Late Dry Season Research Articles

Climate control of cambial dynamics and tree-ring width in two tropical pines in Thailand

Tropical forests are affected by recent climate change, but detailed knowledge how forests in different regions of the tropics respond to changing climate conditions is not sufficiently studied. Our objectives were to evaluate climatic effects on the monthly cambial activity of Pinus latteri and Pinus kesiya and to determine the relationships between climatic variables (precipitation, temperature, and relative humidity) and the tree-ring widths of these two pine species. Cambial dynamics of P. latteri and P. kesiya in subtropical Thailand were studied for two consecutive growing seasons. We observed that monthly rainfall, relative humidity, soil moisture, monthly minimum temperature, and monthly mean temperature were positively related to the number of cambial cell layers and cambial zone width. Moisture in the late dry season and in the beginning of the rainy season was very important in stimulating cambial cell division after a long-term moisture deficit for more than three months. The growth responses to climate in a 128-year-long chronology of P. latteri and an 88-year-long chronology of P. kesiya were similar. Importantly, the amount of rainfall and relative humidity in April and May had positive effects on the tree-ring widths of both pine species. On the other hand, both mean monthly maximum temperature and mean monthly temperature had negative effects on tree-ring widths. P. kesiya is more susceptible to drought, as shown by its correlation with the self-calibrated Palmer drought severity index. The rising temperatures during the recent 30-year observation period clearly show that higher temperatures covered the northern and central regions of Thailand and are likely to reduce the productivity of both pine species.

Hydrodynamics over low-angle dunes at the tidal current limit of the Changjiang Estuary

Hydraulic roughness is a fundamental parameter in the understanding and simulation of hydro- and sediment-dynamics over dunes in fluvial and coastal areas. Completely understanding the links between the turbulent flow field, sediment transport and morphodynamics is key to better quantifying the evolving roughness in time and space. This paper presents two surveys (one in the late flood season and the other in the late dry season), conducted at the tidal current limit of the Changjiang Estuary, analysing flow and bedform dynamics under different water/flow stages. Results show that when compound dunes generate in the late flood season, flow structure was affected by the bed morphology and the velocity profile was segmented into two parts. The lower segment is interpreted to reflect the friction induced by the superimposed small dunes, whereas the upper segment is likely attributed to the combined effect of primary dunes and superimposed small dunes. Moreover, as the lee-side angles of superimposed small dunes fluctuate around 10°, the increase of flow velocity could increase the possibility of generating Flow separation zone (FSZ), consequently resulting in a further effect on flow structure. The correlation between flow resistance and flow strength displays that both the shear stress and roughness length over relatively larger dunes in the deep water are more sensitive to the mean velocity. Low-angle dunes (LADs) with lee-side less than 3° have no effect on flow structure, while for LADs with lee-side angle between 3° and 5°, the roughness length related to bedform is positively correlated to flow velocity, when flow velocity is lower than the equilibrium flow velocity. This implies that the flow expansion over LADs is sensitive to both the lee face and flow strength, thereby affecting LADs' evolution. Furthermore, the bedload transport calculated from empirical equations shows a satisfactory agreement with that estimated from bedform evolution. This result implies that bedload transport induced by shear stress related to LADs’ form is little in this survey area. Besides, in the migrating progress of LADs, their deformation is innegligible and deformation-related bedload transport could occupy nearly 30% of total bedload transport. This finding is significant to studies on migration and deformation of low-angle dunes, and could support studies of numerical modelling, especially on geomorphic module.

Intraseasonal variability of greenhouse gas emission factors from biomass burning in the Brazilian Cerrado

