Decomposition and Nitrogen Dynamics of Tree Pruned Biomass Under Albizia Procera Based Agroforestry System in Semi Arid Region of Bundelkhand , India

Albizia procera is the native and most common agrisilvicultural / agrosilvopastutal tree species of Semi arid regions of Central India. This study focused on pruned biomass decomposition and subsequent nitrogen release from different component viz, leaves, petiole and pod under different pruning regimes of six-year old A. procera in agroforestry system. Fresh pruned biomass (leaves, petiole and pods) of A. procera was collected from field and oven dried. Samples of 5.0 g of each component of the tree were transferred to nylon mesh bags (20x20 cm, 2 mm mesh size), placed at 5-cm depth. The bags were randomly kept on the soil surface below respective tree canopies in experimental field and retrieved monthly up to 6 month. Pod pruned biomass decomposed at faster rate followed by leaves and petiole. Pod showed the highest decomposition coefficient (k) under agroforestry system. A similar pattern was observed for loss of N. Nitrogen release form pruned biomass of A. procera followed the trend: pod >leaves > petiole. Decay rate coefficients were significantly and positively correlated with hemicellulose, N and P concentration of pruned leaves, petiole and pod with strong correlation in pod (r = 0.780). It is further interpretive that decay rate coefficients were significantly and negatively correlated with lignin, lignin/N, C/N, C/P and ADF. The air temperature, soil moisture and soil temperature were found significantly (P<0.05) related with percent weight loss of all component in all land uses during decomposition. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nitrogen added through pruning of A. procera. Current World environment Journal Website: www.cwejournal.org ISSN: 0973-4929, Vol. 12, No. (3) 2017, Pg. 727-735 CONTACT Deepak Maurya drdm.icar@gmail.com National Bureau of Soil Survey & Land Use Planning, RC-Kolkata, India. © 2017 The Author(s). Published by Enviro Research Publishers This is an Open Access article licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License (https://creativecommons.org/licenses/by-nc-sa/4.0/ ), which permits unrestricted NonCommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. To link to this article: http://dx.doi.org/10.12944/CWE.12.3.24 Article History Received: 17 July 2017 Accepted:18 October 2017


Introduction
Agroforestry practices are recommended to achieve soil conservation and it is a sustainable option in improving the livelihood as well as creating opportunities for the rural people of semi arid region of bundelkhand 1 .Most of the tree species recommended are fast-growing, leguminous species which can be pruned to a desirable height at appropriate frequencies.These pruning which consist of leaves and immature stems are added to the soil between crop rows.Therefore, while acting as a physical barrier to trap eroding soil, the trees also act as a source of mulch material to the soil.Gradual decomposition and nutrient release from added pruning could enhance the organic matter and nutrient status of the soil 2,3 and influence the yield of the associated agricultural crop 4,5 .Tree species used in agroforestry differ in their ability to enhance soil fertility through addition of pruning 6,7 .This is because of the inter-species variation in biomass of pruning produced per year 2 , their nutrient contents 8 and the rates of decomposition and nutrient release 7,9 .The rates of decomposition and nutrient release from added pruning are determined by the climatic factors such as rainfall and temperature regimes 9,10,11 and by litter quality as determined by its lignin, polyphenol and nitrogen contents 5,11 .Biomass decomposition and nutrient release play an important part in selection of tree species for agroforestry because of the need to regulate the pattern of nutrient release and synchronize it with the nutrient demand of the associated agricultural crop 2,12 .
Albizia procera is the native and most common agrisilvicultural /agrosilvopastutal tree species of Semi arid regions of Central India.Being a fast growing legume species and having an immense potential for introduction in different types of soils and climatic conditions, it is planted in various states by the Forest Departments and also by farmers under Agro-forestry programmes.It fixes nitrogen through symbiotic bacteria present in root nodules and thus enhances and soil fertility.The present investigation aimed to analyze the impact of Albizia procera based agroforestry on improving soil organic carbon status and nitrogen availability.
Therefore, the objective of this experiment was to characterize and compare the patterns and amounts of biomass decomposition and nitrogen loss from Albizia procera in different land use in the semi arid region of Central India.

