Dry Season Experiment Research Articles

Supplement levels and functional oils to replace virginiamycin for young bulls during early dry season on grasslands and finishing phase in feedlot systems

Aim of study: To assess the effects of replacing virginiamycin (VM) by functional oils (FO) from castor beans and cashew nut on beef cattle system during the early dry season (Experiment I) and during the finishing phase were evaluated the historical effect, keeping the treatments and methods intact (Experiment II).Area of study: These experiments were conducted at the Forage Crops and Grasslands section of São Paulo State University, “Julio de Mesquita Filho” (Unesp–Jaboticabal, São Paulo, Brazil).Material and methods: Two supplementation levels combined with two additives (four treatments in total) were evaluated: LSVM, low supplementation (0.3% body weight [BW]) with VM; LSFO, low supplementation (0.3% BW) with FO, HSVM, high supplementation (0.6% BW) with VM, and HSFO, high supplementation (0.6% BW) with FO. In both experiments, the experimental design was completely randomized with a 2 × 2 factorial arrangement (supplementation levels × additives).Main results: In Exp. I, the additive effect of VM provided greater average daily gain (ADG, p=0.02), higher supplementation level resulted in higher ADG (p=0.04) and the greatest crude protein apparent digestibility (p=0.002). However, no effects were observed between supplementation levels, additives, and interactions (p≥0.11) on voluntary intake and ruminal parameters. In Exp. II, LSVM treatment resulted in lower dry matter intake (p=0.04). Animals maintained on LSFO during the early dry season exhibited lower carcass yield (p=0.004).Research highlights: FO can be used to replace VM in beef cattle diet during the finishing phase in the feedlot without altering animal performance.

Microbial community evolution during the aerobic biodegradation of petroleum hydrocarbons in marine sediment microcosms: Effect of biostimulation and seasonal variations

Evolution of the microbial community structure in crude oil contaminated marine sediments was assessed under aerobic biodegradation during wet (18 °C) and dry (28 °C) seasons experiments, to account for seasonal variations in nutrients and temperature, under biostimulation and natural attenuation conditions. NMDS showed significant variation in the microbial communities between the wet and the dry season experiments, and between the biostimulation and the natural attenuation treatments in the dry season microcosms. No significant variation in the microbial community and oil biodegradation was observed during the wet season experiments due to high background nitrogen levels eliminating the effect of biostimulation. Larger variations were observed in the dry season experiments and were correlated to enhanced alkanes removal in the biostimulated microcosms, where Alphaproteobacteria dominated the total microbial community by the end of biodegradation (54%). Many hydrocarbonoclastic bacterial genera showed successive dominance during the operation affecting the ultimate performance of the microcosms.

Rice cultivation to cope with drought situation by alternate wet and dry (awd) water management system: case study of ratchaburi province, thailand

Alternate wet and dry (AWD) system is an interesting water management system that has been widely promoted to replace continuous flooding (CF) system as an effective water saving technique for rice cultivation. This study was conducted in wet season of 2015 and dry season of 2016 in Ratchaburi Province, Thailand, with a randomised block design to estimate and compare the water used in rice cultivation and grain yield between AWD and CF systems. Water level controlling in rice field of AWD was incomplete in wet season experiment due to rainfall interference, but it was complete in the dry season experiment. It was found (non-significantly) that AWD used less water in rice cultivation than CF. It reduced water use by average about8.13 % for the stages of transplanting to harvesting and 7.51 % for the stage of land preparation to harvesting. Dry field allowing of AWD has positive effects to tiller, panicle numbers and productivity which it increased grain yield by 2.42 % as compared to CF. This increase of grain yield can only be found in complete AWD (AWD in dry season). AWD also found significantly increased water productivity in both wet and dry seasons as compared to CF. Our result suggested that in the case study at Ratchaburi, although less water used in complete AWD than in CF, it was still not significant to show the effective of water used in the incomplete AWD system. More investigation in water consumption with no rainwater interfering is recommended.

