Paul L. G. Vlek

Land Use Dynamic Simulator (LUDAS): A multi-agent system model for simulating spatio-temporal dynamics of coupled human–landscape system: 2. Scenario-based application for impact assessment of land-use policies

Abstract Assessment of future socio-ecological consequences of land-use policies is useful for supporting decisions about what and where to invest for the best overall environmental and developmental outcomes. However, the task faces a great challenge due to the inherent complexity of coupled human–landscape systems and the long-term perspective required for sustainability assessment. Multi-agent system models have been recognized to be well suited to express the co-evolutions of the human and landscape systems in response to policy interventions. This paper applies the Land Use Dynamics Simulator (LUDAS) framework presented by Le et al. [Ecological Informatics 3 (2008) 135] to a mountain watershed in central Vietnam for supporting the design of land-use policies that enhance environmental and socio-economical benefits in long term. With an exploratory modelling strategy for complex integrated systems, our purpose is to assess relative impacts of policy interventions by measuring the long-term landscape and community divergences (compared with a baseline) driven from the widest plausible range of options for a given policy. Models tests include empirical verification and validation of sub-models, rational evaluation of coupled models structure, and behaviour tests using sensitivity/uncertainty analyses. We design experiments of replicated simulations for relevant policy factors in the study region that include (i) forest protection zoning, (ii) agricultural extension and (iii) agrochemical subsidies. As expected, the stronger human–environment interactions the performance indicators involve, the more uncertain the indicators are. Similar to the findings globally summarised by Liu et al. [Science 317 (2007) 1513], time lags between the implementation of land-use policies and the appearance of socio-ecological consequences are observed in our case. Long-term legacies are found in the responses of the total cropping area, farm size and income distribution to changes in forest protection zoning, implying that impact assessment of nature conservation policies on rural livelihoods must be considered in multiple decades. Our comparative assessment of alternative future socio-ecological scenarios shows that it is challenging to attain better either household income or forest conservation by straightforward expanding the current agricultural extensions and subsidy schemes without improving the qualities of the services. The results also suggest that the policy intervention that strengthens the enforcement of forest protection in the critical areas of the watershed and simultaneously create incentives and opportunities for agricultural production in the less critical areas will likely promote forest restoration and community income in long run. We also discuss limitations of the simulation model and recommend future directions for model development.

7. The efficacy and loss of fertilizer N in lowland rice

Nitrogen fertilization is a key input in increasing rice production in East, South, and Southeast Asia. The introduction of high-yielding varieties has greatly increased the prospect of increasing yields, but this goal will not be reached without great increases in the use and efficiency of N on rice. Nitrogen enters a unique environment in flooded soils, in which losses of fertilizer N and mechanisms of losses vary greatly from those in upland situations. Whereas upland crops frequently use 40–60% of the applied N, flooded rice crops typically use only 20–40%. There is a great potential for increasing the efficiency of N uptake on this very responsive crop to help alleviate food deficits in the developing world.This article reviews current use of N fertilizers (particularly urea) on rice, the problems associated with rice fertilization, and recent research results that aid understanding of problems associated with N fertilization of rice and possible avenues to increase the efficiency of N use by rice.

Land-Use Dynamic Simulator (LUDAS): A multi-agent system model for simulating spatio-temporal dynamics of coupled human–landscape system. I. Structure and theoretical specification

This paper presents the concept and theoretical specification of a multi-agent based model for spatio-temporal simulation of a coupled human–landscape system. The model falls into the class of all agents, where the human population and the landscape environment are all self-organized interactive agents. The model framework is represented by four components: (i) a system of human population defining specific behavioural patterns of farm households in land-use decision-making according to typological livelihood groups, (ii) a system of landscape environment characterising individual land patches with multiple attributes, representing the dynamics of crop and forest yields as well as land-use/cover transitions in response to household behaviour and natural constraints, (iii) a set of policy factors that are important for land-use choices, and (iv) a decision-making procedure integrating household, environmental and policy information into land-use decisions of household agents. In the model, the bounded-rational approach, based on utility maximisation using spatial multi-nominal logistic functions, is nested with heuristic rule-based techniques to represent decision-making mechanisms of households regarding land use. Empirical verifications of the models components and the application of the model to a watershed in Vietnam for integrated assessments of policy impacts on landscape and community dynamics are subjects of a companion paper.

