Semi-arid Tropical Environments Research Articles

Can natural undisturbed revegetation restores soil organic carbon to levels under native climax vegetation under tropical semiarid climate?

AbstractLand‐use change has driven soil carbon stock losses in ecosystems worldwide. Implementing agricultural crops and exploiting forest resources trigger the breakdown of soil aggregates, thus exposing organic matter to microbial decomposition and enhancing carbon dioxide emissions, especially in biomes more susceptible to climate extremes as in the tropical semiarid regions. This study was based on the hypothesis that the undisturbed soil from the dry forest (Caatinga biome under natural revegetation in Brazilian semiarid) would have an improvement in the mass of macroaggregates and recover more than 50% of the soil C stock within 10 years. Thus, a field experiment was conducted to investigate soils from the Caatinga biome under native vegetation, “cowpea cropping” for over 30 years, and soil under natural revegetation for over 10 years, after conventional soil cultivation of maize and cowpea, to determine soil and soil‐aggregates carbon stocks and to estimate the recovery rate of these stocks. The proportional mass of aggregates of different sizes and the total stock of particulate organic carbon (POC) were also quantified. The results showed that soil under preserved native vegetation of dry forest Caatinga biome had higher total soil C stock (50.9 Mg ha−1) than that under cowpea cropping (23.2 Mg ha−1) and natural revegetation (45.1 Mg ha−1). The proportional mass of large macroaggregates was higher in soil under native vegetation for all depths. However, soil under cowpea cropping had lower C stocks in macroaggregates, and recovered roughly 63% of the original C stocks, while revegetation recovered 78% of the stock in 10 years. Although the conventional management system for cowpea monoculture aggravated losses in soil carbon stock by more than 50% of the original C stocks, dry forest under natural revegetation recovered 79% of this stock and almost 100% of POC stock in 10 years (~12 Mg ha−1). Furthermore, soil under undisturbed Caatinga dry forest achieved C stock levels equivalent to that of the global average range for semiarid tropical environments. The high recovery rate of C stock in forest soil under natural revegetation indicates the resilience potential of organisms responsible for structural protection of aggregates and the encapsulated soil organic matter content.

A Systematic Review on Advancements in Remote Sensing for Assessing and Monitoring Land Use and Land Cover Changes Impacts on Surface Water Resources in Semi-Arid Tropical Environments

This study aimed to provide a systematic overview of the progress made in utilizing remote sensing for assessing the impacts of land use and land cover (LULC) changes on water resources (quality and quantity). This review also addresses research gaps, challenges, and opportunities associated with the use of remotely sensed data in assessment and monitoring. The progress of remote sensing applications in the assessment and monitoring of LULC, along with their impacts on water quality and quantity, has advanced significantly. The availability of high-resolution satellite imagery, the integration of multiple sensors, and advanced classification techniques have improved the accuracy of land cover mapping and change detection. Furthermore, the study highlights the vast potential for providing detailed information on the monitoring and assessment of the relationship between LULC and water resources through advancements in data science analytics, drones, web-based platforms, and balloons. It emphasizes the importance of promoting research efforts, and the integration of remote sensing data with spatial patterns, ecosystem services, and hydrological models enables a more comprehensive evaluation of water quantity and quality changes. Continued advancements in remote sensing technology and methodologies will further improve our ability to assess and monitor the impacts of LULC changes on water quality and quantity, ultimately leading to more informed decision making and effective water resource management. Such research endeavors are crucial for achieving the effective and sustainable management of water quality and quantity.

Erodibility of two texturally different aggregates as affected by their size and moisture contents under different land uses in semi-arid tropical environments

Erodibility of two texturally different aggregates as affected by their size and moisture contents under different land uses in semi-arid tropical environments

Aggregate breakdown of two texturally different soils under different land-uses in semiarid tropical environments

Aggregate breakdown of two texturally different soils under different land-uses in semiarid tropical environments

Interaction effects of desiccation and temperature stress resistance across Spodoptera frugiperda (Lepidoptera, Noctuidae) developmental stages

