Importance of water consumption by perennial vegetation in irrigated areas of the humid tropics: evidence from Sri Lanka

In tropical, monsoon climates of South-East Asia, irrigation facilities supplement rain in the wet season and enable crops to be cultivated during the dry season. In the Dry Zone of Sri Lanka, 70% of the average annual rainfall of 1000 mm falls in a 3 month period. During the dry season, reference evapotranspiration has less rainfall — about 700 mm, indicating that much additional supply is meant to support crops, mainly paddy. In this climatic context, irrigation has dramatically changed the local environment, creating ecosystems quite similar to that of the wet zone to flourish. In these systems, recharge of shallow groundwater by percolation from irrigated fields, canals, and tanks, has provided a continuous supply of water for natural vegetation and homestead gardens. Much of the water used by this non-crop vegetation is beneficial. Growth of fruit and coconut trees can be quite profitable, while other trees enhance the environment.In 1998, IWMI performed a comprehensive water balance in the command area of the Kirindi Oya irrigation scheme, Sri Lanka, based on surface flow measurements, rainfall data, and estimation of crop water requirements. This water balance showed that evaporation consumed 78% of the total amount of water available for use. The amount of evaporation is split into process depletion (crops for 28%), direct evaporation from tanks (7%), inter-seasonal fallow (10%) and from non-crop vegetation for 55%.The main conclusion from this study is that perennial vegetation as the main component of non-crop vegetation, is a significant consideration in tropical humid environments in planning, management and performance assessment. Designers, managers, and researchers need to specifically incorporate the evaluation of evaporation by non-crop vegetation and perennial vegetation in their approach of water requirements. Further investigation is needed to estimate water consumption by land cover type to assess their respective beneficial use.     

南方湿润地区太阳总辐射估算模型筛选

为筛选适于模拟中国南方湿润地区太阳总辐射的经验模型,将中国南方地区划分为华东、华中、华南和西南4个区域,选用36个辐射站点逐日数据(1994—2016年),采用最小二乘算法优化3种基于温度模型(T₁,T₂和T₃模型)、3种基于日照时数模型(N₁,N₂和N₃模型)和2种混合模型(M₁和M₂模型)的经验参数,并在日、月和年尺度上评价各模型在4个分区的精度.结果表明：在日、月和年尺度上,日照时数模型精度最高,其次为混合模型,温度模型精度最低,日尺度R²分别为0.847～0.898,0.654～0.904和0.435～0.687,月尺度R²分别为0.529～0.857,0.368～0.858和0.334～0.766,年尺度RE为-1.78%～21.86%,-32.88%～24.14%和-37.54%～72.36%;日照时数模型中,N₂和N₃     

Exploring options for sustainable beef cattle ranching in the humid tropics: a case study for the Atlantic Zone of Costa Rica

Options are explored for sustainable, i.e. non-soil-nitrogen (N) mining, beef production in the humid tropical Atlantic Zone of Costa Rica using a modelling approach. Tools used are linear programming and a technical coefficient generator called PASTOR. Due to the combination of high rainfall, highly permeable soils and high N turnover rates, N losses are high and current natural pastures are calculated to mine soil N reserves with 40–60 kg ha⁻¹ year⁻¹. With current financial returns, there is no economic incentive for farmers to convert soil mining natural pastures to sustainable alternatives, viz. grass–legume mixtures or fertilized improved grasslands. When degradation of natural pastures over time due to soil N mining is considered in the model, it becomes economically attractive to replace these pastures with grass–legume mixtures. Sustainable beef cattle ranching is best realized by integrated intensification that raises total economic returns, i.e. use of grass–legumes or fertilized pastures, high levels of feed supplements and improved herd management techniques.     

