THE USE OF GEO-REFERENCED SOIL TEST DATA IN THE HERBERT DISTRICT

Transcription

1 THE USE OF GEO-REFERENCED SOIL TEST DATA IN THE HERBERT DISTRICT By LP DI BELLA 1, RJ COVENTRY 2, M SEFTON 1, PW MOODY 3, M HANKS 4, JK STRINGER 5, RE KERKWYK 1 1 Herbert Cane Productivity Services Ltd., Ingham 2 Soil Horizons Pty Ltd, Townsville 3 Queensland Department of Natural Resources and Water, Brisbane 4 Department of Primary Industries and Fisheries, Townsville 5 BSES Limited, Indooroopilly ldibella@csr.com.au KEYWORDS: Nutrient Management, Soil Testing, Cation Exchange Capacity, CEC, Phosphorus, Calcium, Soil ph, Aluminium, Mill Mud, Herbert River District, GIS, Geo-referenced Samples. Abstract SURFACE soil samples have been collected for many years to develop on-farm nutrient management guidelines but their precise locations were largely unknown because geo-referencing technology was previously unavailable. Consequently, spatial analysis of the data was not possible. Over the past four years, the Herbert Cane Productivity Services Limited (HCPSL) has provided a service to growers to co-ordinate soil sample collection, sample analysis, and reporting of soil test information; a geo-referenced position is recorded for every sample. This information is collated in a spatial database and forms a layer in the geographic information systems (GIS) managed jointly by HPCSL and the Herbert Resource Information Centre (HRIC). Interpretation of the data has provided spatial patterns of soil properties across the district. This paper presents examples of the spatial distribution of different nutrients and soil chemical characteristics such as soil ph, extractable phosphorus, cation exchange capacity, exchangeable calcium and extractable aluminium. It shows how georeferenced soil test data can be used to develop nutrient management strategies within the region and to address specific issues associated with nutrient deficiencies and excesses. Introduction A wide variety of soils are present in the Herbert district. An understanding of the soil differences, at both district and farm levels, provides a basis for nutrient management strategies that reflect the soil diversity, while enabling profitable and sustainable sugarcane production on the coastal lowlands part of the Herbert River catchment (Wood et al., 2003). In the past, growers and agricultural service providers have tested soil samples from cane blocks, but the samples had not been precisely located or spatially referenced. In many 296

2 cases it may be difficult to locate even the field from which the soil samples had been collected because of unclear identification of the sample, a change in block details or property ownership, or simply because the sample collector did not record or cannot remember the soil sample location. To monitor soil nutrient trends over time, it is essential that precise and accurate soil sample records are kept and maintained. The sugar industry has been ineffective in utilising geo-referenced soil samples and in managing soil analytical data, possibly because the appropriate technologies may have been unavailable or not fully understood. The introduction of relatively cheap global positioning systems and user-friendly geographic information systems has created new opportunities for agricultural industries to utilise spatial data better. Since 1996, Herbert Cane Productivity Services Limited (HCPSL) has been applying the guidelines of Webster et al. (1996) in collecting farm data on fertiliser application and pest and disease control measures adopted by growers (Wood et al., 2008). In 2003, HCPSL commenced a soil sampling service in the district, to encourage growers to use soil tests in farm planning and decision making, to monitor soil nutrient levels, and to underpin nutrient management programs. The farm-focused nutrient management programs of HCPSL are designed to assist growers make informed decisions, and to support the adoption of site-specific land management. They are based upon soil specific guidelines developed for the region (Wood et al., 2003) and the Six Easy Steps approach to sustainable nutrient management (Schroeder et al., 2005). This paper presents an overview of aspects of the data extracted from the Herbert District soils database that has been developed during the period In particular, the paper identifies and discusses regional soil chemical trends in cation exchange capacity, exchangeable calcium, extractable aluminium and soil ph, and dilute sulphuric acid extractable phosphorus. Methods Soil test samples are geo-referenced to a specific cane block through the use of the ArcMap geographic information system (GIS) that is upgraded annually. Latitude and longitude coordinates for the centre of a block are generated and recorded in the attributes table of the district cane blocks layer of the GIS. From these coordinates a point file is created for all site attributes recorded. Since the program began, over 700 samples have been collected, analysed by a commercial laboratory, and the results entered into a regional database that includes cane block-specific data (such as crop yield maps, topographic maps, soil maps, and remotely sensed imagery) and is maintained by the Herbert Resource Information Centre (HRIC). All soil tests were analysed through the Incitec Pivot laboratory using analytical methods and procedures approved by the Australian sugarcane industry. Results Cation exchange capacity Wood et al. (2003) assigned the soils of the Herbert District to three categories based on their cation exchange capacity (CEC): Low: less than 3 cmol(+)/kg; Medium: 3 6 cmol(+)/kg; High: greater than 6 cmol(+)/kg. 297