Insects encounter multiple overlapping physiologically challenging environmental stressors in their habitats. As such, the ability of insects to withstand these stressors singly or interactively is fundamental in population persistence. Following its invasion in Africa, Spodoptera frugiperda (Lepidoptera: Noctuidae) has successfully established and spread in most parts of the continent. However, the mechanisms behind its successful survival across arid and semi-arid African environments are relatively unknown. Here, we investigated the water balance of S. frugiperda across its developmental stages. Given the relationships between desiccation stress, temperature stress and other life history traits in arid ecosystems, we also measured interaction effects across metrics of these traits. Specifically, we measured basal body water content (BWC), water loss rates (WLRs) and the effects of desiccation pre-treatment on critical thermal minimum (CTmin), critical thermal maximum (CTmax) and fecundity. Body water content and WLR increased with age across larval instars. However, the effects of desiccation environments on WLRs were more dramatic for 5th and 6th larval instars. The 5th and 6th instars exhibited highest BWC and magnitude of WLRs plastic responses following desiccation treatment. The effects of desiccation pre-treatment on temperature tolerance were less apparent, only significantly improving CTmin in 2nd and 3rd larval instars and reducing CTmax in 5th instars. In addition, desiccation pre-treatment showed no significant effects on fecundity. These results show that water balance traits differ with developmental stage, while the effects of desiccation pre-treatment were more dramatic and inconclusive. The differential desiccation resistance, high proportional BWC and no desiccation pre-treatment effects on fecundity may help the species survive in arid and semi-arid environments. This information provides insights into understanding S. frugiperda survival under desiccating arid and semi-arid tropical environments and is significant in predicting pest outbreaks.

Modelling the spatial variability of soil micronutrients for site specific nutrient management in a semi-arid tropical environment

Deficiency of micronutrients in the soils of semi-arid tropical (SAT) environments is a major limiting factor for crop production. This study aims to model the spatial variability of soil micronutrients in croplands of Thimmajipet block, Mahabubnagar, Telangana, India. We collected 1508 georeferenced surface (0–15 cm) soil samples at a grid interval of 325 × 325 m and analysed them for DTPA extractable fractions of iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) and boron (B). Landform and topographic variables were derived from the digital elevation model of the study area. Results showed that all the micronutrients varied highly (CV > 35%) in the order of Zn > Fe > Cu > B > Mn. The Q–Q plots indicated non-normal frequency distribution for all the micronutrients, and log transformation improved them. We compared spherical, circular, exponential, and Gaussian models of ordinary kriging interpolation to define the spatial variability structure. The spherical model with the lowest RMSE and better r2 values was selected to map the spatial distribution of the micronutrients. The nugget to sill ratio (N:S > 0.75) indicated that the micronutrients were weakly spatial dependent. Multiple regression analysis (p < 0.05) indicated that the micronutrient concentration and spatial distribution were controlled by (1) parent material; (2) CaCO3; (3) OC; and (4) antagonistic nutrient interaction. Further, critical deficiency zones of Zn, Cu, B and Fe were delineated by integrating cadastral map on the spatial distribution maps. Our study demonstrates that the large scale spatial variability mapping of soil micronutrients is a prerequisite for implementing site-specific nutrient management in the SAT regions.

The effects of climate on decomposition of cattle, sheep and goat manure in Kenyan tropical pastures

AimsDecomposition of manure deposited onto pasture from grazing animals represents an important process for carbon (C) and nitrogen (N) cycles in grassland systems. However, studies investigating manure decomposition are scarce; especially in sub-Saharan Africa (SSA).MethodsIn this study, we measured decomposition of three types of animal manure (cattle, sheep, goat) over >1 year using litter bags at four climatically different sites across Kenya. Results Manure dry matter, total C, total N and ammonium concentrations decreased exponentially, with the most rapid decrease occurring during the first few weeks following application, followed by slower changes during the following 2–3 months. Rates of N mineralization were lower than those for C mineralization, resulting in decreasing C/N ratios over time. Generally, cattle manure decomposed faster than sheep or goat manure despite having a higher initial C/N ratio and lower N concentration, with decomposition rates for dry matter ranging from 0.200 to 0.989 k year−1. Cellulose decomposed first, while lignin concentrations increased among all manure types and at all sites.ConclusionsWe found that total manure decomposition rates were positively correlated with cumulative precipitation and aridity index, but negatively correlated with mean temperature. Our results show much slower decomposition rates of manures in semi-arid tropical environments of East Africa as compared to the few previous studies in temperate climates.