Can computer models stimulate learning about sustainable land use? Experience with LUPAS in the humid (sub-)tropics of Asia

In many rice-cultivating regions of east and south-east Asia, competition for land and water resources is strong and increasing. This calls for exploration of future technology and policy options in support of sustainable land (and water) use. Sustainable land use is a complex issue, that involves uncertainties about the dynamics of the biophysical system and the social system, as well as multiple perspectives. The capacity to identify options for sustainable and equitable development depends on the acquisition of knowledge and skills for (a) holistic analysis of the biophysical system dynamics, (b) analysis of the multiple positions, perceptions, values, beliefs and interests of the relevant stakeholders, (c) contemplation of the action needed to fill the gap between the desired socio-technical system and the perceived real-world situation. Learning is contextual and gradual: historically, agricultural scientists have moved from a reductionist to a holistic hard system perspective, while now slowly embracing the interpretive system perspective.     

The climatic potential for beef cattle production in tropical Australia: Part I—Simulating the annual cycle of liveweight change

This is the first of a series of papers dealing with a survey of the agricultural climate as it pertains to the beef cattle industry in northern Australia. Beef cattle production here, as in most of the tropics, is characterised by an annual periodicity of weight gain and loss in train with seasonal water supply and temperatures. Trends in a weekly growth index derived from a simulated water budget and mean daily temperatures were found to correlate with trends in liveweight changes. Criteria for estimating the start and cessation of a ‘green season’ and a ‘dry season’, corresponding to the main liveweight gain and loss periods respectively, are derived and validated using cattle liveweight data from seven locations and both native and improved pastures. Linkage between cattle liveweight change and climate was close on native grass pastures but not on legume-improved pastures.     

The climatic potential for beef cattle production in tropical Australia: Part II— liveweight change in relation to agroclimatic variables

Part I of this series demonstrated a method of simulating a ‘green season’ and a ‘dry season’ which corresponded closely to the main period of liveweight gain and loss respectively of cattle on native grass pastures. This paper attempts to further characterise these seasons, using agro-climatic variables derived from a weekly pasture growth index, as to their quantitative relation to cattle liveweight changes. Neither the duration of the green season nor the variable most closely related to cumulative pasture growth (‘growth weeks’) accounted for much of the variation in amount of gain in the green season. In the dry season, however, the amount of liveweight loss was closely related to the estimated number of weeks without green feed (‘dry weeks’). Extraordinary weight loss in the dry season occurred in the years with few growth weeks in the green season, indicating pasture quantity as well as quality limitations in dry season nutrition in these years. In comparison to the green season, marginal response in liveweight to additional green weeks was over two times as great when cumulated over an entire year; this suggests that the main benefit of prolonging the green season is its effect in shortening the dry season.The problem of generalising from the very few stations with cattle data is discussed.     

Climate change impacts on irrigated maize in Mediterranean climates: Evaluation of double cropping as an emerging adaptation alternative

Because its relevance for the sustenance and livelihood of human systems, the assessment of the impacts that future climatic conditions may have on agricultural productivity becomes a key piece of information for agricultural scientists and policy makers.     

The environmental impacts of the production of concentrated feed: the case of pig feed in Bretagne

Pig production systems often depend to a large extent on concentrated feed imported from outside the farm. This study used the Life Cycle Assessment (LCA) method to assess major environmental impacts associated with the production and on-farm delivery of concentrated feed for pigs. Feed composition was based on average data for Bretagne (France) in 1998 and on published data for wheat-based, maize-based and co-product based feeds. As crop and feed production practices in Bretagne are similar to those in most of western Europe, we conclude that the results of this study apply more largely for western Europe. Depending on feed composition and fertilisation practise for crop-based feed ingredients, the production and delivery of one kg of feed for finishing pigs will produce a eutrophication potential between 3.8 and 9.3 g PO₄-equivalents, a global warming potential between 472 and 792 g CO₂-equivalents, an acidification potential between 3.0 and 6.3 g SO₂-equivalents, a terrestrial ecotoxicity potential between 0.4 and 8.7 g 1,4-dichlorobenzene-equivalents, an energy use between 3.3 and 6.1 MJ, and land use between 1.44 and 2.07 m² year. These impacts are mainly due to the production of crop-based ingredients. The contribution of transport processes was substantial for climate change, acidification and energy use. A feed containing mainly co-products had higher energy use and lower terrestrial ecotoxicity than feeds consisting mainly of non-processed crop-based ingredients. Hypotheses with respect to the fertilisation practices for the feed's main ingredients have a major effect on its impact values. The effect of uncertainty concerning the emissions of N₂O, NH₃, and NO₃ was very large for climate change, and large for acidification and eutrophication. The environmental burdens associated with the production and delivery of pig feed can be decreased by: optimising the fertilisation of its crop based ingredients, using more locally produced feed ingredients, reducing concentrations of Cu and Zn in the feed, and using wheat-based rather than maize-based feeds.     