Severity of gummy stem blight on melon in relation to cultivars, use of fungicides and growing season

ABSTRACT The authors aimed to evaluate the resistance to gummy stem blight and the agronomic traits of the melon crop in the Southern Region of the State of Tocantins, Brazil, in two growing seasons, submitted or not to treatment with fungicides. Two experiments were carried out: dry season (experiment I), and rainy season (experiment II), respectively, comprising the periods from July to October 2013 and from March to May 2014. Six melon cultivars were used in each season. In the dry season: Eldorado 300, Hibrix, Dourado Amarelo, Louro, Gaúcho Redondo and Canarian; and in the rainy season: Eldorado 300, Hibrix, HF-4439, Louro, Gaúcho Redondo and Canarian. Treatments consisted of each cultivar and split plot with (WA) or without fungicides application (NA). All cultivars were susceptible to disease, considering that Gaúcho Redondo was the least susceptible in the dry season. The fungicide application decreased disease severity in the dry season, however the productivity of the crop in treatments without fungicide application were not compromised, due to the late onset of the disease, and ranged from 19.2 t/ha for Eldorado 300 up to 41.9 t/ha for Canarian. The total soluble solids showed average values of 12°Brix, except for cultivar Gaúcho Redondo, which showed brix value lower than commercial standards. During the rainy season, fungicide application did not protect the plants, which did not complete the cycle, resulting in the absence of marketable fruit production. The climatic characteristics observed in the rainy season, with high humidity, leaf wetness and high temperatures are favorable for the development of gummy stem blight in melon plants. Thus, in Tocantins, the dry season is characterized as the best time of year for cultivation, between April and September.

Effects of Fertilization Rate and Water Availability on Peanut Growth and Yield in Senegal (West Africa)

<p>The effects of fertilization rate and water availability on peanut growth and yield of two cultivars were investigated in a series of field experiments at Bambey, Nioro and Sinthiou Malem in Senegal. Both rainy and dry season experiments were conducted over two years between 2014 and 2015, for a total of seven experiments. The first set of four experiments were to evaluate fertilizer application rate on peanut production. One experiment was conducted in the dry season 2014 in Nioro with four levels of fertilizer and one experiment in the rainy season 2014 in each of Bambey, Nioro and Sinthiou Malem with six levels of fertilizer in a RCBD with four replications both. The second set of experiments were to evaluate the effect of different water regimes on peanut production. Experiments were conducted in the dry season of 2014 and 2015 in Bambey and in Nioro 2015. The experimental design was a split plot design with four replications and three levels of water, namely, E, S1 and S2. The effects of fertilization rate on peanut in three different sites were not significantly different between fertilizer levels. However, irrigation treatments were significantly different in all sites during the two years. Under water stressed conditions, the seed yield was more affected than the biomass yield. Seed yield decreased by 33% when stress occurred at flowering period and by 50% when stress occurred during seed filling. The most sensitive period for yield declined was observed during the period of maturation followed to the flowering stage. The interaction between irrigation and fertilizer was not signification in both Bambey and Nioro sites of field experiments. Such experiments should be conducted in field based conditions where occur limited soil nutrients to test higher dose of NPK.</p>

Computer Algorithm for Irrigated Water – Yield Response of Cowpea under Sprinkler Irrigation System

A MATLAB Computer program on cowpea yield was developed to compare the yield obtained from the field under sprinkler irrigation system with the yield predicted by the developed model. Dry season experiment was conducted between January and April of 2014 at Teaching and Research Farm of the Department of Agricultural Engineering, Federal University of Technology, Akure. Soil physical and chemical properties of the experimental site were determined using standard procedures. The cowpea seeds were established on the field and four irrigation water managements were imposed on the crop. An algorithm comprising of existing empirical models from crop production functions were implemented using MATLAB based computer program. Yield response factor, ky and elasticity of water production (EWP) were also introduced into the algorithm in order to determine the maximum production of cowpea during the growing season of the experiment. The field seasonal yield, crop evapotranpiration and total water applied were input into the model to validate it so as to obtain corresponding model output (predicted yield). The model Original Research Article Faloye and Alatise; JAERI, 3(4): 168-184, 2015; Article no.JAERI.2015.045 169 predicted yield well. The yield results show a good degree of correlation with coefficient of determination r 2 equal to 0.96 and 0.98 for linear and quadratic production functions (ETPF) respectively. The optimized water use and yield of cowpea obtained from the developed model during the growing season were 382.34 mm and 0.996 tons/ha. The total amount of water that resulted to the optimum water use and yield was 446.23 mm. This result implies that 92% of total irrigation water applied during the growing season resulted to the optimum production of the crop. The model, therefore, proved to be useful in estimation of possible irrigation water to maximize yield and crop water use of cowpea.

