Semi-arid Savanna Research Articles

Determinants of soil respiration in a semi-arid savanna ecosystem, Kruger National Park, South Africa

Soil respiration, which is a combination of root respiration and microbial respiration, represents one of the main carbon fluxes in savannas. However, it is remarkable how little is known about these components – regarding either process-level mechanisms or quantitative estimates, especially in savanna ecosystems. Given the extensive area of savannas worldwide, this limits our ability to understand and predict the critical changes in the global carbon budget that underlie the phenomenon of global climate change. From May 2000 to April 2001, bi-weekly soil respiration measurements from two savanna types were made in 14 sampling collars (diameter = 100 mm), using a PP Systems EGM-2 respirometer. Results indicated that there was a difference in the rate of respiration between the more clayey Acacia and sandier Combretum savanna soils (p = 0.028). The mean (± s.d.) soil respiration in the Acacia savanna was 0.540 g/m2/h ± 0.419 g/m2/h, whilst it was 0.484 g/m2/h ± 0.383 g/m2/h in the Combretum savanna. We also found that soil respiration was sensitive to soil moisture and soil temperature. The rate of soil respiration at both sites rose to a maximum when soil temperature was at 28 °C and declined at higher temperatures, despite different temperature sensitivities. Soil respiration increased approximately linearly with an increase of soil moisture. In both savanna sites soil is subject to a combination of high temperature and water stress, which controls the fluxes of soil carbon dioxide. We found that the two sites differed significantly in their soil moisture characteristics (p < 0.0001) but not with regard to temperature (p = 0.141), which implies that soil moisture is the main factor responsible for the differences in respiration between Acacia and Combretum savannas.Conservation implications: It is argued for many protected areas that they perform a climate change buffering function. Knowing the soil respiration rate and determining its controlling factors contribute to improved understanding of whether protected areas will be net sources or sinks of carbon in the future.

Temporal dynamics of dry-season water-hole use by large African herbivores in two years of contrasting rainfall in Hwange National Park, Zimbabwe

Abstract:As the dry season progresses in arid and semi-arid ecosystems, rain-fed surface water sources become depleted, forcing most animals to concentrate in the immediate vicinity of the few remaining permanent sources of drinking water. This study investigates the temporal dynamics of use of water-holes by nine African large-herbivore species in the dry season in the semi-arid savanna of Hwange National Park, Zimbabwe, and particularly how annual rainfall influences this temporal dynamics. Two contrasting years in terms of annual rainfall were compared: 2003 (a drought – 362.6 mm) and 2004 (average rainfall – 695.8 mm). In 2003, water-holes were used far more intensively and the level of aggregation of herbivores at water-holes was significantly higher. The temporal dynamics of water-hole use in the dry season differed between the two years: in 2003, the peak of water-hole use started much earlier and lasted 3 mo. Elephants and grazers showed the largest difference in use of water-holes between 2003 and 2004 supporting the suggestion that browsers are less water dependent. This study suggests that annual rainfall should be taken into account when predicting the peak of the dry season.

Large herbivores may alter vegetation structure of semi-arid savannas through soil nutrient mediation

In savannas, the tree–grass balance is governed by water, nutrients, fire and herbivory, and their interactions. We studied the hypothesis that herbivores indirectly affect vegetation structure by changing the availability of soil nutrients, which, in turn, alters the competition between trees and grasses. Nine abandoned livestock holding-pen areas (kraals), enriched by dung and urine, were contrasted with nearby control sites in a semi-arid savanna. About 40 years after abandonment, kraal sites still showed high soil concentrations of inorganic N, extractable P, K, Ca and Mg compared to controls. Kraals also had a high plant production potential and offered high quality forage. The intense grazing and high herbivore dung and urine deposition rates in kraals fit the accelerated nutrient cycling model described for fertile systems elsewhere. Data of a concurrent experiment also showed that bush-cleared patches resulted in an increase in impala dung deposition, probably because impala preferred open sites to avoid predation. Kraal sites had very low tree densities compared to control sites, thus the high impala dung deposition rates here may be in part driven by the open structure of kraal sites, which may explain the persistence of nutrients in kraals. Experiments indicated that tree seedlings were increasingly constrained when competing with grasses under fertile conditions, which might explain the low tree recruitment observed in kraals. In conclusion, large herbivores may indirectly keep existing nutrient hotspots such as abandoned kraals structurally open by maintaining a high local soil fertility, which, in turn, constrains woody recruitment in a negative feedback loop. The maintenance of nutrient hotspots such as abandoned kraals by herbivores contributes to the structural heterogeneity of nutrient-poor savanna vegetation.

