Modelling of planted legume fallows in Western Kenya using WaNuLCAS. (I) Model calibration and validation

Walker, Anthony P.; Mutuo, Patrick K.; Noordwijk, Meine van; Albrecht, Alain; Cadisch, Georg

doi:10.1007/s10457-007-9049-6

Cited by 19 publications

(15 citation statements)

References 32 publications

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“…In accordance with previous studies [41,57,69,70], the range of the GOF statistics and the high correlation between the simulated and observed growth parameters for both the calibration (Figure 3) and the validation (Table 4) are indicative of the ability of the WaNuLCAS model to reproduce the early growth dynamics of the tested afforestation species with an acceptable accuracy and precision. A R 2 value of 0.5, CD value of 0.5-2, and EF value above 0.5 represent a good predicted-to-observed relationship [69].…”

Section: Model Performancesupporting

confidence: 62%

“…While dry-season leaf shed is characteristic for drought-deciduous tree species, its accounting in our simulations resulted in large reductions of the total height rather than D and AGB (results not shown), implying that tree canopy and height are more influenced by this process than D and AGB in the WaNuLCAS model. The lack of calibrated litterfall data may have caused the poor fit of the predicted D and AGB, albeit only during the dry season [57]. Despite these deviations between the observed and simulated values during the dry season, the well-reproduced growth patterns and accurate prediction of D, H, and AGB at the end of the growing seasons (Appendix A, Figure A2) are a sufficient basis for further analyses of plant growth.…”

Section: Model Performancementioning

confidence: 99%

“…The Hodnett and Tomasella [56] pedotransfer function (PTF) in the WaNuLCAS model was used to generate soil hydraulic properties, representative of tropical soil conditions [57]. Default values of initial soil N (ammonium and nitrate) concentrations that were representative of a wide range of tropical cropping systems were used because no site-specific data was collected.…”

Section: Input Data For Wanulcasmentioning

confidence: 99%

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Climate Change Sensitivity of Multi-Species Afforestation in Semi-Arid Benin

Noulèkoun¹,

Khamzina

Naab³

et al. 2018

Sustainability

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Abstract:The early growth stage is critical in the response of trees to climate change and variability. It is not clear, however, what climate metrics are best to define the early-growth sensitivity in assessing adaptation strategies of young forests to climate change. Using a combination of field experiments and modelling, we assessed the climate sensitivity of two promising afforestation species, Jatropha curcas L. and Moringa oleifera Lam., by analyzing their predicted climate-growth relationships in the initial two years after planting on degraded cropland in the semi-arid zone of Benin. The process-based WaNuLCAS model (version 4.3, World Agroforestry Centre, Bogor, Indonesia) was used to simulate aboveground biomass growth for each year in the climate record , either as the first or as the second year of tree growth. Linear mixed models related the annual biomass growth to climate indicators, and climate sensitivity indices quantified climate-growth relationships. In the first year, the length of dry spells had the strongest effect on tree growth. In the following year, the annual water deficit and length of dry season became the strongest predictors. Simulated rooting depths greater than those observed in the experiments enhanced biomass growth under extreme dry conditions and reduced sapling sensitivity to drought. Projected increases in aridity implied significant growth reduction, but a multi-species approach to afforestation using species that are able to develop deep-penetrating roots should increase the resilience of young forests to climate change. The results illustrate that process-based modelling, combined with field experiments, can be effective in assessing the climate-growth relationships of tree species.

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Section: Model Performancesupporting

confidence: 62%

Section: Model Performancementioning

confidence: 99%

Section: Input Data For Wanulcasmentioning

confidence: 99%

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Climate Change Sensitivity of Multi-Species Afforestation in Semi-Arid Benin

Noulèkoun¹,

Khamzina

Naab³

et al. 2018

Sustainability

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“…1. The calculation of the initial pools followed the procedure described by Walker et al (2007) and was based on measured organic soil nitrogen and iteratively changing amounts of each pool until the best goodness of fit (GOF) of observed and simulated plant yields were achieved.…”

Section: Model Calibration and Validationmentioning

confidence: 99%

“…WaNuLCAS has been used to predict mineral nitrogen leaching, the effect of nutrient limitation on tree and crop production and carbon sequestration under fallow systems in tropical ecosystems (Radersma et al 2005;Suprayogo et al 2002;Van Noordwijk and Cadisch 2002;Walker et al 2007Walker et al , 2008. To date, WaNuLCAS has not been widely used to predict erosion under various soil conservation measures.…”