Abstract. Landscape fires, often referred to as biomass burning (BB), emit substantial amounts of (greenhouse) gases and aerosols into the atmosphere each year. Frequently burning savannas, mostly in Africa, Australia, and South America are responsible for over 60 % of total BB carbon emissions. Compared to many other sources of emissions, fires have a strong seasonality. Previous research has identified the mitigation potential of prescribed fires in savanna ecosystems; by burning cured fuels early in the dry season when landscape conditions still provide moist buffers against fire spread, fires are in general smaller, patchier, and less intense. While it is widely accepted that burned area (BA) and the total carbon consumed are lower when fires are ignited early in the dry season, little is known about the intraseasonal variability of emission factors (EFs). This is important because potentially, higher EFs in the early dry season (EDS) could offset some of the carbon benefits of EDS burning. Also, a better understanding of EF intraseasonal variability may improve large-scale BB assessments, which to date rely on temporally static EFs. We used a sampling system mounted on an unmanned aerial vehicle (UAV) to sample BB smoke in the Estação Ecológica Serra Geral do Tocantins in the Brazilian states of Tocantins and Bahia. The protected area contains all major Cerrado vegetation types found in Brazil, and EDS burning has been implemented since 2014. Over 800 smoke samples were collected and analysed during the EDS of 2018 and late dry season (LDS) of 2017 and 2018. The samples were analysed using cavity ring-down spectroscopy, and the carbon balance method was used to estimate CO2, CO, CH4, and N2O EFs. Observed EF averages and standard deviations were 1651 (±50) g kg−1 for CO2, 57.9 (±28.2) g kg−1 for CO, 0.97 (±0.82) g kg−1 for CH4, and 0.096 (±0.174) g kg−1 for N2O. Averaged over all measured fire prone Cerrado types, the modified combustion efficiency (MCE) was slightly higher in the LDS (0.961 versus 0.956), and the CO and CH4 were 10 % and 2.3 % lower in the LDS compared to the EDS. However, these differences were not statistically significant using a two-tailed t test with unequal variance at a 90 % significance level. The seasonal effect was larger in more wood-dominated vegetation types. N2O EFs showed a more complex seasonal dependency, with opposite intraseasonal trends for savannas that were dominated by grasses versus those with abundant shrubs. We found that the N2O EF for the open Cerrado was less than half the EF suggested by literature compilations for savannas. This may indicate a substantial overestimation of the contribution of fires in the N2O budget. Overall, our data imply that in this region, seasonal variability in greenhouse gas emission factors may offset only a small fraction of the carbon mitigation gains in fire abatement programmes.

Hyperspectral Monitoring of Non-Native Tropical Grasses over Phenological Seasons

The miniaturisation of hyperspectral sensors for use on drones has provided an opportunity to obtain hyper temporal data that may be used to identify and monitor non-native grass species. However, a good understanding of variation in spectra for species over time is required to target such data collections. Five taxological and morphologically similar non-native grass species were hyper spectrally characterised from multitemporal spectra (17 samples over 14 months) over phenological seasons to determine their temporal spectral response. The grasses were sampled from maintained plots of homogenous non-native grass cover. A robust in situ standardised sampling method using a non-imaging field spectrometer measuring reflectance across the 350–2500 nm wavelength range was used to obtain reliable spectral replicates both within and between plots. The visible-near infrared (VNIR) to shortwave infrared (SWIR) and continuum removed spectra were utilised. The spectra were then resampled to the VNIR only range to simulate the spectral response from more affordable VNIR only hyperspectral scanners suitable to be mounted on drones. We found that species were separable compared to similar but different species. The spectral patterns were similar over time, but the spectral shape and absorption features differed between species, indicating these subtle characteristics could be used to distinguish between species. It was the late dry season and the end of the wet season that provided maximum separability of the non-native grass species sampled. Overall the VNIR-SWIR results highlighted more dissimilarity for unlike species when compared to the VNIR results alone. The SWIR is useful for discriminating species, particularly around water absorption.

Seasonal surface refractivity patterns in the part of Lagos-Nigeria

The surface refractivity(SF) is essential in estimating the performance of terrestrial radio links. In the troposphere, there are lots of meteorological updraft and downdraft that influence the refractive index. In this study, we examine the seasonal variation of an emerging community in Lagos to design a reliable and efficient radio communication system based on the meteorological parameters.Thirty-nine years dataset between 1980-2018 was used to examine both the surface refractivity and the meteorological drivers that determine the SF patterns. It was observed that early wet season and late dry season were seen to have higher SF values, i.e., 262.03 N-unit and 262.07 N-unit respectively, while early dry and late wet had lower SF, i.e., 261.71 and 261.76 respectively. It is now possible to use the weather forecast to predict the likely SF pattern over the tropics.