Savanna tree-grass competition is modified by substrate type and herbivory

Question: Woody plant and grass interactions in savannas have frequently been studied from the perspective of the response of one growth form on the other but seldom evaluated as two-way interactions. What causes woody plant encroachment in semi-arid savannas and what are the competitive responses of tree seedlings and grasses on rocky and sandy substrates? Methods: In this greenhouse study, we investigated the influence of substrate and grazing on responses to interspecific competition by tree seedlings and grasses. We measured competitive/facilitative responses on biomass and nutrient status of tree seedlings and grasses grown together. Results: Interspecific competition suppressed growth of trees and grasses. Tree seedlings and uncut grass accumulated double the biomass when grown without competition relative to when they competed. Competitive responses varied on different substrates. Grass biomass on rocky substrate showed no response to tree competition, but appeared to be facilitated by trees on sandy substrate. Grass clipping resulted in higher tree seedling biomass on rocky substrate, but not on sandy substrate. There was a positive response of grass nutrient status to competition from tree seedlings. Conclusion: Selective grass herbivory in the absence of browsing or suppression of shade-intolerant grasses by trees are commonly cited reasons behind bush encroachment in savannas. We show that grazing may confer a competitive advantage to tree seedlings and promote bush encroachment more readily on rocky substrates. This may be due to the imposed sharing of the soil depth niche on rocky substrates, whereas possible niche separation on sandy substrates minimizes the advantage conferred by reduced competition.

Changes of woody plant interaction and spatial distribution between rocky and sandy soil areas in a semi-arid savanna, South Africa

We examined the impact of shrub–shrub interactions and soil type (rocky or sandy) on growth and spatial distribution of the two savanna shrub species Tarchonanthus camphoratus and Acacia mellifera. To explore plant interactions, we compared the size of juvenile and mature T. camphoratus shrubs between different locations (under the subcanopy of A. mellifera and in the open). Juvenile T. camphoratus shrubs had similar sizes regardless of location; however, in rocky soil, mature shrubs in the open were larger than those near A. mellifera, implying an inter-specific competitive effect of A. mellifera on T. camphoratus. Juvenile T. camphoratus shrubs grew faster in the sandy than in the rocky area. Furthermore, we used the Wiegand–Moloney O-ring statistics to explore the spatial distribution of T. camphoratus. T. camphoratus showed spatial aggregation, but in the rocky area T. camphoratus juveniles were positively associated with A. mellifera (indicating facilitation as the pattern-creating process), whereas in the sandy area they were positively associated with mature T. camphoratus shrubs (indicating seed dispersal as the pattern-creating process). T. camphoratus exhibited encroachment potential in the sandy area. We showed how spatial pattern analysis can help to explore processes determining woody plant spacing and recommend its further use.

Intraspecific competition between shrubs in a semi-arid savanna

Tree-on-tree competitive interactions may be more important in affecting the distribution of the tree components of savannas than inter-specific competition with grasses. The presence of intraspecific competition is expected to negatively affect inter-tree spacing, individual size distributions and plant physiology as well as survival/mortality. In this field removal experiment on Acacia mellifera, one of South Africa’s most common encroachers on nutrient-poor soils, the growth, water relations and mortalities of shrubs where all neighbouring woody competitors were removed (target) were monitored three times during each of three growing seasons. After 3 years, the nitrogen and carbon isotopic ratios of the study plants were analysed. Target shrubs benefitted from removal of neighbours, resulting in greater growth, less water stress, a relatively small degree of canopy dieback and reduced reliance on N2 fixation. Target shrubs grew by 25 ± 4% in height relative to 7 ± 4% for controls, with the targets suffering a maximum of <15% canopy dieback compared to up to 60% in the controls. Severe environmental stress is known to affect neighbour interactions among shrubs and competition may constrain shrub sizes and avoid density-dependent mortality. In contrast, release from competition in our study may have allowed greater growth of target plants, increasing their total evapo-transpirational leaf surface areas and leaving them vulnerable to drought and water stress. Intratree competition on shallow nutrient-poor soils in savannas may thus aid the persistence of bush encroachment by regulating the sizes of individual shrubs below the threshold of drought vulnerability.