Study Site and Plant material
The study was conducted in six year old A. procera based agroforestry system at research farm of National Research Centre for Agroforestry, Jhansi, Uttar Predesh, India.The experimental field is situated at 25 0 27' North latitude and 78 0 35' East longitudes, 271 m asl in the semi arid region of the Central Indian Plateau.Average annual rainfall of the region is 806 mm, about 80 % of which occurs between June to September with intermittent dry spells.The mean monthly temperature is generally high, with high degree of variation between a maximum 39.8 0 C in May and June and minimum temperature of 5.8 0 C in December and January.In summer, temperature occasionally reached up to 48 0 C. The mean monthly evaporation in the region is highest in April-June (9.40-15.2mm)and it ranges from 1.90-6.00mm during other months of the year.The soil in the experimental field is Parwa representing inter-mixed black and red soil group of bundelkhand region (U.P.), India, falling under the soil order Alfisol.It is medium in texture, moisture retentive and workability, prone to crust whenever drought spell exceeds 2-3 weeks even under mild evaporation situation.
The experiment field was established as agrisilviculture (crop + tree) system in July, 2000 with Albizia procera as the tree component.A. procera was planted in at spacing of 8m x 4m in plot size of 576 m -2 (18 trees plot -1 ) with three replications.Under A. procera blackgram -mustard crop sequence were taken as intercrop.In Kharif season (Black gram) the trails were fertilized with 20 kg /ha N, 40 Kg/ha P and in rabi season (mustered) 60 Kg/ha N, 40 Kg/ha P and 40 Kg/ha K were applied.Inter crop black gram is rainfed in both pruning regime, therefore mustard is irrigated twice a year (1 st at flowering and 2 nd at siliquae formation).

Biomass Decomposition and Nutrient Analysis
Fresh pruned biomass (leaves, petiole and pods) of Albizia procera was collected from field and oven dried at 72 0 C till constant weight.The standard litterbag technique 14 was employed for characterizing litter decomposition dynamics.Samples of 5.0 g of each component of the tree were transferred to nylon mesh bags (20x20 cm, 2 mm mesh size).The bags [270(3x3x5x6)] were randomly kept on the soil surface below respective tree canopies in experimental field.Each month, 5 bags for each biomass component of A. procera were collected from the floor of the different land sues.The biomass samples thus drawn were washed under a fine jet of water using a fine mesh screen to remove all the adhered soil particles, dried at 72 0 C to constant weight, weighed and ground in a Wiley Mill to pass through a 1mm mesh screen.Samples were analyzed for N analysis.

Data Analysis
To evaluate nutrient release pattern, nutrient remaining in the decomposing biomass were estimated by equation 15 % Nutrient remaining = (C/C 0 ) x (DM/DM 0 ) x 10 2 Where, C = Concentration of nutr ient element in decomposition litter at the time of sampling C 0 = Concentration of nutrient element at the beginning of the study DM = Mass of dry matter at the time of sampling DM 0 = Initial dry matter of the biomass kept for decomposition The decay rate coefficient (k) of the decomposing pruned biomass of different component for the entire study period was calculated through the negative exponential decay model 16 as represented by the equation: X / X 0 = e -kt Further, following Olson (1963), the time required for 50 (half life) % weight losses was estimated from k values using the equation: t 50 = In (0.5) / -k = -0.693/ -k Similarly, time taken for 95% decay can be estimated as follows t 0.95 =2.9957/k The effect of land use of Albizia procera on decomposition, nutrient dynamics and cumulative impact on soil properties was tested by means of ANOVA using the General Linear Model of SYSTAT Ver.9 (SYSTAT Inc. 1998).

