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,c
a Dep. of Soils, Punjab Agric. Univ., Ludhiana 141004, Punjab, India
b IRRI, DAPO Box 7777, Metro Manila, Philippines
c Soil and Water Sci. Div., IRRI, DAPO Box 7777, Metro Manila, Philippines
* Corresponding author (j.k.ladha{at}cgiar.org)
Received for publication August 7, 2001. Overapplication of N in cereal crops leads to low N recovery efficiency and risk of NO3 pollution of ground water. The chlorophyll meter, also known as SPAD meter, is a simple, portable diagnostic tool for identifying crop N status. We used it to test need-based N management approaches for rice (Oryza sativa L.) and wheat (Triticum aestivum L.) on a loamy sand in northwestern India. Applying 30 kg N ha-1 each time the SPAD value fell below the critical value of 37.5 resulted in application of 90 kg N ha-1, which produced rice yields equivalent to those with 120 kg N ha-1 applied in three splits. Using a SPAD value of 35 was inadequate for the two rice cultivars because it resulted in application of only 60 kg N ha-1 and, thus, low yields. With high inherent soil fertility resulting in rice yield of >3 Mg ha-1 in zero-N plots, applying N basally or a week after rice transplanting did not further increase yield. Limited experimentation with leaf color chart (LCC) indicated that N management based on LCC shade 4 helped avoid overapplication of N to rice. Wheat responded to N application at maximum tillering (MT) when SPAD value fell below 44. Wheat yield increased by 20% when 30 kg N ha-1 was applied at SPAD value of 42 at MT. Results show that plant need–based N management through chlorophyll meter reduces N requirement of rice from 12.5 to 25%, with no loss in yield.
Abbreviations: AE, agronomic efficiency • CRI, crown root initiation • DAT, days after transplanting • LCC, leaf color chart • MT, maximum tillering • RE, recovery efficiency • SPAD, soil plant analysis development
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