Modelling the long-term consequences of undernutrition of cows grazing semiarid

Undernutrition of cows grazing semi-arid range as a result of drought or heavy stocking rates reduces prenatal and pre-weaning growth of their calves. A mechanistic model has been developed that simulates the productivity of vegetation and cattle on semi-arid savanna rangeland in southern Africa. When cows are stocked at 0.200 cows/ha instead of 0.123 cows/ha the model predicted that empty body weights of their progeny at birth and weaning would be reduced by 2.9 and 43.8 kg, respectively. If all young animals are stocked at 0.22 animals/ha after weaning, differences in empty body weight at weaning are predicted to persist almost unchanged for a further two years. The model also predicted that undernutrition of cattle aged 21 months would be followed by partial compensatory growth. Comparison of simulated results with data from experiments in Zimbabwe indicates that the model realistically simulates the effects of stocking rate on cattle growth.

Impact of land-use type and bark- and leaf-harvesting on population structure and fruit production of the baobab tree ( Adansonia digitata L.) in a semi-arid savanna, West Africa

Non-timber forest products (NTFPs) strongly contribute to livelihood security in the semi-arid tropics. There is increasing concern about the population status of NTFP-providing trees and therefore a need for their sustainable use. Thus, this study examines the impact of land-use type on the multipurpose baobab tree ( Adansonia digitata L.) in Burkina Faso, combined with rates and patterns of bark- and leaf-harvesting, and their impact on fruit production. We compared stands in a protected area (W National Park of Burkina Faso) with those of surrounding communal area (fallows, croplands and villages) to obtain an indication on the status of the baobab population, to assess its harvesting tolerance and to estimate to what extent their actual use is sustainable. Our results reveal that land-use type has an impact on the population structure of the baobab. The size class distribution curve of park stands was inverse J-shape which indicates good rejuvenation, while the curve of fallows, croplands and villages stands was bell-shaped, indicating a lack of recruitment. However, a high number of seedlings were recorded in villages. Nearly all baobabs were pruned and debarked in villages, croplands and fallows while half of the individuals were harvested in the park. Most of the trees were pruned and debarked moderately. Debarking and pruning were slightly size specific. Pruning in interaction with tree-size had a significant impact on fruit production. In contrast, debarking had no effect on fruit production. We conclude that despite the land-use impact and the intense harvesting, baobabs are still well preserved in the communal area due to their longevity, extremely low adult mortality rates and traditional management practices. However, land-use intensifications may lead to increasing pressure on baobab populations in the future. Therefore, adapted management strategies are needed to guarantee the persistence of this important species and to avoid a shortage of baobab products.

African wild ungulates compete with or facilitate cattle depending on season

AbstractSavanna ecosystems are vital for both economic and biodiversity values. In savannas worldwide, management decisions are based on the concept that wildlife and livestock compete for grassland resources[1-4], yet there are virtually no experimental data to support this assumption[1]. Specifically, the critical assessment of whether or not wild ungulates alter livestock performance (e.g., weight gain, reproduction or survival) has rarely been carried out, although diminished performance is an essential prerequisite for inferring competition[1]. Here we use a large-scale experiment in a semi-arid savanna in Kenya to show that wild ungulates do depress cattle performance (weight gain) during the dry season, indicating a competitive effect, but enhance cattle performance during the wet season, signifying facilitation. This is the first experimental demonstration of either competitive or facilitative effects of an assemblage of native ungulates on domestic livestock in a savanna ecosystem, and a unique demonstration of a rainfall-dependent shift in competition-facilitation balance within any herbivore guild. These results are critical for better understanding and management of wildlife-livestock coexistence in savanna ecosystems globally, and especially in the African savanna biome which crucially hosts the last remnants of an intact large herbivore fauna.

