Modelling of Water and Solutes in Permanent Raised Beds

Transcription

1 18 th World IMACS / MODSIM Congre, Cairn, Autralia July Modelling of Water and Solute in Permanent Raied Bed Cook, F.J. 1,2,3, J. H. Knight 1,4, E. Humphrey 5, A.D. McHugh 2, J. Tidall 6, G. Hamilton 7 and C.H. Roth 8 1 CSIRO Land and Water, Bribane, Queenland, 2 The Univerity of Queenland, School of Land Crop and Food Science, 3 CRC for Irrigation Future, ewater CRC, 4 School of Mathematical Science, Queenland Univerity of Technology, Bribane,, Queenland, Autralia, 5 International Rice Reearch Intitute, Lo Baño, Philippine, 6 La Trobe Univerity, Autralia, 7 Department of Agriculture and Food WA, Perth, Wetern Autralia, 8 CSIRO Sutainable Ecoytem, Bribane, Autralia. freeman.cook@ciro.au Abtract: Permanent raied bed (PRB) are an agricultural cultural method that can improve crop productivity and health of oil. Autralian Centre for International Agricultural Reearch (ACIAR) ha funded a number of project in developing countrie but wa concerned that the hort-term benefit may be at the cot of longterm loe due to olute pollution of groundwater or aliniation of the bed. A modelling tudy wa undertaken to conider the water and olute flow in raied bed in relation to the oil phyical propertie to improve undertanding of the PRB ytem. HYDRUS(1D, 2D/3D) wa ued a the modelling platform. The domain ued for the imulation i hown in figure 1. The reult how that a imple model for infiltration into the raied bed i ueful for etimating the width of the raied bed for mot oil epecially if the orptivity wa meaured on a trial bed. Compaction of the furrow between the bed commonly occur due to vehicle traffic. Compaction under the furrow wa imulated and thi howed that water penetration horizontally wa lowed a cumulative infiltration with time wa reduced. However, for the ame amount of cumulative infiltration the penetration horizontally wa greater than when no compaction occurred. Drainage of the bed when an impermeable layer occur in the oil how that a imple inverion of the moiture characteritic relationhip could be ued to etimate the water potential profile in the bed. Thi alo how that for clay oil the bed mut be exceively high for them to drain effectively through eepage to the furrow. The leaching of fertilizer by furrow irrigation wa invetigated to determine at what ditance from the furrow fertilier hould be placed to reduce leaching during irrigation. Thi ditance wa hown to be oil dependent m 0.15 m Saliniation due to evaporation from a hallow water table i likely to occur if a aline watertable occur at < m in and and < m in loam and clay oil unle properly managed. Furrow Keyword: Permanent raied bed, olute tranport, moiture content, infiltration, irrigation 2 m 2 m Figure 1. The domain ued in the generic modelling imulation. No flow boundary condition occur on the right hand vertical boundary and on the left hand vertical boundary below the depth of the furrow. 505

2 1. INTRODUCTION Permanent raied bed (PRB) provide a mean of increaing the crop productivity, profitability and utainability of irrigated and rainfed cropping ytem (Hobb et al. 2008; Connor et al. 2001). Principally thee improvement occur due to improved oil tructure and drainage and the ue of direct-drilling of crop in the bed. PRB for irrigated cropping a an element of conervation agriculture, have been utilied in Mexico, Wetern Aia, Southern Aia, Autralia, Eatern China, part of Africa and the Sub-continent, to improve irrigation water productivity, increae yield, reduce mechanical input and labour, increae fertilier efficiency, and combat alinity and riing water table (Perie et al. 2003; Friedrich, 2003; Hamilton et al., 2003). In rice-wheat ytem of South Aia, irrigation water aving of 20-30% and ignificant yield increae were often reported (Ram et al. 2005; Huein et al. 2003) and are attributed to factor uch a horter irrigation time, improved light interception and reduced water logging. Subtantial yield gain and water aving have been gained from PRB in other region uch a Mexico (Sayre et al. 2005). An evaluation of PRB ytem in Aia and Autralia wa reviewed by Roth et al. (2005). The Autralian Centre for International Agricultural Reearch (ACIAR) ha been funding a number of PRB project in developing nation around the world but i concerned about iue not covered by hort-term tudie. Several of the iue with PRB include a) are there any long-term environmental implication from the introduction of thi technology, b) could the PRB be better deigned, c) where hould fertilier be placed, and d) what are the interaction of PRB with climate and irrigation? Modelling of water and olute tranport in PRB wa een