Good Rainfall Years Research Articles

Climate and Management Practices Jointly Control Vegetation Phenology in Native and Introduced Prairie Pastures

Climate, human disturbances, and management practices jointly control the spatial and temporal patterns of land surface phenology. However, most studies solely focus on analyzing the climatic controls on the inter-annual variability and trends in vegetation phenology. Investigating the main and interacting effects of management practices and climate might be crucial in determining vegetation phenology and productivity. This study examined the impacts of climate and management practices on vegetation phenology and productivity in adjacent native and introduced prairie pastures, which have detailed long-term management records, by combining climate, management, and satellite remote sensing data (e.g., Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat). Modeled gross primary production (GPP) using vegetation photosynthesis model (VPM) was also included to investigate the dynamics of productivity. When comparing the impacts of the same management practices on different pastures, we used paired comparison, namely, comparing the native and introduced prairies side by side in the same year. The interactions of management practices and climate were investigated through comparing years with similar management but different climate (e.g., years with rainfall or not following baling events) in the same pasture. Results showed that air temperature (Ta) was an important factor in determining the start of the season (SOS) and the length of the season (LOS). Total rainfall (RF) during the annual growing season (AGS, derived from vegetation indices (VIs)) had the largest explanatory power (R2 = 0.53) in explaining the variations in the seasonal sums of VIs. The variations in GPP were better explained by RF (R2 = 0.43) than Ta (R2 = 0.14). Using the thermal growing season (March–October) or AGS climate factors did not show large differences in determining the relationships between phenology, GPP, and climate factors. Drought shortened the LOS and decreased GPP. In terms of management practices, grazing generally reduced the VIs and burning induced early greening-up and enhanced vegetation growth. Drought plus other management practices (e.g., grazing or baling) greatly affected vegetation phenology and suppressed GPP. The negative impacts (i.e., removal of biomass) of grazing on vegetation was compensated by enhanced vegetation growth after good RF. This study demonstrated that the interactions of climate and management practices could be positive (burning plus baling in a good RF year) or negative (grazing/baling plus drought), and can significantly affect vegetation phenology and production.

Benefits, equity, and sustainability of community rainwater harvesting structures: An assessment based on farm scale social survey

Rainwater harvesting systems (RWHs) are implemented globally to bridge the frequent water supply-demand gaps. This study explores, through farmer household surveys (n = 492), how farmers perceived the benefits of RWHs, the equitability of benefits, and the role of contextual and psychological factors towards the behaviour of maintaining such systems. The study is carried out in a semi-arid catchment in the Indian state of Gujarat where RWHs, in the form of Check dams (CDs), have been implemented extensively. Results show that the benefits of CDs are perceived in good rainfall years through enhanced availability of water for expanding crops and irrigated areas. Farmers reported limited benefits of CDs in dry years. This is because of limited runoff and no carryover of stored groundwater, due to underlying shallow hard rock aquifer with little primary porosity, from wet years to dry years. Overall, ∼ 40%–50% of sampled farmers reported no benefits from CDs and the benefits decreased with distance. This reflects a spatially inequitable distribution of benefits skewed towards the farmers nearest to the CDs. The sustainability of CDs is a challenge with already ∼40% of CDs reportedly not working and 72.8% of farmers reported doing no maintenance activity. This is because 91.2% of farmers reported playing no role in its construction. The results show contextual (participation during construction, economic indicators) and sociopsychological factors (attention to CD condition, maintenance effort) significantly affect the behaviour towards maintaining the CDs. This highlights the need to complement RWHs with wider drought management and water demand management interventions to achieve drought resilience, and adherence to project exit protocols to secure the sustainability of investments.