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confidence: 99%

Assessing soil conservation strategies for upland cropping in Northeast Thailand with the WaNuLCAS model

et al. 2010

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Soil conservation approaches and agroforestry systems can play an important role in controlling erosion from tropical hillside cropping systems. Experimental testing of their potential application domain and design, however, is costly and time consuming. We, therefore, tested the ability of the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model. The specific objectives of the study were: (i) to evaluate the WaNuLCAS model for predicting water induced erosion under different soil conservation strategies, (ii) to use the model for a better understanding of various soil conservation measures in controlling erosion, and (iii) to assess the magnitude and dynamics of key processes influencing the efficiency of soil conservation measures. A 3-year-data set (2003)(2004)(2005) from a field experiment from the Loei province in Northeast Thailand on the impact of soil conservation (Leucaena hedgerow, Jack bean relay cropping) under minimum tillage on runoff and soil loss was tested. Results indicated that WaNuLCAS was able to predict soil loss and runoff well at the test site; i.e. R 2 = 0.80 and 0.82, respectively. In the calibration procedure a sub data set was used, where adjusting crop development parameters was an important step for improving simulated soil loss (R 2 = 0.75) and runoff (R 2 = 0.89). Soil conservation measures such as Leucaena hedges were effective techniques to control runoff and soil loss. Implementing a dynamic soil structure module in combination with minimum tillage reduced runoff and soil loss via an increase in available macropores and hence drainage over time which improved simulation results. Relay cropping with Jack bean played an important role in the control treatment in reducing soil loss during the third year due to its additional soil cover and positive impact on soil fertility as suggested by the model. Hence, the WaNuLCAS model is a valuable tool to study and understand processes and to explore management options for improving tropical hillside cropping threatened by soil degradation.

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Modelling of planted legume fallows in Western Kenya. (II) Productivity and sustainability of simulated management strategies

2008

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Improved fallow is a technology that can help to raise agricultural productivity in systems of poor soil fertility and low financial capital. Models, once calibrated, can be used to investigate a range of improved fallow systems relatively quickly and at relatively low cost, helping to direct experimental research towards promising areas of interest. Six fallow crop rotations were simulated using the WaNuLCAS model in a bimodal rainfall setting in Kenya over a 10 year period: (A) alternating fallow and crop seasons, (B) one season fallow followed by three seasons crop, (C) one season fallow followed by four seasons crop, (D-F) 1-3 seasons fallow periods followed by 3-5 seasons crop. The strategies were tested using a number of fallow growth rates, soil clay contents, and rainfall amounts to determine the interaction of fallow rotation and biophysical variables on maize (Zea mays (L.)) yield and sustainability (organic matter, N 2 fixation, leaching). The best simulated fallow strategies doubled maize yield compared to continuous maize over a 10 year period. Across all biophysical treatments strategy A and B of no more than three consecutive cropping seasons and of one consecutive fallow season yielded the most maize. This was because fallow benefits were largely due to the immediate fallow soil fertility benefit (IFB) rather than the cumulative benefit (CFB). The difference in yield between the two strategies was through a balance between (1) their interaction with the biophysical variables affecting accumulation of organic matter, hence increasing soil fertility and (2) the extra intrinsic soil fertility used for maize productivity by the inclusion of more cropping seasons within the rotation. We propose the following conceptual framework to manage fallows for maximum maize yield: when environmental factors are strongly limiting to fallow and crop growth then fallow strategy A would be the best strategy to employ (less risk but more labour) and when factors are less limiting then strategy B would be the best to employ.

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Modelling of planted legume fallows in Western Kenya using WaNuLCAS. (I) Model calibration and validation

Cited by 19 publications

References 32 publications

Climate Change Sensitivity of Multi-Species Afforestation in Semi-Arid Benin

Climate Change Sensitivity of Multi-Species Afforestation in Semi-Arid Benin

Assessing soil conservation strategies for upland cropping in Northeast Thailand with the WaNuLCAS model

Modelling of planted legume fallows in Western Kenya. (II) Productivity and sustainability of simulated management strategies

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