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Evaluation of wheat rice yield and carbon storage by agroforestry system of poplar (Populus deltoides BARTR. Ex marsh.) boundary plantation

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  • Save International Journal of A griculture and Forestry 2012, 2(5): 239-246 DOI: 10.5923/j.ijaf.20120205.07 Evaluation of Poplar (Populus deltoides Bartr. Ex Marsh.) Boundary Plantation Based Agri-silvicultural System for Wheat-Paddy Yield and Carbon Storage S. K. Chauhan1,*, R. Sharma1, S.C. Sharma2, Naveen Gupta3, Ritu1 1Department of Forestry and Natural Resources, Punjab A gricultural University, Ludhiana ,141 004 ,India 2RRSKA Ballowal Saunkhri, SBS Nagar, India 3Dept. of Soils, Punjab A gricultural University, Ludhiana, 141 004, India Abstract Wheat and paddy (rice) yield was accessed with respect to aspect as well as distance from the base of poplar tree lines in all the four d irections. Wheat and paddy yield was found maximu m on Southern aspect (4.11t/ha and 5.06 t/ha, respectively), whereas, it was found minimu m on Northern aspect (2.5 t/ha and 4.13 t/ha, respectively). Distance fro m tree base also played significant role on the yield o f grain crops. The y ield of wheat as well as paddy increased with the increase in distance from the boundary tree lines. Crop yield increased with increase in distance fro m 2m to 10 m distance fro m the poplar trees (wheat:2.85 t/ha to 3.63 t/ha and paddy:3.22 t/ha to 5.66 t/ha). However, in control conditions wheat and paddy yield was 4.47 t/ha and 6.96 t/ha, respectively. There was a decrease of 33.75 and 36.15 per cent in paddy and 26.68 and 25.69 per cent in wheat under 5th and 6th year old poplar boundary plantation than the control. Soil para meters (organic carbon, total nitrogen, Available P and K) were also accessed to quantify the effect of this system on nutrients on all the four directions along with the carbon storage in the biomass, which were significantly influenced by the poplar plantation. Keywords Agroforestry, Poplar, Boundary Plantation, Rice-wheat Rotation, Carbon Sequestration 1. Introduction Wheat-Paddy (rice) cropping systems are of immense importance for food security in South Asian countries including Ind ia, p roviding, for examp le, 85 per cent of the total cereal production and 60 per cent of the total calorie intake[1,2]. The traditional rotation s ystem though profitable has not remained sustainable as it has resulted in lowering ground water table, develop ment of co mpact sub-soil layer and nutrient imbalance. It has also put a stigma on the sustainability of future ag ricu lture and ecological balance[3]. Thus, necessitating the diversification in this tradit ional crop rotation. Trees und er ag ro fo restry bes ides p rov id ing th e t ree products, improves soil productivity through ecological and p hys ico -chemical ch an g es . Po pu lu s delt oi d es b as ed agroforestry system is one of the viable alternate land use system to prevent further degradation and obtain biological product ion on s us tainab le bas is in the irrigated agro-ecosystem. Owing to its fast growth, deciduous nature, ma rket ing acceptability and successful intercropping, poplar * Corresponding author: chauhanpau@redi (S. K. Chauhan) Published online at Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved cultivation has become popular among the farmers as a viable alternative to wheat-paddy rotation in north-western states of India. Poplar being a deciduous tree enters in dormancy during winter, therefore suited well to co mpanion crop for ensuring food production and also enhance economic returns to the growers. This species has been grown by farmers as boundary or block plantation, wh ich This improves the physico-chemical propert ies of soil through addition of organic matter in the soil[4,5] and provides alternate sources of income and emp loy ment to the rural poor[6,7]. However, some adverse effects have also been reported by various workers[8-11]. Leaf-fall at sowing poses physical barrier to seed germination and may affect the availability of nutrients/light to developing seedlings but addition of leaves changes the C: N ratio of the soil, wh ich also influence the crop growth[5]. Poplar being sensitive to water logging is unsuitable under rice based cropping system, but boundary plantation of poplar might be an option to continue traditional rotation of rice-wheat for the farmers who seem reluctant to leave the rotation because of assured market/ minimu m support price of the crops. Moreover, the small farmers cannot afford to raise block p lantation at the cost of agricultural crop yield. A large scale area is already under poplar boundary plantation in Punjab and adjoining states[12,13]. In a recent study on tree growing on farm land of 250 villages of Punjab, a ratio of 1:3 in b lock to bund 240 S. K. Chauhan et al.: Evaluation of Poplar (Populus deltoides Bartr. Ex M arsh.) Boundary Plantation Based Agr i-silvicultural System for Wheat-Paddy Yield and Carbon Storage plantations of the poplar has been recorded[14]. There has been no attempt to quantify the wheat-paddy yield and carbon sequestration potential of poplar boundary plantation. The present study was an attempt to determine the effect of Populus deltoides on the yield of rice-wheat and carbon assimilation through poplar based silvo-arable system. 