The Relationship between Climate Change, Variability, and Food Security: Understanding the Impacts and Building Resilient Food Systems in West Pokot County, Kenya

This study integrated local and scientific knowledge to assess the impacts of climate change and variability on food security in West Pokot County, Kenya from 1980–2012. It characterized rainfall and temperature from 1980–2011 and the phenology of agricultural vegetation, assessed land use and land cover (LULC) changes, and surveyed local knowledge and perceptions of the relationships between climate change and variability, land use decisions, and food (in)security. The 124 respondents were aware of long-term changes in their environment, with 68% strongly believing that climate has become more variable. The majority of the respondents (88%) reported declining rainfall and rising temperatures, with respondents in the lowland areas reporting shortened growing seasons that affected food production. Meteorological data for 1980–2011 confirmed high inter-annual rainfall variability around the mean value of 973.4 mm/yr but with no notable trend. Temperature data showed an increasing trend between 1980 and 2012 with lowlands and highlands showing changes of +1.25 °C and +1.29 °C, respectively. Land use and land cover changes between 1984 and 2010 showed cropland area increased by +4176% (+33,138 ha), while grassland and forest areas declined by –49% (–96,988 ha) and –38% (–65,010 ha), respectively. These area changes illustrate human-mediated responses to the rainfall variability, such as increased stocking after good rainfall years and crop area expansion. The mean Normalized Difference Vegetation Index (NDVI) values ranged from 0.36–0.54 within a year, peaking in May and September. For weather-related planning, respondents relied on radio (64%) and traditional forecasters (26%) as predominant information sources. Supporting continuous climate change monitoring, intensified early warning systems, and disseminating relevant information to farmers could help farmers adopt appropriate adaptation strategies.

Protecting girls from droughts with social safety nets

This paper revisits the relationship between agricultural productivity shocks and the infant sex ratio in India and investigates how this relationship changes when households have access to government-provided employment opportunities outside of agriculture. When a household’s preference for sons coincides with adverse agricultural productivity shocks, previous research shows that households tend to disproportionately reduce investments (prenatal and postnatal) in their female children. This behavior leads to a relatively more balanced sex ratio in good rainfall years and a more skewed sex ratio (in favor of boys) in low rainfall years. In a deviation from past work, we find evidence of this effect primarily through prenatal channels in modern India. More importantly, we show that a workfare program that decouples both wages and consumption from rainfall attenuates the relationship between rainfall and the infant sex ratio. Using a back-of-the-envelope calculation, we find that the program could have saved at least 0.7 million girls – relative to boys – if the government had implemented it from 2001 to 2005. Suggestive evidence also indicates that the program may have attenuated the positive effect of birth year productivity shocks on girls’ longer-term height-for-age.

Improving economic water productivity to enhance resilience in canal irrigation systems: a pilot study of the Sina irrigation system in Maharashtra, India

Abstract This paper proposes scenarios to achieve more crop per drop and irrigation for all in water-scarce irrigation systems, with a particular reference to India. It uses economic water productivity (EWP) and water cost curve for EWP as tools to reallocate irrigation consumptive water use (CWU) and identify economically viable cropping patterns. Assessed in the water-scarce Sina irrigation system in Maharashtra, India, the method shows that drought-tolerant annual crops such as fruits and/or fodder should be the preferred option in irrigated cropping patterns. Cropping patterns with orchard or fodder as permanent fixtures will provide sustainable income in low rainfall years. Orchards in combination with other crops will increase EWP and value of output in moderate to good rainfall years. Governments should create an enabling environment for conjunctive water use and allocation of CWU to achieve a gradual shift to high-value annual/perennial crops as permanent fixtures in cropping patterns.

Lethal control reduces the relative abundance of dingoes but not cattle production impacts

Context Lethal control through the application of 1080 baits is widely used in Australia to manage the negative impacts of wild dogs (dingoes, wild domestic dogs and their hybrids) on cattle production, but its effectiveness in this regard is not well understood. Aims To evaluate the efficacy of once yearly 1080 baiting on dingoes and its effects in mitigating predation and sublethal impacts on beef cattle. Methods A replicated experiment with two paired treatments (1080 poisoned and non-poisoned) was conducted on each of four cattle stations of 3782–10 850 km2, over 2.5 years (2000–02) in the southern Northern Territory. The study was undertaken in relatively good rainfall years. Key results Track-based surveys indicated that dingo abundance declined on poisoned relative to non-poisoned areas immediately following a single baiting episode. However, there was no detectable difference about 8 months after baiting. No difference was detected in observed levels of calf damage or calf loss between poisoned and non-poisoned areas. Conclusions The results add to the growing body of consistent evidence that contemporary dingo control practices yield little benefit to rangeland beef producers most of the time. Implications Routine dingo baiting (as currently undertaken) may be largely unnecessary for beef cattle producers in arid and semiarid areas. Alternative strategies and practices to reduce dingo mauling and predation impacts should be investigated using replicated and controlled field studies.