Fantastic beasts and what they ate: Revealing feeding habits and ecological niche of late Quaternary Macraucheniidae from South America

The extinction of the Quaternary megafauna stands out among the evolutionary history of Cenozoic mammals. In South America, nearly 80% of the megamammals went extinct, including the native ungulates Macrauchenia patachonica and Xenorhinotherium bahiense. Little is known about the causes of the macraucheniids’ extinction and their paleobiology. Here, we have reconstructed the dietary habits of M. patachonica and X. bahiense using enamel microwear and occlusal enamel index analyses, and also inferred their niches using species distribution modeling and stable isotope paleoecology, in addition to enamel microwear and occlusal enamel index data. We found that both macraucheniids had grazer-feeding habits, although their environmental requirements were different. M.patachonica could live in colder temperatures and arid, subtropical/temperate ecosystems, while X. bahiense was adapted to warmer temperatures and more humid, semi-arid tropical environments. Thus, despite similar feeding habits, these macraucheniids had distinct environmental requirements and ecological niches, which might explain the disjunction in the South American records.

Pedogenic Processes Derived Plant Available Water Capacity (PAWC) for Rain-Fed Deep-Rooted Crops in Indian Vertisols: A Pragmatic Method

Global pedologists and edaphologists have created a huge database on the properties and management of smectitic Vertisols (cracking clay soils, CCS) but they are not adequate to optimize their use and management. This review is a synthesis of research done in the recent past at ICAR-NBSS, Nagpur, to search for real soil moisture status during crop growth. Despite the fact that the smectitic CCS do retain the highest amount of water both at 33 kPa and 1500 kPa, they have limitations to both rainy season and winter crops in the majority of CCS of central India under semi-arid tropical (SAT) environments due to lack of adequate moisture and poor porosity in their subsoils. Due to these predicaments, farmers of central India are unable to grow both rainy and winter crops in a year. Research indicated that the laboratory determined available water content (AWC) is not fully released during the crop growth period. Thus, the inclusion of AW capacity as one of the soil parameters for soil suitability analysis of cotton is inappropriate and inefficacious bio-physical parameter because soil moisture after cessation of rains remains at 100 kPa for non-sodic CCS and for sodic CCS (ESP &gt; 5 but &lt; 15), it remains at 300kPa. Inadequate soil moisture is due to the impairment of soil hydraulic properties caused by the dispersion of smectitic clays in the presence of both Mg and Na ions on the soil exchange complex. Recent research on depth-wise soil moisture characteristics curves indicates that the release of soil water beyond 800 kPa is negligible in Vertisols, indicating the failure in the release of soil water beyond 800 kPa is due to the dispersion of dominant nano-size smectite. The difficulties in releasing soil moisture at tension at or higher than 800 kPa suggest that moisture in micropores is held very tightly by Mg- and Na- smectite clays and thus, the release of soil moisture beyond 800 kPa is not significant throughout the depth of Vertisols. Therefore, the calculated PAWC considering the soil water held between 100-800 kPa for non-sodic CCS, and for sodic CCS, the soil water held between 300-800 kPa, showed a better significant positive correlation with cotton yields, in comparison to the correlation obtained between PAWC at 100-1500 kPa for non-sodic and 300-1500 kPa by the earlier method. The better correlation highlights how fundamentally pedogenetic processes driven by PAWC controls the movement of rainwater and its retention and release in SAT Vertisols. Therefore, PAWC is a unique bio-physical property, which can act as a guiding principle forthe growing of deep-rooted crops in abiotically stressed Vertisols of Indian SAT areas. In addition, PAWC could be applied as a useful parameter in further revision of agro-ecological sub-regions (AESRs) in black soils areas for better crop planning and ecosystem services of SAT Vertisols.

Soil Quality and Fibrous Mineral in Black Soils of Maharashtra

There are many reports on soil parameters that have both yield-reducing and yield-favouring potential. However, only a few are available on the index soil properties of fibrous minerals containing soils on crop yields in the semi-arid tropical (SAT) regions. These minerals in soils are mostly palygorskite and sepiolite. In the present study, only the palygorskite mineral in black soils (cracking clay soils), its formation and probable influence on soil quality is addressed. The present study was also undertaken to indicate a possible genesis of palygorskite in Indian black soils with and without soil modifiers (Ca-zeolites and gypsum) supporting both rainfed and irrigated agriculture in SAT environments. Palygorskite is absent in aridic/ gypsic/sodic intergrades of black soils (Haplusterts), which might indicate non-interference of soil modifiers in its formation. Palygorskite is present only in sodic black soils (Calciusterts) in Maharashtra and parts of central and western India that contain no soil modifiers, and are under both rainfed and irrigated agricultural systems. The severe impairment of hydraulic properties of palygorskite containing naturally degraded black soils warrants a new research initiative for soils containing fibrous minerals.

