1. S. P. Mazumdar, D. K.Kundu*, A. R.Saha and Debjani Ghosh Crop Production Division ICAR-Central Research Institute of Jute and Allied Fibres, Barrackpore, Kolkata-700120 Effect of long term fertilization on aggregate associated phosphorus under jute-rice-wheat cropping system Materials and Methods The ungrounded sample was used for estimating aggregate size distribution by wet sieving method (Yoder 1936). The clods were spread uniformly on the top of a nest of sieves having pore diameter 4.75, 2, 1, 0.5, 0.25 and 0.11 mm. The nest of sieves was oscillated up and down by a pulley arrangement for 30 min at a frequency of 30 cycles per minute in a salt free water. The water stable aggregates of different sizes were collected from respective sieves and weighed after oven drying at 65°C. In this way, aggregates were fractioned into water stable macroaaggregate (WSMA) and microaggregate (WSMI) categories and the aggregate ratio was calculated following the procedure as given below. Aggregate ratio (AR) of soil: AR = Where Q is the percent of soil particles > 0.25 mm diameter determines by aggregate analysis and S is the percent of soil particles < 0.25 mm diameter determines by aggregate analysis. The mean weight diameter (MWD) and geometric mean diameter (GMD) was estimated following Van Bavel (1949) method. Introduction Soil aggregation plays an important role in maintaining soil structure and sustaining soil fertility. Addition of crop residues, and organic manures improve soil aggregation and aggregate stability. Long term field experiments are essential for providing key information on the impacts of management practices on soil and for assessing the sustainability of cropping systems. Farmyard manure (FYM) and fertilizer applications are important management practices used to improve nutrient status and organic matter in soils and thus to increase crop productivity. However, the effects of long- term jute based cropping system and nutrient management practices on soil phosphorus (P) have barely been investigated in the past. Moreover, it is not fully understood how P added to soils through mineral fertilizers and FYM are distributed in soil aggregates. The hypothesis is that the phosphorus distribution, availability and accumulation in the soil is influenced by application of manure and mineral fertilizers and their rate but also depend on aggregate size. Therefore, the present study was conducted to investigate the effects of integrated nutrient management practices on aggregate size distributions and distribution of P in different aggregate sizes in a jute-rice-wheat cropping system Conclusion Addition of FYM in combination with chemical fertilizers significantly improved the formation of macroaggregates, with a concomitant decrease in the proportion of microaggregates. Total phosphorus was prone to concentrate in the large water stable aggregates. Indian Society of Soil Science Kolkata Chapter, October 8-9, 2015, Kolkata India TreatmentsTreatment detailsNPK doses (kg ha -1 ) JuteRiceWheat T1T1 100% NPK60-13-50120-26-50 T2T2 150% NPK90-19.5-75180-39-75 T3T3 100% N60-0-0120-0-0 T4T4 100% NPK+ F Y M @ 10 t ha -1 in jute 60-13-50120-26-50 T5T5 Control (no input)0-0-0 The long term fertilizer experiment was initiated in 1971 at the experimental farm of CRIJAF, Barrackpore. Different treatments with four replications were laid out under randomized block design. TreatmentsMacroaggregatesMicroaggregatesMWD Aggregate ratio Control33.539.01.040.86 100%N42.334.01.391.24 100%NPK48.136.91.451.30 150%NPK49.237.71.491.28 100%NPK+FYM60.131.21.891.90 Results Fig. 1. Aggregate size distribution Fig. 3. Concentrations of total phosphorus in water stable aggregates Table 1. Structural indices under different treatments Fig. 2. Influence of NPK+FYM on improvement in the occurrence of macroaggregates and decrease in the proportion of microaggregates over control