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In a ®eld experiment, microbiological and chemical amelioration of a highly deteriorated alkaline soil (pH 10.6, exchangeable sodium percentage 95) was undertaken during 1989±92 using two reclamation technologies: namely, growing Karnal grass (Leptochloa fusca) as a ®rst crop in the absence of any amendment (biological reclamation) or applying gypsum as a chemical amendment for dierent cropping sequences. After ten months average dehydrogenase activity, used as a measure of catabolic activity of micro-organisms under anaerobic conditions, was 49.5 mg triphenylformazan (TPF) per g soil in treatments where the soil was reclaimed by growing Karnal grass, compared with 26.8 mg TPF by applying 50% of the estimated requirement of gypsum. After three years of reclamation, average dehydrogenase activity was 118.7 mg TPF per g soil with Karnal grass and 96.1 mg TPF with gypsum. After three years average microbial biomass carbon was 28% greater in the gypsum treatments (206.5 mg per kg soil) compared with Karnal grass treatments (161.7 mg). However, at this stage the ratio between average dehydrogenase activity and microbial biomass carbon was greater with Karnal grass (0.77) than in gypsum treatments (0.47). The microbiological properties changed more than the chemical properties of alkali soil as the time period advanced. After three years of reclamation, the average pH of the alkali soil dropped from 10.6 to 9.45 and the average exchangeable sodium percentage was reduced from 95 to 47.5. The increase in total organic carbon was 64% and in available nitrogen about 38% compared with the original soil. Higher microbial biomass carbon in gypsum treatments corresponded with lower exchangeable sodium percentage, higher availability of nitrogen and potassium and greater total yield of sensitive winter clovers.

Incubation studies in a highly alkali soil showed ammonia volatilization losses from applied nitrogen to be largely governed by pH/alkalinity of the system. Submergence of the soil decreased the pH value resulting in lower losses. The anion of ammonium did not influence the losses. Ammonia volatilization obeyed first order kinetics. The losses were considerably reduced by deep placement of urea but were unchanged with variation in temperature from 20 ~ to 40~ Urea or ammonium sulphate lost similar amounts of nitrogen. Losses from green manure were very low. The results are discussed for their implication in nitrogen fertilizer efficiency and management in alkali soils.

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A field experiment in an alluvial sandy loam saline soil was conducted during the winter (rabi ) season from 1997-98 to 1999-2000 at the Central Institute for Research on Buffaloes, Hisar, to study the effect of saline drainage water (EC = 3.6 -7.4) on five (rabi ) forage crops: oat (Avena sativa), rye grass (Lolium rigidum), senji (Indian clover) (Melilotus indica) berseem (Egyptian clover) (Trifolium alexandrinum) and shaftal (Persian clover) (Trifolium resupinatum). All the crops were established using canal water as pre-sowing irrigation and the various irrigation strategies were imposed subsequently. Irrigation with canal water resulted in a 115 % increase in forage yield compared with the saline drainage water. The results suggested that alternate irrigation with saline drainage water increased the yields of all the forage crops compared with using saline drainage water only. Further, alternate irrigation, starting with canal water, was superior to alternate irrigation starting with saline drainage water because less salt was added in total. Oat produced the largest green-forage yield (32.3 t ha −1 ) in the first year while rye grass gave its maximum in the second (34.6 t ha −1 ) and third years (37.0 t ha −1 ). Persian clover performed better than did Egyptian clover in all the three years. Interaction between species and irrigation treatments was significant. In comparison with canal irrigation water, there was a 36 %, 42 %, 54 %, 68 %, and 85 % yield reduction in rye grass, oat, Persian clover, Egyptian clover and senji, respectively when only saline drainage water was used for irrigation reflecting their relative tolerances of salinity. Yields declined linearly for all crops with increases in the quantity of salt applied. I N T RO D U C T I O NSaline soils are widespread in the arid to semi-arid parts of the world, including in the Indian states of Haryana, Punjab and Rajasthan, where the mean annual rainfall is generally less than 550 mm. It has been estimated that 17 % of the total irrigated area in India is affected by salt (Ghassemi et al., 1995). These soils generally have a shallow saline water table and often remain waterlogged or submerged for quite a long time. As a result, crop production on these soils becomes extremely difficult, yields are very low and cultivation becomes uneconomical. The Hisar district of Haryana, (29 • 10 N; 75 • 46 E, 215 m asl) represents such a situation with an annual precipitation of 425 mm.For successful crop production on such soils, leaching, together with sub-surface drainage, is required to flush out the salts from the root zone. Disposal of the saline