Farming Systems Design 2007

Farming Systems Design 2007 An International Symposium on Methodologies on Integrated Analysis on Farm Production Systems

Field-farm scale design and improvement

September 10-12, 2007 – Catania, Sicily, Italy sponsored by

LA GOLIARDICA PAVESE

The correct citation of articles in this book is: authors, 2007 title. On: Farming Systems Design 2007, Int. Symposium on Methodologies on Integrated Analysis on Farm Production Systems, M. Donatelli, J. Hatfield, A. Rizzoli Eds., Catania (Italy), 10-12 September 2007, book 2 – Field-farm scale design and improvement, pag. ??-??

________________________________________________________________________ Sponsors of the Symposium: The University of Catania The Società Italiana di Agronomia Under the auspices of: C.R.A. - Agriculture Research Council Rome, Italy

Organizing Committee: Salvatore Cosentino Marcello Donatelli Jerry Hatfield Hans Langeveld Andrea Rizzoli Graphics: Patricia Scullion Book composition: Claudia Maestrini

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© 2007 La Goliardica Pavese s.r.l. Viale Golgi, 2 - 27100 Pavia Tel. 0382529570 - 0382525709 - Fax 0382423140 www. lagoliardicapavese.it e-mail: [email protected] All copy-rights reserved. No part of this volume can be reproduced by any mean without the written permission of the Publisher. ISBN 978- 88-7830-474-1 Printed on August 2007 by Global Print, Gorgonzola (MI), Italy

Farming Systems Design 2007


DEHESA MODEL: NEW TOOL FOR RECOVERING TRADITIONAL AGROFORESTRY SYSTEMS OF IBERIAN PENINSULA 1

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C. G. H. Díaz-Ambrona , A. Etienne , J. Almoguera , J. Martínez-Valderrama 1

Dep. de Producción Vegetal: Fitotecnia, Universidad Politécnica de Madrid, E-28040 Madrid, Spain, [email protected] 2 CSIC, Estación Experimental de Zonas Áridas, E-04001 Almería, Spain, [email protected]

Introduction The dehesa is open oak parkland. These woodlands with silvo-pastoral use cover about two million hectares in the Iberian Peninsula. Traditionally annual pastures have been grazed by cows, sheep and also goats while acorns enrich Iberian pig diet, turning out a very appreciated and marketable product. Evergreen oak (Quercus ilex L.) has other uses as fuelwood collection and folder after tree pruning. Besides flora and fauna of the dehesa is exceptionally rich (Schnabel, 1997). In the last years efforts devoted to quantify the varied outputs of dehesa have resulted in different works. Grazing (e.g. Herrero et al., 1998) and forestry models (Gracia, 2005) coexist with methods applied to determine the acorn production in field (Vazquez, 1999). The objectives of this work were (i) to present a computer simulation model of the dehesa system to establish the productivity and the most suitable stocking rate for cattle, sheep, and Iberian pig; and (ii) to explore the key process of the dehesa system in an environment with a large variability such as the Mediterranean climate. Methodology Following the structural methodology of System Dynamics and employing VENSIM ® DSS software we have implemented a model composed by five interacting blocks (climate, soil, pasture, evergreen oak and livestock). The climate submodel contributes with daily data of temperature, solar radiation and precipitation, to calculate reference evapotranspiration applying a simplification of the Priestley-Taylor equation. The soil submodel calculates the soil water balance as cascade model. Pasture equations compute daily forage production and demand considering a fixed stocking rate. Evergreen oak submodel allows knowing oak and acorn biomass. Growth processes are restricted by temperature and soil water availability. In the livestock submodel the actual stocking rate maintained with the own resources and the amount of hogs is calculated, which can be compared to the initial stocking rate, an exogenous variable. Model calibration was based on data from literature and has been validated with field data for acorn and pasture production. Relative root mean square error (RRMSE) and coefficient of residual mass (CRM) were calculated. The model was applied to different tree covers ranging from pasture without tree to 88 mature oak ha-1 (100% soil shade), on Inceptisol soils. In the exposed simulation livestock farm considered is composed of an average herd of 450 kg breeding females, which produces and sells steers up to 200 kg reared on the farm, and pigs that in fatten period –comprehended between 120 to 160 kg of life weight– are fed with acorns. Rate of conversion of 13,5 kg acorns per kg of life weight has been considered for hogs. Total income was calculated from market prices of 2.2 euros kg-1 for steers and 2.61 euros kg-1 for hogs. Results Simulated average annual acorn production in seven location of southwest Spain (Extremadura) was 9.60 kg by tree while observed was 9.73 kg by tree (RRMSE 33%), coefficient of residual - 62 -