Integrating in-situ, Landsat, and MODIS data for mapping in Southern African savannas: experiences of LCCS-based land-cover mapping in the Kalahari in Namibia

Integrated ecosystem assessment initiatives are important steps towards a global biodiversity observing system. Reliable earth observation data are key information for tracking biodiversity change on various scales. Regarding the establishment of standardized environmental observation systems, a key question is: What can be observed on each scale and how can land cover information be transferred? In this study, a land cover map from a dry semi-arid savanna ecosystem in Namibia was obtained based on the UN LCCS, in-situ data, and MODIS and Landsat satellite imagery. In situ botanical relevé samples were used as baseline data for the definition of a standardized LCCS legend. A standard LCCS code for savanna vegetation types is introduced. An object-oriented segmentation of Landsat imagery was used as intermediate stage for downscaling in-situ training data on a coarse MODIS resolution. MODIS time series metrics of the growing season 2004/2005 were used to classify Kalahari vegetation types using a tree-based ensemble classifier (Random Forest). The prevailing Kalahari vegetation types based on LCCS was open broadleaved deciduous shrubland with an herbaceous layer which differs from the class assignments of the global and regional land-cover maps. The separability analysis based on Bhattacharya distance measurements applied on two LCCS levels indicated a relationship of spectral mapping dependencies of annual MODIS time series features due to the thematic detail of the classification scheme. The analysis of LCCS classifiers showed an increased significance of life-form composition and soil conditions to the mapping accuracy. An overall accuracy of 92.48% was achieved. Woody plant associations proved to be most stable due to small omission and commission errors. The case study comprised a first suitability assessment of the LCCS classifier approach for a southern African savanna ecosystem.

Effect of leaf size, thorn density and leaf accessibility on instantaneous intake rates of five woody species browsed by Matebele goats ( Capra hircus L) in a semi-arid savanna, Zimbabwe

Browse instantaneous intake rate (IIR) is a product of bite size and bite rate which are constrained by plant morphology. We studied the effects of leaf size, thorn density and leaf accessibility on the IIRs of five browse species in semi-arid savanna over three leaf phenophases using cafeteria-style trials. Bite size was influenced by leaf size and bite rate by leaf accessibility, while thorn density had an impact on both bite size and bite rate. The lowest IIRs were recorded on the small leafed Acacia tortilis which also had the highest thorn density. Dichrostachys cinerea had the highest IIRs due to the large bite sizes. Although Terminalia prunioides and Commiphora pyracanthoides had small leaves, their arrangements in clusters allowed for higher IIRs, which were comparable to those of the large leafed D. cinerea. Instantaneous intake rate showed no clear trend in relation to leaf phenophase, although at early leaf the goats cropped smaller bites because of the small size of the newly sprouting leaves. We conclude that leaf size influenced IIRs through bite size, leaf accessibility through bite rate and thorn density through both bite size and bite rate.

The effects of grazing, fire, nitrogen and water availability on nutritional quality of grass in semi-arid savanna, South Africa

The impacts of fire and grazing management on grass nutritional quality in semi-arid savannas may depend on inherent variation in rainfall and soil nutrient status. We examined the effects of grazing, fire, nitrogen addition, and watering treatments on the nutritional value of grass in a field experiment in the Northern Cape, South Africa. Surprisingly, water addition had no effect on grass quality and biomass in this dry savanna, perhaps because of the above-average rainfall during this study. Nitrogen addition resulted in increased levels of crude protein and biomass, as well as crude protein and gross energy in the early and late wet seasons, respectively. Grazing alone generally had little effect on grass quality, although grass in grazed plots had higher levels of crude protein (CP) in the late wet season and phosphorus (P) in the dry season. Grass biomass was greater in plots protected from grazing. There was more CP and P mass per unit area in fenced (ungrazed) plots during the wet season. Fire interacted with addition of nitrogen and grazing to increase grass quality. Soil nitrogen availability appears to be the most important factor affecting nutrient quality of grasses in the wet season in this semi-arid ecosystem.

Management intervention affects river-bound spatial dynamics of elephants

The potential consequences of growing elephant populations are a cause of debate and concern in many African conservation areas. Even though space use of elephants is central to understanding their biodiversity consequences, few studies explicitly consider how different management strategies influence elephants’ spatial utilization of landscapes. Here we study elephant’s spatial dispersion patterns in relation to different sized rivers under different management regimes by analyzing aerial census data collected annually during the mid dry-season between 1985 and 2007 across the 19,485 km 2 Kruger National Park. We found that different sized rivers can be used as a simple proxy for elephant density gradients in the dry-season. This has implications for stratifying and designing elephant impact monitoring programmes in semi-arid savannas. Furthermore, we found that dry-season elephant densities increased around rivers in a period after culling was stopped and large-scale artificial water provision reduced. Most importantly, these localized density increases were not spatially homogeneous, with culling and water provision having a greater suppressing effect on the localized densities around larger rivers than around smaller rivers and areas far removed from rivers. Assuming a positive correlation between elephant density and elephant impact, the impact of elephants around larger rivers has increased disproportionably compared to areas around smaller rivers and areas far removed from rivers since management stopped culling and reduced large-scale water provision. Since areas around the larger rivers have unique functional, structural and compositional characteristics, they should receive specific attention in impact monitoring programmes and elephant management policies. Furthermore, we recommend that if artificial waterholes are provided in semi-arid systems, it should not be located close to rivers that are mostly dry nor in areas far from rivers as this may compromise the spatio-temporal refugia that these areas afford aspects of biodiversity that are sensitive to continuous elephant impact.