2. Material and Methods Paddy-wheat is the most do minant crop rotation of irrigated agricu lture in north-western states of India. Effect of poplar boundary plantation was quantified to access the potential of this agroforestry system for crop yield productivity and carbon storage/assimilat ion. A field e xperiment was conducted during 2004-2006 on the farme rs’ field at Balachaur, SBS Nagar, Punjab, India (31°6’5”N and 76°23’26’E at 355 m above the mean sea level). The site is characterized by sub-tropical to tropical climate with hot and dry summers fro m April to June, hot and humid fro m July to September and cold winter fro m December to January. The average annual rainfall during 2004-06 was 571 mm, wh ich was more or less equal to the norma l in the region (586 mm). The experimental soil was sandy loam (0-15 cm) in texture. The soil was found slightly alkaline in reaction and low in organic carbon, low in alkaline KMnO4-extractable N, med iu m in 0.5N NaHCO3-extractable P and mediu m in NH4OAc-extractable K. 2.1. Experi mental B ackground The experiment was started in 2004 with paddy crop followed by wheat for two years. The field was dry tilled once with discs plough and twice with cult ivator and levelled with a wooden plank. The p lots to be puddled were surrounded by bunds of 15-20 cm height and flooded with 5-7 cm of water. Puddling was done with tractor. About one month old seedlings of Pusa-44 were transplanted manually. The field was kept submerged till 15 days before the harvest of the crop. The crop was harvested with co mbine harvester in October and wheat (PBW 343) was sown with seed drill at a row to row distance of 22.5 cm in the first week of November. A ll reco mmended practices of Punjab Agricultural Un iversity, Ludhiana (India) for crop cultivation were followed. The crop was harvested in April. One year old poplar plants of G- 48 clones were transplanted in January, 2002 on the boundary of 196x75m2 plot at a distance of 2.5 m (160 trees/ha). There was no other special management practices follo wed for poplar except pruning of the tree fro m second year. 2.2. Trees Data The trees at random on all the four directions were measured for their top height, diameter at breast height (DBH) and crown spread. The total height was measured with Mu ltimeter (in metres) fro m ground to top of the trees. The diameter at breast height (1.37 m above the ground level) was taken with the help of digital calliper. Precautions were taken that the point of measure ment was clean and c lear, knots or any other abnormality at 1.37 m was avoided and diameter was recorded at slightly higher or lo wer points as convenient. Crown spread was measured using metre tape and two poles holding straight touching to the outmost tip of the opposite sides of tree at perpendicular to the row direction. The distance between these two poles were recorded with the help of measuring tape. Leaf-fa ll data was recorded in the month of January (1x1m2 quadrat) at an interval of 2m upto 10m fro m the tree line on all the directions. The poplar tree height was significantly variable on different sides, through DBH and canopy spread were at par on all the directions (Table 1). Table 1. Tree growth parameters under poplar boundary plantation Tree row on DBH direction (cm) East West North So ut h CD (5%) 22.29 21.42 22.38 20.46 NS 2005 Height (m) 23.91 19.68 18.03 20.3 1.08 Crown spread (m)* 7.29 6.99 6.34 6.43 NS *Perpendicular to the row direction DBH (cm) 24.33 24.10 25.51 22.97 NS 2006 Height (m) 25.31 20.43 19.83 22.89 0.98 Crown spread (m)* 7.91 6.80 6.15 6.24 NS 2.3. Grain Yiel d The each direct ion of the field was divided into three equal parts and each part was considered as a replication leaving 20m distance at the corners to avoid dual direction effect. The grain yields were recorded fro m 1 m2 area at 2, 4, 6, 8 and 10 m d istance fro m the base of the poplar trees on each direction and grain yield was extrapolated to be expressed in t ha-1 by bringing the produce at 14 per cent grain moisture content. 