Cultivated Plots Research Articles

Soil microbial biomass dynamics in grassland and agroecosystem receiving varying resource quality soil inputs in dry tropics

Atwo year field experiments were conducted to evaluate the effect of land use conversion and management strategies variation through addition of varying resource quality soil inputs on soil microbial biomass dynamics, under rice-wheat-summer fallow crop sequence in tropical dryland agroecosystem. The treatments involved addition of equivalent amount of N through chemical fertilizer (CF) and three organic inputs, viz. Sesbania shoot (high quality resource, HQR), wheat straw (low quality resource, LQR) and Sesbania+wheat straw (mixed quality, MQR) besides control (CO) and grassland (GF). On annual mean basis, cultivation of grassland decreased the MBC (−51%) and MBN (−52%) level in soil. Relative to control, application of WS+SS considerably increased the level of MBC (+77%) and MBN (+87%) in soil, instead of SS, WS and CF. In all cultivated plots, a distinct seasonal and temporal variation in microbial biomass C and N were found contrary to GF. Both soil MBC and MBN level increased from rice to wheat period and reached maximum during summer fallow; during rice, the pattern in decreasing order was HQR>MQR>LQR>CF>CO; wheat period, MQR>LQR>HQR>CF>CO; summer fallow, MQR>LQR>HQR>CF>CO. It is concluded that cultivation exerts negative effects on the concentration of soil microbial biomass. Application of varying resource quality exogenous soil inputs maintains the microbial biomass level in soil, differentially. Addition of MOR was most effective for sustained buildup of microbial biomass in soil throughout the cycle, rather than HQR, LQR or CF. The fertility of soil in term of soil microbial biomass can be maintained by regulating the resource quality of exogenous inputs, and these results will help in designing the management strategies for sustaining long term soil fertility in these tropical dryland agroecosystem.

Response of humic acid structure to soil tillage management as revealed by analytical pyrolysis

The effects on the structural features of humic acids (HA) from dryland farming soils under long term management practices have been approached by analytical pyrolysis (Curie-point pyrolysis-gas chromatography/mass spectrometry, Py-GC/MS). The field experiments (started in 1987) include conventional, minimum and no-tillage plots, as well as non cultivated plots. The HAs isolated from the various plots showed significant differences in their pyrolytic behavior, in particular regarding the total abundances of alkyl pyrolysis compounds (fatty acids, alkenes and alkanes). The occurrence of very short-chain fatty acids (C5–C11) in uncultivated plots could be indicative of constitutional alkyl structures in the relictual HA from undisturbed soil. The effect of soil tillage managements substantially increased total abundances of fatty acids in plots under conservation practices (mainly no-tillage).The HAs from uncultivated soils showed the greatest percentages of alkanes and alkenes. This was associated to the increased proportions of even C-numbered alkene homologues from C12 to C18, possibly related to the incorporation of microbial compounds during the humification process. High percentage of alkylbenzenes and catechols were also characteristic of the uncultivated plots. The increased proportions of methoxyphenols, in special of the syringyl (dimethoxyphenyl) type, in HAs from plots subjected to conventional tillage pointed out to humification processes based on progressive alteration of plant lignins. From the viewpoint of soil quality, the results suggest comparatively advanced transformation stages of the HA from uncultivated plots, which means that conservation tillage practices seems to lead to increasing soil C levels, at expenses of the accumulation of comparatively recent organic matter derived either from altered lignins and/or microbial biomass.