Sustainability of groundwater through community-driven distributed recharge: An analysis of arguments for water scarce regions of semi-arid India

Study Region: Semi-Arid Regions of Marathawada, Vidarbha and Saurashtra in IndiaStudy Focus: To understand and evaluate the impact of Managed Aquifer Recharge (MAR) efforts.New Hydrological Insights for the Region: Since 1990, the Saurashtra region of Gujarat, India witnessed a massive community-based distributed groundwater recharge movement, initially catalyzed by NGOs and later supported by the government. The region has witnessed visible improvement in groundwater resources during recent years, which was attributed by some researchers to the recharge movement. A competing hypothesis holds that improvement in groundwater levels in Saurashtra are a result more due to a succession of good rainfall years during 2001–2014, aided by transfer of surface water from a big dam on Narmada River, rather than the distributed recharge movement. We develop and implement a 2-way test of these competing hypotheses: First, we compare groundwater recharge patterns in Saurashtra during a recent period of high rainfall years with a similar period before the onset of the recharge movement; second, for both these high rainfall periods, we also compare groundwater recharge patterns in two other comparable aquifer and terrain regions, viz., Vidarbha and Marathawada in Maharastra, which did not experience recharge movement on the same scale as Saurashtra did. Our results support the hypothesis that the community supported distributed recharge movement is the key to improved groundwater recharge in Saurashtra during 2004-09.

The Effect of Land-Use on Herbaceous Production and Grazing Capacity in the Molopo District of the North West Province, South Africa

There are three main types of rangeland management systems in South Africa, namely commercial livestock farming, communal livestock farming and game farming. In commercial farming you normally find one manager/owner with a specific management plan, whilst communal farming is characterized by numerous land users with no specific management plan. The communal areas are also normally overstocked and this overstocking leads to rangeland degradation. In this study the effect of two land-uses (commercial and communal) on herbaceous production and grazing capacity were studied. It was clear from the results that the herbaceous production of the communal rangelands was lower than that of the commercial rangelands. The grazing capacity figures showed that sustainable farming practices were also not possible if the communal rangeland is in a poor condition – this was not even possible in good rainfall years.

Missing Girls, Income Shocks, and Consumption Smoothing

This paper revisits the relationship between agricultural productivity shocks and the infant sex ratio in India and investigates how this relationship changes when households have access to government-provided employment opportunities outside of agriculture. When a household's preference for sons coincides with adverse agricultural productivity shocks, previous research has shown households tend to disproportionately reduce investments (prenatal and postnatal) in their female children. This behavior leads to a relatively more balanced sex ratio in good rainfall years and a more skewed sex ratio (in favor of boys) in bad rainfall years. We find evidence of both prenatal and postnatal channels in India and show that a workfare program, which decouples both wages and consumption from rainfall, attenuates the relationship between rainfall and the infant sex ratio. Using a back-of-the-envelope calculation and the assumption that females should never significantly outnumber males, the program could have saved around 550 girls per district per year -- relative to boys -- if the government had implemented it in the years 2001 to 2005. Additional results on postnatal channels show substantial impacts on long-run health outcomes of surviving girls, as rainfall no longer differentially affects girls' height-for-age, relative to boys', following the implementation of the program. In an important deviation from previous research, the entirety of the relationship between the sex ratio and rainfall is apparently driven by sex-selective abortions, not infant mortality.

