Chlorophyll meter - a decision-making tool for nitrogen application in wheat under light soils

Nitrogen (N) in plants is generally diagnosed by a soil test and plant tissue analysis. However, such analyses are costly in terms of time and money and are not easily accessible by researchers and extension workers, let alone farmers. Alternative cost-effective methods are required for rapid analysis of the N status of crops and to guide N management in wheat. The objective of this study was to assess whether the SPAD values using a leaf chlorophyll meter could be used to apply N at the maximum tillering (MT) stage of irrigated spring wheat grown under light soils of South Asia. Experiments were conducted over two years under light soils at the Wheat Research Centre (WRC), Dinajpur, Bangladesh. Treatments were 80, 100 and 120 kg N ha−1, applied two-thirds as basal and one-third at the crown root initiation (CRI) stage along with additional 10, 20 and 30 kg N ha−1 (first year) and 0, 10, 20 and 30 kg N ha- (second year) at MT. Rates at MT were determined on the basis of SPAD values, which fell below the critical value of 37.5, recorded at 45 days after sowing (DAS). SPAD values recorded at 55 and 65 DAS were positively correlated with grain yield (GY), indicating that the application of extra N at MT influences wheat GY. Our results have two major implications: (i) SPAD values based on a leaf chlorophyll meter can be used for N application and (ii) extra 30 kg N ha-1 at MT is recommended for achieving maximum GY of irrigated spring wheat under the light soils of South Asia.