Soil acidity acclaims paramount importance among the chemical and the electrochemical characteristics that influence soil fertility and crop production. Detailed investigations were carried out to find out the acidity characteristics of wetland rice soils of Kerala,the southern most State of Indian Peninsula and to suggest suitable ameliorative measures to alleviate the acidity. Twelve soil profiles and 120 surface samples representing the major rice growing tracts of Kerala were used for this study.

Characterisation of acidity in major wetlands of Kerala

Name of wetland	Active acidity	Exchange acidity	Non exchange acidity	Potential acidity
	Dry pH 1:1(H2O)	cmol(+)kg-1	cmol(+)kg-1	cmol(+)kg-1
Vellayani-Tropic Fluvaquent	4.35	1.58	17.42	19.00
Karamana-Typic Tropaquent	5.28	0.41	13.59	14.00
Kari(Thakazhi) -Typic Sulphaquent	3.20	16.40	113.65	130.05
Karapadom(Nedumudi) -Aeric Tropaquept	4.31	3.31	32.59	35.90
Kayal(D Block) -Typic Hydraquent	4.44	4.93	36.67	41.60
Pokkali(Njarakkal) -Sulphic Tropaquept	3.18	8.03	33.17	41.20
Kole(Anthikkad) -Typic Tropaquept	4.63	1.38	28.62	30.00
Kaipad(Pazhayangadi) -Tropic Fluvaquent	5.27	0.69	15.00	15.69
Pattambi-Aeric Kandiaqult	4.93	0.49	18.81	19.30
Kattampally-Tropic Fluvaquent	5.46	0.16	19.63	19.79
Wynad-Typic Tropaquent	4.83	0.34	12.86	13.20
Chittoor-Petrocalcic Calciustert	6.99	0.12	19.13	19.25

All the soils studied were acidic except black soils of Chittoor.  Maximum exchange acidity was noticed in Kari soils (16.4 cmols) followed by Pokkali soils (8.03 cmols) and the minimum in Chittoor soils (0.12 cmols). Major part of potential acidity was constituted by non exchange acidity (pH dependent acidity) because pH dependent charges are more in Kerala soils having kaolinite as the predominant clay mineral and high content of sesquioxides. Path coefficient analysis of important acidity contributing factors and the correlation and regression analysis of soil characteristics indicated that exchangeable aluminum was the best parameter for measurement of acidity. Exchangeable aluminum method for calculating lime requirement was found to be the best for all soils.  Polder cultivation with low rates of lime (1000 kg ha-1) in split doses and washing 2 or 3 times after maintaining 10cm water level can be recommended for economic returns from Kari and Pokkali lands which are acid sulphate soils.  Subsurface tile drains are used to remove acidity as well as salinity. Keeping the soil under submergence as for as possible was found to be the best remedy for these soils. High dose of lime application caused reacidification of soil at a faster rate especially in soils having high potential acidity.  Rice-fish farming and Rice-livestock(Duck)farming were found to be remunerative in these areas. Studies on submergence showed that all the wetlands except the acid sulphate soils attained a pH value of 5.5 within two weeks of submergence. They did not require lime to raise the pH for rice cultivation. A rapid chemical and electro chemical changes occurred within two weeks of submergence and there after the processes tended to stabilize. The stable milieu favoured rice because the nutrient supply was adequate and the level of toxins was low. The present study underlines the cheap and easy method of alleviating acidity of major wetlands by optimum submergence and scientific water management. Further the study revealed the feasibility of liming in soils with severe acidity.