Are ditch networks optimised for mitigating rill erosion in cultivated Mediterranean landscapes? A numerical experiment

Rill erosion frequently occurs in Mediterranean cultivated landscapes due to high rainfall intensities, low soil organic matter concentrations and low vegetation coverage. Among other rill erosion mitigation practices, farmers have historically built ditch networks to intercept runoff upstream of cultivated plots. However, the construction and maintenance of these ditches generate indirect costs for farmers and land managers. Therefore, a compromise must be found between these costs and the efficiency of the ditch network for mitigating erosion. Thus, tools and methods are required for determining an optimised cost-efficient compromise or for diagnosing existing ditch networks.This paper proposes an experimental approach to test in silico how well an actual soil conservation practice (i.e., a ditch network) reaches a cost-efficiency compromise at the catchment scale. The costs are approximated from the density of the ditches, and the rill erosion mitigation efficiency is summarised using an aggregated modified stream power index. The actual ditch network is compared to a set of virtual ditch networks that are generated by a stochastic network simulator that optimises the network geometries with regard to preventing rill erosion. This approach was applied in four small vineyard sub-catchments located in the Peyne catchment in Languedoc, southern France. Actual ditch networks are compared to virtual networks, which present a large range of ditch network densities.The ditch network highly mitigates rill erosion because the Stream Power Index (SPI) values exponentially decrease with the ditch network density and because the actual SPI maps are homogeneous. In addition, the results from the four different sub-catchments indicated that the rill erosion risk was mitigated by using minimal drainage network lengths, which suggested that the actual ditch networks that resulted from historical farmers were optimised.The proposed approach can be used to determine if the efficiency of ditch networks for mitigating erosion can be improved.

Landscape-scale variability of soil health indicators: effects of cultivation on soil organic carbon in the Usambara Mountains of Tanzania

Land-use change continues at an alarming rate in sub-Saharan Africa adversely affecting ecosystem services provided by soil. These impacts are greatly understudied, especially in biodiversity rich mountains in East Africa. The objectives of this study were to: conduct a biophysical baseline of soil and land health; assess the effects of cultivation on soil organic carbon (SOC); and develop a map of SOC at high resolution to enable farm-scale targeting of management interventions. Biophysical field surveys were conducted in a 100 km2 landscape near Lushoto, Tanzania, with composite soil samples collected from 160 sampling plots. Soil erosion prevalence was scored, trees were counted, and current and historic land use was recorded at each plot. The results of the study showed a decline in SOC as a result of cultivation, with cultivated plots (n = 105) having mean topsoil OC of 30.6 g kg−1, while semi-natural plots (n = 55) had 71 g OC kg−1 in topsoil. Cultivated areas were also less variable in SOC than semi-natural systems. Prediction models were developed for the mapping of SOC based on RapidEye remote sensing data for January 2014, with good model performance (RMSEPcal = 8.0 g kg−1; RMSEPval = 10.5 g kg−1) and a SOC map was generated for the study. Interventions will need to focus on practices that increase SOC in order to enhance productivity and resilience of the farming system, in general. The high-resolution maps can be used to spatially target interventions as well as for monitoring of changes in SOC.

Sustainable leaf harvesting and effects of plant density on wild leek cultivation plots and natural stands in Southern Quebec, Canada

Overharvesting reduces the populations of wild leek in deciduous temperate forests of North America. Forest farming relying on planted bulbs that are fertilized and selectively harvested could enhance and sustain wild leek production. Density reduction following bulb harvest could improve yield in natural wild leek stands that reach growth-limiting densities. Limiting the harvest to leaves may also provide an alternative form of exploitation, but could slow growth by reducing both carbon and nutrient reserves depending on the timing and intensity of such harvest. Our objectives were to assess the effects of (1) planting density and post-harvest density reduction, and (2) the timing and intensity of leaf harvest on subsequent growth and reproduction of wild leek. Three experiments were established. Bulbs were planted at densities from 44 to 356 bulbs m−2, covering the range surveyed in natural populations. Plots in dense populations were subjected to up to 40 % bulb harvest. In cultivated plots, either half or all the leaves on each plant were harvested, from 15 to 25 days after unfolding. Plants growing in higher density plots exhibited slower growth and reproduction rates, but greater productivity per cultivated area. A similar effect, albeit marginal, was obtained following bulb harvests in natural populations. Harvesting leaves did not affect survival, but delaying the harvest and harvesting only half of the leaves favored subsequent plant growth. We recommend harvesting down to a fixed bulb density rather than harvesting a percentage of bulbs, and harvesting leaves only as ways to ensure sustainable exploitation of leeks.