a a way to invetigate ome of thee iue. The two-dimenional modelling program HYDRUS2D (Simunek, 1999) wa ued to imulate water and olute tranport a) initially for a generic PRB to invetigate the interaction of the propertie of the bed with height, pacing, fertilizer placement etc, and then b) four cae tudie from ACIAR project in India, Pakitan, Indoneia and China were imulated. A quai-analytical olution for infiltration into PRB i compared with the numerical imulation from HYDRUS2D, to determine if thi could provide a imple guide to etimating bed width. In thi paper we concentrate on the undertanding gained from the generic modelling and only conider reult from each of the particular project when thi add to the inight gained. Here we will preent a ynthei of the finding of thi modelling (for more detail ee Cook et al., 2007). 2. METHODS Both the HYDRUS1D (Simunek et al., 1998) and HYDRUS2D/3D (Simunek, 1999) program were ued in the imulation. Thee olve the Richard equation for flow of water in oil: ( ) θ / t = k( h). h U (1) where θ i the volumetric water content [L 3 L -3 ], k i the hydraulic conductivity which i a function of ψ [L] the matric potential, h i the hydraulic head [L], U i a ink term [L 3 L -3 T -1 ] and i the vector differential operator. The tranport of olute i convective diffuion equation which for a non-reactive and aborbed olute i: ( θ ) θc/ t = D c + qc Uc (2) where D i the diperion coefficient [L 2 T -1 ], c i the olute concentration [M L -3 ] and q i the volumetric flux denity [L T -1 ]. The domain that wa ued in the imulation ue the concept of ymmetry of flow about the centre of the bed o that only half the bed ha to be imulated (Figure 1) Infiltration Infiltration into the bed wa imulated uing HYDRUS2D for three different oil type viz clay, loam and and from the data bae aociated with HYDRUS2D. Thi range of oil propertie wa choen to provide the likely range of oil propertie that will occur. Some field oil may till occur outide of the range of thee propertie. Thee imulation are taken a being the true value when compared with the quaianalytical olution approach outlined below. The oil phyical propertie for thee oil baed on the oil moiture retention model of van Genuchten (1980) are preented in Table 1. For the generic irrigation modelling we conidered water flow to occur by furrow irrigation from a furrow at the left hand boundary of the domain. Infiltration wa imulated with a contant head condition on the urface of the furrow with the head varying with the depth in the furrow (i.e. the head at the bae wa 0.15 m), and with the uppermot part of the furrow 0 m. The bottom boundary condition wa aumed to be either 506

3 free drainage, or no-flow which bound the range of poibilitie. The effect of compaction in the furrow wa alo imulated by reducing the hydraulic conductivity of the oil under the furrow to a depth of approximately 0.1 m. Table 1. Soil phyical propertie and van Genuchten (1980) parameter for oil choen from the HYDRUS2D databae. See ection 3.3 for definition of α and n. Soil θ r (m 3 m -3 ) θ (m 3 m -3 ) α (m -1 ) n K (m -1 ) S (m -1/2 ) Sand x10-5 5x10-3 Loam x x10-3 Clay x10-5 5x10-3 Thee infiltration imulation were compared with a implified model of infiltration into the furrow uing the 2-parameter infiltration equation of Philip (1957). Detail on the derivation of thee are in Cook et al. (2007). Thee imple infiltration equation predict the poition of the wetting front in both the vertical and horizontal plane from the furrow. They are: * ( ) θ ( ) zt () = S t+ At / Δ, t t = S/( K A) ( ) = I + Kt / Δ θ, t> t, I = S t + At * * * * * where z(t) i the penetration depth for a piton wetting front [L], S i the orptivity (Philip, 1957) [L T -1/2 ], A i a parameter related to aturated hydraulic conductivity (K [L T -1 ]) and a good etimate i A= 0.36K, t * i the joining time (Philip, 1987) and Δ θ = θ θn i the water content difference between the initial value θ n and the aturated value θ. If the penetration depth required i ome value Z related to the rooting depth of the crop, then the time for the penetration depth to reach thi depth (τ [T]) i: 2 (3) * 4 /4, τ = S + AZΔθ S A τ t ( θ ) = ZΔ I / K, τ > t * * The width that the wetting front will have penetrated into the bed during thi time (W) i: (4) W = 2 τλ K / Δ θ (5) c where λ c i the macrocopic capillary length cale and can be etimated from S K and Δθ (White and Sully, 1987) Solute To determine how the placement of fertilizer would affect the lo of olute from the bed during irrigation a layer of non-adorbed olute wa placed on the bed urface and the ditance horizontally from the furrow edge to where the olute front occur wa determined. The