Although drought intensity increases aflatoxin contamination, drought tolerance does not lead to less aflatoxin contamination

Drought stress is known to increase aflatoxin contamination in groundnut and establishing a possible relationship between drought tolerance and resistance to aflatoxin contamination could contribute to a more efficient selection of aflatoxin-resistant genotypes. In recent work, the reference collection of groundnut had been assessed across seasons varying for drought intensity, i.e. two moderate temperature (rainy season) and two high temperature (dry season) experiments under well-watered (WW) and water stress (WS) conditions (Hamidou et al., 2012, 2013). Here aflatoxin concentration (AC) in seeds is measured in these trials, first for possibly identifying germplasm with low aflatoxin concentrations and second for investigating possible relationships between aflatoxin concentration and drought tolerance. Drought stress intensity increased aflatoxin concentration in seeds and higher aflatoxin contamination was observed under combined drought and high temperature conditions than under drought alone. No germplasm with lower AC than resistant check (55-437) were found. Aflatoxin contamination showed very high GxE interactions, which suggest that selection for resistance to aflatoxin contamination must be specific to environment. Across trials, using means for each environment, there was a clear positive relationship between the aflatoxin concentration and the grain yield reduction due to drought, indicating that a higher drought severity led to higher aflatoxin concentration. However, within trial, the same relationships applied to individual genotypes, or to cohorts of tolerant/sensitive genotypes, were not significant. The major conclusion of this work is that while drought intensity did increase the level of aflatoxin contamination, as expected and previously reported, there seemed to be no direct relationship between tolerance to drought and aflatoxin concentration, suggesting that the mechanisms of drought tolerance and aflatoxin contamination are likely not common.

Calibration and validation of a soil water simulation model (WaSim) for field grown Amaranthus cruentus

A water simulation model (WaSim) to simulate the growth and development of Amaranthus cruentus as well as the components of water balance for a typical sandy-clay-loam soil of Akure has been described. Dry season experiments were carried between January and March of 2005 and 2006. Amaranthus seeds were established on the field and three irrigation water managements were imposed on the crop to determine its response to water deficit at its different phenological stages. Amaranthus growth and development, evapotranspiration (ET) and rooting depth were calibrated by fitting the most sensitive variables to obtain the corresponding model output. The model simulated crop growth and crop cover well, the coefficient of determination r 2 =0.9 and the difference between simulated and measured root depth is not significant at P<0.001. The actual evapotranspiration (AET) from the model prediction and the measured value gave a fairly high coefficient of correlation r=0.7 at P<0.001. The mean bias error (MBE) and the root mean square error of yield estimates between the measured and the model prediction are -0.4444 and 1.35 respectively at P < 0.001. The model was considered effective and appropriate for daily simulation of water balance, water requirement of crops and in climate effects on crop production.

Capability of &lt;i&gt;Streptomyces&lt;/i&gt; spp. in Controlling Bacterial Leaf Blight Disease in Rice Plants