2.4. Carbon Storage Th e rand o mly co llect ed p lan t s amp le s (wheat/paddy/poplar) were analysed for C content. The carbon content in different plant co mponents (above and below ground) was estimated on CHNS analyser to calculate the carbon storage in each component of poplar (stem, branch, bark, leaves and root) and crops. The total carbon storage was computed by using the carbon values of respective component and mult iplying the same with the biomass of each co mponent derived through the regression equations developed in prevailing conditions[15]. These values were further extrapolated on hectare basis by mu ltip lying with standing biomass per hectare. The soil samples were collected fro m all the four directions at variable distances (2, 4, 6, 8 and 10 m) fro m the tree lines and centre of the field at 0-15, 15-30 and 30-60 cm depths. Soil was analysed for carbon, total nitrogen, available P & K. The results of net carbon accumulation in the tree co mponents have been determined to substantiate the environmental benefits of tree planting on agricultural land. The data on growth, bio mass, carbon allocation in poplar and International Journal of A griculture and Forestry 2012, 2(5): 239-246 241 wheat were statistically analysed after following the established procedures[16]. Significant differences between treatments (age of poplar plantations and sole crop with four replicates) means for growth, b io mass and carbon storage were tested at p ≤ 0.05 using least significant difference test. 3. Results and Discussion 3.1. Crop yiel d Poplar boundary plantation of five and six years age were assessed for their effect on the intercrops (paddy and wheat). Aspect as well as distance fro m the boundary had significant effect on the grain yield of wheat and paddy (Fig. 1). The visual observations made for rice and wheat crop growing with poplar as boundary plantation revealed that the growth of the crop plants were poor as we moved towards the poplar tree line in each direction fro m the centre of the field. The establishment of crop was poor near the tree line. This resulted in overall decline in the rice –wheat crop y ield near the plantation line. During both the years, the trend of crop behaviour was same with respect to direction and distance fro m poplar rows. There was a decline of nearly 33.75 and 36.15 per cent in paddy and 26.68 and 25.69 per cent in wheat during 2004-05 and 2005-06, respectively. The reduction in paddy yield was mo re than the wheat yield reduction. No study on paddy with poplar has been carried out earlier though there are studies on wheat crop. Figure 1. Performance of paddy-wheat rotation under poplar boundary plantations 242 S. K. Chauhan et al.: Evaluation of Poplar (Populus deltoides Bartr. Ex M arsh.) Boundary Plantation Based Agr i-silvicultural System for Wheat-Paddy Yield and Carbon Storage 8.00 West North South Control East 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 2004 2005 2004-05 2005-06 Rice Wheat Distance (m) from poplar boundary Figure 2. Effect of boundary plantation of poplar on grain yield (Mg ha-1) of rice and wheat Table 2. Leaf litter (dry wt) in poplar boundary plantation Distance from tree 2m 4m 6m 8m 10m Mean CD (5%) Direct ion s Distance from tree Direct ions x Dist ance from tree Litter in different row direction (gm/quadrat) East ern W est ern Northern 103.91 247.58 245.58 49.92 215.92 226.58 25.25 210.91 146.92 12.58 170.58 97.25 13.58 130.25 73.58 41.048 195.05 157.98 20.42 22.82 45.65 So ut h ern 191.25 124.58 97.58 54.25 33.91 100.31 Mean 197.08 154.25 120.17 83.665 62.83 123.6 Aspect-wise, Southern aspect (Northern side tree row direction) recorded maximu m paddy yield (5.06 and 5.21 t/ha), whereas, on Northern aspect (southern side tree row direction) had minimu m y ield (4.13 and 3.94 t/ha) during both the years i.e., 2004-05 and 2005-06 (Fig. 1 and 2). Straw yield was also affected by the aspect and distance from the boundary tree line but the interaction of aspect x distance fro m the boundary was found non-significant. Reduction in wheat yield (grain and straw) in field p lot with poplar boundary have also been recorded earlier[17,18]. As the distance from the tree line increas es, the crop yield improves considerably. The progressive grain and straw reduction with advancement in age was attributed to the increased canopy and root competit ion for mo isture and nutrients. Poor crop performance near the poplar tree lines has also been reported by several other workers[19,20] and imp rovement with increasing distance can be attributed to the reduced root competition and shade affect with increase in distance from the