ENHANCING FERTILIZER NITROGEN USE EFFICIENCY IN IRRIGATED RICE BY USING A CHLOROPHYLL METER AND LEAF COLOUR CHART

Nitrogen (N) is a key nutrient element for achieving the high yield potential of modern rice varieties. In order to improve rice growth and increase profitability, farmers in many parts of world are applying excessive fertilizer N doses than required. This is true in rice crop grown in Indo-Gangetic plain of northwest India and leads to lowering the N recovery efficiency which is not more than 50% (Katyal et al., 1985 and Bijay-singh et al., 2001). For rice in Punjab, 120 kg N/ha is recommended in three equal splits applied at transplanting, 21 days after transplanting (DT) and 42 DT. These N fertilizers, application events may not synchronize well with need patterns of the plants, leading to N losses through NH 3 volatilization, NO 3 leaching, nitrification and denitrification or both (Aulakh and Bijay-Singh, 1997) and enhances low fertilizer N use efficiency. The present recommendation of 120 kg N/ha to rice is based on soil test crop response functions and do not take into account on the spot yield limiting factors like changing weather and crop conditions. Stalin et al., (1996) also found that fertilizer N recommendations on soil test basis in flooded rice are not appropriate for achieving higher yields. The recent research has shown that there is a need of sufficient N supply beyond panicle initiation (after 42 days) in order to lengthen the duration of photosynthetic activity, and for meeting N demands during grain filling period (Peng et al., 1996). Peng and Cassman (1998) demonstrated that recovery efficiency can be increased by 78% by topdressing urea at panicle initiation stage. Therefore, achieving higher yields and N use efficiency, there is need to manage fertilizer N more efficiently by making its application based on actual needs of rice plant. The Chlorophyll meter, also known as SPAD (soil plant analysis development) instantly and reliably measure the leaf greenness, which is linear to leaf chlorophyll content of rice leaves. Therefore, this instrument has the potential to provide insight into the N status of rice plants, on the spot detects N deficiencies, and shows a great promise as a tool for improving N management. It is true that farmers cannot afford chlorophyll meter due to its high cost. Therefore, another nondestructive, simple and cheap diagnostic tool leaf colour chart (LCC), efficient in determining N fertilizer application to rice according to crop demand and can be used as an alternative to chlorophyll meter (Avijit et al., 2011). Therefore, a study for fine-tuning of fertilizer N program to actual needs of plant under field conditions, reducing the risk of yield-limiting N deficiencies or costly overfertilizing by using a chlorophyll meter and LCC was carried out.