Sources of fish in the ephemeral western iishana region of the Cuvelai–Etosha Basin in Angola and Namibia

The triangle between the Kavango and Kunene rivers is drained by the Cuvelai, an ephemeral and deltaic drainage system covering more than 100 000 km2. In good rainfall years, the area becomes populated by fish communities dominated by five species migrating southward towards the endorheic Etosha Pan, the basin’s terminal sump. When water dries up, fish subsequently die-off and their sudden appearance in rainy years has captivated scientists for decades. The current study was prompted by hitherto untapped indigenous knowledge through narratives of opportunistic fish harvesting of migrating fish at temporary connections between the Kunene River and the Cuvelai- Etosha Basin. A reconnaissance fish survey in 2017 was complemented by digital satellite images and elevation data analyses. Results support the presence of at least three major ephemeral fish migration routes. The dominant fish genera migrating upstream in Kunene tributaries comprise Enteromius, Oreochromis and Clarias, all eurytopic and known to undertake upstream, lateral and downstream migrations on floodplains. Although other notable fish refugia in the Cuvelai–Etosha Basin are yet to be identified, there is a necessity for the protection and management of these migration routes in tandem with studies on the nature and extent of this inter-basin fish migration under climate change and variability.

Breeding Sorghum Using Induced Mutations: Future Prospect for Namibia

In arid and semi-arid regions of the world sorghum stands out as a climate change-ready crop with high potential for the production of food, feed, fodder, fiber and fuel in the face of increasing human population. The present review highlights induced mutation breeding technique as a potential tool for improving sorghum in Namibia. The review discussed the following issues; crop improvement using mutagens, mutant screening, selection and evaluation, impact of induced mutation breeding, factors for declining production and future implication of sorghum mutation breeding. In Namibia, severe drought stress resulting in total crop failure has become frequent. This is partly a consequence of farmers growing crop varieties which cannot withstand impact of drought. As such Namibia has limited drought tolerant varieties available for the diverse agro-ecologies. Farmers keep growing the familiar landraces which performs well in good rainfall years but fails to produce stable yield with irregular and erratic rainfall. Thus, breeding new sorghum varieties of high yield and quality combined with multiple agronomic traits including pest and disease resistance and high efficiency in nutrient and water use is needed. Induced mutation is one of the breeding methods utilized worldwide to supplement conventional breeding for developing superior varieties with desirable traits in different crops. Development of high yielding, drought tolerant, and dwarf sorghums with early maturity enables effective utilization of available soils moisture and in optimizing plant density for achieving higher yield in farmers’ fields. Recombination breeding through exploitation of natural genetic variability and mutation breeding to reduce the plant height without disturbing agronomic superiority of elite lines is recommended for sorghum improvement in Namibia.

Temporal and Spatial Analysis of Rainfall and Associated Normalized Difference Vegetation Index (NDVI) over the Pune District, India

Introduction: With increasing population, demands for agricultural products are increasing in tropical countries like India. However, vegetation cover is decreasing to meet the human requirements. Rainfall through hydrological cycle plays an important role in the vegetation growing cycle. It acts as a determining factor for agriculture and food security. Since agricultural products are monsoon rainfall dependent, it is essential to know the changes in the vegetation cover and trends and its relationship with the climate change. This will be helpful in accurate prediction of vegetation cover and therefore in management of loss and damages to the economy of the country. Therefore, a detailed understanding of the relationship between rainfall variability and vegetation cover is very important.Method: An attempt has been made in this paper to study the distribution of rainfall over the Pune district (Maharashtra state, India) and its impact on NDVI during 1971-2012. Analysis of data was carried out by programming, ERDAS & GIS technique using Landsat MSS and Resourcesat data and Microsoft Excel functions.Results: The results indicated that the NDVI values changed in relation to different amount of precipitation showing that about 54% and 13% of area remained barren during 1972 and 2009 drought years respectively.Conclusion: The NDVI has been used to monitor the response of vegetation cover to rainfall and this showed that vegetation cover has drastically reduced during drought years of1972 and 2009, whereas there is increase in vegetation cover during good rainfall years of 1975 and 2010. The comparative study of rainfall pattern and NDVI will be useful to farmers (agricultural section), engineers (irrigation sector) and water resources management point of view.