tree line. Ho wever, the losses to agricultural crops can be well co mpensated by the inco me obtained through the sale of trees . Perusal of figures 1 and 2, revealed variab le influence on yield at different directions, wh ich can be attributed to micro -site enrich ment caused by favourable environment due to shade and leaf litter addition. The yield on southern aspect was more than northern aspect because of better growing conditions i.e., insolation and higher litter addit ion. Though due to more shade on northern aspect photosynthetic activity gets reduced, whereas, on southern aspect, mo re insolation resulted in stepped-up photosynthetic activity and stomata remain open for long period with no water stress under irrigated condition. The southern aspect allows maximu m light on the field throughout the day[21]. The leaf shedding during winter in the sheltered area also resulted in poor performance of wheat crop. Leaf–fall befo re sowing gets incorporated in soil but after the sowing interfere in the emergence and/or seedling growth of wheat crop. The proportion of leaf fall is inversely related to the wheat crop yield. However, during summer, the paddy crop is main ly affected by shade, since the crop is irrigated and International Journal of A griculture and Forestry 2012, 2(5): 239-246 243 supplemented with reco mmended fertilizers; therefore, there is least possibility of mo isture/nutrient stress. The addition of large quantity of leaf litter through leaf fall on southern aspect may be another fact o r fo r en h an ced y ie ld (Tab le 2) . Th e p h y s ica l environ ment gets improved, thus resulting in more efficient nutrient utilizat ion. Addition of leaf litter and nutrient through poplar leaf has also been estimated by number of other workers ([5,18,22-25]. Plant nutrient uptake increases adjacent to the poplar tree rows due to leaf b io mass addition, thus increase the nutrient use efficiency. 3.2. Soil Organic Carbon and Other Chemical Properties Trees in association with agricultural crops increase the soil carbon status, though the changes depend upon the quality and quantity of litter input, decomposition rate and carbon release. The changes in micro-environment under tree canopy (soil mo isture, temperature, etc.), pro liferation of root system and enhanced biological activ ity also favour the carbon stock in the soil. Ho wever, the continuity in the system is ess ential; otherwise the build-up in organic carbon may revert back to its orig inal under commercial agriculture. A decreasing trend in soil organic carbon (SOC) was observed with soil depth in all the poplar p lantations and plots without poplar trees. It was low in control plot compared to the spots near the tree line on all the four directions of poplar plantations at three soil depths (Fig. 3). There was a decreasing trend in SOC as we move away fro m the poplar boundary line. The differences in SOC were observed with different directional aspects also. The SOC was higher in northern and southern row directions than the eastern and western directions, however, the control plots had minimu m SOC. The increase organic build-up in the top layer near the tree lines was due to the addition of litter, pruning material and tree roots. Similar observations were reported earlier also[5,21,26,27]. On account of recycling of organic matter, h igher organic carbon was observed in soil under intercropping poplar plantation than a site without trees[28]. 65-88 per cent higher soil organic carbon stock in agroforestry system than rice-wheat system have been recorded earlier[29], even hot water soluble and microbial carbon have also been reported higher in poplar based agroforestry system than rice-wheat rotation. Addition of leaf litter (d ry wt) in 1m2 quadrat with respect to the row direct ions and distances from the boundary plantation revealed significantly different values on all the directions and distances. Maximu m leaf litter (195.05 g m) was recorded on western row direction, whereas, minimu m (41.04 g m) on eastern side. It reduced gradually fro m 197.08 gm at 2m d istance from boundary to 62.83 g m at 10 m distance from the boundary. Maximu m value (247.58 g m) was on the western direction at 2m distance from the boundary, whereas, minimu m value (12.58 g m) on eastern row d irection at 10 m distance (Table 2). The lo wer litter on the south-eastern row directions and higher on the north-western direction indicated that the wind direction was north-western to south-eastern during the leaf shedding period, wh ich is normal direction during the winters in this part of the country. This has also been reflected in the leaf shedding pattern. 