Problem statement: Bacterial Leaf Blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo ) is the most damaging disease in lowland rice grow ing areas in Indonesia. Streptomyces spp. have been known as a producer of antimicrobia l compounds that can be used as biocontrol agents. This study examined the ability of three p romising indigenous Streptomyces isolates which were previously selected from in vitro agar media and greenhouse test to suppress natural infection of Xoo during dry and wet season trials in 2009/2010 a t the Muara Experimental Research Station, Bogor West Java, Indonesia. Approach: Streptomyces isolates (PS4-16, LBR-02 and LSW-05) were applied through seed coating in a peat-based carrie r followed by seedling soaking, spray treatment, or combination of both methods, either singly or in c ombination of two or three isolates. The number of Streptomyces population in the peat carrier at the time of inoc ulation was above 10 7 cell g -1 . The efficacy of Streptomyces was compared to that chemical spray using NORDOX 56 WP (a.i., zinc oxide 56%) and non-treatment. Treated and untreated seeds were grown in plots (5 ×5 m 2 ) and set in a randomized complete block design with four replications. Results: In the dry season experiment, application of Streptomyces spp. reduced BLB severity when compared to that of untreated plots, although did not reduce BLB incidence. PS4-16, applied singly through seed coating followed by seedlin g soaking, reduced the Area Under Disease Progress Curve (AUDPC) at 70 Days After Planting (DAP) to 1458, which was equally effective to the chemical s pray (AUDPC value 1434) and simultaneously promoted plant height and gave the highest rice yie ld. In the wet season trial PS4-16 and LBR-02, appl ied singly or in dual combination through seed coating followed by seedling soaking, suppressed BLB severity, PS4-16 was confirmed as the most effective isolate by reducing the AUDPC to 1923, which was not significantly different to the AUDPC value obtained from chemical spray treatment (1934). Conclusion/Recommendations: All Streptomyces isolates had a tendency to increase plant and yie ld compared to the chemically-sprayed and non-treated plots. For successful biological control of rice BL B, further development of a better formulation for lon g-term storage with an effective population density of Streptomyces and an assessment of its field efficacy in multi-l ocation trials are needed.

Response of upland rice agronomic parameters to variable water supply

Rice response to water application is necessary for increased productivity; hence, this study was aimed at establishing the agronomic responses of rice crop to differential water supplies. A two-year dry season experiment was conducted on the research farm of International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. Two upland rice varieties (NERICA 2 and NERICA 4) were planted on a 5 m×5 m plot in a randomized complete block design with four treatments and two replicates based on different water application. Irrigation scheduling was designed as 100%ET, 75%ET, 50%ET and 25%ET for the treatments weekly. Agronomic parameters such as plant height, root depth, canopy shading (CS), leaf area index (LAI), panicle and tiller configuration, biomass and grain yield in relation to crop water use were obtained and the results were subjected to statistical analysis. Average values of highest plant height (89.0 and 100.3 cm), deepest root depth (22.1 and 23.8 cm), panicle diameter (3.9 and 4.5 cm), panicle length (26.1 and 25.7 cm), LAI, 3.27 and 3.95, CS, 0.22 and 0.99 were obtained for both NERICA 2 and NERICA 4 respectively. Leaf width (1.3 and 1.4 cm), total tillers (14 and 12) and leaf length (36.9 and 38 cm) were also observed for the two varieties respectively. The highest total grain and biomass yields of 1.94 t/ha and 1.95 t/ha were observed in 100%ET treatment for NERICA 2 while the least values of 0.29 t/ha and 1.09 t/ha were observed in 25%ET treatment. As for NERICA 4, the highest values (1.90 t/ha and 2.27 t/ha) were from 100%ET and the least (0.38 t/ha and 2.29 t/ha) in 25%ET. The result of ANOVA showed significant differences in biomass and grain yield, LAI, CS, plant height and root depth among treatments (P<0.05) stressing the domineering influence of water in agronomic response of

Behavioural pattern of upland rice agronomic parameters to variable water supply in Nigeria