Environmental fate of the insecticide cypermethrin applied as microgranular and emulsifiable concentrate formulations in sunflower cultivated field plots

A field dissipation and transport study of the insecticide cypermethrin applied as microgranular (MG) and emulsifiable concentrate (EC) formulations has been conducted in field sunflower cultivations and bare soil plots with two different slopes (1% and 5%). The dissipation of insecticide in soil (on planting rows) was monitored for a period of 193days. Cypermethrin residual concentrations in the upper soil layer (0–10cm), 2days after soil application (DASA), ranged from 0.53 to 0.73μgg−1 when the maximum values were observed 7 DASA, ranged from 1.06 to 1.23μgg−1. The dissipation rate was better described by first-order kinetics. The average half-life in cultivated (tilled and planted) plots was 23.07 and 24.24days for soil slopes 5% and 1%, respectively. In uncultivated (tilled but not planted) plots the respective values were 22.01 and 22.37days. The insecticide was found below the 10cm soil layer occasionally in few samples at low concentrations (<0.02μgg−1). In runoff water it was detected once (7days after foliar application, at levels below LOQ), when in sediment it was detectable for seven samplings. The maximum values were observed 7days after foliar application, when they reached 0.097 and 0.143μgg−1 in cultivated plots with soil slopes 1% and 5%; and 0.394 and 0.500μgg−1 in uncultivated plots, respectively. The amount of cypermethrin which was transferred by the sediment remained at low levels (less than 0.01% of the totally applied active ingredient), even in plots with 5% inclination. The insecticide was detected in leaves and stems of the sunflower plants after the foliar application up to the day of harvest. On the contrary, in roots it was detectable during the whole cultivation period. No residues were detected in flowers or seeds.

Variation in soil fertility influences cycle dynamics and crop diversity in shifting cultivation systems

Smallholder farming in Amazonia is practised mostly through shifting cultivation, which under low population pressure is well adapted to the low-fertility soils that predominate in uplands and to the lack of external inputs. In this paper we investigate the effects of soil heterogeneity (in terms of fertility and texture) on shifting cultivation systems in Central Amazonia. We focus on the effect of soil variation between anthropogenic upland soils (Amazonian Dark Earths, ADE) and surrounding soils on the size and location of cultivation plots, on the cultivation cycle, and on the diversity and assemblage of crops. We found that more fertile soils are cultivated more intensively (with shorter fallow periods, higher frequency of cultivation, shorter cycles and higher labour requirements) and with different crop assemblages, and have similar or larger numbers of crop species and/or landraces. Current smallholder farming systems along soil gradients between ADE and non-anthropogenic soils show that enhanced soil fertility can favour synergies between intensification and diversification in shifting cultivation.

Commons and the legacy of the past. Regulation and uses of common lands in twentieth century Spain

The authors explore the transformation of common lands in Spain in the second half of the 20th Century, when the nation experienced significant structural and political changes. If the 19th Century was defined by privatisation of common lands, the 20th Century experienced slight growth, but there were differences among the regions. Although the legal definition and classification of common lands is fixed, and was determined by the municipal entity, new formulas (such as the montes vecinales en mano común regulated in 1968) appeared to solve the tension between the state and local control. Ultimately, flexibility was the main characteristic of the regulations which allowed for adapting uses to a diversity of regional circumstances. Along with the productive and environmental regulations, the use of common lands for social purposes through the distribution of plots for cultivation was emphasised. Nevertheless, at the end of the 20th Century Spanish legislation concerning common lands was more focused on earlier norms than on the future.