The impacts of climate change on livestock and livestock systems in developing countries: A review of what we know and what we need to know

Despite the importance of livestock to poor people and the magnitude of the changes that are likely to befall livestock systems, the intersection of climate change and livestock in developing countries is a relatively neglected research area. Little is known about the interactions of climate and increasing climate variability with other drivers of change in livestock systems and in broader development trends. In many places in the tropics and subtropics, livestock systems are changing rapidly, and the spatial heterogeneity of household response to change may be very large. While opportunities may exist for some households to take advantage of more conducive rangeland and cropping conditions, for example, the changes projected will pose serious problems for many other households. We briefly review the literature on climate change impacts on livestock and livestock systems in developing countries, and identify some key knowledge and data gaps. We also list some of the broad researchable issues associated with how smallholders and pastoralists might respond to climate change. The agendas of research and development organisations may need adjustment if the needs of vulnerable livestock keepers in the coming decades are to be met effectively.     

Evaluation of the effect of energy price change on beef production management strategies in Hawaii

A dynamic programming approach was used to evaluate the effect of changing the energy input to product price relationship on the beef production management decision. The results of the three applications (low-to-low, high-to-low and high-to-high input-product price relationship) emphasized the importance of the input-product price relationships on the beef production management decision process. The optimal beef production management strategies were generally consistant with beef production management practices followed in Hawaii under those input-product price relationships.     

Hydrological impacts of rainwater harvesting (RWH) in a case study catchment: The Arvari River, Rajasthan, India. Part 1: Field-scale impacts

Rainwater harvesting (RWH), the small-scale collection and storage of runoff to augment groundwater stores, has been seen as a solution to the deepening groundwater crisis in India. However, hydrological impacts of RWH in India are not well understood, particularly at the larger catchment-scale. A key element to grasping RWH impact involves understanding the generated recharge variability in time and space, which is the result of variability in rainfall-runoff and efficiency of RWH structures. Yet there are very few reported empirical studies of the impact of RWH. Catchment-scale impacts are best studied using a water balance model, which would require a basic level of field data and understanding of the variability. This study reports the results of a 2-year field study in the 476 km² semi-arid Arvari River catchment, where over 366 RWH structures have been built since 1985. Difficulties associated with working in semi-arid regions include data scarcity. Potential recharge estimates from seven RWH storages, across three different types and in six landscape positions, were calculated using the water balance method. These estimates were compared with recharge estimates from monitored water levels in 29 dug wells using the water table fluctuation method. The average daily potential recharge from RWH structures varied between 12 and 52 mm/day, while estimated actual recharge reaching the groundwater ranged from 3 to 7 mm/day. The large difference between recharge estimates could be explained through soil storage, local groundwater mounding beneath structures and a large lateral transmissivity in the aquifer. Overall, approximately 7% of rainfall is recharged by RWH in the catchment, which was similar in the comparatively wet and dry years of the field analysis. There were key differences between RWH structures, due to engineering design and location. These results indicate that recharge from RWH affects the local groundwater table, but also has potential to move laterally and impact surrounding areas. However, the greatest weakness in such analysis is the lack of information available on aquifer characteristics, in addition to geology and soil type.     