Adapting to climate change for food security in the Rift Valley dry lands of Ethiopia: supplemental irrigation, plant density and sowing date

SUMMARYStudies on climate impacts and related adaptation strategies are becoming increasingly important to counteract the negative impacts of climate change. In Ethiopia, climate change is likely to affect crop yields negatively and therefore food security. However, quantitative evidence is lacking about the ability of farm-level adaptation options to offset the negative impacts of climate change and to improve food security. The MarkSim Global Climate Model weather generator was used to generate projected daily rainfall and temperature data originally taken from the ECHAM5 general circulation model and ensemble mean of six models under high (A2) and low (B1) emission scenarios. The FAO AquaCrop model was validated and subsequently used to predict maize yields and explore three adaptation options: supplemental irrigation (SI), increasing plant density and changing sowing date. The maximum level of maize yield was obtained when the second level of supplemental irrigation (SI2), which is the application of irrigation water when the soil water depletion reached 75% of the total available water in the root zone, is combined with 30 000 plants/ha plant density. It was also found that SI has a marginal effect in good rainfall years but using 94–111 mm of SI can avoid total crop failure in drought years. Hence, SI is a promising option to bridge dry spells and improve food security in the Rift Valley dry lands of Ethiopia. Expected longer dry spells during the shorter rainy season (Belg) in the future are likely to further reduce maize yield. This predicted lower maize production is only partly compensated by the expected increase in CO2 concentration. However, shifting the sowing period of maize from the current Belg season (mostly April or May) to the first month of the longer rainy season (Kiremt) (June) can offset the predicted yield reduction. In general, the present study showed that climate change will occur and, without adaptation, will have negative effects. Use of SI and shifting sowing dates are viable options for adapting to the changes, stabilizing or increasing yield and therefore improving food security for the future.

Climate Resilient Intercropping Systems for Rainfed Black Soils of Andhra Pradesh and Maharashtra

The assessment studies on different intercropping systems along with their respective sole crops were implemented with active participation of farmers in Yagantipalle village of Kurnool district (Andhra Pradesh), Aurangabad and Nandurbar districts of Maharashtra during 2011 to 2014 as a part of National Initiative on Climate Resilient Agriculture (NICRA) project. The main objective of the study was to popularize climate resilient rainfed intercropping systems in black soils to mitigate climate variability. Intercropping of foxtail millet + pigeonpea (5:1) was identified as best climate resilient system in black soils (kurnool district) of Andhra Pradesh. This system on an average enhanced pigeonpea seed equivalent yields by 406 and 191 kg/ha compared to sole crops of foxtail millet and pigeonpea and recorded 41% of yield advantage over sole crops. In Aurangabad district of Maharashtra, soyabean + pigeonpea (4:2) and pigeonpea + green gram (1:2) were identified as climate resilient intercropping systems. Cotton + greengram (1:1) intercropping system was suitable during medium and good rainfall years in black soils of Aurangabad district. In Nandurbar district of Maharashtra, soybean + pigeonpea (3:1) was found stable over different rainfall patterns. On an average, the intercropping system of soybean + pigeonpea (3:1) recorded 73% higher net income than sole pigeonpea. Though the seed yields of intercrops were reduced by 15–20% than respective sole crops in intercropping system, the seed yields of intercropping system was always higher (30 to 60%) than sole crops. Hence, adoption of intercropping systems in rainfed black soils is climate resilient system and also helps in improving food security in rainfed areas.

Spatiotemporal variation in the endangered Thymus decussatus in a hyper-arid environment

Aims: Arid environments are resource limited, with scarcity of water the key limiting factor, but hyper-arid environments are rarely studied. We test for spatial and temporal variation in ecologically important characteristics to deduce plant adaptations to the extreme climate. Methods: The endangered Sinai Thyme (Thymus decussatus) exists as a set of patches on mountaintops within the St Katherine Protectorate, South Sinai, a hyper-arid environment with rare events of good rains (every 10–15 years). Important Findings: From spatial and temporal patterns of plant mortality, size, condition and flowering among 10 patches on the Mt Sinai massif, we deduce that the incidence and amount of flowering responds relatively quickly (1–2 years) to rainfall fluctuations, but plant growth respond only very slowly. Small individuals are most at risk of death during drought, and a high proportion of plants were dead at the end of 8 years of very low or no rainfall. No recruitment of seedlings was observed even in years of good rainfall. Droughts are expected to become increasingly frequent due to climate change; this may have important consequences for Sinai Thyme and also its associated herbivores, such as the Critically Endangered Sinai Baton Blue (Pseudophilotes sinaicus) whose larval stage feeds exclusively upon the flowers of this plant.