Vegetation pattern divergence between dry and wet season in a semiarid savanna – Spatio-temporal dynamics of plant diversity in northwest Namibia

African savannas are primarily used as pastures and are subject to changes in climate and management strategies. For sustainable management of these landscapes ecological knowledge on seasonal and long-term variability in plant community composition and the availability of green biomass is essential. In this study, we assessed the effects of dry and wet season on species richness and beta diversity for three sites along a gradient of increasing vegetation cover and precipitation in northwest Namibia. A hexagonal systematic sampling design was used to record floristic data. The Simple Matching, Soerensen, and multi-plot similarity coefficient and distance decay analyses were applied for examining beta diversity. Analyses were repeated while separating the plots according to the presence of woody vegetation. Species richness nearly doubled from dry to wet season; compositional similarity increased from dry to wet season and with increasing aridity of the study sites; distance decay was more pronounced in the dry season without any link to the precipitation gradient. Woody elements in the landscape, which occur along drainage lines or as tree islands, govern spatial and seasonal plant diversity fluctuations. Monitoring them is important for conservation strategies and for establishing grazing rules that ensure a sustainable use of savanna ecosystems.

Nocturnal and seasonal patterns of carbon isotope composition of leaf dark-respired carbon dioxide differ among dominant species in a semiarid savanna

The C isotope composition of leaf dark-respired CO(2) (δ(13)C(l)) integrates short-term metabolic responses to environmental change and is potentially recorded in the isotopic signature of ecosystem-level respiration. Species differences in photosynthetic pathway, resource acquisition and allocation patterns, and associated isotopic fractionations at metabolic branch points can influence δ(13)C(l), and differences are likely to be modified by seasonal variation in drought intensity. We measured δ(13)C(l) in two deep-rooted C(3) trees (Prosopis velutina and Celtis reticulata), and two relatively shallow-rooted perennial herbs (a C(3) dicot Viguiera dentata and a C(4) grass Sporobolus wrightii) in a floodplain savanna ecosystem in southeastern Arizona, USA during the dry pre-monsoon and wet monsoon seasons. δ(13)C(l) decreased during the nighttime and reached minimum values at pre-dawn in all species. The magnitude of nocturnal shift in δ(13)C(l) differed among species and between pre-monsoon and monsoon seasons. During the pre-monsoon season, the magnitude of the nocturnal shift in δ(13)C(l) in the deep-rooted C(3) trees P. velutina (2.8±0.4‰) and C. reticulata (2.9±0.2‰) was greater than in the C(3) herb V. dentata (1.8±0.4‰) and C(4) grass S. wrightii (2.2±0.4‰). The nocturnal shift in δ(13)C(l) in V. dentata and S. wrightii increased to 3.2±0.1‰ and 4.6±0.6‰, respectively, during the monsoon season, but in C(3) trees did not change significantly from pre-monsoon values. Cumulative daytime net CO(2) uptake was positively correlated with the magnitude of the nocturnal decline in δ(13)C(l) across all species, suggesting that nocturnal δ(13)C(l) may be controlled by (13)C/(12)C fractionations associated with C substrate availability and C metabolite partitioning. Nocturnal patterns of δ(13)C(l) in dominant plant species in the semiarid savanna apparently have predictable responses to seasonal changes in water availability, which is important for interpreting and modeling the C isotope signature of ecosystem-respired CO(2).