Bats (Chiroptera) of Bidoup Nui Ba National Park, Dalat Plateau, Vietnam

We determined species diversity, seasonal reproduction, and echolocation patterns in the bat community of Bidoup Nui Ba National Park (BNBNP), Lam Dong Province, on the Dalat Plateau of the Central Highlands of Vietnam. We documented 27 species with 211 individuals captured in 26 994 m2 mist-net-hours and 3015 m2 harp-trap-hours of effort. We found five species of pteropodids and 22 species of insectivorous bats in four families, including regional records and species seldom captured in Vietnam. Bat species richness at BNBNP is now known to be 33 species, including six found in a prior study. Based on the inverse Simpson Index of Diversity, evenness of captures was low, reflecting the high abundance of a few species with many species documented by just one or two individuals. Insectivorous bats were pregnant in the late dry season, but not during the wet season when lactation occurred and volant juveniles were captured. Echolocation call characteristics were determined for 19 species of insectivorous bats. Call patterns were consistent with some but not all reports in the literature from elsewhere in southeast Asia. This suggests the existence of cryptic species or geographic and habitat variability in echolocation calls of southeast Asian bats that requires further study.

Variations in chemical nutrients and mineral concentrations of water hyacinth (Eichhornia crassipes Mart. Solms- Labauch)

Laboratory studies were conducted to evaluate changes in chemical nutrients and mineral concentrations of water hyacinth as influenced by the season of harvest, habitat and morphological parts of the plants. Proximate composition (DM, CP, CF, EE and ash), fiber fractions (NDF, ADF and ADL) and concentrations of minerals (Ca, P, K, Na, Mg, Fe, Zn, Mn, and Pb) in water hyacinth harvested from canal, lagoon, river and dam at the early and late period of wet and dry seasons were determined. Results showed that CP, EE and ash contents of water hyacinth harvested from the different water bodies differ (P < 0.05). Dry matter and CP values ranged from 7.68 to 7.96 and 10.32 to 10.40 g/100g DM in water hyacinth from river and dam respectively. Effects of the season on the chemical nutrient composition of water hyacinth were not significant (P> 0.05) except for DM that was highest (8.22) in the late dry season. Water hyacinth harvested from the different water bodies contains relatively high levels of minerals that vary (P<0.05) with the season of harvest. The high CP and mineral concentrations of water hyacinth suggests that the plant can be used as fodder for ruminant livestock production. 

Nigerian Journal of Animal Production Effect of generational differences, housing systems and seasonal variations on the reproductive performance of rabbits raised in humid tropics

Reproductive data from 24 does (Chinchilla X New Zealand White) of twenty weeks, were analyzed to determine the effect of generation, housing systems and season on the reproductive performance of rabbits raised in the humid tropics. The experiment was carried out during four seasons namely: early dry season (EDS-September to November), late dry season (LDS-December to February), early rainy season (ERS-March to May) and late rainy season (LRS-June to August). The study was repeated in the second generation and the data obtained were subjected to analysis of variance in a 2x2x4 factorial arrangement. Factors considered were generations, housing systems, and seasons respectively. Highest breeding efficiency of 83.33% was obtained in the first generation and maximum litter size at birth (35) and weaning (28) were observed in caged-does that kindled in EDS of first and second generations respectively, while does housed on deep litter system produced the smallest litter size at birth (24) and weaning (18) in the ERS of the second generation. Highest (12) and least (4) pre-weaning losses were recorded in caged-does that kindled in ERS of the first and second generation respectively, whereas highest average birth weight (120.58g) was observed in litters of deep litter-does that kindled in EDS of the second generation. These results indicated that the production of rabbits for breeding purposes is better achieved during early dry season (September-November) and also revealed that deep litter system allows satisfactory performance and has comparative advantage over wooden cage system considering the reduction in housing cost and can be used to improve the nutritional status of the family and also to obtain some supplementary income.

