Calibrating the leaf colour chart for need based fertilizer nitrogen management in different maize (Zea mays L.) genotypes

Large field to field variability restricts efficient fertilizer N management when broad based blanket recommendations are used in maize (Zea mays L.). To achieve higher yields and to avoid nitrogen (N) deficiency risks, many farmers apply fertilizer N in excess of crop requirement in maize. Field experiments were conducted for five years (2005–2009) to establish and evaluate threshold leaf colour to guide in-season need based fertilizer N topdressings in four maize genotypes. Colour (of the first top maize leaf with fully exposed collar) as measured by comparison with different shades of green colour on a leaf colour chart (LCC) and maize grain yield was significantly correlated. The Cate–Nelson plot of chlorophyll (SPAD) meter/leaf colour chart values against relative grain yield of 0.93 for the experiments conducted during first two years indicated that LCC shade 5 during vegetative growth stages and LCC shade 5.5 at silking stage (R1) can guide crop demand driven N applications in maize. Evaluation of the established threshold leaf greenness during the next three years revealed that fertilizer N management using LCC 5 starting from six-leaf (V6) stage to before R1 stage resulted in improved agronomic and N recovery efficiency in different maize genotypes. There was no response to fertilizer N application at R1 stage. The study revealed that in maize, fertilizer N can be more efficiently managed by applying fertilizer N dose based on leaf colour as measured by LCC than blanket recommendation.

Research highlightsThe generally followed blanket recommendation of applying fixed N dose at fixed time intervals is not adequate for obtaining high agronomic and recovery efficiency of fertilizer N in maize. Matching fertilizer N supply with crop demand using threshold LCC shade 5 saved 25–50% fertilizer N. This study provides evidence for the usefulness of LCC guided need based fertilizer N management technology in assuring high yields and improvement in fertilizer N recovery efficiency. LCC being a cost effective, simple and farmer's friendly gadget can be easily used even by small and illiterate farmers. Thus the blanket recommendations of applying fixed N dose at fixed time intervals should be replaced with need based fertilizer N management technology using LCC in maize.