Lekhika Borgohain

 1.0 Introduction
A hill may refer to a particular section of flat terrain without a massive summit. The total forest cover is around 7,082,730 sq. km, which is about 21.54 percent of the total area of the country. The forest area may be differentiating into dense, moderately dense and slightly dense forest. Hill States in India with only 18 percent of geographical area of the country account for 34 percent of the total forest cover and in between 2015-17, India has added 6,778 of forest area. The low productivity of the agricultural sector in hilly areas is largely attributed to low and decreasing soil fertility due to many factors such as soil acidity, soil erosion, continuous cropping and inadequate sustainable soil fertility management. About 21 million ha of acid soils are found in NEH (North Eastern Hill) region including Sikkim with maximum area under Arunachal Pradesh (6.8 Mha) followed by Assam (4.7 Mha), Meghalaya, (2.24 Mha), Manipur (2.19 Mha) and Mizoram (2.0 Mha). Soil acidity is associated with hydrogen (H), aluminium (Al), iron (Fe) and manganese (Mn) toxicities to plant roots and corresponding deficiencies of plant available phosphorous (P), molybdenum (Mo), calcium (Ca), magnesium (Mg) and potassium (K), which negatively affects soil fertility and productivity. In acid soils with a high mineral content, the primary factor limiting plant growth is Al toxicity.

2.0 Reasons of Soil Acidification Under Hilly Region
Soil acidification rates are a function of the total H+ ion equivalents added or generated in the soil and the buffering capacity of the soil (Coote et al., 1989). In the case of plant induced processes, reactions that causes acid generation are carbon assimilation (Felle, 1988), uptake and assimilation of nitrogen (Bolan et al., 1991; Barman et al., 2014) and uptake and assimilation of sulphur (Ezekiel, 2006). Also, regular ammonium based fertilizer use is one of the major contributors of soil acidification under managed ecosystems. The Al released from soil minerals under acid conditions occurs as Al(OH)2+, Al(OH) and Al(H2O)3+, which is also a source of acidity to the soil causes toxicity and greatly reduced yield and crop quality (Godsey et al., 2007; Jovanovic et al., 2006). Also, researchers have found that soil acidification can be induced by elevated CO2 (Chand and Mondal, 2000). Long term application of nitrogenous fertilizers at higher rate significantly decreases the soil pH and exchangeable bases (Ca² and Mg²) but significantly increases the exchangeable Al (Jackie et al., 2010).

3.0 Management Practices
Liming is an important practice to achieve optimum yields of all crops grown on acid soils. Application of lime at an appropriate rate brings several chemical and biological changes in the soils, which are beneficial or helpful in improving crop yields on acid soils. The liming of acidic soils result in the release of P for plant uptake; this effect is often referred to as ‘‘P spring effect’’ of lime (Bolan et al. 2003). The effectiveness of liming materials also depends on the organic matter of the soil. The highest values of buffering capacity index (BCI=1.49) and LR (18 t ha-1) was associated with the soil with highest OM content (4.89%). Similarly; the lowest BCI (0.55) and LR (5.6 t ha-1) was found in the soil having the lowest OM content (1.03%). OM content of soil was strongly correlated with BCI (r= 0.824**, p< 0.01) and LR (r= 0.862**, p< 0.01) (Manoj 2012). Evidences are also there that the management of acid soil can also be done by application of burnt lime which contains about 92.5% CaCO₃ (Kisinyo et al., 2012).

4.0 Future Strategies
There is a need of complete database of acidity affected areas to know its trend so that it will be helpful in demarcated the area which have low acidity, medium acidity and highly acidity. The data should be user interface in the form of GPS or GIS based. Moreover balance fertilization should be adopted and research should be done to develop acid tolerant varieties. Industrial waste such as Paper Mill Sludge (PMS), Spent lime (sugar factory waste), also waste like Bagasses, oilcakes etc. can be used as ameliorant.

5.0 Conclusion
Soil acidity is a major problem for agricultural productivity worldwide. No doubt, Liming is an important practice to achieve optimum yields of all crops grown in acid soils. But there are also some other management practices by which we can control soil acidification processes. Development of acid tolerant crop, Balance fertilization, intense grazing practices and modified cropping practices will also reduce the soil acidity to a great extent. Integrated Nutrient Management (INM) also plays a major role in reducing the soil acidity in hilly areas.

  • A.A. Ezekiel (2006). Strategies for improving crops use-efficiencies of fertilizer nutrients in sustainable agricultural systems. Pakistan J. Nutr. 5(2): pp.85-193.
  • C.B. Godsey, D.B. Pierzynski and R.E. Mengel (2007). Evaluation of common lime requirement methods. Soil Sci. Soc. Ame. J. 71: pp.843-850
  • D.R. Coote, S. Singh and C. Wang (1989). A proposed methodology for assessing the relative impact of acid rain and nitrogenous fertilizers on acidity of agricultural soils in Canada. Can .J. Soil Sci. 69: pp.611-627
  • H.H Felle (1988). pH Regulation in Anoxic Plants.Annals of Botany. 96: pp.519–532
  • J.K. ManoJ, S. Hazarika, B.U. Choudhury, T. Ramesh, B.C. Verma and Bordoloi (2012). Liming and Integrated Nutrient Management for Enhancing Maize Productivity on Acidic Soils of Northeast India. Indian Journal of Hill Farming. 25(1): pp.35-37
  • J.P. Chand and B. Mondal (2000). Nature of acidity in soils of West Bengal. J. Ind. Soc. Soil Sci. 48: pp.20-26.
  • L.S. Jackie, H. Zhang, K. Girma, W.R. Raun and C.J. Penn (2010). Soil acidification from long-term use of nitrogen fertilizers on winter wheat. Soil Sc. Society of American Journal. 75: pp.957-964
  • M. Barman, L.M. Shukla, S.P. Datta and R.K. Rattan (2014). Effect of applied lime and boron on the availability of nutrients in an acid soil. J. Plant Nutr. 37(3): pp.357-373.
  • N.K. Fageria and V.C. Baligar (2008). Ameliorating soil acidity of tropical oxisolby liming for sustainable crop production. In. SPARKS DL, editor. Advances in Agronomy.99.Brazil: Academic press. pp.345-389
  • N.S. Bolan and M.J. Herdley (2003). Role of Carbon, Nitrogen and Sulfur cycles in soil acidification. “Handbook of soil acidity”. New York: Rengel Z: pp. 29-56
  • P.O. Kisinyo, P.A. Opala, S.O. Gudu, C.O. Othieno,  J.R. Okalebo, V., Palapala and A.N.  Otinga (2012). Recent advances towards understanding and managing Kenyan acid soils for improved crop production. African J. of agricultural research.9 (31): pp.2397-2408
  • Z. Jovanovic, I. Djalovic and M. Kovacevic (2006). Influences of liming on vertisol properties and yield of field crops. Cereal Res.Commun. 34: 517-520
About the author: Ms Lekhika Borgohain completed my B.Sc. in Agriculture & M.Sc. in Soil Science from Assam Agricultural University (AAU), Jorhat- 13, Assam (India). At present, I am pursuing Ph.D. in the Department of Soil Science, AAU, Jorhat. I am the recipient of ‘Meritorious Bayer’s fellowship, 2019’ for my Ph.D research work. I am engaged with various writings and also with social works. Along with my Ph.D course I am pursuing a international 1 year course (International Agriculture and Rural Development) offered by Cornell University, New York. For that I have visited to Cornell University, USA for 15 days and learned about Agriculture in developed country.

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