CADMIUM CONCENTRATION IN GRAIN GROWN UNDER ORGANIC FARMING SYSTEMS AND USING ALTERNATIVE FERTILISERS

Transcription

1 CSI RO AUST RALIA CSIRO LAN D and WATER TECHNICAL REPORT 13/1997 The material contained herein has not been refereed. It may be quoted as a personal communication following written consent of the authors. CADMIUM CONCENTRATION IN GRAIN GROWN UNDER ORGANIC FARMING SYSTEMS AND USING ALTERNATIVE FERTILISERS D.P. Oliver, C. Penfold, J. Derrick, G.D. Cozens and the late K.G. Tiller

2 INTRODUCTION The use of alternative farming systems and alternative fertilisers is gaining greater prominence with increasing emphasis on sustainable agriculture. Campbell (1989) defines a sustainable agricultural system as one which maintains the productive capacity of the land and economic viability, while minimising energy and resource use, and optimising the rate of turnover and recycling. The main source of Cd in traditional agricultural systems in Australia is phosphatic fertilisers (Williams and David, 1973; Tiller, 1988). Until recently the maximum permissible limit (MPL) for Cd concentration in wheat grain was 0.05 mg kg -1, set by the National Food Authority (NFA, 1993). In 1997 the limit was raised to 0.10 mg kg - 1 (ANZFA, 1997). Despite the MPL being doubled concerns have arisen that grain Cd concentrations may be exceeding this limit when grown under conventional agricultural systems. In this study the effects of different farming systems and unconventional fertilisers on Cd concentration in wheat grain were assessed. MATERIALS AND METHODS Roseworthy experiments Grain was obtained from two experiments at Roseworthy campus, University of Adelaide. The experiments are situated on a hard setting red-brown earth, ph W and average annual rainfall 440 mm. i) Alternative Farming Systems The alternative farming systems experiment was established in The four farming systems being investigated are organic, biodynamic, conventional and an integrated low-input treatment. A summary of the management strategies for each system is presented in Table 1 and the trial design is shown in Fig. 1. Details of inputs of phosphorus-containing fertilisers to the treatments are given in Table 2. The experiment is set up with two fields per treatment. In 1992 grain (Triticum aestivum cv Machete) and soil for Cd analysis was sampled from a 2m control strip located within the field (Fig. 1). ii) Alternative Fertilisers Experiment The second experiment was established in 1989 and studied the effects of conventional and organic fertilisers on various aspects of crop growth. The experiment involved a medic (Medicago sativa cv Paraggio) and barley (Hordeum vulgare cv Galleon) rotation in two phases. The treatments are listed in Table 3. In 1991 and 1993 barley grain from whole plots (15.0 m x 1.4 m) in Phase 2 was sampled for Cd analysis. Soil was sampled from each plot of Phase 2 in Chemical analysis of the fertilisers is given in Table 4. 2

3 Table 1 Management strategies of the four farming systems in the Alternative Farming Systems experiment, Roseworthy. Fertilisers/ Ameliorants Pest and weed control Organic Biodynamic Integrated Conventional Mineral rock and/or Biodynamic organic and/or synthetic composted animal manure preparations synthetic cultural/mechanical cultural/mechanical cultural/mechanical pesticides/cultural (pesticides during mechanical initial stages) Rotations 1989 oats/medic for hay oats/medic for hay oats/medic for hay wheat 1990 wheat/slashed oats/medic for medic/lucerne for peas grazing grazing 1991 vetch/beans/oats for green manuring vetch/oats for hay medic sprayed with glyphosphate medic (sown) for grazing 1992 wheat wheat wheat wheat Table 2. Inputs of phosphorus-containing fertilisers to the Alternative Farming Systems experiments, Roseworthy. Organic Biodynamic Integrated Conventional Jomoco - 6:6:0 100 kg ha -1 AMF Biophosphate 162 kg ha -1 North Carolina Reactive rock 0:13.4:0 100 kg ha -1 Gypsum Jomoco 5 t ha -1 Legume mix 0:5:3:4 93 kg ha -1 DAP 19:13:0 50 kg ha -1 North Carolina Reactive rock 0:13.4:0 111 kg ha -1 - NeoMin 0:0.1:2 120 kg ha -1 Superphosphate 0:20:0 39 kg ha -1 Pivot Humus Booster (Biosolids) 1.5:1.5:0.5 1 t ha -1 Superphosphate 0:20:0 46 kg ha -1 Jomoco Organic Fish 4,5:3:2:3 120 kg ha -1 Pivot Humus Booster 1.1 t ha -1 Superphosphate 0:9:0 119 kg ha -1 3