A conceptual model of natural land degradation based on regressive pedogenesis in semiarid tropical environments

AbstractLand degradation occurs in all the climatic regions, however, the adverse effects are more pronounced in the semiarid tropical (SAT) environments due to increasing aridity and water scarcity. Though natural processes can also cause land degradation, it is generally attributed to anthropogenic factors. In this study, we elucidate the role of climate and landscape driven soil forming processes in land degradation through a conceptual model. For this, morphological, physical, and chemical properties of the soils occurring in a part of the SAT Deccan Plateau region, India, were characterized. The trend of climatic variables, namely, the mean annual rainfall, potential evapotranspiration, and maximum summer temperature during the last century (1901–2010) showed that the increase in aridity negatively influenced the soil forming processes. The results showed that rainfall variability, temperature, potential evapotranspiration, and hydrological behaviour of the SAT soils were the primary drivers of the soil forming processes and they were identified through examination of the soil variability by factor analysis. The depth distribution of selected indicators (% clay, pH, calcium carbonate, exchangeable sodium percentage, exchangeable magnesium percentage, and hydraulic conductivity) indicated that the current pedogenic processes operating in the SAT environment caused the undesirable modification in soil properties. Through our conceptual model, we discuss the mechanism of the formation of pedogenic carbonate, subsoil sodicity, and subsequent reduction in hydraulic conductivity which leads to the land and vegetation degradation in the SAT environments.

Soil quality index (SQI) as a tool to evaluate crop productivity in semi-arid Deccan plateau, India

Assessment of soil quality index (SQI) using only the surface soil properties provides an incomplete information as the crop productivity is influenced by both surface and subsurface properties, with the latter being inherently linked to pedogenic processes. Two different SQIs were estimated for soil surface (0–15cm) and control section (0–100cm) using soil profile data of six identified soil series in part of semi-arid tropical (SAT) Deccan plateau and correlated with crop yield. Principal component analysis (PCA) and expert opinion (EO) methods were used for selecting minimum soil data set (MDS). Additive and weighted index methods were compared for SQI estimation. SQI obtained showed variation as PCA and EO methods produced different results. In general, weighted index SQIs were better correlated with crop yield than the additive index SQIs for both PCA and EO methods. EO derived weighted index SQI were comparable for both surface and control section except for few cases and consistent in their correlation with the crop yield, indicating its better performance as compared to PCA. Reason is that the PCA is a data dimension reduction technique whereas EO method is primarily conceived by the experts on cause-effect relationship of soil properties (such as hydraulic conductivity, CaCO3 and exchangeable sodium percentage) that are influenced by regressive pedogenic processes in SAT environments. Results showed that consideration of both surface and control section soil properties helps in establishing a good relationship between soil functions and management goal. In addition, it also satisfies the need to integrate both surface and subsurface soil information for soil quality assessment.

Sweet Sorghum Planting Effects on Stalk Yield and Sugar Quality in Semi‐Arid Tropical Environment

Sweet sorghum [Sorghum bicolor (L.) Moench] has potential as a bioenergy crop for producing food, fiber, and fermentable sugar. Unlike dryland grain sorghum, little information is available on the influence of staggered planting and genotypes, especially in semiarid tropical environments. The objectives of the present study were (i) to quantify the effects of planting time and genotype on stalk and biomass yields, juice sugar quality, and (ii) to identify the most productive genotypes and planting windows for sustainable feedstock supply. Four commercial sweet sorghum genotypes (SSV84, SSV74, CSV19SS, and CSH22SS) were planted on five planting dates (1 June, 16 June, 1 July, 16 July, and 1 August) during the rainy (June–October) season of 2008 and 2009 in Hyderabad (17°27´ N, 78°28´ E), India. Planting in early and mid‐June produced significantly (P ≤ 0.05) higher fresh stalk yield and grain yield than later planting dates. Commercial hybrid CSH22SS produced significantly more stalk, grain, sugar, and ethanol yield over genotypes SSV84 or SSV74. Based on the stalk yield, juice sugar quality, sugar, and ethanol yields, the optimum planting dates for sweet sorghum in semiarid tropical climate is early June to early July. Planting sweet sorghum during this time allows more feedstock to be harvested and hence extends the period for sugar mill operation by about 1 mo, that is, from the first to the last week of October.

Genetic variability in high temperature effects on seed-set in sorghum.

