MSc

An investigation was undertaken with the main objectives of estimating the status of available micronutrients, viz., iron, manganese, zinc, copper, molybdenum and boron in the major rice soils of Kerala and their correlation with the relevant physic – chemical properties of the soils.
Five major rice soil groups of kerala, viz., lateritic alluvium, Kari, Karapadom, Kayal and coastal sandy alluvium from different parts of South Kerala were used for the study. Thirty samples each from two depths (0 – 20 and 20 – 40 cm) were collected from the five soil groups.
The physic – chemical characteristics of the various samples showed wide variations. The soils were all heavy textured except the coastal sandy alluvium, which was loamy sand. All the soils were acidic in reaction. Karisoils had the highest content of organic carbon and the lateritic and coastal sandy alluvium, the lowest.
Total nitrogen was lowest in the coastal sandy alluvium and highest in the Kayalsoils. Low contents of available nitrogen were recorded in the coastal sandy alluvium and in the lateritic alluvium. Total phosphorus was low in the Karapadom soils as compared to the other soil groups. Available phosphorus was rather high in all the soil samples. Total potassium was lowest in the coastal sandy alluvium and highest in the Kari soils. Exchangeable potassium was comparatively high in Kari, Karapadam and Kayal soils. Lateritic alluvium contained medium amounts and coastal sandy alluvium the lowest levels of exchangeable potassium. Total calcium and magnesium were lowest in the coastal sandy alluvium. The Kari and Kayal soils contained relatively higher amounts of these elements. Exchangeable calcium and magnesium were also very low in the coastal sandy alluvium.
The highest levels of available iron and copper were found in Karapadom soils and the lowest in the coastal sandy alluvium. Available manganese was highest in the lateritic alluvium and lowest in the coastal sandy alluvium. Significantly high contents of zinc were recorded in Karapadom soils and very low levels in the coastal sandy alluvium. Available molybdenum was significantly high in lateritic alluvium and very low in the coastal sandy alluvium. Kari, Karapadom and Kayalsoils contained significantly higher amounts of boron compared to the lateritic alluvium and the coastal sandy alluvium.
No definite variation in the distribution of the micronutrient elements with depth was noticed except for molybdenum, which decreased significantly with depth.
Available iron was negatively and significantly correlated with pH in Kari soils and non – significantly in lateritic alluvium, Kayal and coastal sandy alluvium. Available iron was positively and significantly correlated to organic carbon in lateritic and coastal sandy alluvium. Significant positive correlation of available iron with available phosphorus was observed only in the coastal sandy alluvium. In the lateritic and coastal sandy alluviums significant positive correlations of available iron with exchangeable potassium were noticed. No antagonistic relations of available iron with other micronutrients was observed.
In Kari soils significant negative correlation between available manganese and pH was noticed, whereas, in the lateritic alluvium and Karapadom soils it was significantly positive. The relation of available manganese with organic carbon was positive and significant in Kari soils, but the correlation with clay was negative and significant. Total nitrogen was positively and significantly correlated with available manganese in lateritic alluvium and Kari soils. Significant negative correlations of available manganese with available phosphorus was noticed in lateritic alluvium and Karapadom soils. Available manganese was positively and significantly correlated with total potassium in Kayal soils. In lateritic alluvium, coastal sandy alluvium and Kayal soils, available manganese was positively and significantly correlated with exchangeable calcium and magnesium. Positive significant correlations of available manganese with available iron, zinc and boron in Kari soils and with available copper and zinc in the Karapadom soils were observed.
The correlation of available zinc with pH was positive and significant in Karapadom soils. In Kayal soils highly significant positive correlation was noticed between available zinc and organic carbon. Available zinc was positively and significantly correlated with exchangeable potassium in lateritic alluvium, Kayalsoils and coastal sandy alluvium.
Available copper was positively and significantly correlated with pH in Kari, Karapadom and Kayal soils. The correlation of available copper with organic carbon was negative and significant in the Kari and Karapadomarea. Available copper was also negatively and significantly correlated with available phosphorus in these soils. In coastal sandy alluvium the correlation was positive and significant. Available copper was positively and significantly correlated with total potassium in lateritic alluvium, Kari and coastal sandy alluvium. With exchangeable potassium the same trend was noticed in the Kari and Kayalsoils.
In coastal sandy alluvium the correlation between available molybdenum and pH was negative and significant, whereas in the other soil groups it was non – significant. Available molybdenum was positively and significantly correlated with organic carbon in lateritic and coastal sandy alluvium. The correlation of available molybdenum with exchangeable calcium and magnesium noticed in the lateritic alluvium and Kayal soils was significantly positive.
Hot water soluble boron was significantly and negatively correlated with pH in Kari soils. Significant positive correlations of hot water soluble boron with organic carbon was noticed in Kari and Kayalsoils. Correlations of boron with the coarse sand fraction noticed in the coastal sandy alluvium was positive and significant.