The contribution of maize cropping in the Midwest USA to global warming: A regional estimate

Agricultural soils emit about 50% of the global flux of N₂O attributable to human influence, mostly in response to nitrogen fertilizer use. Recent evidence that the relationship between N₂O fluxes and N-fertilizer additions to cereal maize are non-linear provides an opportunity to estimate regional N₂O fluxes based on estimates of N application rates rather than as a simple percentage of N inputs as used by the Intergovernmental Panel on Climate Change (IPCC). We combined a simple empirical model of N₂O production with the SOCRATES soil carbon dynamics model to estimate N₂O and other sources of Global Warming Potential (GWP) from cereal maize across 19,000 cropland polygons in the North Central Region (NCR) of the US over the period 1964-2005. Results indicate that the loading of greenhouse gases to the atmosphere from cereal maize production in the NCR was 1.7 Gt CO₂e, with an average 268 t CO₂e produced per tonne of grain. From 1970 until 2005, GHG emissions per unit product declined on average by 2.8 t CO₂e ha⁻¹ annum⁻¹, coinciding with a stabilisation in N application rate and consistent increases in grain yield from the mid-1970’s. Nitrous oxide production from N fertilizer inputs represented 59% of these emissions, soil C decline (0-30 cm) represented 11% of total emissions, with the remaining 30% (517 Mt) from the combustion of fuel associated with farm operations. Of the 126 Mt of N fertilizer applied to cereal maize from 1964 to 2005, we estimate that 2.2 Mt N was emitted as N₂O when using a non-linear response model, equivalent to 1.75% of the applied N.     

Coordinated pest management decisions in the presence of management externalities: The case of greenhouse whitefly in California-grown strawberries

Optimal pest management can be compounded by externalities associated with management decisions among adjacent crop fields managed by agricultural producers. In this paper, a bioeconomic model is used to measure the effects of management decisions on optimal pest management. The case of the greenhouse whitefly invasion of California-grown strawberries is considered. Results show that coordinated pest management decisions among host crop growers may improve returns, but only during certain parts of the strawberry growing season. Two generalizable pest management policy implications are presented.     

Managing natural resources of watersheds in the semi-arid tropics for improved soil and water quality: A review

Soil, water and production systems constitute the most important natural resources of a watershed in the rainfed agro-ecosystem; and for sustainability of the production systems they need to be in harmony with the environment. To learn from the past research, a review is made of literature on the impact of natural resource management practices on soil and water quality in the semi-arid tropical regions of India. The results from long-term on station field experiments show that an integrated use of soil and water conservation practices with balanced plant nutrition can not only sustain increased productivity but also maintain soil quality at the watershed or catchment level. Natural resource management practices that conserve soil and water also help to maintain surface and groundwater quality. The changes in soil and water quality, as impacted by natural resource management practices, need to be monitored and assessed on a continuing basis as the outcome of such research offers valuable opportunity for the implementation of corrective management practices, as and when needed.     

对农村老年人口养老的主要问题分析

目前农村老年人养老现状不容乐观.家庭养老功能弱化,社区养老机制滞后,社会福利、政府救济和低保投入严重不足等,导致绝大多数农村老年人处在家庭边缘和社会保障体系之外.     

GAMEDE: A global activity model for evaluating the sustainability of dairy enterprises. Part II – Interactive simulation of various management strategies with diverse stakeholders

GAMEDE is a stock-flow dynamic simulation model designed with farmers to represent dairy farm functioning and the consequences of the farmer’s daily management decisions for whole-farm sustainability. Sustainability is evaluated according to its three pillars: technico-economic viability, respect for environment, and social liveability. The model provides original information for a better understanding of the processes regulating nitrogen dynamics within the farm, and the factors determining farmers’ decisions and practices. Model implementation experiments have revealed that GAMEDE is also a useful tool to support discussions and to generate knowledge exchange among various stakeholders who play an important role in the development of farm sustainability: farmers, extension agents and researchers.While a majority of researchers and advisers are specialised and a majority of farmers fix their attention on specific and narrow themes of farm management, such a comprehensive model can help stakeholders complement their knowledge to gain a holistic view of the farming system. This holistic and integrated view is crucial: (i) for researchers who wish to explain diversity in farming systems and understand decisional and biophysical processes and their interrelated effects operating in such complex agro-ecosystems, (ii) for advisers whose aim is to define alternative management strategies applicable in practice, i.e. taking into account farm specificities, and (iii) for farmers who must choose practices compatible with their resources, assets, constraints and objectives.Holism can also improve versatility and thus the generic character of models. Issues are narrowly specified and greatly vary both among categories of stakeholders (e.g. scientists versus farmers) and within each category (e.g. among farmers). A comprehensive model that: (i) details all farm management operations, and (ii) represents their effects on different spatio-temporal levels and on the three sustainability dimensions, is more likely to respond to the various issues facing different stakeholders. We argue that capacity of models to respond to stakeholders’ questions has to be considered in future evaluations of decision support systems.     