Multilevel habitat preferences of Apodemus sylvaticus and Clethrionomys glareolus in an intensively cultivated agricultural landscape

Small mammals are considered good model species for assessing the global effects of habitat loss and fragmentation in agricultural landscapes. With the aim of investigating the composition and habitat preferences of the small mammal community in an intensively cultivated area, we sampled the three main “macro-habitats” (wood patches, poplar plantations and crops) available on the western plain of the River Po (North Italy). The influence of habitat variables on each species’ occurrence was assessed at three different scales of observation: “macro-habitat”, “micro-habitat” (i.e. vegetation layers at trap sites) and the landscape level (i.e. land cover in plots of 500 m radius centred on each trap line). Overall, 3344 trap-nights yielded 169 Apodemus sylvaticus, 28 Clethrionomys glareolus and two Sorex araneus. The first species was dominant in all macro-habitats, while the other two species were trapped only in residual wood patches. The thickness of the fine litter was the main micro-habitat factor affecting the occurrence of both C. glareolus and A. sylvaticus in woods, while sites with herbaceous vegetation cover were preferred by the latter species in poplar plantations. Intraclass correlation coefficients showed that sites with thick litter or high herb cover were neither exclusive nor predominant in wood patches and poplar plantations, respectively, suggesting that the choice for micro-habitat parameters is subordinate to that of macro-habitat characteristics, mainly tree and shrub cover. At the landscape scale, no habitat variable affected the occurrence of both species. At the macro-habitat level, the strong selection for wood patches by both wood mice and bank voles and the negligible occurrence of small mammals in cultivated plots pointed out the major role for conservation played by residual semi-natural habitats in agricultural landscapes.

Effect of organic cultivation of rooibos tea plants (Aspalathus linearis) on soil nutrient status in Nieuwoudtville, South Africa

The shoots of rooibos (Aspalathus linearis (Burm.f.) R.Dahlgren) plants, cultivated organically by small-scale farmers in Nieuwoudtville, are harvested for the production of tea. These practices could lead to decreasing soil fertility. It was hypothesised that soil from cultivated rooibos plots will have lower nutrient concentrations than soil from adjacent uncultivated plots. Soil and shoot samples were collected in December 2005, 2006 and 2009 from cultivated fields of increasing plot age and from adjacent uncultivated plots on three farms, and analysed for nutrient concentration. Compared with the uncultivated plots, no measured soil nutrients including concentrations of phosphorus (P), exchangeable potassium (K), magnesium (Mg) and calcium (Ca), and soil carbon (C) decreased in cultivated plots over the five-year period of assessment. Soil C correlated positively with concentrations of soil exchangeable K, Mg and Ca, and sodium (P<0.001), indicating that soil C is an important indicator of soil fertility. Foliar P increased, and consequently the nitrogen:P ratio decreased in cultivated relative to uncultivated plants, implying higher P-uptake by cultivated plants. Overall, organic rooibos cultivation in Nieuwoudtville appears to be sustainable in terms of maintaining soil nutrition because soil nutrient status did not decrease over the five-year period.

Modeling the erosion-induced fractionation of soil organic carbon aggregates on cultivated hill slopes through positive matrix factorization

The lack of information concerning the compositions and erosion-induced redistributions of soil aggregates will limit our understanding regarding the stability and the fate of eroded soil organic carbon (SOC). In this work, we develop a tool for modeling the erosion-induced fractionation of soil aggregates and characterizing their compositions and redistribution pathways in the landscapes. Erosion-induced redistributions of soil organic carbon (SOC) on cultivated hill slopes with contour hedgerows planted to reduce soil and nutrient losses were investigated by the 137Cs tracing technique combined with soil composition characterization. The soil composition in 56 samples taken across cultivated plots was treated using the positive matrix factorization (PMF) method of receptor modeling. Five factors driving the interrelationships between the soil parameters and 137Cs in the plots were interpreted as representing the five types of soil aggregates, which were fractionated in situ according to their compositions, specific densities, and redistribution pathways under erosion forces combined with tillage and conservation measures. According to the PMF model, approximately three quarters of the 137Cs activity was attributed to the SOC aggregated with sand particles, which accounted for 33% of the SOC concentration and was identified as the light, labile SOC fraction. There was another labile SOC-sand aggregates, which did not contain 137Cs and accounted for 13% of the SOC concentration. The heavy, stable fraction that accounted for 44% of SOC concentration was in the SOC-clay aggregates, which contain the largest amounts of N, P, K, Kdis, and the highest CEC. The labile SOC-sand aggregates were concentrated in the depositional areas above the hedgerows whereas the stable SOC-clay aggregates were found in the eroding areas between the hedgerows. Labile SOC was depleted in the cultivated plot without conservation measures, but it was retained appreciably in the four cultivated plots with hedgerows.

