using deionised water. The >2 mm fraction, consisting mainly of decaying vegetation, was discarded. All other sediment size fractions were air-dried, homogenised and stored at 4 °C. Rice plant samples were washed with deionised water to remove adherent soil particles then oven-dried at 60 °C until constant weight was achieved. Whole plant samples were weighed and then separated into parts (grain, husk, straw and root) which were then weighed individually. All plant parts were cut into small pieces and ground into fine powders using a ball mill, with standard cleaning practices employed between