The response of rice crop to water application is of paramount importance to researchers as it helps in determining its agronomic development. The study was aimed at establishing the agronomic responses of rice crop to differential water supply. A two-year dry season experiment was conducted at the research farm of International Institute of Tropical Agriculture, IITA Ibadan, Nigeria. Two upland rice varieties (NERICA 2 and NERICA 4) were planted on a 5 × 5 m plot in a randomized complete block design with four treatments based on different water application. Agronomic parameters such as plant height, root depth, canopy shading, leaf area index, panicle and tiller configuration, biomass and grain yield in relation to crop water use were obtained and the results were subjected to statistical analysis. Maximum plant height (89.0 and 100.3 cm), maximum root depth (22.1 and 23.8 cm), panicle diameter (3.9 and 4.5 cm), panicle length (26.1 and 25.7 cm), leaf area index (LAI) 3.27 and 3.95, canopy shading (CS) 0.22 and 0.99 were obtained for both NERICA 2 and NERICA 4, respectively. Leaf width (1.3 and 1.4 cm), total tillers (14 and 12) and leaf length (36.9 and 38 cm) were also observed for the two varieties respectively. The highest total grain and biomass yields of 1.94 and 1.95 t/ha were observed in treatment A for NERICA 2 while the least values of 0.29 and 1.09 t/ha were observed in treatment D. As for NERICA 4, the highest values (1.90 and 2.27 t/ha) were from A and the least (0.38 and 2.29 t/ha) in D. The result of ANOVA showed significant differences in biomass and grain yield, LAI, CS, plant height and root depth among treatments (P > 0.05). Specific behavioural pattern to differential water application was observed in the development of agronomic parameters monitored during the experiment. This was indicative that water is a major yield - influencing factor in rice production. Key words: Upland rice, LAI, CS, agronomic parameters, water supply.

Vertical structure of aerosols and water vapor over West Africa during the African monsoon dry season

Abstract. We present observations of tropospheric aerosol and water vapor transport over West Africa and the associated meteorological conditions during the AMMA SOP-0 dry season experiment, which was conducted in West Africa in January–February 2006. This study combines data from ultra-light aircraft (ULA)-based lidar, airborne in-situ aerosol and gas measurements, standard meteorological measurements, satellite-based aerosol measurements, airmass trajectories, and radiosonde measurements. At Niamey (13.5° N, 2.2° E) the prevailing surface wind (i.e. Harmattan) was from the northeast bringing dry dusty air from the Sahara desert. High concentrations of mineral dust aerosol were typically observed from the surface to 1.5 or 2 km associated with the Saharan airmasses. At higher altitudes the prevailing wind veered to the south or southeast bringing relatively warm and humid airmasses from the biomass burning regions to the Sahel (&lt;10° N). These elevated layers had high concentrations of biomass burning aerosol and were typically observed between altitudes of 2–5 km. Meteorological analyses show these airmasses were advected upwards over the biomass burning regions through ascent in Inter-Tropical Discontinuity (ITD) zone. Aerosol vertical profiles obtained from the space-based lidar CALIOP onboard CALIPSO during January 2007 also showed the presence of dust particles (particle depolarization (δ)~30%, lidar Ångström exponent (LAE)&lt;0, aerosol backscatter to extinction ratio (BER): 0.026~0.028 sr−1) at low levels (&lt;1.5 km) and biomass burning smoke aerosol (δ&lt;10%, LAE: 0.6~1.1, BER: 0.015~0.018 sr−1) between 2 and 5 km. CALIOP data indicated that these distinct continental dust and biomass burning aerosol layers likely mixed as they advected further south over the tropical Atlantic Ocean, as indicated an intermediate values of δ (10~17%), LAE (0.16~0.18) and BER (0.0021~0.0022 sr−1).

Aerosol direct radiative forcing over Djougou (northern Benin) during the African Monsoon Multidisciplinary Analysis dry season experiment (Special Observation Period‐0)

