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«International 17 Workshop th Nitrogen The was jointly organised by Teagasc and AFBI Printed by Print Depot Suggested citation Authors, 2012. Title ...»

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References Betteridge, K., Andrewes, W.G.K. and Sedcole, J.R. 1986. Intake and excretion of nitrogen, potassium and phosphorus by grazing steers. J. Agr. Sci. 106, 393-404.

Keating, B.A., Carberry, P.S., Hammer, G.L., Probert, M.E., Robertson, M.J., Holzworth, D., Huth, N.I., Hargreaves, J.N.G., Meinke, H., Hochman, Z., McLean, G., Verburg, K., Snow, V., Dimes, J.P., Silburn, M., Wang, E., Brown, S., Bristow, K.L., Asseng, S., Chapman, S., McCown, R.L., Freebairn, D.M. and Smith, C.J. 2003. An overview of APSIM, a model designed for farming systems simulation. Eur. J. Agron. 18, 267-288.

Nitrogen Workshop 2012

Use of a systems model to estimate the impact of management decisions on nitrate leaching under intensive cropping Sharp, J.M. a, Thomas, S.M. a, Fraser, P.M. a, Brown, H.E. a a The New Zealand Institute of Plant and Food Research Limited, Private Bag 4704, Christchurch 8140, New Zealand

1. Background & Objectives There is a growing need for agricultural systems models to address the implications of management decisions on nutrient cycling and losses. Tools to predict the effects of land management on groundwater quality are needed by both farmers and policy makers. While there are models that can estimate nutrient losses from single crops there are few that can give meaningful outputs for cropping rotations and simultaneously assess the impacts of complex management decisions. The Agricultural Production Systems sIMulator (APSIM) is a suite of modules that enable the simulation of systems covering a range of plant, animal, soil, climate and management interactions (Keating et al., 2003). In this paper we report a test of APSIM to simulate nitrate (NO3) leaching with data from a field experiment, designed to measure the effects of irrigation and fertiliser on year-round nitrogen (N) losses. The model can then be used to determine its assessment of the most appropriate management for the system.

2. Materials & Methods Data were collected from a field trial with a factorial combination of N fertiliser rates and irrigation managements in a randomised block design. The experiment was established at Lincoln, Canterbury, New Zealand in spring 2004 on a well-drained, intensively cropped soil. It included four replicates of two crop rotations: potatoes – winter fallow – spring peas – winter fallow – potatoes – triticale and potatoes – winter wheat – winter fallow – potatoes – triticale. Each main plot was split into two different irrigation rates (optimum (W1) and either increased frequency or increased amount (W2)), and these sub-plots were split again into three different N fertiliser rates (nil (N0), optimum (N1) and excess (N2)). Irrigation was applied using drip lines and N fertiliser as calcium ammonium nitrate. Soil mineral N, crop dry matter, crop N, soil water content and leachate N concentration were measured at regular intervals throughout the trial. Nitrogen leaching, calculated using the soil solution NO3 concentration measured from samples collected in ceramic cups and the drainage calculated by APSIM through the use of a water balance model, was compared with simulations from APSIM 7.3. APSIM allowed the integration of crop models with an underlying soil module which simulates soil water movement and nutrient supply. The crop modules used were ‘potato’, ‘wheat’, ‘triticale’ and ‘fieldpea’. The soil water module SoilWat was used. The soil description (e.g. soil texture, bulk density, soil carbon and N) and initial values were provided from soil profile data collected at the start of the experiment. Soil NO3-N was reset to measured values at the beginning of each part of the rotation.

3. Results & Discussion APSIM accurately simulated the amount of N taken up by the crops at harvest. The primary source of N loss from the system was NO3 leaching, with predictions of annual leaching exceeding the observed. Estimates of leaching, both experimentally and in APSIM, are a product of drainage and the soil solution NO3 concentration. While there were no direct measurements of drainage in the field experiment with which to test APSIM against, intensive measurements of soil water content were taken.