Effect of season on Ejaculate Quality of three phenotypes of Nigerian Local Cocks

Twenty four (24) adult Nigerian local cocks comprising 8 normal, 8 frizzle and 8 naked-neck were subjected to two ejaculations per week for seven weeks in each season (early rain, lale rain, early dry and late dry seasons) using the massage technique. Ejaculates were subjected to both physical and chemical evaluations. Results showed a significant (P<0.01) seasonal effects between phenotypes in reaction time. In all the seasons, naked-neck and frizzle cocks had higher (P<0.01) ejaculate volume, sperm motility and total sperm than normal cocks. A highly significant (P<0.01) phenotype by season interaction was observed with naked-neck producing better quality ejaculates during the dry season when compared to other phenotypes. Significant (P<0.05) differences were noted in the percent abnormal sperm among the seasons. There were no significant season by phenotype interactions (P>0.05) in most of the chemical parameters (Na+1, K+1, Ca2+, Mg2+, and total protein) evaluated. However, a gradual increase in seminal protein was observed among the phenotypes with a peak during late dry season. The cations (particularly sodium, potassium and calcium) and chloride constituents of ejaculates were significantly lower during the late dry season than at most other seasons. From these results it was concluded that the naked-neck and frizzle cocks appear superior to the normal cocks in semen output and quality under the humid tropical environment.

Effect of coat colour on heat stress among West African Dwarf sheep

This experiment was conducted to investigate the effect of coat colour on heat stress among West African Dwarf sheep. A total number of twenty-four West African Dwarf sheep with different coat colour types were used for the experiment. Rectal temperature (RT), respiratory rate (RR) and pulse rate(PR) were taken on each animal before sunrise and when they returned from grazing in the afternoon during late dry season ( January-March) and early rainy season (April June ). Blood samples were collected for evaluation of packed cell volume (PCV), red blood cell count (RBC), white blood cell count (WBC), plasma sodium (Na+) and potassium (K+). Coat colour had significant (P<0.01) effect on PT, RR, PR and heat stress index (HI).Animals with black coat colour (aaB-SS) had the highest mean value for all parameters followed by brown mouflon and brown with extensive white, while the badger face coloured sheep(A-B-ss) had the least mean value. There were significant (P<0.01) differences between males and female in RT (38.69± 0.02 and 38.83± 0.02oC), RR (56.09± 0.58 and 59.94± 0.65 breaths/min), PR (74.67 ±0.39 and 77.92± 0.46 beats/min) and HI (1.60±0 0.19 and 1.63± 0.02) respectively. Season had significant (P<0.01) effect on RT, RR, PR, HI. Coat colour also had significant (P< 0.05) effect on RBC, WBC, Na + and K+. There + +were appreciable difference between female and male in RBC, WBC, Na and K . Seasonal variation also significantly affected these blood parameters. However, PCV was not significantly (P>0.05) affected by variation in coat colour, sex and season. From the results obtained, it can be concluded that coat colour type had significant effect on heat stress in WestAfrican Dwarf sheep.

An appraisal study of donkey in three Northern states of Nigeria

This qualitative study on donkey was conducted in Bauchi, Kano and Kebbi States of Nigeria. The objective of the study was to understand the role, significance and potential areas needing intervention in donkey rearing in the rural setting. The study was also used to obtain first-hand baseline information on the state of knowledge on the donkey in the states surveyed. Sixty two locations were visited comprising 36 from Kebbi, 19 from Bauchi and 17 from Kano States respectively. Rapid Rural Participatory Appraisal (RRPA) technique with check list of questions and farmers' participation was employed in villages/towns randomly selected to cover all the ecological zones in each of the three States. A meeting of one to two hours was organized with the farmers and donkey owners. Observations were made on donkeys at home and in the field. Problems mentioned by respondents included: Colics (Anomari),ulcerative lymphangitis, inflammation of the tongue, interdigital dermatitis, ear sore, fistulous withers, unknown causes of lameness and nervous system disorder called locally as "chinkai chinkai". There were generally poor or no veterinary facilities and services in most of the villages and towns. It was not the farmers practice to take donkeys to clinic for treatment. Mortality was high during the late dry season in most places but also occurred in the rainy season in some places. Areas for further investigations were also highlighted.