Effects of herbivore exclosures on variation in quality and quantity of plants among management and habitat types in a semiarid savanna

The effects of grazing on plant biomass, plant quality, species evenness, species diversity and species composition were determined among management types (communal, commercial and game) and among habitat types (open savanna, rocky and pan) in a semiarid savanna in South Africa. Over three growing seasons we compared fenced and unfenced plots among all management and habitat types. Fenced plots had greater mean plant height as well as higher crude protein (CP) and phosphorus (P) yields (= concentration ¥ biomass). The only significant difference in species composition between fenced and unfenced plots was observed in the pan habitat type during the third growing season. Negative effects of grazing were more pronounced in the commercially managed area than under other management types, although the higher abundance of poisonous plants under communal management is of considerable concern. The open savanna habitat had the highest plant biomass and lowest CP and P levels, while the reverse was true for the pan habitat type. Most parameters assessed showed significant effects between fenced and unfenced plots towards the end of the study only because species composition in fenced plots was altered by competition between species normally suppressed by grazing.

Effect of leaf size, thorn density and leaf accessibility on instantaneous intake rates of five woody species browsed by Matebele goats (Capra hircus L) in a semi-arid savanna, Zimbabwe

Effect of leaf size, thorn density and leaf accessibility on instantaneous intake rates of five woody species browsed by Matebele goats (Capra hircus L) in a semi-arid savanna, Zimbabwe

Profile distribution of total and available Sulphur and boron in sandy soils of Nigerian semi-arid savanna .

The total and available sulphur and boron forms were determined in sandy soils formed from sand dunes, sandy alluvial terrace and sandstone formation in northwestern Nigeria. Hot water and Morgan’s solution (sodium acetate/acetic acid solution buffered at pH 4.8) were used as extractants for available boron while calcium phosphate solution was the extractant for available sulphur. In the surface horizons, in all the sandy soils, total boron ranged from 2.03 to 170.85 mg kg-1 soil, while subsoil values varied from 0.59 to 135 mg kg-1 soil. The means of the total boron are highly significantly (p=0.001) different among the sandy soils. The means of hot water extractable boron (Bhw) are also significantly (p=0.05) different for the sandy soils. Generally boron values are significantly higher in the surface horizons than in the sub-surface horizons. In terms of magnitude, the sandy soils may be arranged as follows: Rabah terrace > Wurno sandstone > Sangiwa dunes > Illela dunes > Sokoto dunes. The mean values of calcium phosphate extractable sulphur are significantly (p=0.05) different among the sandy soils. Values in the surface horizons are also generally higher than the sub-surface horizons. The values of Sc are higher in the sand dune soils than the sandstone and terrace soils within the study area. By the critical limits of 0.1 to 0.2 mg kg-1 given in the literature for Nigerian savanna soils, the sandy soils understudied appear to be slightly above this limit especially for the terrace and sandstone soils. For the sand dune soils the surface horizons are marginally adequate but the subsoils are below the critical limit. If thecritical limit of 4 mg kg-1 quoted in the literature is considered, all the sandy soils understudied are deficient in available sulphur except for soils derived from Illela sand dune, which are only marginally sufficient. For optimum crop production on sandy soils within the study area, sulphur and boron addition through the use of boronated single supper phosphate and other sulphur-based fertilizers should therefore, be encouraged.

Erratum to: Tree-grass coexistence in a flood-disturbed, semi-arid savanna system

Erratum to: Tree-grass coexistence in a flood-disturbed, semi-arid savanna system

Response of Roselle (Hibiscus sabdariffa L.) to Farmyard Manure and Nitrogen-fertilizer in the semi-arid savanna of Nigeria

Field experiments were conducted during 1998 and 1999 rainy seasons at the Dry Land Teaching and Research Farm of Usmanu Danfodiyo University, Sokoto, to study the response of roselle to farmyard manure, nitrogen and their interaction on the growth and yield of roselle. Treatment consisted of factorial combination of four rates of farmyard manure (0, 2.5, 5.0 and 7.5 t/ha) and four levels of nitrogen fertiliser (0, 25, 50 and 75 kg N/ha) laid out in a randomized complete block design replicated three times. The result showed that there was significant response to applied manure and N-fertiliser on number of leaves up to 5 t/ha manure and 50 kg N/ha. There was no significant increase in calyx yield by raising manure rate from 2.5-7.5 /ha or nitrogen rate from 50 to 75 kg N/ha. Thus, 2.5 t/ha manure and 50 kg N/ha were considered adequate for calyx production in roselle in Sokoto Semi-arid Tropics. However, for maximum number of vegetable leaves additional manure (5-7.5 t/ha) and N fertilizer (50-75 kg N/ha) may be necessary.