Long-term effects of fertilization on some soil properties under rainfed soybean-wheat cropping in the Indian Himalayas Ved Prakash 1 , Ranjan Bhattacharyya 1 , Govindan Selvakumar 1 *, Samaresh Kundu 1 , and Hari Shanker Gupta 1 1 VivekanandaInstituteofHillAgriculture,IndianCouncilofAgriculturalResearch,Almora±263601,Uttaranchal,India AcceptedJuly12,2006 Summary This study aims to examine the effects of long-term fertiliza- tion and cropping on some chemical and microbiological properties of the soil in a 32 y old long-term fertility experi- ment at Almora Himalayan region, India) under rainfed soy- bean-wheat rotation. Continuous annual application of recommended doses of chemical fertilizer and 10 Mg ha ±1 FYMonfreshweightbasisNPK+FYM)tosoybeanGlycine max L.)sustainednotonlyhigherproductivityofsoybeanand residual wheat Triticum aestivum L.) crop, but also resulted inbuild-upoftotalsoilorganicCSOC),totalsoilN,P,andK. Concentration of SOC increased by 40% and 70% in the NPK + FYM±treated plots as compared to NPK 43.1 Mg C ha ±1 ) and unfertilized control plots 35.5 Mg C ha ±1 ), respec- tively. Average annual contribution of C input from soybean was 29% and that from wheat was 24% of the harvestable abovegroundbiomassyield.AnnualgrossCinputandannual rate of total SOC enrichment from initial soil in the 0±15cm layerwere4362and333kgCha ±1 , respectively, for the plots under NPK + FYM. It was observed that the soils under the unfertilized control, NK and N + FYM treatments, suffered a net annual loss of 5.1, 5.2, and 15.8kg P ha ±1 , respectively, whereas the soils under NP, NPK, and NPK + FYM had net annual gains of 25.3, 18.8, and 16.4kg P ha ±1 , respectively. There was net negative K balance in all the treatments ran- ging from 6.9kg ha ±1 y ±1 in NK to 82.4kg ha ±1 y ±1 in N + FYM±treated plots. The application of NPK + FYM also recorded the highest levels of soil microbial-biomass C, soil microbial-biomass N, populations of viable and culturable soil microbes. Key words: long-termexperiment/soilorganicC/soilmicrobial- biomassC/soilmicroorganisms/FYM/inorganicfertilizers/ sandyloamsoil ã 2007WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 1436-8730/07/0204-1 J. Plant Nutr. Soil Sci. 2007, 170, 1±10 DOI: 10.1002/jpln.200622032 1 1 Introduction Agriculturalpracticesthatimprovesoilqualityandagricultural sustainability have received much attention from researchers and farmers. In any agro-ecosystem, soil receives consider- able annual carbon C) inputs through left-over biomass of leaf-fall, stubble, roots, and root exudates as well through external sources like farmyard manure FYM) and compost. Among the agricultural practices in particular cultivation and organic amendments regulate the soil microbial biomass; this affects Cmineralization, nutrient cycling, and turnover of organic matter OM) McGill et al., 1986). Seasonal crop growth may influence soil microbial dynamics by altering the temporal and spatial distribution of organic inputs Franzluebbers et al., 1995), and a decline in the microbial biomass occurs after the introduction of arable agriculture Saviozzi et al., 1994). Nutrient fluxes through microbial bio- massareofatleastoneorderofmagnitudefasterthaninthe remaining OM Dalal, 1998) leading to the suggestion that microbial biomass could be used as an important indicator of changes of soil health and soil quality as influenced by agri- culturalmanagementpracticesSparling,1997).Hence,influ- ence of long-term application of chemical fertilizer and man- uresonsoilbiologicalhealthisanimportantareaofinvestiga- tionforassessingsustainability.Thebiologicaldegradationof soil is a less understood area, and it is caused due to the decline in diversity and activity of soil microflora and fauna. Often it is observed that increased inputs compensate for and mask losses in productivity associated with soil degrada- tionEivazi etal.,2003). Microorganisms, that comprise the Soil microbial-biomass SMB) pool, control the flow of C and cycling of nutrients in soil. The SMB is regarded as a major nutrient sink during C immobilization growth) and a source duringmineralization decay). This fundamental process is important to the long- term conservation of SOC through the production of precur- sors of humic substances. The formation and stabilization of macro-aggregates in FYM-treated soils is likely to be a key mechanism for the protection and maintenance of SOM Beare et al. 1997) and microbial habitat Dick, 1992). Soil microbial properties such as microbial biomass, distribution and activity of microbial populations have been used to pre- dictsoilbiologicalstatusandtheeffectsoffarmmanagement practices on soil quality Kaur et al., 2005). The critical cause-effect relationship between soil management and soil quality can only be established through long-term experi- mentsLal and Stewart,1995). Incorporation of OM in the form of FYM enhances the organic-C level of the soil Kundu et al., 2002) and has direct and indirect effects on soil properties and processes. Long- term experiments LTEs) are valuable for evaluating the effects of continuous cropping on the capacity of a system to sustain nutrient supply and productivity Gami et al., 2001). Several LTE's conducted in S Asia, show yield trends and build ups of SOC of varying degrees in treatments which received annual carbon inputs through external application of FYM, while in some locations, annual application of NPK only showed marginal build up of SOC Gami et al., 2001; Bhandari etal.,2002; Nambiar ,1994).However,moststudies were restricted under irrigated conditions in rice-wheat sys- tems.Wefoundnoreportofyieldtrends,annualCinput,and soil chemical and microbiological properties under a long- *Correspondence:Dr.G.Selvakumar; e-mail:gselva74@rediffmail.com