Sorghum (Sorghum bicolor (L.) Moench) is grown as a dryland crop in semiarid subtropical and tropical environments where it is often exposed to high temperatures around flowering. Projected climate change is likely to increase the incidence of exposure to high temperature, with potential adverse effects on growth, development and grain yield. The objectives of this study were to explore genetic variability for the effects of high temperature on crop growth and development, in vitro pollen germination and seed-set. Eighteen diverse sorghum genotypes were grown at day : night temperatures of 32 : 21°C (optimum temperature, OT) and 38 : 21°C (high temperature, HT during the middle of the day) in controlled environment chambers. HT significantly accelerated development, and reduced plant height and individual leaf size. However, there was no consistent effect on leaf area per plant. HT significantly reduced pollen germination and seed-set percentage of all genotypes; under HT, genotypes differed significantly in pollen viability percentage (17-63%) and seed-set percentage (7-65%). The two traits were strongly and positively associated (R2=0.93, n=36, P<0.001), suggesting a causal association. The observed genetic variation in pollen and seed-set traits should be able to be exploited through breeding to develop heat-tolerant varieties for future climates.

Dominant species’ resprout biomass dynamics after cutting in the Sudanian savanna-woodlands of West Africa: long term effects of annual early fire and grazing

The potential of forest to regenerate after harvesting is a key element for sustainability of the ecosystem. For semi-arid tropical savanna environments, managing resprouts after tree cutting is ideally suited because of the natural ability of many indigenous species to regenerate vegetatively. Regeneration in this ecosystem is, however, prone to many disturbance factors such as fire and grazing by livestock. In this paper, we used a factorial experiment to examine the long-term effects of annual early burning and grazing on dominant species' resprout biomass dynamics after selective cutting in the Sudanian savanna-woodlands of Burkina Faso, West Africa Burning decreased shoot mortality of Crossopteryx febrifuga while grazing increased that of Detarium microcarpum. Burning, in later measurement years, reduced resprouts' size of Acacia macrostachya, C. febrifuga and D. microcarpum while an increased basal area was observed for Combretum glutinosum. There was no significant evidence of grazing hampering growth. Moderate livestock grazing could be integrated in the forest management prescriptions in Burkina Faso for the sake of multi-purpose uses, while more attention should be paid to burning practices to lower fire severity, as complete fire exclusion is utopian in this savanna ecosystem.

Potential productivity and water requirements of maize–peanut rotations in Australian semi-arid tropical environments—A crop simulation study

The growing demand for maize (Zea mays L.) in intensive livestock and other industries has opened up fresh opportunities for further expansion of the maize industry in Australia, which could be targeted in relatively water rich semi-arid tropical (SAT) regions of the country. This crop simulation study assessed the potential productivity and water requirements of maize peanut (Arachis hypogaea L.) rotations for the SAT climatic zone of Australia using the Agricultural Production Systems Simulator (APSIM) model. APSIM was configured to simulate maize (Pioneer hybrid 3153) either in the dry (May�October) or wet season (November�April) and peanut (cv. Conder) in the following season for three soils found at Katherine (14.48°S, 132.25°E) from 1957 to 2008. The simulated mean total yield potential of the dry season maize and wet season peanut (DMWP) rotation (15�19.2 t/ha) was about 28% greater than the wet season maize�dry season peanut (WMDP) rotation because of the higher yield potential of maize in the dry season compared to in the wet season. These high yields in the DMWP rotation have been achieved commercially. The overall simulated irrigation water requirement for both rotations, which varied from 11.5 to 13.8 ML/ha on different soils, was similar. The DMWP rotation had 21% higher water use efficiency. Similar yield and water use efficiency advantages of the DMWP rotation were apparent for eight other agriculturally important locations in the Northern Territory, Western Australia and Queensland. The simulations for Katherine also suggested that the irrigation requirement of the two rotations could increase by 17.5% in El-Nino years compared to La-Nina years for only a small gain in yield, which has implications for climate change scenarios

Genotype-environment interaction in chickpea (C. arietinum L.) for adaptation to humid temperate and semi-arid tropical environments

Eight chickpea genotypes were evaluated for seed yield and maturity time at three temperate locations in Japan and one semi-arid tropical location in India over a two-year period to obtain baseline information on chickpea adaptation to Japan. The average seed productivity under Japanese environments, except in the northern area with growth under cool and semi- humid climatic conditions and a longer photoperiod, was lower than that in the semi-arid tropical environment in India. The kabuli chickpeas, especially, ICCV 92311 and ICCV 92337, showed a higher productivity in northern Japan. For chickpea cultivation in Japan, it is recommended to adopt modified agronomic practices to reduce humidity in the crop canopy, for example, wider plant spacing, cultivation under rain shelter, and selection of genotypes with a high assimilate remobilization rate as well as resistance to higher humidity-promoted diseases. Growing chickpea crop in the northern part of Japan by adopting such agronomic practices and the right genotypes could be suitable. However, a larger number of studies should be carried out to analyse the various mechanisms that contribute to a better adaptation of chickpea to environments with a high soil moisture and humidity.

