of sandy soils and its implications for soil classification and management. Aust. J. Soil Res. 32, 603-19. King, P. M. (1981). Comparison of methods for measuring severity of water repellence of sandy soils and assessment of some factors that affect its measurement. Aust. J. Soil Res., 19, 275-85. 7
Northcote, K. H., Hubble, G. D., Isbell, R. F., Thompson, C. H. and Bettenay, E. (1975). A Description of Australian Soils. CSIRO, Wilkie Pty. Ltd., Clayton, Victoria. Obst, C. (1994). "Non-wetting Soils: Management problems and solutions at 'Pineview', Mundulla." Proc 2nd National Water Repellency Workshop, Perth, Western Australia, August 1994. Stoneman, T. C. (1990). An introduction to the soils of the Albany Advisory District - descriptions, illustrations and notes on eight common soils. West. Aust. Dept. Agric. Bulletin 4203, pp 19. Summers, R. N. (1987). The Induction and Severity of Non-Wetting in Soils of the South Coastal Sandplain of Western Australia. M.Sc. Thesis, Uni. Western Australia, Inst. Agric., Dept. Soil Sci., Feb. 1987, pp 107. Wetheby, K. G. (1984). The extent and significance of water repellent sands on the Eyre Peninsula. South Aust. Dept. Agric. Tech. Report 47, pp 11. Keywords : claying, water repellent soil, sand, hydrophobicuty, organic matter, crop yield Mots clés : argile, sol imperméable, sable, hydrophobicité, matière organique, rendement des cultures 8