Effect of paddy straw enrichments on nitrogen availability in sandy regosol

Sandy regosol is the major soil group existing in Batticaloa District, Eastern Province, Sri Lanka. They are largely dominant in the cultivated area in this narrow strip along the sea. Regosols of sandy are usually nutrient-poor. Humus accumulatiou in the topsoil improves the nutrient supply. N content of soil show a distinct decrease as soil textuie becorne coarser (Millea 2004). Therefore proper N management is important for sandy regosol.


Introduction
Sandy regosol is the major soil group existing in Batticaloa District, Eastern Province, Sri Lanka.
They are largely dominant in the cultivated area in this narrow strip along the sea.Regosols of sandy are usually nutrient-poor.Humus accumulatiou in the topsoil improves the nutrient supply.N content of soil show a distinct decrease as soil textuie becorne coarser (Millea 2004).Therefore proper N management is important for sandy regosol.
Manures behave differently as sources of available nitrogen due to differences in the amounts and forms of nitrogen in the manure (Qian and   Schoenau, 2001).Availability of nitrogen from organic sources is mainly influenced by the rate of mineralization.Nitrogen mineralization is a microbiological process in which C:N ratio is an important factor affecting the rate of mineralization (Mueller et a\.,1998).
Among the crop residues paddy straw is the most available organic material in Sri Lanka and the nutrient content of soil can be increased by its application to the soil (Amarasiri and   Wjckramasinghe, 1988).Due to its high C:N ratio and slow decomposition rate.paddy straw needs more attention to increase their efficient use in Agriculture.Enrichment of paddy straw with other materials which enhance the decomposition of paddy straw may be a useful practice in their efficient soil management.Ariyaretne (2008) also repported that the incorporation ofplant residue like paddy straw with high C: N ratio into the soil takes long duration for decomposition; therefore N is not available to the plants temporarily.Thus suitable enrichment of paddy straw for quick decomposition of straw is important.
Effective microorganisms (EM) is a liquid microbial inoculant that contains assorted culture of beneficial fertilizer without fermentative microorganism such as lactic acid bacteria (Lactobacillus Spp), yeast (,lac charomyces spp), photosynthetic bacteria (Rhodops eudo monas spp), actinomycetes and fermenting fungi (Takashi Kyan et a|.,1999).Application EM has been reported to result in rapid proliferation ofits constituent beneficial microorganism.The beneficial organisms have also been ascribed with the ability to encourage the mineralizationof soil organic matter, which is the main mechanism through which EM could some benefit soil health and plant nutrition (Piyadasa, 1995).Plants with lower C:N ratio is usually considered to decompose quickly than those with higher C:N ratio (Pan and Papendick, 1 97ll).Gliricidia could be anributedto the inrproventent ofthe rhizosphere by the added organic lnatter, especially those with a lower C:N ratio (Graves et a|.,2004).The present studywas undertaken to ascertain the effect ofpaddy straw enrichments with Gliricidia and EM on N availability in sarrdy regosol.

Matcri:rls and Methods
The laboratory experiment was conducted at Eastern University, Sri Lanka which is located in the low country, dry zone of Sri Lanka.The soil used in this study was sandy regosol (pH 6.9, C 0.41%,N 0.0356%).Three organic materials used: paddy straw (C:N ratio 63:1, N 0.612%) , EM treated paddy straw ( N 0.88%) and Gliricidia (N 4.1%).
EM treated paddy straw EM extended solution was prepared by mixing five litres of EM stock solution and five litles of molasses in 100litres of water.This mixture was kept in a closed container for 10 days.After that, this extended EM solution was added to the paddy straw and mixed thoroughly.EM treated paddy straw was kept in an airlight bag.It rvas ready to use when it had sweet fermentecl snrcll and white filamentous fungi on the surface.
S. Heerthihah, P. and T. Geretharan Ten Kg of air dried and sieved (2mm rnesh sieve) soil was filled in blac( polythene bag which had the dime rrsion of 30cm x 40cm.The treatments were sole application of paddy straw (51.64 g paddy straw/10 kg soil), enriclrnrent of paddy straw with effecti vc r n i croorgan i sms (EM) (39 .43g EM treated paddy straw/ l0 kg soil) and enrichment of paddy straw with Gliricidia (4.18 g Gliricidia I 25.82 g paddy straw/l0 kg soil) all on equal nitrogen basis at the rate of 0.3479 N/ lOkg soil.Four treatments included control (no nitrogen source) were replicated five times in a completc ly randomized design.
The treatments r,vere incr-rbated for 10 weeks and keptrnoist duringthc incubatiorr.The soil analysis was carried out to lneasure soil available N by kjeldhal method (Jackson, 1973) at 2 weeks intervals.Data were analyzed using SAS statistical package and treatments means were separated in Duncan'i mLrltiple range test.