Thermal stability of soil organic matter was affected by 23-yr maize and soybean continuous cultivation in northeast of China

Long-term continuous cropping affects the biochemical quality of soil organic matter (SOM), but whether the effects are relevant with their thermal stability is less clear. In northeast China, long-term continuous cropping occurred frequently owing to higher yield and economic interest requirement. To verify the thermal stability properties of SOM affected by the long-term continuous cropping, the study focused on 23-yr continuous cultivated maize and soybean plots, where the effect of cropping is likely to be detected. Bulk soils sampled in 1991 and 2014 were studied by thermogravimetry and differential scanning calorimetry (DSC). The results showed typical bimodal peaks in DSC curve in bulk Mollisols. A labile fraction peak was observed at 354–366 °C low-temperature zone and recalcitrant fraction one at high temperature of 430–438 °C. Energy density (J mg−1 OM) was greater in soybean plots compared to maize plots; in contrast, long-term continuous maize cultivation also increased energy density, in reverse in soybean plots after 23-yr cultivation. The DSC-T50, temperature at which half of energy release occurred, typically showed larger responses to long-term cultivation than crop species. Results obtained support the hypothesis of a potential link between long-term continuous cropping and the thermal stability of SOM, and a correlation with crop species.

Soil structure changes due to different land-use practices in the central Zagruos region, Iran

In this study, the effect of land-use treatments and the feasibility of fractal dimension to quantify soil aggregate stability were investigated in the central Zagrous, Iran. For this purpose, the non-linear fractal dimension (Dnl), linear fractal dimension (Dl) and the mean weight diameter (MWD) of aggregates were compared. Soil samples from three sites with four adjacent land-use types, namely: forest area (F), cultivated lands adjacent to forest (CAF), pasture (P) and cultivated lands adjacent to pasture (CAP) were collected. Results showed that soils under cultivated lands had higher bulk density (BD) (1.30–1.38 Mg m−3) compared to the adjacent soils under forest (1.19 Mg m−3) and pasture (1.21 Mg m−3). In the 0–15 cm layer, soil organic matter (SOM) content in the cultivated plots were respectively 30% and 31% lower compared to the forest and pasture soils. The lowest CVs belonged to Dnl (5–8%) demonstrating that Dnl was more accurate than Dl (8–14%) and MWD (30–53%) methods. CAP had the largest value of Dnl, while P had the smallest value of Dnl. Difference of Dnl between forest and pasture was not significant, whereas both of them significantly differed from CAF and CAP. Dl did not differ significantly between forest and CAF. There were significant differences between forest and pasture for the measured MWD. Both fractal dimensions had negative correlation with MWD, SOM, hydraulic conductivity (HC) and macroaggregates (>0.25 mm) and positive correlation with BD and total porosity (TP).

