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Site-Specific nitrogen Management in Dry Direct-Seeded Rice Using Chlorophyll Meter and Leaf Colour Chart

Pedosphere 2015年第1期25卷 72-81页

作者： Ali Mohamed ALI Harmit Singh THInD Sandeep SHARMA YADVInDER-SInGH Department of Soil Science Punjab Agricultural University Department of Soil Fertility and Microbiology Desert Research Centre

The need to maintain high rice yields and improve fertilizer nitrogen(n)-use efficiency has fueled the use of tools such as leaf colour chart(LCC) and chlorophyll meter(SPAD meter) in managing fertilizer n based on colour of the leaf. Field experiments were conducted during 2011 to 2013 at Ludhiana, India to assess the need for basal n application and to establish critical threshold values of leaf greenness as measured by LCC and SPAD meter for formulating strategies for in-season management of fertilizer n in dry direct-seeded rice(DDSR). Avoiding application of n at sowing did not adversely affect rice grain yield, indicating that basal n application in DDSR was not necessary and might lead to reduced n-use efficiency. Monitoring n uptake rate during the growing season of DDSR suggested that n uptake rate peaked at the two growth stages: maximum tillering(42 to 56 days after sowing(DAS))and panicle initiation stages(70 to 84 DAS). Using the Cate-nelson procedure, critical LCC and SPAD meter values for fertilizer n application worked out to be 4 and 37, respectively. Real-time fertilizer n management strategy based on applying 30 kg n ha-1whenever SPAD meter or LCC readings fell below the critical values maintained optimum rice yields along with higher n-use efficiency than that observed by following blanket recommendation for fertilizer n in the region. The fixed-time variable-dose strategy consisted of applying prescriptive doses of 20 kg n ha-1at 14 DAS and 30 kg n ha-1at 28 DAS and corrective doses of 30, 40 or 50 kg n ha-1at 49 and 70 DAS depending upon LCC shade to be ≥ 4, 4–3.5, or nd SPAD meter readings to be ≥ 40, 40–35, orn optimal rice yield along with higher n-use efficiency as compared to the blanket recommendation. This study revealed that in DDSR, fertilizer n could be managed more efficiently using the tools of LCC and SPAD meter than the current blanket recommendation.

关键词： basal n application critical value grain yield leaf greenness n-use efficiency

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