Nitrogen Workshop 2012

APSIM predicted soil water content well in all layers except in the top layer for potato crops. This discrepancy may be due to differences in the soil bulk density between the potato ridges and furrows not simulated by APSIM. Nevertheless, through all of the soil layers, APSIM simulations track the observed data through time, and responded to changing soil water content with the wetting and drying of soil. Given that measured irrigation and rainfall data was used by APSIM for the water inputs to the system and that the soil water content is well approximated by APSIM simulations, drainage from the system appears to be simulated appropriately. This therefore suggests that the overestimation of annual leaching in the APSIM simulations may be due to an overestimation of soil solution NO3 concentration passing down through the layers of the soil profile, or that some leaching events were not adequately captured by the field monitoring.

Within APSIM’s SoilWat module the saturated and unsaturated flows of soil water are used to calculate the redistribution of solutes using a ‘mixing’ algorithm (APSIM Undated). Essentially solute movement is calculated as the product of the water flow and the solute concentration in that water. The solute concentration leaving a layer is calculated from the solute concentration entering that layer, modified by mixing between water draining through the layer and the water already in the layer. In APSIM 7.3 it is assumed that both saturated and unsaturated flow have mixing efficiency factors of 1.0, which assumes drainage water is fully mixed with the water present in the layer. If this assumption is relaxed, so that when there is saturated flow there is not complete mixing, as might occur during preferential flow, less solution NO3 will be moved down through and out of the soil profile. For this modelling study an efficiency factor of 0.7 gave the best fit of predicted annual NO3 leaching values to those observed in the experiment.





The modified model was then used to determine an appropriate management strategy for the rotations in question which balanced achieving high yields and minimising NO3 leaching losses.

APSIM and other similar agricultural system models that can reliably simulate the effects of management on nutrient losses over crop rotations have great potential for helping land users and policy makers make management and land use decisions that avoid adverse environmental impacts.

4. Conclusion The importance of datasets such as this, with multiple crops within rotations, and intensive N and water measurements, to parameterise and test systems models is highlighted. APSIM successfully simulated the N and water balance of this crop rotation. However, analysis showed that APSIM over-estimates the leaching of mineral N through the soil profile, and when adjustments are made, estimates of leaching are much improved. There is also a need for better understanding of the controls of solute mixing within the soil profile, and modifications are required to account for ridges and hollows seen in potato crops. The system model was then applied to determine a management strategy of this system that balanced the priorities of increasing yield and minimising NO3 leaching.

References APSIM (Undated). SoilWat Documentation. http://www.apsim.info/Wiki/SoilWat.ashx. APSIM Initiative.

Keating, B.A, Carberry, P.S, Hammer, G.L, Probert, M.E, Robertson, M.J, Holzworth, D, Huth, N.I, Hargreaves, J.N.G, Meinke, H, Hochman, Z, McLean, G, Verburg, K, Snow, V, Dimes, JP, Silburn, M, Wang, E, Brown, S, Bristow, K.L, Asseng, S, Chapman, S, McCown, R.L, Freebairn, D.M and Smith, C.J. 2003. An overview of APSIM, a model designed for farming systems simulation. European Journal of Agronomy 18, 267-288.

Nitrogen Workshop 2012

Use of chemical amendment of dairy cattle slurry to reduce phosphorus losses from dairy cattle slurry while allowing land spreading of slurry to meet nitrogen requirements.

Brennan, R.B.a, Healy, M.G.a, Lanigan,G.b, Fenton, O.b a Civil Engineering, National University of Ireland, Co. Galway, Rep. of Ireland.

b Teagasc, Johnstown Castle, Environmental Research Centre, Co Wexford, Rep. of Ireland.

1. Background & Objectives Under the European Union Water Framework Directive (EU WFD), River Basin District (RBD) managers must implement Programmes of Measures (POM) by 2012 within a catchment where an individual waterbody has been classified as below good status or are at risk of not reaching at least “good ecological status” by 2015. It is widely documented that many waterbodies in Europe will not achieve the desired water quality status by 2015 due to catchment buffering and long transit times (Cherry et al., 2008). Chemical amendment of dairy cattle slurry has been proposed as a mitigation measure to reduce incidental phosphorus (P) losses from agriculture (Brennan et al., 2011a). Brennan et al. (2011b) showed that amendments were effective at reducing incidental P losses with no adverse effect on suspended sediment (SS) or metal release. In subsequent work, Brennan et al. (unpublished) examined pollution swapping potential due to effects of amendments on greenhouse gas (GHG) losses and on nitrogen (N) in runoff. The aim of the present study was to discuss the feasibility of chemical amendment of dairy cattle slurry in Ireland.

