Richard Bell

The Better Fertiliser Decisions for Cropping project (BFDC) (2009-2012) was completed to provide comprehensive information to improve fertiliser decisions for the cropping industry in Australia (Speirs et al. 2013a). The WA component provides interpretation of results from crop nutrient application experiments for the WA cropping system, and developed a tool for estimating nutrient losses from cropping systems soils. The BFDC-WA project aims to use the 4R principles by producing a series of bulletins on nutrient management for the cropping system of WA.

A range of strategies are needed to ensure flexible and effective treatment of waste from catfish ponds at a range of different types of operations and throughout the year. A diverse range of chemical, microbial and biochemical products may be suited for this purpose, including a number that are commercially available, but their efficacy has not been independently tested. The soil bacteria, Pseudomonas stutzeri, was isolated from catfish ponds and tested for its ability to reduce NH4-N loads in waste water. In laboratory tests at Cantho University promising denitrification activity was obtained but this could not be reliably reproduced in studies at Murdoch University or in tests at CLRRI. Commercially available preparations for waste water treatment were found to be variably effective, but the most promising materials assessed were the biological preparations from plant materials, Yucca extract and crushed Moringa oleifera seeds. Ozone treatment of the wastewater appears to have a limited role in oxygenation of the wastewater and reducing NH4-N. Aquatic plants with or without fish such as tilapia were promising options for improving water quality in settling ponds. Despite the diverse range of approaches examined no single technology was developed to a point where scale-up to field or operational scale was feasible.

In the Mekong Delta of Vietnam, water quality is critically important for human health and wellbeing as well as ecosystem function. Catfish farming in the Mekong Delta, which is mostly confined to the provinces of An Giang, Cantho, Dop Lap and Vinh Long, is considered to be a significant source of water pollution in those provinces. A survey of 240 catfish farmers in An Giang and Cantho provinces, and of Clarias fish farmers in Cantho Province confirmed that discharge of waste water and solid waste from these operations is directly to public water sources in canals and rivers in over 75 % of cases. Water consumers in the areas where catfish ponds are prevalent had a strong perception that catfish pond discharge was the major cause of degraded water quality. Water sampling at 2 points of discharge in An Giang over a 5-month period confirmed that discharge causes canal water to exceed discharge standards for COD, TSS and NH4. However, even background levels were generally above the levels set for household use in Vietnam. Two case studies showed that passing Clarias fishpond waste water or water laden with catfish waste through rice fields improved its quality substantially, by decreasing TSS, COD, BOD, N and P. Coupled with evidence that catfish and Clarias fish pond wastes can be an effective partial replacement of rice fertiliser requirements, these results indicate that recycling solid waste and waste water from fishponds could be promoted as an effective technology for improving quality of public water ways. The recent decline in density of active catfish ponds in the Mekong Delta, during to poor profitability, may be having a beneficial effect on water quality.

Waste from intensive catfish aquaculture production has become a pollutant of surface waters in the Mekong Delta, Vietnam. In the present study, the aim was to treat the solid waste from catfish ponds in the Mekong Delta by land application to padi fields so that the nutrients could be recovered by rice crops as a fertilizer substitute. A field experiment was commenced in the wet season 2007and continued for 6 consecutive rice crops using three doses of solid wastes (1, 2 and 3 tonne/ha) in combination with 1/3 or 2/3 of the recommended inorganic fertiliser rate (60N-17P-24K in wet season and 80N-17.4P-49.8K/ha in the dry season in kg/ha). Rice yields were generally similar in all treatments in each of the 6 consecutive crops, except that wet season yields declined by ?? with 1/3rd the fertiliser dose with only 1 t of solid waste. Moreover, with 3 t of solid waste ha, 1/3rd fertiliser dose gave higher yields in the dry season than with 2/3rd dose. With straw removal, generally N and K balances were positive in the wet season when yields were low, but negative in the dry season. With straw retention, all K balances were strongly positive but N balances were only positive with the higher solid waste and N fertiliser rates. Phosphorus balances were always strongly positive. Mean levels of organic C, N, available P, K and Zn increased in soils over the course of 6 rice crops. These results suggest that the fishpond solid waste replaced 1/3 to 2/3 of the fertiliser normally applied and confirmed that solid wastes from fishponds can be recycled for rice culture to mitigate pollution of waterway and reduce fertiliser costs.

Soil Profile Description Soil profiles were described using a combination of codes and definitions from the Food and Agriculture Organisation and the Department of Agriculture and Food Western Australia (FAO-ISRIC 1990; Purdie 1999; FAO-CSIC 2002). These codes and descriptions were compiled into a booklet entitled ‘Dataset and Code Definitions for the Soil Survey of Cambodia’. A data sheet for recording soil profile information at each site was also produced. Soil profiles were classified using the Cambodian Agronomic Soil Classification (CASC) (White et al. 1997) and World Reference Base for Soil Resources (IUSS 2006). Soil Chemical Analysis Laboratory analysis was completed on all horizons for a selection of the soil profiles. These soil samples were analysed by CSBP laboratories in Western Australia. All soil samples were air-dried, ground and sieved (<2 mm particle diameter). The following tests were used (i) electrical conductivity and pH in 1:5 soil:water suspension and pH in 0.01M CaCl2 (Rayment and Higginson 1992, pp15-23); (ii) organic carbon concentrations, (Walkley and Black 1934); (iii) concentration of exchangeable cations, Gilman and Sumpter method (Rayment and Higginson 1992, pp 164-169); (iv) DPTA trace elements (copper, Cu; zinc, Zn; manganese, Mn; iron, Fe) (Rayment and Higginson 1992, pp 110-114); (v) nitrate and ammonium nitrogen (Searle 1984); (vi) available phosphorus and potassium, Colwell method (Rayment and Higginson 1992, p 64); (vii) extractable sulphur (Blair et al. 1991); (viii) boron (Rayment and Higginson 1992, pp 115-120). The soil chemical data can be found in Tables 1 to 3 at the end of this report. Data Collection and Reporting For each soil profile, location information was collected using a hand held GPS. This has enabled mapping of the data, and will enable users of the data in the field to return to soil profile locations. All soil profile data has been placed into an Access database currently maintained by the Soil and Water Group at CARDI. Other districts included in this study were Ou Reang Ov in the Province of Kampong Cham and Tram Kak in the Province of Takeo. Results of these surveys can be found in soil survey reports for each district. In addition the results of these soil surveys have been used to generate soil-land unit maps of each district (Hin et al. 2005a,b,c) and assist in the assessment of land capability for field crops in each district (Bell et al. 2005a,b).

The acceleration of crop diversification in Cambodia in lowlands and in uplands could be facilitated by a process for the assessment of land capability for non-rice crops. Maize, soybean, mung bean, sesame and peanut appear to be the crops of most interest initially for land capability assessment, together with cassava and sugar cane. Land capability was determined for maize, soybean, mung bean, sesame and peanut in Banan district, Battambang province. Limiting factors for crops were identified, and land qualities rated for the soil types identified previously in a soil survey of the district. The main Soil groups on Banan district are Toul Samroung, Kein Svay and Kompong Siem. The calcareous phase of Kompong Siem soils that occurs on the lower slopes of limestone hills has low capability for non-rice cropping with alkalinity and waterlogging being the most likely limiting factors. By contrast, the Kein Svay soil has high capability for non-rice crops especially on the high levee banks. Toul Samroung soil, where it occurs in slightly elevated land within the rice plains, has fair capability for non-rice crops, but it is not recommended for non-rice crops in the main wet season due to inundation risk.