The purpose of this work is to investigate the direct radiative forcing of aerosols over the supersite of Djougou (northern Benin) during the African Monsoon Multidisciplinary Analyses dry season experiment. We focus our simulations on the top of atmosphere, bottom of atmosphere, and atmosphere radiative forcings. During the dry season period, Sun photometer measurements indicate a rather turbid atmosphere with a mean aerosol optical depth for the overall period of 0.78 ± 0.24 (at 440 nm). The aerosol absorption coefficient estimated at the surface ranged between 2.3 and 37.3 Mm−1 (mean value 15.2 ± 10.6 Mm−1 at 520 nm) and the scattering coefficient between 44.5 and 232.3 Mm−1 (mean 145 ± 59 Mm−1 at 520 nm). This leads to a single scattering albedo of between 0.81 and 0.98 (at 520 nm) with a mean (and standard deviation) value of 0.91 ± 0.05, indicating moderately absorbing aerosols. In parallel, micropulse lidar measurements indicate the presence of two distinct aerosol layers, with a first one located between the surface and 1 km and a second one located above 1.5–4.0 km. On the basis of surface and aircraft observations, sunphotometer measurements, lidar profiles, and Moderate Resolution Imagaing Spectroradiometer sensor an estimation of the daily clear sky direct radiative forcing has been estimated for the 17–24 January 2006 period. Simulations indicate that aerosols reduce significantly the solar energy reaching the surface (mean ΔFBOA = −61.5 W/m2) by reflection to space (mean ΔFTOA = −18.4 W/m2) but predominantly by absorption of the solar radiation into the atmosphere (mean ΔFATM = +43.1 W/m2). The mean heating rate at the surface and within the elevated biomass burning layer is considerably enhanced by 1.50 and 1.90 K day−1, respectively.

Piecemeal versus one-time harvesting of sweet potato in north-eastern Uganda with special reference to pest damage

In north-eastern Uganda, the sweet potato crop of small subsistence farmers is severely affected by many pests, including (rough) sweet potato weevils, nematodes and millipedes. Field experiments with sweet potato ( Ipomoea batatas (L.) Lam.) were conducted at Arapai Station in Soroti District, northeastern Uganda in three consecutive seasons to study the differences between the indigenous practice of harvesting piecemeal in combination with storage ‘in-ground on plants’ and one-time harvesting after crop senescence, with special reference to damage caused by sweet potato weevils ( Cylas spp.), rough sweet potato weevils ( Blosyrus spp.), millipedes (Diplopoda) and nematodes. The area has two rainy seasons per calendar year, the first one with long, reliable rains and the second one with short, unreliable rains. Severe sweet potato weevil damage in the vines was responsible for the mortality of 46% of the plants in Experiment 1, which was carried out during the first rainy season. Starting 3 months after planting (MAP), sizable storage roots could be harvested, although their number and weight declined after 4 MAP with piecemeal harvesting. The highest storage-root yield (17.8 Mg ha −1) was found in Experiment 2 (second rainy season) at the final harvest. The yield of storage roots stored ‘in-ground on plants’ during the prolonged dry season (Experiment 3) was very low compared with the yields of Experiment 1 (first rainy season) and Experiment 2 (second rainy season). Sweet potato weevil damage of the storage roots was significantly less with piecemeal harvesting than with onetime harvesting, and piecemeal harvesting also increased the quality of the storage roots for human consumption and commercial purposes. However, with piecemeal harvesting the rough sweet potato weevil ( Blosyrus spp.) caused more storage root damage than with one-time harvesting. No statistically significant differences between the two types of harvesting were found for damage caused by nematodes or millipedes. It was concluded that piecemeal harvesting of sweet potato storage roots contributes to the control of sweet potato weevil in both vines and storage roots and hence improves the quality of the harvested roots. As rainfall distribution affects the population dynamics of this weevil this method can only be used during a limited period of the year.

OPTIMIZING OVITRAP USE FOR AEDES AEGYPTI IN CAIRNS, QUEENSLAND, AUSTRALIA: EFFECTS OF SOME ABIOTIC FACTORS ON FIELD EFFICACY

Insecticide-treated lethal ovitraps are used for control of the dengue vector Aedes aegypti in north Queensland, Australia. In an effort to optimize their use, the influence of deployment height, premise shading, and protection from wind on trap efficacy was assessed in field experiments. Sticky ovitraps were used as a proxy for lethal ovitraps because they provide a direct measure of adult visitation rates. Sticky ovitraps deployed at ground level for 1 wk captured significantly more female Ae. aegypti (mean +/- SE, 1.7 +/- 0.4) than those set at 1.75-m elevation (1.0 +/- 0.3). Setting traps on the leeward side of houses significantly improved collections during a dry season experiment but not in the wet season. Traps set at lightly or heavily shaded premises performed equally well. To determine the optimum number of ovitraps to set per premise, five treatments making up different numbers of traps (1, 2, 4, 6, or 8) were trialled in a Latin square experimental design. Female Ae. aegypti collections increased as more traps were deployed, although mean collections by using 4 (2.6 +/- 0.6), 6 (2.4 +/- 0.5), or 8 traps (4.8 +/- 1.3) could not be separated statistically, suggesting that 4 traps was the optimum number for routine deployment.