value of D i taken a m baed on the domain ize (Simunek et al. 1999). The imulation to conider fertilizer placement were run until drainage occurred at 2 m. Thi i poibly more water than hould enibly be applied in a ingle irrigation but ince leaching of alt from the oil i alo required (Cook et al., 2006) imulated irrigation i not far from the requirement and a the wahout ditance (X c ) i time dependent reult are alo applicable for le irrigation. X c wa calculated a the horizontal ditance to where the concentration of olute wa 99% of the initial concentration of 1mmol m -3. We alo imulated evaporation from the oil urface with a aline water table at a contant depth. Three depth viz, and m were choen for the watertable depth. From thee imulation we determined the time it would take for the olute to reach the oil urface (T1) and for the concentration at the urface to increae by 100 time that at the water table (T2). Simulation were carried out with initial concentration of 1 mmol m -3 for fertilizer wahout and aliniation imulation. For the aliniation imulation a contant potential evaporation rate of 5 mm day -1 wa aumed. 507

4 a Cook et al., Modelling water and olute in permanently raied bed 2.3. Drainage Drainage from the bed i poible through eepage from the ide of the bed a well a through the bottom of the bed. To invetigate thi we choe the two extreme imulation where drainage only occurred through eepage face on the ide of the bed and where both eepage face and free drainage from the bottom of the domain occurred. The initial oil condition wa aturation throughout the domain. Simulation were run for 10 day and no flow at the oil urface wa aumed, o only drainage and not drying by evaporation wa conidered, o that only the effect of internal oil drainage could be conidered. 3. RESULTS AND DISCUSSION 3.1. Infiltration The penetration of the wetting front into the bed uing the imple model gave reaonable reult for the horizontal penetration (W) except for the clay oil (Fig.2c). S wa initially calculated from the horizontal infiltration rate into a oil column with a head of zero at the intake urface uing HYDRUS1D. The head during the HYDRUS2D imulation varied from 0.15 m to zero, o S wa calculated again uing an the intake head value of 0.15 m. When thi latter value of S (head = 0.15 m) i ued the prediction of W for the clay oil when compared to the HYDRUS2D imulation improve markedly. For the loam and and oil the improvement wa not o dramatic when S wa calculated with a head of 0.15 m. The vertical penetration (z(t)) wa calculated with the imple model compared well with the HYDRUS2D imulation with ome underetimation at early time and ome overetimation at long time (Fig 2def). Thi indicate that the imple infiltration model could be ueful for deign of bed width if S wa meaured for that oil with the intake urface head that will be applied during infiltration. After 1 day of infiltration W i greatet for the clay due to much larger value of S for thi oil. The effect of a compaction zone under the furrow wa imulated and thi howed that the penetration horizontally wa lower a infiltration overall wa reduced. However, for the ame amount of infiltration, penetration horizontally wa greater (Cook et al., 2007). Thi mean it will take longer for the water to reach the centre of the bed when compaction of the furrow occur, but le water will be required Solute The reult howed that X c with time were imilar for the and and loam oil (Fig 3a) but that when X c i plotted veru cumulative infiltration (I) the clay and loam oil are imilar (Fig 3b). Thi ugget that wahout i reduced for a 100 mm irrigation event when fertilizer i placed on the urface at ditance of 5, and 5 m from the edge of the furrow, for and, loam and clay repectively, then wahout could be reduced. Thu placement of oluble agrochemical away from the furrow edge would reduce leaching loe and poible efficacy. However, imulation for each of the application cae tudie howed that rainfall carried the fertilizer down the oil profile and into the flow path of the irrigation water, reulting in limited reduction in leaching from placement of the fertilizer (Cook et al., 2007). Thee reult, however, are only for highly oluble and non-adorbed fertilizer. There will till be an advantage in placing fertilizer, and other agrochemical away from the furrow edge and in the plant row, particularly if dry condition are likely after application. W (m) W (m) W (m) b HYDRUS2D Simple model a d HYDRUS2D Simple model S (ψ = 0.15 m) c Figure 2. Penetration of wetting front horizontally into the bed from the edge of the furrow (W); a) and, b) loam (lower time cale ued), and c) clay, and the vertical penetration below the furrow (Z); d) and, e) loam and f) clay. The econd line for the clay i where a different value of S wa ued (ee text). Note different time and length cale are ued. e f Z (m) Z (m) Z (m) 508

