Multivariate Approach to Characterizing Soil Quality of Gabonese’s Ferralitic Soils

Assessing soil quality is essential for crop management and soil temporal changes. The present study aims to evaluate soil quality in the Ferralitic soils context countrywide. This assessment was done using multivariate soil quality indice (SQI) models, such as additive quality index (AQI), weighted quality indexes (WQIadd and WQIcom) and Nemoro quality index (NQI), applied to two approaches of indicator selection: total data set (TDS) and minimum data set (MDS). Physical and chemical soil indicators were extracted from the ORSTOM’s reports resulting from a sampling campaign in different provinces of Gabon. The TDS approach shows soil quality status according to eleven soil indicators extracted from the analysis of 1,059 samples from arable soil layer (0 - 30 cm depth). The results indicated that 87% of all provinces presented a very low soil quality (Q5) whatever the model. Among soil indicators, exchangeable K+ and Mg2+, bulk density and C/N ratio were retained in MDS, using principal component analysis (PCA). In the MDS approach, 50 to 63% of provinces had low soil quality grades with AQI, WQIadd and NQI, whereas the total was observed with WQIcom. Only 25% of provinces had medium soil quality grades with AQI and NQI models, while 12.5% (NQI) and 25% (AQI) presented high quality grades. Robust statistical analyses confirmed the accuracy and validation (0.80 r P ≤ 0.016) of AQI, WQIadd and NQI into the TDS and MDS approaches. The same sensitivity index value (1.53) was obtained with AQI and WQIadd. However, WQIadd was chosen as the best SQI model, according to its high linear regression value (R2 = 0.82) between TDS and MDS. This study has important implications in decision-making on monitoring, evaluation and sustainable management of Gabonese soils in a pedoclimatic context unfavorable to plant growth.

Antioxidant Protection Mechanisms Reveal Significant Response in Drought-Induced Oxidative Stress in Some Traditional Rice of Assam, India

Drought tolerance levels and antioxidant protection mechanisms were evaluated for 21 traditional rice varieties of Assam, India, along with Sahbhagi Dhan （drought tolerant） and IR64 （drought sensitive） as controls. Drought was imposed in hydroponic culture with polyethylene glycol 6000 （PEG6000） that was initially standardized with different concentrations. All the rice varieties showed apparent decreases in growth characteristics under drought stress （initially at 15% for 7 d followed by 20% PEG6000 for 7 d in Yoshida medium）. On the basis of standard evaluation score （SES）, eight rice varieties showed high drought tolerance which were carried forward for further biochemical analyses. Based on different morpho- physiological parameters, SN03 （Bora）, SN04 （Prosad Bhog）, SN05 （Kola Joha）, SN06 （Helash Bora）, SN08 （Salihoi Bao）, SN12 （Kola Amona）, SN20 （Ronga Bora） and SN21 （Sok-Bonglong） were identified as promising drought tolerant varieties. The non-enzymatic antioxidants activities viz., glutathione, ascorbate and enzymatic antioxidant activities such as superoxide dismutase （SOD）, catalase （CAT）, guaiacol peroxidase （GPX）, ascorbate peroxidase （APX）, glutathione reductase （GR） in shoots and roots of all the selected varieties revealed significant level of protection mechanisms as compared with controls. Enhancement in activities of the overall antioxidant enzymes including SOD, GPX, CAT, GR and APX under drought stress reflects their role in the adaptation process under water stress.