Agronomic Response of Soybean Varieties to Plant Population in the Guinea Savannas of Nigeria

The agronomic responses of three contrasting soybean [Glycine max (L.) Merr.] varieties to plant populations were examined in two distinct agro‐ecological locations (at Samaru Zaria and Samaru‐Kataf), both in the Guinea savanna of northern Nigeria in 2009, 2010, and in 2011 growing seasons. Three soybean varieties: TGx1835‐10E, TGx1904‐6F, and TGx1448‐2E differing in maturity duration (early, medium, and late maturing, respectively), were evaluated at four plant populations (266,700, 333,300, 533,300, and 666,700 plants ha−1) using a split plot arrangement in randomized complete block design with three replications. The plant populations were the main plots, whereas varieties were subplots. The proportion of intercepted photosynthetically active radiation (IPAR) and leaf area index (LAI) increased with increasing plant population at both locations, indicating that high leaf area indices and high degree of canopy closure at higher plant population intercepted more light than the canopy at lower population and subsequently resulted in relatively high grain and fodder yields. At both locations, optimum plant populations ranged from 533,300 to 666,700 plants ha−1 across the years. The northern Guinea savanna location (Samaru Zaria) produced more pods m−2, grain yield, and fodder at higher plant populations than that at the southern Guinea savanna (Samaru‐Kataf). Varieties TGx1448‐2E and TGx1904‐6F intercepted higher proportion of IPAR had higher LAI and produced a greater number of pods m−2, seeds m−2, grain yield, and fodder than TGx1835‐10E at both locations in years of good rainfall. These data suggest that soybean yields in the Guinea savanna of northern Nigeria can be increased using higher plant populations than those currently recommended.

MONITORING OF STRUCTURAL COMPONENTS AND WATER BALANCE AS AN AID TO WETLAND MANAGEMENT USING GEOSPATIAL TECHNIQUES – A CASE STUDY FOR NALSAROVAR LAKE, GUJARAT

Abstract. The hydrologic variability greatly influences the structural components of wetlands that have a great bearing on habitats for avifauna, aquatic fauna including fish etc. This paper highlights the results of a study carried out to derive changes in open-water and vegetation, and also water balance for Nalsarovar Lake, Gujarat. MODIS 8-day composite data for three consecutive years viz 2002/03, 2003/04 and 2004/05 were used to study the seasonal and inter annual dynamics of water regime in the lake. Digital elevation model derived using Shuttle Radar Topographic Mission data with interpolated bottom topography was used to generate elevation contours and compute water volume from water spread data. The reference data of 2002 (drought year) shows the maximum extent of wetland to be 8.06 km2 with emergent vegetation of recorded as 2.36 km2 and open-water as 5.70 km2. The rainfall has an impact on the preferred habitat availability for various species of avifauna and it is noted that emergent vegetation present in the lake completely dried up by summer 2002, a rainfall deficit year but revived again in the preceding year i.e. 2003 which was a good rainfall year with 46.68 km2 under emergent vegetation and 61.96 km2 under open-water. The 2002 being a drought year has shown very low reference storage (0.256 MCM), which has shown a gradual decrease in the storage to 0.00019 MCM in March 2003. The reference storage also registered a steep increase to 18.165 MCM in October 2003 and decreased 1.264 MCM in March 2004. From this study it is evident that water level of about 9 m elevation at the end of the rainy season is found to be optimal for maintaining various habitats that in turn support the avifauna for the rest of the lean period.

Double-Cropped Soybean and Wheat with Subsurface Drip Irrigation Supplemented by Treated Swine Wastewater

