Evaluation of soil suitability to rice-based cropping system in the River Island of Majuli, Assam

A reconnaissance soil survey was undertaken in the river island of Majuli sub-division, the biggest ‘char’ area of the river Brahmaputra for mapping of the soils. Three physiographic units viz. active flood plain, lower terrace and upper terrace were recognized in the island. Four soil series namely Majuli, Pakajara, Lahangaon and Ratanpur were identified. Their spatial distribution showed the occurrence of Majuli and Pakajara series on the active flood plain, Pakajara and Lahangaon series on lower terrace and Ratanpur and Lahangaon series on upper terrace. These soils remain inundated during the rainy season and therefore, the soil drainage is very poor and has resulted in the formation of low chroma (≤2) mottles in the subsoils of all the series. The Majuli and Pakajara series are coarse textured with dominantly sand, loamy sand and sandy loam texture distributed irregularly with depth. The Lahangaon and Ratanpur series have somewhat finer texture dominated by loam and silt loam. These soils are neutral to slightly alkaline. They have high content of organic carbon in the surface layer. The cation exchange capacity is generally low in the soils except Ratanpur series which has CEC values more than 9 cmol(p+)kg−1 soil in all the horizons. The cropping intensity is low in the island. The suitability evaluation of these soils is made to help in choosing a suitable crop in the post-rainy season and improve the cropping intensity. Cultivation of rice during the rainy season is an automatic choice as the soils remain inundated. The soils are evaluated to grow crops like wheat, potato, cabbage, French bean, tomato, cowpea, pea and rapeseed in the post-rainy season. The Ratanpur soil series is suitable for most of the crops due to loam or silt loam texture. The Pakajara and Lahangaon series are moderately suitable for most of the crops as their coarse texture is the limitation. The sandy texture of Majuli series in most parts of control section is a serious limiation for crop growth. However, the sandy loam surface with high organic matter makes this soil marginally suitable to most of the crops including rice and wheat. The suitability evaluations, discussed on the basis of soil characteristics, will help the farmers in making decisions with regard to crop selection for the post-rainy season.