Improving efficiency of water use for irrigated rice in a semi-arid tropical environment

Irrigation water accounts for almost 40% of total variable production costs for rice ( Oryza sativa L.) cropping in the Burdekin River Irrigation Area, northern Australia. Increasing the efficiency of water use would improve the economic viability of growers and long-term environmental benefits would also be likely due to lower water tables and decreased salinisation in irrigation areas. The aim of these studies was to maximize grain yield by optimizing its functional components: water use, efficiency of water use for dry matter production (WUE dm) and harvest index (HI). The responses of dry matter and yield in rice (cv. Lemont) to five methods of irrigation were studied in a wet and dry season in the region. Applying a permanent flood at sowing, the 3-leaf stage (traditional) and prior to panicle initiation were compared with two unflooded methods: saturated soil culture (SSC) and intermittent irrigation at weekly intervals. Saturated soil culture consisted of growing rice on raised beds of height 0.2 m and width 1.2 m, with water maintained in the furrows (0.3 m wide) some 0.1 m below the bed surface. The results of these studies show that it is not necessary to flood rice to obtain high grain yield and quality. The trend was for yield to increase with water supply, but there was no significant difference in yield and quality between SSC and traditional flooded production, although SSC used about 32% less water in both seasons. Therefore the efficiency of water use for grain production (WUE g, g m −2 mm −1) was higher in SSC than in traditional flooded production in the wet season and a similar trend existed in the dry season. There were no differences between SSC and the traditional method of irrigation in any of the grain quality components measured, indicating that this water saving method did not lower grain quality. Weed growth was generally higher in unflooded treatments, although weed populations in SSC and traditionally flooded rice were equivalent in the dry season, suggesting that weeds can be controlled in SSC. Saturated soil culture provides a viable alternative to flooded rice production for growers in semi-arid tropical environments. Substantial reductions in variable costs of production are attainable by reducing water use without reducing yield and quality.

The Chokla Sheep in India

SummaryThere are approximately 41 million sheep in India, 0.51 million of which are made up by the Chokla population. This breed is generally found around Churu, Jhunjhunu, Sikar and bordering areas of the Bikaner, Jaipur and Nagaur districts of Rajasthan. The animals have a light to medium-sized body, a small head and are reddish brown or dark tan in colour as far as the middle of the neck, with a white body. The skin is pink. The ears are small to medium in length and tubular in shape. The Chokla sheep are hardy and well adapted to arid and semi-arid tropical environments and are suited for the region where migration is a common practice. The Chokla is a comparatively fine-wool producing type among the Indian sheep. The wool produced by Chokla animals is heterogeneous in quality and generally mixed with coarser fleece of other sheep for their utilisation as carpet wool.

Effect of water availability pattern on yield of pearl millet in semi-arid tropical environments

Throughout much of the semi-arid tropics, fluctuations in grain yield can largely be attributed to differences in timing and intensity of drought stress. Since seasonal rainfall in these environments is often poorly related to grain yield, the aim of this paper was to establish a relationship between water availability and grain yield for pearl millet (Pennisetum glaucum (L.) R. Br.), grown across 24 semi-arid tropical environments in India. We used a simple soil water budget to calculate a water satisfaction index (WSI) throughout the season. The cumulative WSI at maturity explained 76% of the variance in grain yield. This was three times as much as explained by actual rainfall, because WSI accounted for differences in water losses and pan evaporation. A classification of environments into four groups of water availability patterns explained 75% of the environmental sum of squares for grain yield. For a subset of 13 environments, environmental differences in grain number could also be explained by water availability patterns, whereas differences in grain mass were related to both water availability and temperature. Our results indicate that cumulative WSI, which is an integrated measure of plant-available water, can provide an adequate estimation of the environmental potential for yield in environments where grain yield is mainly limited by variable availability of water.