Results and Discussion
Available nitrogen content in soil soil nitrogen content indicated that there was significant influence of nitrogen sources and incubation stages on available nitrogen content of soil as P value is less than 0.05.Results inclicated that in all stages the available N was least in soil amended with paddy straw (63:1) than control and paddy straw enrichment.This may be due to the utilization ofN by microo.rganisms to decompose the oYganic matter, especially with rice straw, which has a higheir C: N ratio.Mubarak et al.   (2001 ) similarly reported N-immobilization shortly after incorporating crop'residue with high C:N ratio; when soil was incubated with straw alone, At 2"d week of incubation soil available nitrogen content was on par in paddy straw enrichments and in control treatment, but was significantly higher than sole paddy straw treatment.This may be due to soil nitrogen immobilization , the greater C availability in the organic system apparently supports a more active microbial biomass with greater N demand, th us prom ot ing immob i I ization and mineralization of NO3 (Burger and Jackson,  2003).Addition of an organic material with a high C:N ratio induces the irnrnobilization of inorganic N.
Results of experiment further indicated that in treatments of paddy straw enriched with EM and Gliricidia the available soil N content was significantly superior to its sole application.By mixing slow N release paddy straw with highly decomposable Glyricidia the mineralization pattern of soil altered.Glyricidia decomposes quickly and release soil inorganic N wh ich can be utilized by microorganisms to meet its urgent N need for their activity.Paddy straw contributes organic matter to soil and hence increase the long term residual effect of Glyricidia.Application of EM to the paddy straw significantly increased its potential to provide more inorganic N than sole application of straw.
Hussain et al. (1991) reported that EM enhanced the decomposition and mineralization of organic materials resulting in higher N peroentages compared with their respective controls.
Thev also stated that rice straw was the least deconrposed which may have resulted from their inabilit,r to retain sufficient moisture to support act ive ru icrobial decornposition.
Among these treatments, the available N content ranked first in treatment received paddy straw enriched with EM and was followed by the treatment received paddy straw along with Gliricidia at all stages incubation (Tablel).This may be due to the impact of EM on the rate of decornposition as the microbial activity higher in EM treatm e nt.In Glyr i c i d i a enriched treatment, initial N availability may be low due to temporary immobilization of available N for the decomposition of high C:N materials.Results also showed that the available soil N was significantly different between enriched pad dy straw with Gl ir ic id ia and EM at lOth week of incubation only.This may be treated straw than the Gliricidia treated one during the period of incubation.
Periodical changes in available N (mglKg of soil) The results indicated that the inorganic nitrogen content in soil amended with paddy straw was drastically decreased up to 2"d week of incubation due to its high ratio of carbon to nitrogen and was continued until 6'h week of incubation and then increased.Yadvindar singh et al. (1988) indicated that the addition rice straw rvith high C:N ratio resulted in immobilizatiotl ol'_\ tlrroughout the incubation.Ocio et al. (1991) re ported that most of the microbial biomass N forrned due to the incorporation of rice straw was derived from the organic N contained in the straw itself.These findings suggest the microbial populations are able to assimilate the organic N and inorganic N for the formation of their cells.
AGRTEAST 2010 (9) Due to this least available N was recorded in paddy straw amended soil throughout the incubation period.In the soil received straw with Glyricidia and straw with EM, the available N decreased slightly up to 2.d week of incubation and then increased.Ad dition of Glyricidia alongwith paddy straw reduced the N immobilization in soil due to its rapid decomposition (lower C:N ratio) and higher ].{ content.The-refore input of easily

Conclusions
Results indicated that availability of soil N was influenced by incubation period and paddy str,aw enrichment.The available nitrogen content was higher in enriched paddy straw treatment than its sole application.Between the enrichment treatments nitrogen availabilitywas higher in EVI treatment then G I ir i c i d i a tr eatment.Thi s fi nding concludes that the addition of an organic material with a high C:N ratio induces the immob jlization of inorganic N.But 2 weeks after incubation there was an increase in soilnitrogen availability.This was slightly higher thanthe Gliricidia treatment.This indicates that addition of EM stimulates the easy decomposition and mineralization of nutrients from applied organic materials.Fatunbi and Ncube (2009) stated that the decomposition and mineralization of nutrients from added organic materials was positively influenced by the application of EM.

Figure 1 .
Figure 1.Effect ofpaddy straw enrichments on soil available N during incubation period Soil received EM treated paddy str4y also caused slight immobilization at initial stage of incubation.

Table 1 :
Effect of nitrogen sources on nitrogen availability of soil followed by the same leffer within the column are not significantly different according to the Duncan rnultiple range test at 5%o level. Means