3 Of the 700 soil test results entered into the HCPSL soil database, 25% of the CEC determinations were in the low group, 44% were in the medium group, and 31% were in the high group. The soils with low CEC are typically located on lighter textured, sandy soils with low organic matter levels (Figure 1). What appear to be unusually large numbers of soil tests with high CEC are located close to the Victoria and Macknade sugar mills, and on the Herbert River floodplain in the vicinity of Abergowrie where the upper Herbert River leaves the confines of its rocky gorge and discharges over the coastal lowland part of its catchment. Fig. 1 The regional pattern of cation exchange capacities (cmol(+)/kg) of soils of the Herbert sub-districts. Phosphorus Phosphorus (P) is routinely applied as DAP fertiliser or in mill mud products to cane fields in the Herbert district as a part of the crop fertilising program. During the past 24 months, application rates have decreased in response to dramatic increases in fertiliser and fuel prices. Even though application rates have decreased, there is evidence of excessively high residual levels of extractable P in the soils. Table 1 and Figure 2 highlight the soil test results within sub-districts of the Herbert region for soil P contents that have been extracted by the BSES (0.005 M H 2 SO 4 ) method. The lowest content of extractable P recorded was 4 mg/kg and the highest was 340 mg/kg, 298

4 indicating a very wide range in plant-available P in the soils of the district (Figure 5). Sixty percent of soil tests in the HCPSL soil database had BSES extractable P levels greater than the critical value for sugarcane growth of 50 mg/kg, indicating that supplementary P applications to such soils are not required. Table 1 Mean soil test results ( ) for BSES extractable soil P for sub-districts within the Herbert region. Sub-district No. of samples Min P Max P Average P (mg/kg) (mg/kg) (mg/kg) Macknade Victoria Estate Toobanna Garrawalt Foresthome Halifax Four Mile Sunnybank Cordelia Bambaroo West Ripple Creek Lower Stone Helens Hill Hawkins Creek Long Pocket Elphinstone Lannercost Leach Tara Seymour Lannercost Extension Yuruga Mid Stone Fairford Trebonne Bambaroo East Blackrock Hamleigh Upper Stone Coolbie Rollingstone Figure 2 clearly indicates that there is a strong relationship between soil P contents and paddock locations close to the local sugarcane mills. In the past, application rates of wet tonnes /ha of mill mud (from Victoria Mill) and mill mud/ash mixtures (from Macknade Mill) have been applied to cane fields in the region. The cost of transport has generally limited the distribution of mill products to areas close to the mills. The application rates have decreased slightly too approximately 100 wet tonnes /ha in the past two years due to modification of truck application equipment developed by commercial spreading companies in the region; but the lower rates are only applied when requested by the grower purchasing the product. Even at 100 wet tonnes /ha, excessive rates of P are being applied to some soils and repeat applications are common. The reasons for the high P levels found in Herbert soils are due to several factors, including: High or prolonged applications of P from fertiliser or mill products as a component of the farm's nutrient management program (Wood et al., 2008). 299

5 Fig. 2 Average BSES extractable soil phosphorus (mg/kg) of soils of the Herbert sub-districts. Unfounded grower perceptions that plant cane will not effectively germinate and establish without the application of P, regardless of the P status of the soil. Naturally high levels of soil P are found in some of the alluvial soils of the Herbert cane growing area (Wood et al., 2003). A large proportion of the region is regularly flooded and phosphorus-rich sediment is deposited on the flooded farms, especially those in the Lower Herbert floodplain areas downstream of Ingham, and those upstream in the vicinity of the Abergowrie flats below the Herbert River gorge (Figure 5). Nevertheless, Bartley et al. (2003) suggested that detailed patterns of erosion and sediment movement were difficult to define over the Herbert floodplain. Regular applications of mill mud to cane land in close proximity to the two sugarcane mills in the district is the most likely controlling factor. This may explain the high contents of extractable P and the high CECs of the soils which are found close to the mills in the Macknade and Victoria Estate subdistrict areas and adjacent sub-districts (Figures 1 and 2). 300

6 Soil ph The optimal soil ph water for the growth of most plants is between 6.0 and 7.0 (Glendinning, 2000), however sugarcane is very tolerant of more acidic, lower ph soils. It is recommended that ph of surface soils be maintained at levels above ph water 5.5 (where possible) to ensure adequate cane and legume break-crop growth and to prevent subsurface acidification (Webster and Wilcox, 1999). Figure 3 shows average soil ph water values for each sub-district region. The Herbert district average soil ph water is 5.0. Soil ph values as low as 3.2 have been determined after continued farming of sugarcane in non-acid sulphate soils, but these are isolated instances. Fig. 3 Average soil ph water values for soils of the Herbert sub-districts. Soil ph water levels vary across the district and between farms as a result of: Soil parent material and soil type. The removal of large amounts of biomass at harvest which produces a high net acid addition rate to the sugarcane system (Moody and Aitken, 1997). Soils with a low ph buffer capacity (such as light textured soils) will therefore acidify quickly in comparison to heavier textured, clay and / or organic matter-enriched soils. Farming practices such as the use of heavy applications of sulfate of ammonia and other forms of acidifying, nitrogenous fertilisers (Glendinning, 2000). 301