Decomposition and Decomposition Coefficient
Average weight loss pattern in decomposing different components of pruned biomass of A. procera is shown in fig 1, 2 and 3. Weight loss pattern in six months under different land uses followed the trend: cropping > Fallow > A. procera + cropping for leaves; Cropping > A. procera + cropping > Fallow for the petiole and A. procera + cropping > Cropping > Fallow for pod.Data is further showen (Table 1) that for 95 per cent decay, pruned biomass leaves, petiole and pod is to took 568, 767 and 831 days; 969, 1046 and 1094 days; 414, 432 and 445 days, respectively, correspondingly under A. procera + cropping, cropping and fallow.3).Percent weight loss of leaf pruned biomass was positively correlated with air temperature and was significant (P<0.05)only in A. procera unpruned + crop.However, the soil temperature and soil moisture was positive and significantly (P<0.01)correlated with percent weight loss of leaf pruned biomass respectively in all land uses.Percent weight loss of petiole showed positive and significant (p<0.01)correlation with soil moisture and soil temperature in all land uses, while air temperature was significant only in A. procera unpruned + crop.Furthermore, soil moisture and soil temperature were also significantly (P<0.01)correlated with percent weight loss of pod, in all land uses.Linear regression for the significant effect of climatic factors on percent weight loss (Table 4) was analyzed.The air temperature, soil moisture and soil temperature were found significantly (P<0.05)related with percent weight loss of all component in all land uses during decomposition.

Nitrogen Release
Result shown for N release from decomposing pruned biomass indicate that N content during decomposition increased initially followed by decrease.Figure 4 shows that leaf pruned biomass under cropping released higher N during decomposition followed under A. procera + crop and fallow.Petiole decomposition under cropping released 80.6 % N and was in the order: cropping > A. procera unpruned + crop (74.7 %) > fallow (64.1%).N content in decomposing pod pruned biomass increased initially.A. procera + crop, cropping, fallow, respectively.The corresponding N release from decomposing A. procera pod pruned biomass was 90.3, 93.7 and 90.6 percent.
Figure 5 shows that N release from decomposing A. procera petiole pruned biomass differed widely among different land uses.Data showed that irrespective of different pruning and land use, N content in decomposing petiole pruned biomass increased initially and decreased finally.The final N content in decomposing petiole pruned biomass under A. procera unpruned + crop, cropping and fallow was 0.456, 0.371 and 0.667 per cent, respectively.From N release data (figure-6) it is evident that A. procera pod pruned biomass released N at faster rate followed by leaf and petiole.Across component of decomposing biomass, A. procera pruned biomass under cropping released maximum N and minimum N release was under fallow.

Discussion
Substrate (litter/biomass) quality, climate and quantity and quality of decomposer organisms are the primary determinants of any biomass decay rates 17,18 .In the present work, the differences in rates of decomposition of different components of litter and biomass of A. procera under different land uses could be related to differences in substrate (litter/biomass) quality (Table 2) and variations in micro environment beneath A. procera in cropping and fallow.The higher concentration of N and lower C/N ratio in the biomass of A. procera was probably responsible for its faster decomposition and lower concentration of N in the petiole of A. procera brought slower rate of decomposition.A positive effect of N concentration on decomposition was also reported by several workers 19,20,21,22,23,24 .In A. procera, higher rate of biomass decomposition in agroforestry systems than to fallow might be due to high fertility status in agroforestry systems as evident from results of this study and favorable microenvironment for microbial population.Earlier, Anderson and Swift 25 have pointed out that soil of high fertility favour faster rate of decomposition.Conducive microclimate under agroforestry systems might have also played role in faster litter decay as reported by several workers 7,26,27,28 .

Fig. 4 :
Fig. 4: N release from decomposing leaves biomass of A. procera under different land use

Table 3 : Pearson correlation coefficients between pruned biomass weight loss and environmental factors under A. procera based different land uses. environmental Pearson Correlation factors Leaves Petiole Pod A. procera unpruned + crop
* Significant at P < 0.05, ** P < 0.01

Table 4 : Linear Regression between pruned biomass weight loss and environmental factors under A. procera based different land uses.
This research work was conducted at the form and all lab work was carried out in the lab of National Research Centre for Agroforestry, Jhansi.I am very thankful to Director NRC-AF, Jhansi for his kind support and mentorship.I am to express out my appreciation to the Dr. R. S. Yadav, my PhD supervisor for sharing his pearls of wisdom with us during the course of this research.I am also thankful to our colleagues who directly or indirectly involved in form or lab work and provided expertise that greatly assisted this research work.