5 a b x c (m) x c (m) 0.1 Sand Loam Clay I (m) Figure 3. Wahout ditance (X c ) with a) time and b) cumulative infiltration (I) for and, loam and clay oil. The other olute imulation conidered the rie of alt in the bed when a aline watertable exit. The imulation how what i now conventional widom with regard to capillary rie from aline watertable (Fig 4). The reult are, the water table mut be cloe to the urface < m for and oil to caue aliniation, for the clay and loam oil the time for the olute to reach the urface of the bed i imilar but when the watertable depth (Z w ) i < m the time required to reach 100 mmol m -3 i le for the loam oil due to it greater hydraulic conductivity, and loam and clay oil require fluhing event to reduce alt at leat once per year when the Z w < m Sand T1 Sand T2 a Loam T1 Loam T2 Clay T1 Clay T2 b Z w (m) Z w (m) Figure 4. Depth of the watertable (Z w ) with time for olute to reach the oil urface (T1) and increae to 100 mmol m -3 (T2); a) and oil and b) loam and clay oil. Note different cale on both axi in each panel. Initial imulation for the Indoneian and China PRB cae tudie indicated that olute would accumulate up in the middle of the bed. Thi poible build up of alt wa teted in greater detail for the China cae tudy and found to be occurring. Irrigation management i being adjuted to prevent thi becoming a long term iue. The Pakitan cae tudy where rainfall wa greater than, in particular, that in China, alt did not accumulated in the bed Drainage Drainage of the bed wa imulate with the domain initially aturated, and free drainage at 2 m. Reult how that after 10 day approximately 70, 20 and < 2mm had drained from the and loam and clay oil repectively (Fig 5). Even though the clay oil ha the lowet matric potential through out the profile the airfilled poroity wa the lowet and poor aeration problem i likely (Cook et al., 2007). Thi indicate that the bed are unlikely to ait with drainage of clay oil and that evaporation will be the main driver of lowering 509

6 the water content in thee oil type (Cook and Raam, 2002). Thi i an extreme cae and bed are likely to have a better tructure and le likely to become anaerobic. When the bottom boundary condition on the domain i changed to a no-flow condition the drainage of the bed can only occur by eepage through ide of the bed. Thi lead to a ituation where the watertable fixe the matric potential at zero at the bae of the bed. It can be hown (Cook et al. 2007) that the water content profile in the bed can be decribed by: Drainage (m) 0.8 Sand Loam Clay Drainage, clay (m) ( ) 1/ n 1/ m Zb = p/ p Δθ 1 / α (6) where α i a parameter related to the airentry potential, n i a parameter related to the rate of change of water content with matric potential, z i the height of above the bottom of the bed and m= n 1/ n, Δ θ = θ θ and p = θ θr, θ r i the reidual water content,. Thi equation i derived from the van Genuchten (1980) equation. Equation (6) wa able to fit the imulated reult for drainage from the bed very well (Figure 6). For Δθ = 0.1 the value of Z b calculated for the three oil are 6, 0.37 and 91 m for and, loam and clay oil repectively. What thi how i that bed are unlikely to be ueful in providing extra drainage of the oil for clay with no tructure. However, the bed are known to improve drainage on uch oil poibly through the removal of urface water and the evaporative drying due to the extra Figure 5. Cumulative drainage with time for and, loam and clay form an initially aturated domain with free drainage on the bottom boundary. Sand θ (m 3 m -3 ) Depth (m) urface area (Cook et al., 2007). Thi could allow earlier planting to occur in ome climate. Thu narrow bed where the increaed urface area i greater would be more ueful in drying out of clay oil than wide bed. 4. CONCLUSIONS Our imulation give inight into the behaviour of PRB during ome irrigation, olute tranport and drainage cenario. Thee will ait in improving the deign of future more pecific PRB imulation. Inight obtained include: Sand vg Sand H Loam vg Loam H Clay vg Clay H Figure 6. Comparion of water content profile in the centre of the bed form imulation (H) with etimate uing equation (5) (vg). An approximate infiltration equation i ueful in the deign of bed width, but only when the orptivity i directly meaured, Agro-chemical placed on the oil urface and away from the furrow edge leach le when furrow irrigation occur than if place up to the furrow edge, but rainfall reduce the potential effect of thi placement, Saliniation of the oil i likely with a teady-tate aline watertable at < m in and and < m in loam and clay oil unle actively managed, PRB are unlikely to ait with drainage of untructured clay oil but are a ueful way to increae drainage in wet climate for loam and and oil Loam and Clay θ (m 3 m -3 ) 510

