GUWAHATI: A study on the sand and silt-deposited areas of Lakhimpur and Dhemaji districts conducted by the Regional Agricultural Research Station (RARS), North Lakhimpur, under Assam Agricultural University (AAU) has suggested sustainable crop management for improvement of agro-ecosystems dominated by sandy soils.
The study also observed that until and unless a systematic watershed management was implemented on the Arunachal hills to prevent erosion, no crop and soil management strategies would be permanently successful in the sand-deposited areas of the Assam plains.
Vast tracks of cropland in the two districts have turned barren following large-scale accumulation of sand from the floodwaters of the Brahmaputra and its tributaries, including Subansiri, Dikrong, Singora, Ranganadi, Simen, Nonoi, Ghagor, Boginadi, Jiadhol, Moridhol, Eradhol, Samarajan, etc.
The sand- and silt-affected area (including riverine sand area) bases on visual interpretation and satellite imagery during January-February 2014 for Dhemaji is 145.76 sq km, and 118.45 sq km for Lakhimpur during the same period.
The crop survey and screening revealed successful growing of a few crops like rice (varieties like Bali Sali and Kekowa Bao), millets, blackgram, garlic, French bean, linseed, sugarcane, sweet potato, chilli, colocasia, yam, tapioca, brinjal, bamboo, jackfruit, gooseberry, sisum, arhar, Assam lemon, pumpkin, cauliflower, cabbage, knolkhol, potato, tomato, apple ber, broom grass and aromatic plants like vetiver, citronella, etc.
Dr Prabal Saikia, Chief Scientist, RARS, told that, depth of deposition varied from a few centimetres to 3-4 metres. Therefore, cropping strategies are to be different for areas having different depth depositions. The approach will also vary depending on the type of deposition and soil fertility. A site specific nutrient management is better in such situations than blanket recommendations of fertilizers.
The study recommended scrapping of the top layer (when the depth of deposition is too high) for non-agricultural purposes like highway construction, etc. Crops like watermelon, dwarf bananas, etc., may be grown in deep pits after application of sufficient organic matter.
The study revealed that the quantity and quality of sand and silt casting differed with the source river. Deposits of sand also differed in depth, and in physical and chemical properties. The surface soil acidic quality varied widely across the study areas in the two districts, ranging from very strongly acidic to moderately alkaline. The organic carbon content also varied from very low to medium.
The other members of the research team were Dr Bikram Borkotoki, Junior Scientist, RARS, Dr Subal Maibangsa, Head, KVK, Karbi Anglang, AAU and Dr Niloy Bora, Professor, College of Horticulture, AAU.
River source-wise physical and hydrological properties for the Brahmaputra, Ranganadi, Jiadhal, Jalakiasuti, Dulung and Durpang for different depths had also been calculated using modelling software developed by the United States Agricultural Research Service (USDA) in cooperation with the Department of Biological System Engineering, Washington State University. Depth-wise penetration resistance has also been found out using penetrometer.