The wastewater from swine production facilities has been typically managed by treatment in anaerobic lagoons followed by land application. However, there have been considerable advances in superior treatment technologies. Wastewater from one of these technologies was effective for subsurface drip irrigation of bermudagrass. The objectives of this experiment were to assess accumulation of soil nitrogen and carbon along with grain yield, dry-matter accumulation, and plant nitrogen accumulation of soybean [Glycine max (L) Merr., cv.] and wheat [Triticum aestivum (L), cv.] when supplementally irrigated with treated swine effluent via subsurface drip irrigation (SDI). The soil series was Autryville loamy sand (loamy, siliceous, subactive, thermic Arenic Paleudults). Its low unsaturated hydraulic conductivity of 0.0017 ± 0.0023 mm h−1 caused problems with water movement to either the soil surface or laterally to adjoining soybean and wheat roots. This condition contributed to complete crop failure in soybean in 2 years and generally poor yields of wheat. In a good rainfall year, the soybean yield was somewhat satisfactory and benefited from the supplemental irrigation. In that year, nonirrigated and irrigated soybean mean yields were 1.55 versus 1.98 Mg ha−1, respectively. The mean yield of wheat was only 1.06 Mg ha−1, and it was not affected by irrigation. The means for soil nitrogen and carbon in the 0- to 15-cm depth were 414 and 5,679 mg kg−1, respectively, and they were not affected by the water treatments. Thus, neither soil conditions nor soybean/wheat production were greatly enhanced by the SDI system.

A parsimonious optimal foraging model explaining mortality patterns in Serengeti wildebeest

Based on data collected over 24 years in the Serengeti in Tanzania, Sinclair and Arcese (1995) indicated that the sensitivity of blue wildebeest Connochaetes taurinus to predation risk by lions Panthera leo may cause them to change habitats between open (low risk) and wooded (risky) habitats. They found that, in poor rainfall years, predators kill wildebeest that are in better condition than those that die of natural causes. In good rainfall years, predators kill wildebeest that are in worse condition than those that die of natural causes. Sinclair and Arcese (1995) proposed the “predation-sensitive food” hypothesis. This hypothesis suggests that, as food becomes limiting, animals take greater risks to obtain more food, and some of these animals are killed. I propose a more parsimonious hypothesis based on the marginal value theorem that is consistent with the observations made by Sinclair and Arcese (1995). Wildebeest follow a single decision rule in good and poor rainfall years, viz. move when foraging elsewhere increases your rate of intake of nutritious food. Similarly, predators follow a single decision rule in good and poor rainfall years, viz. take the prey item that maximizes the intake of energy per unit effort expended. This parsimonious model does not require differences in predator sensitivity as required by Sinclair and Arcese's (1995) model. I indicate ways in which my model can be falsified.

Yield and environmental benefits of ameliorating subsoil constraints under variable rainfall in a Mediterranean environment

Subsoil constraints to root growth exacerbate frequent water and nutrient limitations to crop yields in Mediterranean-type environments. Amelioration of subsoil constraints can relieve these limitations by opening root-access to subsoil water and nutrients. However, decisions in subsoil amelioration are hampered by seasonally variable yield responses in these environments. We used the APSIM model to analyse the impact of subsoil constraints on yield and yield variability. The simulated yield data were used to calculate the financial benefits of subsoil amelioration across several scenarios. There was a strong yield-dependence on accessible soil water governed by root depth. Root depth development was limited to a minimum of either the effect of subsoil constraints or the weather-dependent depth of the soil wetting front. Insufficient rainfall in dry years or in a drier region often resulted in shallow soil wetting fronts and correspondingly shallow roots even in the absence of subsoil compaction. In these situations, there is little response to subsoil amelioration. Positive yield responses and positive financial returns to subsoil amelioration are therefore greater in good rainfall years and are more likely in a wetter region. A yield response to amelioration is also greater in coarser textured sand than finer textured sandy loam in an average rainfall season because the same amount of rainfall results in a deeper wetting front in sand than in sandy loam. Hence, roots in a sand are required to grow deeper compared to a sandy loam to access the same amount of water and therefore benefited more from subsoil amelioration in an average rainfall year. In wet years, sands leach more nitrate than sandy loam, which decreases yields and the response to subsoil amelioration in sands is more than in the sandy loam. Environmental threats occur along with yield loss when roots cannot access subsoil water. These include increased nitrate leaching and deep drainage due to unused water remaining in the soil profile. By allowing roots to access deep soil water, ameliorating subsoil is expected to yield financial gains in average to good rainfall seasons and decrease the environmental risk of drainage and leaching loss. The financial gains are expected to offset potential financial losses in dry and dry finish seasons especially in coarser textured soils and wetter environment.