4 Table 3. Treatments in Organic Fertiliser experiment at Roseworthy. Treatment No. Treatment 1. Jomoco: pelletised chicken manure 2. Jomoco: complete organic cropping fertilizer 3. Neutrog: cropping mix 4. Neutrog: base product 5. Australian Mineral Fertilisers: Biophosphate 6. Australian Mineral Fertilisers: Alkaphos Extra 7. Hifert: Triple super (0:20:0) 8. Hifert: DAP/ Sulphate of ammonia 9. Composite mix, continuing: Jomoco: legume cropping fertilizer - 5 parts Jomoco: pelletised chicken manure - 5 parts Hifert: Triple super - 3 parts 10. Control (no fertilizer applications) 11. Top: Gro-wel 12. Health Script International: Neo-min 13. Everard Mining Company: Tryaton 4

5 Table 4 Chemical analysis (mg/kg) of organic fertilisers used in Alternative Fertiliser experiment at Roseworthy. Jomoco chicken manure Jomoco organic fertilizer Neutrog cropping mix Neutrog base product Biophosphate Alkaphos Extra Al B Ca Cd Co Cr Cu Fe K Mg Mn Na Ni P Mo S Zn Table 4 continued. Triple Super DAP/ sulphate of NH 3 Neomin Humus Booster Tryaton Al B Ca Cd Co Cr Cu Fe K Mg Mn Na Ni P Mo S Zn Ardlethan, New South Wales experiments The experiments at Ardlethan, NSW compared wheat yield responses to superphosphate and Morocco phosphate rock on an organic and a conventional farm. The organic farm had been managed without synthetic fertilisers since 1962 while the other farm had been managed using conventional systems for many years. Further details of the experiments and the sites are given in Dann et al. (1995). 5

6 The two sites were located on neighbouring properties. Wheat (Triticum aestivum cv Banks) from both sites was provided for Cd analysis in 1992 from the following treatments: control, Morocco phosphorus 40 kg P ha -1 and single superphosphate 40 kg P ha -1. The soil ph Ca at the organic and conventional experiments was 5.57 and 4.42, respectively (Dann et al., 1995). The EDTA Cd concentrations in the soil was and mg kg -1 at the organic and conventional experiments, respectively. Cadmium analyses of grain Details of the digestion procedure are given in Oliver et al. (1993). One gram of grain was digested at o C in 8 ml concentrated nitric acid and 1.5 ml perchloric acid until the volume was reduced to 1 ml. After adding 19 ml of deionised water and adjusting the ph to between 3 and 4 with ammonium acetate, the cadmium was complexed with 0.5% ammonium pyrrolidine dithiocarbamate (APDC). The complexed cadmium was then extracted into 10 ml di-iso-butyl ketone (DIBK), mixed well and allowed to separate. The aqueous layer was removed and the cadmium was back-extracted into 10 ml 3% nitric acid. One third of the samples were repeated to check the precision of the procedure. To check the reproducibility of the analytical procedure our own standard grain samples were included in every batch of eighty samples. Two samples of wheat flour (National Bureau of Standards No. 1567a) were also included in every third batch. The expected cadmium concentration + standard deviation for this standard sample was ug g -1 and the mean value obtained was ug g -1. Soil analyses Soil ph was measured by shaking samples (5 g) with 25 ml of 0.01M calcium chloride for one hour. The ph of the supernatant was measured within an hour using a Metrohm 632 ph meter. EDTA-extractable cadmium was measured by shaking soil samples (10 g) with 25 ml of 0.05 M EDTA (ph 6) for seven days at 20 o C (Clayton and Tiller, 1979). Carbon dioxide was allowed to evolve from calcareous soils by shaking the sample, releasing the stopper and allowing the sample to stand for two hours. The solutions were analysed on a flame AAS for cadmium. RESULTS AND DISCUSSION Roseworthy Experiments Alternative Farming Systems The Cd concentrations in grain from the alternative farming systems experiment were low and ranged from mg kg -1. The farming systems had no significant effects on Cd concentration in grain. Alternative Fertilisers Experiment No significant differences in Cd concentration in grain were found with the different fertilisers used in this experiment despite the very high Cd concentration of DAP/sulphate of ammonia fertiliser (55.5 mg Cd/kg) compared with the other fertilisers (Table 4). However, there were significant (P<0.001) differences in Cd concentration in grain between 1991 and 1993 (Fig. 2). The mean Cd concentration in 6