7 Spoil from acid sulphate soils that was spread over cane blocks. This practice occurred in the past and has now been addressed as a part of the district s acid sulphate soil management practices. Such soils account for less than 1% of the total number of samples in the soil database. Removal of the topsoil by laser levelling practices during drainage works, exposing acid sub-soils(in some areas). Soil calcium Exchangeable calcium (Ca) contents of the soils vary considerably throughout the district depending on: soil parent material soil type calcium applications in the form of agricultural lime, gypsum, dolomite, or calcium contained in mill mud. Low exchangeable Ca levels are common in the district, especially in soils located in the western and southern areas (Figure 4). Exchangeable Ca levels below 0.6 cmol(+)/kg were found in 11 % of the soil samples in the database and one third of the samples had levels below 1.5 cmol(+)/kg, which is considered to be the critical level for growing cane within the region. The lowest recorded exchangeable Ca level in the database was 0.04 cmol(+)/kg. A least squares linear regression analysis revealed that there was no statistical relationship between exchangeable Ca and ph water (r 2 = 0.33). Fig. 4 Average exchangeable calcium (cmol(+)/kg) of soils of the Herbert sub-districts. 302

8 Soil aluminium Extractable aluminium and aluminium saturation levels vary considerably throughout the district due to: soil ph soil parent material soil type soil CEC. (A) (B) Fig. 5 Average soil aluminium contents of soils of the Herbert sub-districts: (a) extractable aluminium (cmol(+)/kg) (b) aluminium saturation (%). While the absolute contents of extractable aluminium in the soils are relatively low (Figure 5a), the degree of aluminium saturation in the soils is high to very high (Figure 5b). The relationship between extractable aluminium and soil acidity was shown by a least squares linear regression analysis in which there was a significant (P <0.01) relationship between extractable aluminium and ph water (r 2 = 0.81). This is similar to that reported by Mengel and Kirkby (1982). Excess aluminium cations in the soil solution inhibit plant root development and Hazelton and Murphy (2007) suggested that 5% aluminium saturation is the threshold for desirable plant growth. Slattery et al. (1999) have shown sugarcane to be one of the few crops that can tolerate soils with high extractable aluminium contents and achieve its maximum potential yield in moderately aluminium-toxic soils without significant effects on plant 303

9 growth from aluminium toxicity. Nevertheless, Slattery et al. (1999) suggested that, as the soil acidifies and its extractable aluminium contents increase, the growth of even the most aluminium-tolerant plants will be affected. Discussion Sugarcane production in the Herbert region is facing some significant challenges in order to maintain soil fertility levels and to address specific nutrient management issues. The use of geo-referenced soil test data will assist growers and industry make informed decisions about nutrient and soil fertility management. CEC, soil ph, calcium, and aluminium Our investigations have shown that large areas of the Herbert region have soils with a combination of low CEC, low soil ph, low exchangeable Ca, high extractable aluminium and high aluminium saturation levels. Low Ca and ph levels will cause significant problems when growers are considering growing ph sensitive crops such as soybeans and other legumes, melons, pumpkins and maize. Figure 6 shows the poor growth, decreased crop vigour and chlorosis of Meringa cowpea as a consequence of low soil ph, low soil Ca and high soil aluminium levels on a legume cover crop grown in the Herbert in Fig. 6 Effects of low soil ph, low calcium and high aluminium contents on the growth of a Meringa cowpea crop in the Herbert district in It has been noted by local agronomy and extension staff in the Herbert district that particular sugarcane varieties, like Q200, produce higher yields and a longer ratoon cycle on soils with higher levels of soil Ca. Wood et al. (2003) reported that soils with ph water levels greater than 5.5 are desirable for plant growth in the Herbert as concentrations of aluminium, both in the soil solution and on exchange sites, are minimised above ph