2. Materials & Methods A controlled agitator experiment was designed to identify the most effective chemical amendment to reduce dissolved reactive phosphorus (DRP) release to water overlying grassed soil cores, which received un-amended and amended dairy cattle slurry. In addition to effectiveness, the feasibility of these amendments was determined based on several criteria: estimated cost of amendment, amendment delivery to farm, addition of amendment to slurry, and slurry spreading costs due to any volume increases. The best amendments were then added to slurry immediately before it was surface applied to grassed-soil in laboratory runoff boxes, which were subjected to simulated rainfall events. Analysis of overland flow showed that PAC (poly-aluminium chloride, the most commercially available form of AlCl3) was the most effective amendment for decreasing DRP losses in runoff following slurry application, while alum proved to be the most effective for total P (TP) and particulate P (PP) reduction. The incidental loss of metals (aluminium (Al), calcium (Ca) and iron (Fe)) in runoff during all experiments was below the maximum allowable concentrations (MAC) for receiving waters. Following this, the ‘pollution swapping’ potential of the amendments was examined. A laboratory-scale gas chamber experiment was conducted to examine emissions of ammonia (NH3), nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2).

3. Results & Discussion Following beaker experiments the four best amendments were selected for further study based on effectiveness and feasibility. At optimum application rates the amendments selected were: ferric chloride (FeCl2), which reduced the DRP in overlying water by 88%, aluminium chloride (AlCl3) (87%), alum (83%) and lime (81%). The runoff-box results verified these findings and following while the gas chamber experiments allowed pollution swapping to be considered as part of the decision making criterion. The amendments recommended for a field study were, from best to worst: PAC, alum and lime. This component of the study investigated how soil and chemically amended slurry interactions affects amendment effectiveness under field conditions. The results of

Nitrogen Workshop 2012

this field study validated the results from the laboratory-scale studies. Alum and PAC reduced average flow-weighted mean concentration (FWMC) and total loads of DRP, dissolved un-reactive phosphorus (DUP), PP and TP in runoff, while amendment of slurry with lime at the rate examined in this study was not effective at reducing P losses. Alum amendment significantly increased average FWMC of ammonium-N (NH4-N) in runoff water during the first rainfall event after the slurry was applied (an 84% increase). This study compiled these results to give a feasibility analysis for chemical amendments in Ireland.

–  –  –

4. Conclusion Chemical amendments are very effective at reducing P loss from dairy cattle slurry and have been found to have no significant adverse effects or global warming potential and N loss to ground water.

Chemical amendment of dairy cattle slurry is not currently feasible however it is possible that it may form part of a strategic P management programme in future. The next step is to examine the use of chemical amendment of dairy cattle slurry at farm and catchment scale.

References Brennan R.B., Fenton O., Rodgers M. and Healy M.G. 2011a. Evaluation of chemical amendments to control phosphorus losses from dairy slurry. Soil Use and Management 27, 238-246.

Brennan, R.B., Fenton, O., Grant, J. and Healy, M.G. 2011b. Impact of chemical amendment of dairy cattle slurry on phosphorus, suspended sediment and metal loss to runoff from a grassland soil. Science of the Total Environment 409, 5111-5118.

Cherry K.A., Shepard M., Withers P.J.A. and Mooney S.J. 2008. Assessing the effectiveness of actions to mitigate nutrient loss from agriculture: A review of methods. Science of the Total Environment 406, 1-23.

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Using the Eurotate_N crop model to optimize nitrogen fertilization in potato crop Olasolo, L., Vázquez, N., Suso, M.L, Pardo, A SIDTA, Government of La Rioja. Ctra. Mendavia-Logroño NA-134, km.90. 26071. Logroño, Spain

1. Background & Objectives Eurotate_N is a decision support system for soil-plant interactions based on the use of nitrogen in crop rotations and can be used to compare the effects of different fertilizer rates and other management practices, within a wide range of production systems and climatic conditions across Europe (EU-Rotate, 2002). Due to the high nitrate concentration in groundwater, the alluvial plain of The Oja River (North Spain) has been designated a Nitrate Vulnerable Zone (NVZ). In this area, the prevalent crops are cereals, potatoes, peas and green beans. The performance of Eurotate for potatoes and green beans has been evaluated in previous studies (Olasolo, 2011; Olasolo, 2009).



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