Waterlogging can affect both the availability of micronutrients in the soil and the plant's ability to absorb nutrients from the soil. Together, these effects alter the nutrition of plants and consequently the productivity of crops. Waterlogging generally increases the availability of iron and manganese in the soil, but total plant levels sometimes decline because the roots cannot function efficiently when they are stressed for oxygen. Waterlogging generally decreases the soil availability of zinc and copper, and plant tissue concentrations of these micronutrients generally decline under waterlogging. However, concentrations of copper and boron may remain constant, decrease or increase under waterlogging. For example, in a waterlogging experiment on cotton at Narrabri in Jan.1987, when siphons were run for 32 h instead of 4 h per irrigation, the uptake of Zn, Mn and Fe was reduced by 28%, 15% and 8%, respectively. However, Cu uptake increased by 14%