The thin green line: sustainable bioenergy feedstocks or invaders in waiting

Numerous fast growing and highly competitive exotic crops are being selected for production of renewable bioenergy. Tolerance of poor growing conditions with minimal inputs are ideal characteristics for bioenergy feedstocks, but have attracted concern for their potential to become invasive. Miscanthus × giganteus is one of the most promising bioenergy crops in the US, but grower adoption is hindered by high establishment costs due to sterility. Newly developed fertile tetraploid M. × giganteus may streamline cultivation while reducing establishment costs. However, fertile seed dramatically increases the potential propagule pressure, and thus probability of off-site plant establishment. To empirically evaluate the invasive potential of fertile M. × giganteus in the Southeastern US, we compared fitness and spread potential relative to ten grass species comprising 19 accessions under both high and low levels of competition and disturbance. We chose species known to be invasive in the US (positive controls: Arundo donax, naturalized M. sinensis, M. sacchariflorus, Phalaris arundinacea, Sorghum halepense) and non-invasive (negative controls; Andropogon gerardii, ornamental M. sinensis, Panicum virgatum, Sorghum bicolor, Saccharum spp.). This novel design allows us to make relative comparisons of risk among species with varying invasiveness. After three years of establishment and growth in Blacksburg, Virginia, neither aboveground disturbance nor interspecific weed competition influenced fitness for fertile M. × giganteus or our positive and negative control groups. Fertile M. × giganteus produced 346% and 283% greater aboveground biomass than our positive and negative species, respectively. However, fertile M. × giganteus produced 74% fewer inflorescences m-2 than our positive controls and 7% and 51% fewer spikelets inflorescence-1 than the positive and negative control species. After 18 months of growth, we observed the vegetative and seedling spread of three of our positive control species (S. halepense, P. arundinacea, and M. sacchariflorus) outside the cultivated plot into receiving areas of both high and low competition. After 24 months of growth, numerous species were observed outside the cultivated plot including fertile M. × giganteus and 50% of negative control species. Notably, in three years sterile M. × giganteus ‘Illinois’ and Arundo donax never moved from the cultivated plot. The addition of fertile seed appears to increase the potential for offsite movement, but within the geographic confines of our empirical evaluation, fertile M. × giganteus seedlings are more similar to native P. virgatum and were not nearly as fast growing or as competitive as our positive control S. halepense. The use of numerous species providing relative comparisons allow us to draw important conclusions which may help prepare for widespread commercialization, while providing novel methodology for ecological risk assessment of new species.

Study on Issues and Remedies of Waterlogging in Hirakud Command - Key to Enhance Crop and Water Productivity

The present study deals with finding out the causes of rising groundwater table that creates waterlogging in the Hirakud command of Odisha. The study reveals that during the 55 years of construction of the project, the groundwater table in the command has risen by more than 5 m. In the head reach, the rise is more as compared to the lower reach. The main factors that contribute to the waterlogging are (i) faulty water management practice (ii) intensive rice-rice cultivation (iii) plot to plot irrigation in rice field instead of using field channel (iv) continuous canal flow etc. Some remedies to reclaim the waterlogged areas and decrease the groundwater table are also mentioned in this paper. Construction of parallel field surface drain at 10 m drain spacing is recommended in the ayacut to decline the rising groundwater table which may facilitate the farmers to grow even some non-rice crops in the ayacut and increase water productivity.

Profile distribution and degradation of soil properties of an ultisol in Nsukka semi-humid area of Nigeria

Better understanding of how soils respond to land use is needed to enable science-based land management interventions. The present study investigated the relative changes in properties of ultisol under conventional tillage for arable crops and compared with fallowed plot (greater than 10 years of continuous no-till fallow) in the semi-humid Nsukka of southeastern Nigeria. Soil samples were collected from designated profile horizons for determination of soil properties. In cultivated plot relative to fallowed plot, soil erodibility increased by 2.5% (Ei + 0.11), total porosity decreased by 1.1%, whereas macro- and microporosity increased by 3.4 and 7.1%, respectively. Soil saturated hydraulic conductivity increased by 4.9%. The degree of topsoil saturation with water was similar in both the cultivated and the fallowed plots. Soil pH increased (7%) when exchangeable acidity increased (21.3%, +0.46 cmol (+) kg-1). Losses of organic carbon (28%, -2.58 gkg-1), total N (26%, -0.17 gkg-1), available P (47%, -2.63 mgkg-1), Ca (55%, -1.75 cmol (+) kg-1), CEC (17%, -1.11 cmol (+) kg-1), and base saturation (11.3 %) due to cultivation were observed. Since the fallowed plot that was previously under cultivation was able to show more favourable values of the measured soil properties than the cultivated plot without human activity, the study deduces that an ultisol can be resilient. Key words: Ultisol, land use system, soil property, semi-humid, Nigeria.