Incidence of trypanosomosis in a Muturu herd at Nsukka, South-Eastern Nigeria

A herd of 38 Muturu cattle under semi-intensive system of management at the University of Nigeria, Nsukka Agricultural Farm, southeastern, Nigeria, was examined for the presence of trypanosome infection over a one year period (April, 1998 - March, 1999). The aim was to assess the incidence of trypanosoniosis and factors that may affect its occurrence variation. Infection was widespread in the herd (67.9%) during the period. Out of the factors (season, sex and age) only season showed a significant effect on the occurrence of trypanosomosis. The incidence was highest in the third quarter of the year corresponding 10 the late rainy season period, followed by the fourth quarter (early dry season, and was least in the first quarter (late dry season). This seasonal incidence varied between 2.6% (CI, 0.3 - 9.196) to 20.396 (CI,12.0-30.8%) 411 the infections were due to Trypanosoma vivax and the principal tsetse vector was Glossina tachinoides. Parasitaemic animals were able to control anaemia as their PCPs vere similar to those of uninfected animals (P>0.05). The importance of these findings in relation to the general epizootiology of trypanosomosis and animal production in the area is discussed.

SEASONAL VARIATIONS IN SEMINAL CHARACTERISTICS OF WEST AFRICAN DWARF SHEEP IN THE HUMID TROPICS

Semen collected from six mature West African Dwarf (WAD) rams by artificial Vagina, twice weekly for one year, early and late rainy season, and early and late dry season, showed no significant difference in volume of ejaculate and progressive motility of sperm. There was significant difference in sperm concentration, total sperm per ejaculate, total motile sperm per ejaculate and abnormal sperm. Seasonal changes in characteristics of the semen were associated with seasonal changes in temperature, indicating the detrimental effects of heat, even on indigenous stock.

Influence of irrigation intervals on dry matter yield, concentration of crude protein, calcium and phosphorus in Lablab purpureus and Sorghum almum fodder in the sudan savanna zone of Nigeria

Irrigation trials were conducted in the late dry season (March to June) with Lublab (Lablab purpureus) and Columbus grass (Sorghum almum) in the Sudan savanna of Nigeria. The objective of this study was to determine the dry matter yield (IDM/ha), crude protein (CP), calcium (Ca) and phosphorus(P) in dual-purpose lablab bean and Sorghum almum at 3 irrigation schedules (5, 7 and 10 days irrigation interval). The results obtained showed dry matter yield in lablab increased (P<0.05) and varied from 1.7 to 11.7 IDM/ha. Calcium and P concentrations differed significantly (P<0.05). Mean CP for the lablab was 15.57%. Dry matter yield obtained for Sorghum almum varied (P<0.05) from 11.07 to 19.6 tDM/ha. Concentration of CP and Ca rose and declined thereafter with a mean concentration of 9.86% for CP und 0.08% for Ca while P declined consistently (P<0.05). Intervals of irrigation days had a relationship (P<0.05) with DM/ha, Ca and P in lablab. The increasing trend in foruye yield with increased irrigation interval showed optimum irrigation interval was not attained. It is therefore recommended that longer irrigation intervals be tried to determine the optimum irrigation interval after which forage yield would be depressed due to moisture stress. From the results of the present study Sorghum almum and lablab would be grown successfully at a 10-day irrigation interval.

Grazing behaviour and forage selection pattern of heifers in the range

The grazing behaviour of eight yearling white Fulani heifers was studied in two season of year in the south western zone of Nigeria. Time spent on different activities such as drinking, walking, grazing, resting and ruminating were determined using direct eye observation technique. The types of forage selected in both seasons were identified. Visual observations revealed that behaviour was influenced by seasons. The heifers spent 2, 8, 15, 14 and 62% of their time drinking, ruminating, resting, walking and grazing respectively as overall percentage for the two seasons. The forage selection pattern revealed that forbs were mostly selected in the late dry season and grasses in the early rain season. The forages selected in the late dry season were Panicum maximum, Cynodon dactylon, Ipomea aquatical, Leucaena leucocephela, Centrosema mole and Althernanthera dentata. In the early rain season forages selected include Setaria bartata, Echinochloa stagirina, Pennisetum purpureum and Panicum maximum regrowth. It is therefore concluded that the study provides a quick insight into behavioural and forage selection pattern of heifers. Therefore the study can be used to assess grazing animal nutrition condition.