Simulation of beef cattle production systems in the Llanos of Colombia—part I. Methodology: An alternative technology for the tropics

A simulation model was developed to study voluntary forage intake, energy requirements for maintenance, liveweight change and calving rate of grade Zebu cows in the Llanos of Colombia. Multiplicative correction factors were fitted to intake and maintenance requirement prediction equations researched from the literature to account for reduced intake due to sparse regrowth of recently burned native savanna and to conditions of mineral deficiency, increased intake and decreased maintenance requirement during periods of high compensatory gain during the rainy season, and increased intake and maintenance requirement due to the effects of lactation and gestation. A frequency distribution was constructed relating liveweight at time of mating to subsequent calving rate, and this was used to simulate the calving rates of cow herds in the Llanos. Use of the model would allow prediction of the amount of improved pasture or supplemental feed that would be necessary to raise calving rates in a particular herd to an acceptable level, defined as at least three calves per cow every four years. The model was fitted by computer and was then run on programmable calculators. This type of simulation is suited to regions of the world in which computer time is expensive or unavailable. Verifications, validations and experimentation with the model are presented in a companion paper.     

The intertemporal impact of soil erosion on non-uniform soil profiles: A new direction in analyzing erosion impacts

Soil erosion studies by economists have utilized relatively simple yield response functions compared to productivity simulation models used by soil scientists in order to endogenously solve for optimal management schemes. This paper combines the optimization techniques of previous economic studies with a more complex measure of soil productivity than simply soil depth which has been used previously. An illustrative model demonstrates how erosion affects different types of soil profiles found in the United States and isolates three different ways that erosion can impact productivity. Estimation procedures that do not account for the non-uniform nature of soil profiles can misstate the impact of soil erosion on cropland productivity. The framework, though perhaps overly simplified for direct use, disentangles the impacts of soil erosion into substitution, mixing and depth effects and suggests how varied profiles should be managed in different ways according to how each is impacted by erosion.     

Quality of groundwater for irrigation in tropical karst environment: The case of Yucatán, Mexico

The Yucatán Peninsula has the largest reserve of water in Mexico. It is generally believed that groundwater is of good quality although its agricultural quality has been scarcely studied. The aims of this study were to identify and characterize zones with distinctive groundwater qualities for agricultural use in Yucatán. Water samples were collected at 113 supply wells. The concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃⁻, SO₄²⁻, NO₃⁻, Cl⁻ and the electric conductivity (EC) were determined. Sodium adsorption ratio (SAR), potential salinity (PS) and effective salinity (ES) were also calculated. A geostatistical analysis by kriging interpolation was performed. ES, PS and SAR as well as Na⁺, EC, Cl⁻, SO₄²⁻, and Ca²⁺ were selected to make maps, in accordance with the values of semivariogram and values of cross-validation. The map of the ES was taken as the base to make the map of zones of agricultural quality groundwater. The quality of karstic groundwater in the state of Yucatán cannot be recommended for agriculture in Zones I (EC and ES), II (EC, Chlorides, PS and ES) and III (EC, sulfates and ES); in Zones IV and V the water is of medium quality and in the Zone VI, water is considered good for agricultural use. This information will be relevant in decision-making for government's agricultural and environmental planning.