Laboratory simulation of the salt weathering of schist: 1. Weathering of schist blocks in a seasonally wet tropical environment

AbstractData describing sediment generation focusing on the temporal evolution of size gradation are required for the prediction of long‐term landform evolution. This paper presents such data for the salt weathering of a quartz‐chlorite schist obtained from the Ranger Uranium Mine in northern Australia. Rock fragment samples are subjected to three different climate regimes: (1) a dry season climate; (2) a wet season climate (both based on observations at the Ranger site); and (3) an oven‐drying sequence designed to test the sensitivity of the weathering process by exposing the rocks to more extreme temperatures. Two MgSO4 salt solutions are applied, one being typical of wet season runoff and the other a more concentrated solution. Salt solution is applied daily in the wet season experiments and once only at the beginning of the dry season experiments. Results of the experiments reveal four stages of weathering. The kinetics of each stage are described and related to the formation of sediment of different sizes. Wet season climate conditions are shown to produce greater moisture variability and lead to faster weathering rates. However, salt concentrations in the wet season are typically lower and so when climate is combined with observed salt concentrations, the dry and wet season experiments weather at approximately equal rates. Finally, small variations in rock properties were shown to have a large impact on weathering rates, leading to the conclusion that rock weathering experiments need to be carefully designed if results are to be used to help predict weathering behaviour at the landscape scale. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Feed blocks as a supplement for goat kids grazing natural Tunisian rangeland during the dry season

Two experiments were conducted to investigate the effects of PEG and feed blocks on digestion of shrub species consumed by goats (experiment 1) and kid growth while browsing during the dry season (experiment 2). In experiment 1, in vitro gas production was determined using a rumen fermenter. Six shrub species were incubated separately ( Erica arborea, Phillyrea angustifolia, Pistacia lentiscus, Myrtus communis, Quercus suber, and Viburnum tinus). Effects of polyethylene glycol (PEG 4000) and feed block supply were investigated. In experiment 2, 21 local kids, 18.75 (±1.4) kg body weight (BW) were allowed to browse in shrub-lands and allocated to three treatments in a production trial lasting 147 days (July–December). Control group receive no supplement, whereas the two other groups received either PEG-free (B) or PEG-containing feed blocks (B-PEG). All shrubs were low in crude protein (59–91 g kg −1 dry matter) but high in total condensed tannins; mean content was 43 g kg −1 DM (8.8–65) for bound condensed tannin and 205 g kg −1 DM (10.8–363) for free condensed tannin. Gas volume produced after 24 h differed among shrub species (P<0.05). V. tinus produced the highest volume (77.8 ml g −1 organic matter) and Q. suber the lowest (35 ml g −1 OM). The mean rate of fermentation was 0.135 h −1 (0.121–0.150 h −1). PEG addition increased gas production by 48.5%, volatile fatty acid by 38.4% and organic matter fermented by 41.7% of the mixture of shrubs (P<0.05). In the practical trial, the use of blocks with and without PEG avoided BW loss of the goats under dry season. While the control group lost 19 g day −1, the bloc supplemented groups grew at 12 g day −1 (−PEG) and 24 (+PEG) g day −1.

Wet and dry season ecosystem level fluxes of isoprene and monoterpenes from a southeast Asian secondary forest and rubber tree plantation

Canopy scale fluxes of isoprene and monoterpenes were investigated in both wet and dry seasons above a rubber tree (Hevea brasiliensis)/secondary tropical forest in the Yunnan province of southwestern China. Drought conditions were unusually high during the dry season experiment. The eddy covariance measurement technique was used to measure isoprene fluxes, while monoterpene fluxes were modeled based on leaf level emission measurements. Maximum observed isoprene fluxes occurred during the wet season and daytime average fluxes were about 1 mg C m−2 h−1. Dry season fluxes were much lower with a daytime average of 0.15 mg C m−2 h−1. Wet season isoprene fluxes compare quite well with isoprene fluxes observed from other tropical forests. Monoterpene fluxes came, almost entirely, from Hevea brasiliensis, which is a light-dependent monoterpene emitter. Modeled wet season total monoterpene fluxes were about 2 mg C m−2 h−1 (average for the daytime), and in the dry season were undetectable. Extreme drought conditions, and the drought deciduous nature of Hevea brasiliensis may be the cause of the low dry season fluxes.