Farming Systems Design 2007


mass (CRM) 0,05. Simulated grass production was 1311 kg ha-1 and observed was 1333 kg ha-1 (RRMSE 15% and CRM 0.02). The model was applied to different open oak parklands of Extremadura. Maximum stocking rate was 0.70 cows ha-1 and 0.62 hogs ha-1. The simulation of different soil types gave a variation coefficient of 20.8% in cows and 8.9% in hogs; meanwhile the simulation of different climate produced a variability of 3.2% and 5.4% respectively. Taken into account soil type distribution in Extremadura and land uses we obtained a potential of 1,658,933 cows and 750,962 hogs. Today stocking rate is 0.5 cows ha-1, simulated stocking rate is 0.65 cows ha-1. Stocking rate (cows ha-1) has increased steadily from 0.25 in 1986 to 0.5 in 2006, as consequence of European subsidies regulated by CAPs (Pulido, 2002). Although our model shows that even higher stocking rate values are possible it has to be pointed out that soil erosion can be triggered by overgrazing (Schnabel, 2001). In fact southwestern dehesas have been included in Spain risk desertification scenarios (Ministry for the Environment, 2007).

1.2 1.0 0.8 0.6

Cows Hogs Total income Total income + UE subsidies

800 700 600 500 400 300 200 100 0

Total income (Euros ha-1)

Stocking rate (Head ha-1)

Figure 1 shows how subsidies applied to dehesa systems increase pasture grazing to the detriment of fattening pigs with acorns. After twenty years of subsidies management of land has lead to intensification of grazing damaging trees recruiting and therefore thinning out the forest (Plieninger, 2007). The Dehesa model reveals that similar economic results can be achieved turning to high-quality production such as pigs fed with acorns, keeping appropriated tree covers to protect soil from erosion. Figure Si ul tion o dehes stoc ing r te co s nd hogs nd tot l inco e or di erent tree co er Conclusions

The Dehesa model is a fine procedure to estimate average acorn and pasture production. Its application for experimental simulation of tree cover showed a 0.0 0 25 50 75 100 reduction of cows’ stocking rates with both the Tree cover (%) increased of tree density and hogs potential. The total income per hectare showed a maximum value among 25 to 50% percent of tree cover (22 to 44 mature trees ha-1). In the Extremadura region there is not decoupling of cows’ EU-subsidies. Subsidies increase income related to herbivores, and farmers are not investing to maintain a high tree density. 0.4 0.2

Ac no ledg ents This work was financed by the Spanish “Ministerio de Educación y Ciencia” through the research project AGL2005-03665: del e ric r res al ara la i ulaci de is e as dehesad s

Re erences C. Gracia et al., GOTILWA+: Un modelo de crecimiento forestal basado en procesos ecofisi ológicos, 2005. Cuadernos de la Sociedad Española de Ciencias Forestales18, 21-28. M. Herrero et al., The plant/animal int erface in models of grazing systems, 1998. Agricultural sytems modelling and simulation, 495-542. Ministry for the Environment, National Program of Action against Desertification, 2007. Working Paper. Secretaría General de Medio Ambiente, Madrid, Spain. T. Plieninger, Compatibility of livestock grazing with stand regeneration in Mediterranean holm oak parklands, 2007 Journal for Nature Conservation 15, 1-9. F. Pulido, La Producción Animal en la Dehesa Extremeña, 2002. Libro blanco de la agricultura, Ministerio de Agricultura, Pesca y Alimetación, Spain. S. Schnabel, Soil erosion and runoff production in a small watershed under silvo -pastoral landuse (dehesas) in Extremadura, Spain, 1997. Geoforma Ediciones. Logroño, Spain. Vázquez F.M. et al. Estimación de la producción de bellotas de los encinares de la provincia de Badajoz en 1999, 1999. Solo Cerdo ibérico 14, 67-75. - 63 -