Comparative effects of three seasons on seed population and viability of cattle, sheep and goat dungs in South-West Nigeria

An experiment to determine the effects of seasonal variations on population and viability of seeds in the faeces of ruminant animals was conducted between April to December 2001 using two breeds of cattle, sheep and goats. Three samples were collected per breed from three animals that were tagged for uniformity of data collection. Sampling took place weekly, in the mornings before the animals were taken out for grazing. The highest (P<0.05) total number of seeds, seeds/g dry weights and total number of viable seeds were recovered from cattle, while the least were from goats, but the reverse was the case for percentage viability. The weights of the faeces were significantly (P<0.05) higher in the rainy season than the dry season. The weights of the faeces reduced gradually as the dry season sets in. Likewise, there were more seeds in the early rain than in the late rain and early dry season, with the percentage viability higher in the late rains and early dry season than the early rainy season. There were more broadleaved weeds and sedges in the early rain than late rain and early dry season but the reverse was the case for grasses. In conclusion, although there were more faeces and consequently more seed production in the rainy season, however, but the viability was lower than in the dry season. Also, seeds of broadleaved plants were more in the rainy season while those of grasses were more in the dry season. More seeds and number of viable seeds were recovered from the faeces of cattle than sheep and goats in all the seasons due to the higher weights of faeces but the percentage viability was higher for sheep and goat than cattle.

Effects of genotype and season on the productive performance of commercial egg-type chickens in the derived savanna zone in Nigeria


 
 
 
 Twelve (12) month production records of two commercial egg-type chickens, Nera Black (NB) and Isa Brown (IB) reared on a commercial farm in Ilora, Oyo State, Nigeria were analysed to assess effects of season and genotype on their performance. The production record was sorted according to the two recognized major seasons: wet (April-September) and dry (October-March) in the study area. Besides, the each major season was further partitioned into two sub-seasons namely: early rainy season (ERS: April-June), late rainy season (LRS: July-September), early dry season (EDS: October-December) and late dry season (LDS: January-March). Results of data analysis showed that genotype had no significant effect (P>0.05) on all the performance indices. Conversely, season significantly (P<0.05) affected all the performance parameters evaluated and hens performed better in wet seasons compared with dry months. There was significant (P<0.05) genotype by season interaction effect on egg production but not (P>0.05) for other productive parameters. IB strain performed better in wet season most especially in LRS while NB hens had better performance in dry season. Results from this study indicated that regardless of the season, the two egg strains should be employed for commercial egg production but adequate measure should be taken to combat the adverse effect of thermal stress on the welfare and performance of layers in the study area most especially in LDS months. Discrepancies in genotype by season interaction suggest genetic basis to differences in performances and physiological abilities of the investigated egg-strains to cope with stresses emanating from change in season.
 
 
 

'Now it’s not a billabong': eco-cultural assessment of billabong condition in remote northern Australia

Globally, the value of integrating multiple knowledge systems is being recognised in ecosystem assessments, monitoring and management. This paper describes a participatory eco-cultural assessment of freshwater billabongs in the South East Arnhem Land Indigenous Protected Area, northern Australia, that drew on Indigenous ecological knowledge (IEK) and Western science using social and natural science research methods. IEK holders were concerned about feral ungulates trampling and consuming traditional bush food resources and reducing water quality, affecting eco-cultural values of billabongs. We recorded qualitative IEK and conducted a multivariate snapshot assessment of billabong physiochemical water quality, ground condition, yarlbun (water lily) cover and macroinvertebrate assemblage that showed distinct seasonal variation. Although both knowledge systems revealed indicators of seasonal change over 1 year, IEK also revealed longer-term changes and that degradation of billabongs in the late dry season was exacerbated by feral ungulates. This participatory research illustrates how the condition of freshwater systems can be assessed using cross-cultural techniques, how these techniques can reveal more nuanced understandings of eco-cultural condition and the value of including IEK for setting ecological baselines and recording long-term change.