10 Mengel and Kirkby (1982) reported that soil acidity and high aluminium levels in the root zone restrict a plant's ability to access water and nutrients. More recent studies, such as those reviewed by Slattery et al. (1999), have also reported that the root systems of plants are damaged in soils where excessive contents of extractable aluminium compromise plant growth. Wood et al. (2003) also showed that the availability of nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur all decrease in the Herbert district as the soil ph levels decrease, and indicated that soil ph and Ca levels should be monitored to ensure adequate cane growth. The extent of soils with a combination of low CEC, low soil ph, low exchangeable Ca, high extractable aluminium and high aluminium saturation levels in the Herbert catchment indicates a major soil constraint to plant growth in the region. These issues can be addressed by the following practices: base farm nutrient management plans on soil and leaf tissue testing data in conjunction with other data such as yield maps, soils maps, topographic maps, and remote sensing imagery develop farming systems to conserve organic matter and to maintain soil structure using practices such as reduced tillage, controlled traffic, and rotational cropping make strategic applications of calcium sources such as agricultural lime, mill mud, or finely ground rock dust to address soil ph issues make strategic applications of calcium-based products such as agricultural lime, gypsum, mill mud, dolomite, or rock dust to address low calcium levels in soil. The use of these products, with the exception of gypsum, will also induce a beneficial increase in soil CEC, and a reduction in aluminium saturation, as a consequence of increasing the soil ph (Webster and Wilcox, 1999). monitor the soil condition routinely through the use of a geo-referenced soil testing database system adopt the strategies highlighted in the Six Easy Steps program to ensure sustainable nutrient management. Phosphorus The high incidence of soils in the Herbert district with adequate or excessive contents of acid extractable P (values greater than 50 mg/kg) highlights the need to review current farming nutrient management practices and mill by-product application practices associated with P usage. Methods to distribute mill mud further from the sugar mill and onto blocks of low P status should be considered as a regional strategy for managing the best use of the product. Other nutrients present in mill mud such as calcium, magnesium, trace elements, and organic carbon could be of significant benefit to many of the low CEC soils to the south and west of Ingham (Figure 1). The Six Easy Steps approach to best practice nutrient management recommends that applications of P should be based on soil test results to avoid over-applications on soils that already have high levels of the nutrient. Grower demonstration plots should be established on soils with high extractable P levels to demonstrate to growers that cane can be established and grow well without the application of the nutrient. 305

11 Conclusions The use of geo-referenced soil test data has shown to be worthwhile for the on-going monitoring of nutrient levels within cane blocks, within farms, within sub-districts, and across the region. It is recommended that this activity continue into the future and that the data are regularly reviewed. The case studies presented in this paper highlight the benefits of a geo-referenced soil test data base and possible uses of such a system. The interpretation and presentation of other soil chemical properties is an on-going task. Growers should be encouraged to continue to take soil tests to monitor soil nutrient levels. Soil test data should not be used in isolation but linked to other sources of spatial data such as soil maps, crop yield maps, topographic maps, and remotely sensed images to assist in making informed decisions on farm management practices. The use of geo-referenced soil test data will assist growers to become more profitable and sustainable and will provide a mechanism to monitor productivity and environmental impacts associated with nutrient management issues in the future. REFERENCES Bartley R, Henderson A, Prosser IP, Hughes AO, McKergow L, Lu H, Brodie J, Bainbridge Z, Roth CH (2003) Patterns of erosion and sediment and nutrient transport in the Herbert River Catchment, Queensland. CSIRO Land and Water Technical Report. Glendinning JS (2000) Australian soil fertility manual. Fertiliser Industry Federation of Australia and CSIRO. (CSIRO Publishing: Collingwood). Hazelton PA, Murphy BW (2007) Interpreting soil test results: What do the numbers mean? (CSIRO Publishing: Collingwood). Mengel K, Kirkby EA (1982) Principles of plant nutrition. (International Potash Institute: Bern, Switzerland). Moody PW, Aitken RL (1997) Soil acidification under some tropical agricultural systems. 1. Rates of acidification and contributing factors. Australian Journal of Soil Research 35, Schroeder BL, Wood AW, Moody PW, Panitz JH (2005) Sustainable nutrient management. Delivering the message to the Australian sugar industry. Proceedings of South African Sugar Technologists Association 79, Slattery WJ, Conyers MK, Aitken RL (1999) Soil ph, aluminium, manganese, and lime requirement. In Soil analysis: an interpretation manual. (Eds KI Peverill, LA Sparrow, DJ Reuter) (CSIRO Publishing: Collingwood). Webster K, Burgess D, Beattie R (1996) Benchmark report on north Queensland fertiliser use. (Ed. E Kain) 14 pp. (BSES: Indooroopilly, Australia). Webster K, Wilcox T (1999) Maintaining soil fertility. (BSES: Indooroopilly). Wood AW, Schroeder BL, Stewart RL (2003) Soil specific management guidelines for sugarcane production: Soil reference booklet for the Herbert district. CRC Sugar Technical Publication, CRC for Sustainable Sugar Production, Townsville, 92 pp. Wood AW, Holzberger G, Kerkywk RE, Dwyer R, Schroeder BL (2008) Trends in nutrient applications in the Herbert River district from 1996 to Proceedings of the Australian Society of Sugar Cane Technologists 30,