Use of labelled fertilizers in fertigation research

With modern irrigation system, traditional soil application of fertilizers has serious limitations, and fertigation is gaining increasing importance as the environmental and economic pressures on agricultural production grow. With fertigation, the fertilizers, at concentrations based on the crop nutrient requirements, are conveyed by the irrigation water to the wetted volume of the soil, where most of the active roots of the irrigated crops are developed. Fertigation is an effective means of controlling the timing and placement of fertilizers and of improving fertilizer use efficiency by reducing nutrient looses from leaching, volatilization and/or fixation in the soil to less available forms. However, only limited an insufficient scientific background and information are available on the concentration of nutrients in the irrigation water, the form of fertilizer required by the crops during their growing stages, and the behaviour of different fertilizers in soil under fertigation. Fertigation, practised empirically, may create serious agricultural, environmental and public health problems. Some of these are the high NO3-N concentration in vegetables and fruits and the residual NO3-N accumulation in soils which, through leaching, may pollute the water resources. A description is given of the techniques developed for experimental application of labelled fertilizers, and some results of fertigation experiments are presented. Particular attention is given to those results obtained from 15N and 32P experiments which indicate the superiority of fertigation as a result of the substantial increase in uptake of fertilizers compared with traditional soil fertilizer application. (author). 20 refs, 2 figs, 10 tabs