0.6 0.045 0.04 0.5 0.035 0.4 0.03 0.025 0.3 0.02 0.2 0.015 0.01 0.1 0.005 0 0 Organic Carbon (%) 13500---361005 CSoNWEonoteuarrttssotthlh Control 2 4 6 8 1 0 Total N (%) 0-15 15-30 30-60 Control East West South North Control 2 4 6 8 1 0 Available P (Kg/ha) Available K (Kg/ha) 35 30 25 20 15 10 5 0 0-15 15-30 30-60 Control East West South North Control 2 4 6 8 10 160 140 120 100 80 60 40 20 0 0-15 15-30 30-60 Control East West South North Control 2 4 6 8 10 Figure 3. Soil nutrient status on all the four directions (east, west, north & south) and control in poplar boundary plantation at different distances from tree rows (2,4,6,8 & 10m) and depths (0-15, 15-30 & 30-60cm) 244 S. K. Chauhan et al.: Evaluation of Poplar (Populus deltoides Bartr. Ex M arsh.) Boundary Plantation Based Agr i-silvicultural System for Wheat-Paddy Yield and Carbon Storage Carbon content (Mg ha-1) 12 10 8 6 4 2 0 timbe r East West North South firewood twigs & leaves roots Figure 4. Carbon storage in different poplar tree components at different directions Total nitrogen and available P & K (kg/ha) of soil was found higher in the top layer and decreased with increase in depth, however, the differences in contents with distance fro m the tree line were non-significant but slightly better than the control plot (Fig. 4). The higher nutrient content in 0-15c m horizon than the lower depths was due to the nutrient cycling and surface enrich ment through biomass. The annual leaf fall wh ich is not removed eventually is incorporated into the soil as plant residue and also the roots cut during the cultivation adds organic matter in the top layer of the soil. The change in the soil carbon pool would have a significant effect on the g lobal carbon budge[30]. Soil being a b ig resource plays a vital role in carbon cycle. 3.3. Carbon Storage The carbon concentration in t imber, roots, firewood and twigs + leaves was estimated to be 45.67, 47.82, 46.56 and 45.50 per cent, respectively. The bio mass estimates revealed that all tree co mponents varied in terms of carbon stock among themselves (Fig. 4). The stem contributed 74.78 per cent carbon followed by roots (10.31 %), firewood (9.04 %) and twigs + leaves (5.87%). The stem wood mentioned here still contains about 10-15 per cent of wood, wh ich will not go to durable products but as fuel wood (lops and tops/wastage fro m industries, etc.). The carbon stock in d ifferent carbon pools under study indicated that vegetation stock i.e., above-ground biomass contributed the maximu m towards aggregate carbon pool under agroforestry system. The litter co mbined with roots contributed the least towards the aggregate C-stock, which was almost negligible in co mparison to other pools. The incremental carbon potential, however, depends upon the productivity of the components (poplar and wheat-paddy here). Average carbon sequestration potential in agroforestry in India has been estimated to be 25t/ha over 96 million hectares[31] but there is considerable variation in different regions depending upon the biomass production[32]. Variable carbon sequestration figures have been reported in poplar based systems as well[12,33-35], which are dependent upon tree geometry, clones used, site factors, management aspects, etc. 4. Conclusions The above results revealed that the losses to both the crops were significantly higher with increasing tree canopy depth towards tree rows. The growth and yield of crops increased progressively as the distance fro m t ree line increases. These results clearly indicated that the crop raised on northern and eastern aspect showed poor performance in terms of their growth and yield than southern and western aspect. Therefore, for boundary plantation, the tree rows should be preferred in the order of north, east, west and south direction of the farm. The systemhas huge potential for carbon storage in b io mass as well as in soil. Poplar based agroforestry has contributed substantially to the ecological, economic and social function, resultantly farmers a re e xtensively adopting the poplar-crop co mbination to diversify the traditional rice-wheat crop rotation, thus increasing the tree cover as well. ACKNOWLEDGEMENTS Authors are thankful to the Indian Council of Agricu ltural Research, New Delhi (India) for providing the financial support for conducting the investigations. The support of Sh. O.P. Chaudhary, Progressive Farmer, Balachaur (SBS Nagar, Punjab, India) is also gratefully acknowledged. REFERENCES International Journal of A griculture and Forestry 2012, 2(5): 239-246 245 [1] J. Timsina, D.J. Connor, Productivity and management of rice-wheat cropping systems: issues and challenges. 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