Traits associated with improved P-uptake efficiency in CIMMYT's semidwarf spring bread wheat grown on an acid Andisol in Mexico

Phosphorus deficiency is a major yield limiting constraint in wheat cultivation on acid soils. The plant factors that influence P uptake efficiency (PUPE) are mainly associated with root characteristics. This study was conducted to analyze the genotypic differences and relationships between PUPE, root length density (RLD), colonization by vesicular arbuscular and arbuscular mycorrhizal (V)AM fungi and root excretion of phosphatases in a P-deficient Andisol in the Central Mexican Highlands. Forty-two semidwarf spring-bread-wheat (Triticum aestivumL.) genotypes from CIMMYT were grown without (−P) and with P fertilization (+P), and subsequently in subsets of 30 and 22 genotypes in replicated field trials over 2 and 3 years, respectively. Acid phosphatase activity at the root surface (APASE) was analyzed in accompanying greenhouse experiments in nutrient solution. In this environment, PUPE contributed more than P utilization efficiency, in one experiment almost completely, to the variation of grain yield among genotypes. Late-flowering genotypes were higher yielding, because the postanthesis period of wheat was extended due to the cold weather at the end of the crop cycles, and postanthesis P uptake accounted for 40–45% of total P uptake. PUPE was positively correlated with the numbers of days to anthesis (at −P r=0.57 and at +P r=0.73). The RLD in the upper soil layer (0–20 cm) of the wheat germplasm tested ranged from 0.5 to 2.4 cm cm-3 at –P and 0.7 to 7.7 at +P. RLD was the most important root trait for improved P absorption, and it was positively genetically correlated with PUPE (at –P r=0.42 and at +P r=0.63) and the number of spikes m-2 (at –P r=0.58 and at +P r=0.36). RLD in the upper soil layer was more important with P fertilizer application. Without P fertilization, root proliferation in the deeper soil profile secured access to residual, native P in the deeper soil layer. (V)AM-colonisation and APASE were to a lesser degree correlated with PUPE. Among genoptypes, the level of (V)AM-colonisation ranged from 14 to 32% of the RLD in the upper soil layer, and APASE from 0.5 to 1.1 nmol s-1 plant-1 10-2.

Environmental correlation of three-dimensional soil spatial variability: a comparison of three adaptive techniques

An appropriate inclusion of spatial variation of soils is becoming increasingly important for spatially distributed ecological modelling approaches. Even though soils are anisotropic vertically and laterally, most soil spatial variability studies have focused on the lateral variation of soil attributes over the landscape. This study characterizes the complexity of three-dimensional variations of individual soil attributes and examines the possibility of predicting soil property distribution using three different regression approaches: artificial neural networks (ANN), regression trees (RT) and general linear models (GLM). Thirty-two physiochemical attributes of 502 soil samples were collected from 64 soil profiles on a slope at Bicknoller Combe, Somerset, UK. After a principal component analysis, five soil attributes were selected to test for environmental correlation, assuming they reflect dominant pedological processes at the hillslope. Vegetation occurrence, soil types, terrain parameters and soil sample depth were used as predictors. Prediction using environmental variables was most successful for soil attributes whose spatial distribution is strongly influenced by lateral hydrological and slope processes with relatively simple depth functions (e.g. total exchangeable bases, Mn oxides and soil pH). These soil attributes also showed a high mobility, which implies that their spatial distribution quickly reaches an equilibrium with current slope processes. Soil taxonomic information only marginally improved the performance of models constructed from surface information such as vegetation and terrain parameters. On the other hand, soil attributes whose vertical distribution is strongly governed by vertical pedogenesis or unknown factors were poorly modelled by environmental variables due to stronger nonlinearity in their vertical distribution. Soil taxonomic information becomes more important for predicting these soil attributes. As an empirical modelling tool, GLM with interaction terms outperformed the other two methods tested, ANN and RT, in terms of both the simplicity of the model structure and the performance of derived empirical functions.

Ammonia volatilization from flooded soils

Ammonia volatilization from flooded soils has been studied for over half a century. In reviewing the literature on this subject, it becomes clear that there is no consensus on the importance given to this loss mechanism. In part, the differences of opinion can be explained by the fact that ammonia losses were studied in different environments, but to a great extent it seems due to the wide diversity of techniques used to study this loss mechanism.The many factors that influence ammonia volatilization from flooded soils are chemical, biological, and environmental in nature. These various factors are reviewed in depth and discussed with respect to their implications for measurement techniques and for soil, fertilizer, and water management.The major objective of this paper is to familiarize the reader with the most current developments in thinking about the mechanisms and extent of ammonia loss and hopefully to stimulate meaningful research on ammonia volatilization from flooded soils. Such research should be conducted in a wide range of agroclimatic conditions utilizing measurement techniques that are valid or for which the limitations are clearly understood. A better appreciation for the importance of ammonia volatilization will provide the impetus to research and development in fertilizer technology and management aimed at preventing such losses.

