Assessment of soil quality in the post flood scenario of AEU 6 in Thrissur and Malappuram districts of Kerala and mapping using GIS techniques

Abstract

Kerala State experienced a devastating flood in 2018, causing significant damage to agricultural sector and human life. Major crop systems in the State have been negatively impacted, with more than 80 per cent of paddy fields including in kole lands. Kole land (AEU 6) is a low lying area situated 0.5m to 1m below mean sea level, which spread over an area of 13,632 ha in coastal parts of Thrissur and Malappuram districts of Kerala. Considering the damage caused by the flooding to the kole lands, the present study was carried out in the flood affected areas of kole lands in order to put forward post flood management strategies. A survey was carried out to identify the flood affected locations in kole lands. Hundred georeferenced composite soil samples were collected from seven block panchayats viz., Mullassery, Anthikkad, Cherpu, Irinjalakkuda, Puzhakkal, Perumpadappu and Ponnani of Thrissur and Malappuram districts and analysed for different physical, chemical and biological soil quality indicators. The results showed that the soils of kole lands were low in bulk density and high in porosity while particle density varied from 2.05 to 2.67 Mg m-3. Maximum water holding capacity and soil moisture content of the soil samples ranged from 18.11 to 73.49 per cent and from 12.00 to 41.60 per cent respectively. High mean weight diameter of soil was also noticed in the study. The soils were acidic in reaction and the exchangeable acidity varied from 0.05 to 2.2 cmol (+) kg-1. Electrical conductivity was below toxic level. The organic carbon was shifted towards medium to high level from low to medium after the flood. Available nitrogen content was high with a mean of 704.59 kg ha-1. Availability of phosphorus and potassium were in the medium status within 55 and 44 per cent of samples respectively. Among the secondary nutrients, available calcium was sufficient in 64 per cent of soil sample while available magnesium was deficient in 72 per cent of soil samples and available sulphur was sufficient in 89 per cent of soil samples. The micro nutrients like available Fe, Mn and Zn were high in AEU 6. Available copper was sufficient in 83 per cent of soil samples, whereas available boron was deficient in all the soil samples. Effective cation exchange capacity of soil in AEU 6 varied from 0.62 to 9.00 cmol (+) kg-1. Among the biological attributes, kole lands showed high dehydrogenase activity while microbial biomass carbon was found medium in 58 per cent of soil samples. Available Ca, S, N, porosity, exchangeable acidity, available Fe, Zn, particle density and available B formed the minimum data set for soil quality index. The highest mean soil quality index was recorded in Mullassery block panchayat and the lowest mean was in Cherpu block panchayat. Relative soil quality index varied from 25.93 to 72.22 per cent with 63 per cent of soils showing poor soil quality and 3 per cent showing high soil quality. Nutrient index was high for nitrogen and medium for phosphorus, potassium and organic carbon in kole lands. Significant positive correlations were observed between organic carbon and available nitrogen, organic carbon and soil moisture content. Negative correlation existed between bulk density and porosity, organic carbon and bulk density. The post flood study in kole lands revealed that drastic changes in soil environment had occurred with more than 50 per cent of soil samples falling in low soil quality range. Hence, proper adoptions of site specific soil management practices are essential to improve the soil fertility in kole lands.