Abandonment of Conservation Agriculture by Smallholder Farmers in Zimbabwe

This paper examines the determinants of abandonment of conservation agriculture (CA) techniques among smallholder farmers in Zimbabwe. The analysis uses four rounds of a balanced panel from a survey aimed at monitoring CA adoption among farmers who participated in CA promotion projects. Findings indicate that a large share of farmers who had adopted CA during the period of active promotion eventually abandoned the practice in the absence of support from non-governmental organisations (NGOs). Households with more farming experience, bigger household sizes and a greater number of cultivated plots were less likely to stop using CA. In turn, wealthy households and farmers in the drier areas were more likely to stop using CA. The finding that persistent adoption is more prevalent among the poor, supports claims that CA is a pro-poor technology. Lastly, we find a strong, negative and robust relationship between continued NGO support and abandonment of CA. This finding suggests that improved support institutions are necessary to ensure that farmers continue to use CA as a productivity-boosting and sustainable farming method.

Limitations of the Temporary

Vacant land invites occupation, both by ruderal vegetation and spontaneous human intervention. This active engagement—taking the form of art installations, cultivated plots, or domestic appropriations—is often unplanned and temporary. Capable of existing outside of market forces, the projects are realized efficiently, but without long-term durability. Their short-term value is undeniable but so is their vulnerability. This is especially true of landscape projects on abandoned lands. The limitations of temporary projects are elaborated across diverse occupation types, including guerilla activities, pop-up projects, design collaborative work, and short-term land leases. The argument is structured around four main points. First, public space needs to be unregulated and diverse, not just on a temporary basis in leftover spaces. Second, landscape projects require time to develop to perform culturally and ecologically. Third, temporary projects can be placeholders that limit the need for long-term re-visioning. Finally, cities with large inventories of abandoned land require greater restructuring than the temporary can promote. The temporary functions well as programmatic overlay or an event landscape to activate an existing, clearly articulated, often vibrant, space rather than as a catalyst for systemic urban change in places of disinvestment.

DETERMINANTS OF CROP YIELD AND PROFIT OF FAMILY FARMS: EVIDENCE FROM THE SENEGAL RIVER VALLEY

SUMMARYThis paper investigates the determinants of the performance of family farms in Senegal using both production and profit functions. The econometric analysis is based on agricultural inputs and outputs information from a survey of 504 agricultural households, member of a farmer organization in the Saint Louis region in 2009. Our main results indicate that the size of the cultivated plots has a negative effect on crop yields, representing diseconomies of scale. This finding suggests potential for improvements in farm management and organization. We also find that the development of commercialization sectors and loans could boost agricultural inputs. In terms of profitability, our results show that yields and prices play significant and important roles for all crops. An increase in the bargaining power of farmers would be required to increase unit prices and consequently their profits.

Floral biology of &lt;i&gt;Adolphia infesta&lt;/i&gt; and the reproductive profile of Colletieae (Rhamnaceae)

The reproduction of the shrub Adolphia infesta was studied in a population included in a Mexican agricultural landscape with small, cultivated plots and fragments of natural habitat. Adolphia infesta had reproductive traits consistent with those known for its tribe Colletieae, including small zoophilous flowers exposed to both xenogamous, geitonogamous and visitor-facilitated intrafloral pollination, with selfing being at least partially hindered by self-incompatibility. Visual and olfactory cues, together with easily accessible rewards (nectar and pollen), explain the diversity (68 species of 29 families) of insects attracted to the flowers. However, only a small subset can be considered potential pollinators (honeybee and three muscoid flies). In late floral development, pedicel bending brings the developing fruit to an upright position, which might later optimise explosive seed dispersal. The finding of this trait in A. infesta makes fruit erection a synapomorphy of the Adolphia – Discaria – Kentrothamnus clade of the tribe Colletieae. At the study site, A. infestaplayed a significant role as food source for the local anthophilous insect community, and through its flower visitors, the plant was indirectly connected to 11 other plant species. Knowledge derived from community studies should be applied in conservation initiatives directed at enhancing farmers’ appreciation of extant local biodiversity.