<i>Corrigendum to:</i> Impacts of fire on soil organic carbon stocks in a grazed semi-arid tropical Australian savanna: accounting for landscape variability

Fire and grazing are commonplace in Australian tropical savannas and the effects of these management practices on soil organic carbon stocks (SOC) is not well understood. A long-term (20 years) experiment studying the effects of fire on a grazed semi-arid tropical savanna was used to increase this understanding. Treatments, including frequency of fire (every 2, 4 and 6 years), season of fire [early (June) vs late (October) dry season] and unburnt control plots, were imposed on Vertosol grassland and Calcarosol woodland sites, which were grazed. Additionally long-term enclosures [unburnt (except the Calcarosol in 2001) and ungrazed since 1973] on each soil type adjacent to each site were sampled, although not included in statistical analyses. SOC stocks were measured to a soil depth of 0.3m using a wet oxidation method (to avoid interference by carbonates) and compared on an equivalent soil mass basis. Significant treatment differences in SOC stocks were tested for, while accounting for spatial background variation within each site. SOC stocks (0–0.3m soil depth) ranged between 10.1 and 28.9tha<sup>–1</sup> (Vertosol site) and 20.7 and 54.9tha<sup>–1</sup> (Calcarosol site). There were no consistent effects of frequency or season of fire on SOC stocks, possibly reflecting the limited statistical power of the study and inherent spatial variability observed. Differences in the response to frequency and season of fire observed between these soils may have been due to differences in clay type, plant species composition and/or preferential grazing activity associated with fire management. There may also have been differences in C input between treatments and sites due to differences in the herbage mass and post-fire grazing activity on both sites and changed pasture composition, higher herbage fuel load, and a reduction in woody cover on the Vertosol site. This study demonstrated the importance of accounting for background spatial variability and treatment replication (in the absence of baseline values) when assessing SOC stocks in relation to management practices. Given the absence of baseline SOC values and the potentially long period required to obtain changes in SOC in rangelands, modelling of turnover of SOC in relation to background spatial variability would enable management scenarios to be considered in relation to landscape variation that may be unrelated to management. These considerations are important for reducing uncertainty in C-flux accounting and to provide accurate and cost-effective methods for land managers considering participation in the C economy.

Provision of urea–molasses blocks to improve smallholder cattle weight gain during the late dry season in tropical developing countries: studies from Lao PDR

Context Large-ruminant production in developing countries is inefficient with low growth rates and declining weights, particularly in the dry season. Aims The impact of ad libitum supplementation of cattle with high-quality molasses blocks (20 kg) containing either 8% urea (UMB) or nil urea (MB), was examined. Methods Field trials on smallholder farms compared weight changes and average daily gains (ADG = g/day) data of young calves <8 months of age (n = 25); growing calves 8–24 months (n = 35) and lactating cows (n = 46), of the indigenous breed when accessing either UMB or MB, with data being collected at Weeks 1, 4, 8 and 12. A pen study was also conducted at a research station involving mature, lactating crossbred cows (n = 37). Surveys of farming families experiencing use of the blocks was conducted (n = 20). Key results On smallholder farms, animals accessing UMBs were heavier than those accessing MBs at every collection day and in young calves these differences were statistically significant (P < 0.05). ADGs were higher in cattle accessing UMB than in those accessing MBs. Young calves had the highest ADG (251–265 g/day), followed by growing calves (198–237 g/day) and lactating cows (187–190 g/day), although differences in ADG between UMB and MB cohorts were not considered significant (young calves P = 0.562; growing calves P = 0.509; and lactating cows P = 0.993). Results from the pen study identified that ADGs were not significantly different (P = 0.933) between crossbred cows accessing MBs (236 g/day) and cows accessing UMBs (229 g/day). Surveys of farmers using blocks confirmed that their animals were calmer and healthier, and had better coat condition with minimal external parasites; these farmers wished to purchase the blocks and were willing to pay a mean up to US$6.5 ± 2.3 per block. Conclusions Provision of UMBs and MBs in Laos in the late dry season improved cattle growth rates, which is consistent with previous studies and far superior to the base-line data from Laos demonstrating declining ADGs. Farmers considered that the blocks contributed greatly to herd management and improved sale-ability of their cattle. Implications Provision of molasses blocks on low-input smallholder farms in developing countries significantly improves production efficiency, offering an ‘entry point’ intervention while forages are becoming established.