Site-Specific Fertilizer Nitrogen Management in Less and High N Responsive Basmati Rice Varieties Using Newly Developed PAU-Leaf Colour Chart

ABSTRACT

Fertilizer nitrogen (N) management in long-grained aromatic basmati rice (Oryza sativa) is critical because both below and above the optimum N application rate adversely affects yield. Multi-location field studies were conducted in northwestern India to formulate a site-specific N management (SSNM) strategy for basmati rice by monitoring the greenness of the fully expanded top leaf of the crop plants using a leaf color chart (PAU-LCC) specially developed at Punjab Agricultural University, Ludhiana. The green colour intensity of the successive panels of PAU-LCC increases with consistent decrease in optical reflectance by 1.6% (at 550 nm wavelength) and thus provides better precision in quantifying leaf colour greenness over the IRRI-LCC (the LCC developed at International Rice Research Institute, Philippines). The threshold leaf greenness at which a variety will respond to fertilizer N was found to be equal to LCC shade 3.5 and 4.0 for less and high N responsive varieties, respectively. Monitoring leaf greenness using LCC at weekly intervals and application of 10 kg N ha⁻¹ whenever leaf greenness was less than the specified threshold level constituted the appropriate SSNM strategy. The SSNM produced grain yield equivalent to soil-test-based fixed N rates but with 20 to 60% less N fertilizer. Significantly higher agronomic (average 40.8 vs. 24.5 kg grain kg⁻¹ N) and recovery (average 76.1 vs. 52.7%) efficiencies of fertilizer N were recorded with SSNM than with soil-test-based fixed fertilizer N rates. The SSNM also reduced N₂O and GHG emissions by 20.1 and 23.6% as compared to soil-test-based fertilizer N rates.

KEYWORDS:

• Basmati rice
• PAU-leaf color chart
• precision N management
• soil-test N use

Acknowledgements

The research was funded by Department of Biotechnology (DBT), Govt. of India, and BBSRC under the international multi-institutional collaborative research project entitled Cambridge-India Network for Translational Research in Nitrogen (CINTRIN) (DBT Grant No.: BT/IN/UK-VNC/42/RG/2014-15; BBSRC Grant No.: BB/N013441/1).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the department of biotechnology, ministry of science and technology [BT/IN/UK-VNC/42/RG/2014-15].