7 grain in 1993 was approximately 6-8 times higher in 1993 than in 1991 (Fig. 2). The reason for the annual differences in grain Cd concentrations are not clear. Ardlethan experiments The Cd concentrations in grain from this experiment were much higher than those from the Roseworthy experiments ranging from to mg kg -1. The lower concentrations in grain from Roseworthy are most likely due to the higher soil ph at Roseworthy. The higher ph would minimise Cd availability for plant uptake since the proportion of Cd ions that are hydrolysed would be higher and there would be a greater number of adsorption sites. Significantly (P<0.001) higher Cd concentrations were found in grain from the single superphosphate treatment compared with the control and the Morocco P treatment for both the conventional and organic farming systems(fig. 3). This is most likely due to higher Cd concentrations in the single superphosphate compared with the other fertilisers. Unfortunately no fertiliser samples were available for analysis. The Cd concentrations in grain were significantly (P<0.001) higher for all treatments grown under the conventional farming system compared with the organic system (Fig. 3). This is possibly due to the addition of lime, at 0.5 t ha -1, to the organic site in 1989 while no lime had been applied to the conventional site (Dann et al., 1995). Although Oliver et al. (1996) found the effect of liming to minimise Cd concentration in grain decreased with time, the ph at the organic site was still higher than at the conventional site (5.57 at the organic site and 4.42 at the conventional site) which explains the lower grain Cd concentrations at the organic site. It is not possible from this study to determine the effects of conventional versus organic farming on grain Cd concentrations due to the over-riding effects of ph differences at the two sites in the Ardlethan experiments. Further, although there was no effect of farming system on grain Cd concentration, any possible effect may have been masked by the high soil ph ( ), which would decrease the Cd concentration in soil solution making it less available for plant uptake. ACKNOWLEDGMENTS The authors acknowledge the financial support of the Grains Research and Development Corporation. The contribution of Mr Brett Nietschke to the Roseworthy Fertilizer trial is greatly appreciated. 7

8 REFERENCES ANZFA (1997). Australian and New Zealand Food Standards Code. Standard A12 - Metals and Contaminants in Food. Australian and New Zealand Food Authority. (Aust. Govt. Publ. Service:Canberra). Campbell, A. (1989). Bridging the gap between conventional and sustainable agriculture - The role of whole farm planning. Aust. J. Soil Water Cons. 2, Clayton, P.M., and Tiller, K.G. (1979). A chemical method for the determination of heavy metal content of soils in environmental studies. CSIRO Australia, Division of Soils, Technical Paper No p. Dann, P.R., Derrick, J.W., Dumaresq, D.C., and Ryan M.H. (1995) The response to superphosphate and reactive rock phosphate by organic and conventional grown wheat. Aust. J. Exp. Agric. 36, NFA (1993). Australian Food Standards Code. National Food Authority. (Aust. Govt. Publ. Service:Canberra). Oliver, D.P., Schultz, J.E., Tiller, K.G., and Merry, R.H. (1993). The effect of crop rotations and tillage practices on cadmium concentration in wheat grain. Aust. J. Agric. Res. 44, Oliver, D.P., the late Tiller, K.G., Conyers, M.K., Slattery, W.J., Alston, A.M. and Merry, R.H. (1996). Effectiveness of liming to minimize uptake of Cd by wheat and barley grain grown in the field. Aust. J. Agric. Res. 47, Tiller, K.G. (1988). Cadmium accumulation in the soil-plant system: an overview in relation to possible transfers to agricultural products. In Cadmium accumulations in Australian agriculture: National Symposium, Proceedings No. 2. (Eds. J. Simpson and W. Curnow.) pp (Aust. Govt. Publ. Services: Canberra). Williams, C.H. and David, D.J. (1973). The effect of superphosphate on the cadmium content of soils and plants. Aust. J. Soil Res. 11,