Yield response of rice ( Oryza sativa L.) genotypes to drought under rainfed lowlands : 4. Vegetative stage screening in the dry season

Screening for drought resistance of rainfed lowland rice using drought score (leaf death) as a selection index has a long history of use in breeding programs. Genotypic variation for drought score during the vegetative stage in two dry season screens was examined among 128 recombinant inbred lines from four biparental crosses. The genotypic variation detected for drought score in the dry season was used to examine the reliability of the dry season screening method to estimate relative grain yield of genotypes under different types of drought stress in the wet season. Large genotypic variation for drought score existed in two experiments (A and B). However, there was no relationship between the drought scores of genotypes determined in these two experiments. Different patterns of development and severity of drought stress in these two experiments, i.e . slow development and mild plant water deficit in experiment A and fast development and severe plant water deficit in experiment B, were identified as the major factors contributing to the genotypes responding differently. Larger drought score in the dry season experiments was associated with lower grain yield under specific drought stress conditions in the wet season, but the association was weak to moderate and significant only in particular drought conditions. In most cases, a significant phenotypic and moderate genetic correlation between drought score in the dry season and grain yield in the wet season existed only when both drought score and grain yield of genotypes were affected by similar patterns and severity of drought stress in their respective experimental environments. The dry season environments used to measure genotypic variation for drought score should be managed to correspond to relevant types of drought environment that are frequent in the wet season. The efficiency of using the drought score as an indirect selection criterion for improving grain yield for drought conditions was lower than the direct selection for grain yield, and hence wet season screening with grain yield as a selection criterion would be more efficient. However, using drought score as a selection index, a larger number of genotypes can be evaluated than for wet season grain yield. Therefore, it is possible to apply higher selection intensities using the drought score system, and the selected lines can be further tested for grain yield in the wet season.

Micropulse lidar observations of tropospheric aerosols over northeastern South Africa during the ARREX and SAFARI 2000 dry season experiments

During the Aerosol Recirculation and Rainfall Experiment (ARREX 1999) and Southern African Regional Science Initiative (SAFARI 2000) dry season experiments, a micropulse lidar (523 nm) instrument was operated at the Skukuza Airport in northeastern South Africa. The lidar was colocated with a diverse array of passive radiometric equipment. For SAFARI 2000, a daytime time series of layer mean aerosol optical properties, including layer mean extinction‐to‐backscatter ratios and vertical extinction cross‐section profiles are derived from the synthesis of the lidar data and aerosol optical depths from available AERONET Sun photometer data. Combined with derived spectral Angstrom exponents, normalized broadband flux measurements, and calculated air mass back‐trajectories, the temporal evolution of the surface aerosol layer optical properties is analyzed for climatological trends. For dense biomass smoke events the extinction‐to‐backscatter ratio is between 50 and 90 sr, and corresponding spectral Angstrom exponent values are between 1.50 and 2.00. Observations of an advecting smoke event during SAFARI 2000 are shown. The smoke was embedded within two distinct stratified thermodynamic layers causing the particulate mass to advect over the instrument array in an incoherent manner on the afternoon of 1 September 2000. Significant surface broadband flux forcing of over −50 W/m2 was measured in this event. The evolution of the vertical aerosol extinction profile is profiled using the lidar data. Finally, observations of persistent elevated aerosol layers during ARREX 1999 are presented and discussed. Back‐trajectory analyses combined with lidar and Sun photometer measurements indicate the likelihood for these aerosols being the result of long‐range particulate transport from the southern and central South America.