Rapid assessment of specific leaf area and leaf nitrogen in peanut (Arachis hypogaea L.) using a chlorophyll meter

The present study investigates the potential use of a hand-held portable SPAD chlorophyll meter for rapid assessment of specific leaf area (SLA) and specific leaf nitrogen (SLN), which are surrogate measures of transpiration efficiency(TE) in peanut (Arachis hypogaea L.). The effects of sampling (leaf position, time of sampling and leaf water status) and climatic factors (solar radiation and vapour pressure deficit, VPD) on SLA and SPAD chlorophyll meter reading (SCMR) were studied in a range of peanut genotypes grown under field and greenhouse conditions. The correlation between SLA and SCMR was significant (r = -0.77, P < 0.01) for the second leaf from the apex but the correlation declined for leaves sampled from lower nodal positions. The diurnal fluctuation in SLA ranged from -20% to +10%, whereas SCMR was relatively unaffected by these diurnal changes. Solar radiation and VPD during the sampling period had a significant influence on the relationship between SLA and SCMR, largely through their effects on SLA. However, standardization of SLA for these environmental factors significantly improved the relationship between SLA and SCMR from -0.50 to -0.80 (P < 0.01), suggesting that, when protocols for leaf sampling and SLA measurements are followed, SCMR call be a surrogate measure of SLA. There were significant relationships between SLN and SCMR (r=0.84, P < 0.002) and SLN and SLA (r=-0.81, P < 0.01). These significant interrelationships amongst SLA, SLN and SCMR suggested that SCMR could be used as a reliable and rapid measure to identify genotypes with low SLA or high SLN (and hence high TE) in peanut.