Soil microbiological parameters as indicators of soil quality under improved fallow management systems in south-western Nigeria

Soil microbiological and soil biochemical parameters (pH, exchangeable basic cations, inorganic and organic phosphorus pools, total organic carbon and total nitrogen, microbial biomass carbon, acid and alkaline phosphatase, β-glucosidase and protease activity) were identified as indicators of soil quality under improved fallow management systems with senna, leucaena and pueraria on severely degraded and non-degraded soil. Principal component analysis demonstrated that soil organic matter related nutrient dynamics was the major contributor to explain the total variance (>80%) of the sites under the prevailing experimental conditions. Highest loadings with the major principal component were provided by microbial biomass, alkaline phosphatase, total N, β-glucosidase and organic C. Contrasting fallow management systems (alley cropping, live mulch, planted fallow, controls in long-term experiments) at three sites differing in degree of soil degradation could be evaluated adequately by these indicators. β-Glucosidase indicated soil quality changes better than total organic carbon. Alkaline phosphatase was more sensitive than microbial biomass in characterizing the effects of improved fallow management on site degradation. Acid phosphatase and protease were not considered sensitive indicators for soil quality evaluations of these long-term management trials. Pueraria sustained soil quality on the non-degraded site but did not improve the severely degraded site, suggesting that pueraria is a soil fertility maintenance crop. In contrast, senna improved the degraded sites and more so on the most severely degraded site. Apparently, senna can be considered a suitable candidate for soil restoration purposes.

Fate of fertilizer nitrogen applied to wetland rice

Dramatic increases in the production and use of fertilizer N in rice-growing countries have occurred during the past decade. In developing Asia, fertilizer N production has increased from 3.6 × 106 t in 1970 to an estimated 18 × 106 t in 1982/83, of which 85% will be urea (Stangel 1979). Expanded use of N fertilizer is being combined with fertilizer-responsive rice varieties and increased areas under irrigation in an all-out effort to produce enough food for the vast Asian population. Unfortunately, N fertilizer, which is already a costly input for the rice farmer, is becoming more expensive in response to the rising cost of the oilbased feedstocks used in fertilizer production. It is therefore imperative that N fertilizer is used efficiently.

Carbon storage and root penetration in deep soils under small-farmer land-use systems in the Eastern Amazon region, Brazil

The north-east of Pará state in the Eastern Amazon of Brazil was settled over 100 years ago. Today the region is an agricultural landscape with variously-aged secondary vegetation and fields with annual cultures, plantation crops and pastures. The effect of these different land covers on carbon sequestration as well as on water and nutrient extraction remain subject of debate. Therefore, we assessed the importance of land use on soil carbon stocks by measuring various C fractions and root biomass (0–6 m) in slash-and-burn systems and (semi-) permanent cultures. An extensive root system down to at least 6 m depth was present under various secondary vegetation stands and slashed and burned fields recently taken into cultivation as well as under a primary forest. Shallower rooting patterns were evident under (permanent) oil palm (4.5 m) and (semi-permanent) passion fruit plantations (2.5 m). Carbon storage in soils of traditional slash-and-burn agriculture up to 6 m depth (185 t ha-1) was not significantly lower than under a primary forest (196 t ha-1) but declined significantly under (semi-) permanent cultures (to 146–167 t ha-1). Compared to above-ground C losses, soil C losses due to slash-and-burn agriculture may thus be small. This is an argument for maintaining the secondary vegetation as part of the agricultural land-use system, as the root system of its trees is conserved and thus C is sequestered also at greater depth.

The role of fertilizers in sustaining agriculture in sub-Saharan Africa

African farmers have relied traditionally on fallowing for up to 15 years to restore soil fertility. Leaving land unproductive for such periods is a luxury many regions cannot afford, given the contemporary decline in per capita food production (1%/year). Thus, alternative soil fertility maintenance measures such as agroforestry, novel intercropping systems, residue conservation, the use of manure, soil amendments, and fertilizer have recently been given greater emphasis. The Food and Agriculture Organization (FAO) estimates that 75% of the increase in regional food production must come from intensive production. However, fertilizer use in sub-Saharan Africa is only one tenth of the world average. The small size of fertilizer markets in most countries is an important contributing factor in relatively high farm-gate prices and low fertilizer use. There is significant scope for improving the efficiency of fertilizer procurement and distribution in the region. Most countries can substantially reduce farm-gate prices by changing to higher analysis formulas, relaxing specifications, importing in bulk and bagging locally, and improving systems of distribution. Various options of fertilizer production are discussed in this context. Intensification in areas where environmental constraints are limited and surplus production can be marketed may alleviate the demographic pressures to cultivate marginal land where increased land and labor productivity is unlikely. Although substantial effort should be made to research sustainable farming system options for marginal lands, efforts in the more resilient environments should concentrate on increased crop production, using inputs where feasible. Provisions should be made for adequate support in the infrastructural, institutional, and policy spheres to transform these regions into granaries.