7 ACKNOWLEDGMENTS The Autralian Centre for International Agricultural Reearch i thanked for funding thi project. All of the taff that worked on the variou ACIAR cae tudie in the donor countrie and Autralia that collected, proceed and provided data are gratefully acknowledged. REFERENCES Connor D.J., J. Timina, and E. Humphrey, (2001), Propect for permanent bed for rice-wheat ytem. Improving the productivity and utainability of rice-wheat ytem: iue and impact. Proceeding of an international ympoium, held at the 2001 Annual Meeting of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Charlotte, NC, USA, 22 October Cook F.J., J.H. Knight, E. Humphrey, J. Tidall, J. McHugh, and G. Hamilton, (2007). Modelling water and olute procee and cenario for optimiation of permanent raied bed ytem in China, India, Pakitan and Indoneia. ACIAR Report LWR , 108p. Cook F.J., N.S. Jayawardane, D.W. Raam, E.W. Chriten, J.W. Hornbuckle, R.J. Stirzaker, and K.L. Britow, (2006), The tate of meauring, diagnoing, ameliorating and managing olute effect in irrigated ytem. CRC for Irrigation Future Technical Report, No. 04/06, October Cook F.J., and D.W. Raam, (2002). An analytical model for water table dynamic during drainage and evaporation. Journal of Hydrology, 263, Friedrich, T. (2003). Engineering for conervation Agriculture Trend, concept and challenge in the global perpective. International Soil Tillage Reearch Organiation, 16 th Triennial Conference July The Univerity of Queenland, Bribane Autralia. Hamilton, G., D. Bakker, D. Houlbrooke, R. Hetherington, and C. Spann, (2003), Permanent raied bed prevent waterlogging and increae productivity of dryland farming in area in Wetern Autralia. International Soil Tillage Reearch Organiation, 16 th Triennial Conference July The Univerity of Queenland, Bribane Autralia. Hobb, P.R., K. Sayre, and R. Gupta, (2008), The role of conervation agriculture in utainable agriculture. Philophical Tranaction of the Royal Society B-Biological Science, 263(1491): Huain, Z., M. Shafiq, I. Haan, and R. Majid, (2003). Succe of permanent raied bed in a maize-wheat ytem in Pakitan. International Soil Tillage Reearch Organiation, 16 th Triennial Conference July The Univerity of Queenland, Bribane Autralia. Perie, R., C. Bluett, B. Wightman, A. Rab, and N. Ilam, (2003), I controlled traffic changing oil tructure under raied bed in Southern Victoria? International Soil Tillage Reearch Organiation, 16 th Triennial Conference July The Univerity of Queenland, Bribane Autralia. Philip, J.R. (1957), The theory of infiltration:4. Sorptivity and algebraic infiltration equation. Soil Science 83: Philip, J.R. (1987), The infiltration joining problem. Water Reource Reearch, 23(12), Ram, H., J. Yadvinder-Singh, J. Timina, E. Humphrey, S.S. Dhillon, K. Kumar, and D.S. Kler, (2005) Performance of upland crop on raied bed in northwetern India. Evaluation and performance of raied bed cropping ytem in Aia, Autralian and Mexico, Ed C.H. Roth, R.A. Ficher and C.A. Meiner, ACIAR Proceeding no. 121, Roth, C.H. R.A. Ficher and C.A. Meiner, (2005) Evaluation and performance of raied bed cropping ytem in Aia, Autralian and Mexico, ACIAR Proceeding no Sayre, K., A. Limon, and B. Govaert, (2005). Experience with permanent bed planting ytem CIMMYT, Mexico. Evaluation and performance of raied bed cropping ytem in Aia, Autralian and Mexico, Ed C.H. Roth, R.A. Ficher and C.A. Meiner, ACIAR Proceeding no. 121, Simunek, J., M. Sejna, and M. Th. van Genuchten, (1998) The HYDRUS-1D oftware package for imulating the one-dimenional movement of water, heat, and multiple olute in variably-aturated media. Verion, IGWMC - TPS - 70, International Ground Water Modeling Center, Colorado School of Mine, Golden, Colorado, 202pp. Simunek, J., M. Sejna, and M. Th. van Genuchten, (1999) The HYDRUS-2D oftware package for imulating two-dimenional movement of water, heat, and multiple olute in variably aturated media. Verion, IGWMC - TPS - 53, International Ground Water Modeling Center, Colorado School of Mine, Golden, Colorado, 251pp. White, I., and M.L. Sully, (1987) The macrocopic and microcopic capillary length and time cale from field infiltration. Water Reource Reearch, 23, Van Genuchten, M. Th. (1980), A cloed-form equation for predicting the hydraulic conductivity of unaturated oil. Soil Science Society of America Journal, 44,