A Critical Review of the Water Balance and Agronomic Effects of Conservation Tillage under Rain‐fed Agriculture in Ethiopia

About 80% of Ethiopia's population is involved in rain‐fed agriculture. Moisture stress coupled with traditional tillage with breaking ard plough, locally known as ‘Maresha ’ are the major limiting factors for agricultural production. Soil erosion, low infiltration and decline agricultural productivity because of conventional tillage implement have been frequently reported. In order to curve this situation and meet the huge food demand of the growing population, different conservation tillage systems have been implemented. However, there is limited information about the impacts of the practices. This review paper therefore aimed at providing adequate information concerning the impacts of the practices on water balance and crop yield. Systematic, best evidence and narrative review techniques were used. Results revealed that the application of conservation tillage had brought significant improvement on water balance and agricultural production. Researchers found over 50% decreased in surface runoff, 9 to 40% improvement in water productivity and good crop transpiration (T = 53 mm season⁻¹), compared to conventional tillage T = 49 mm‐season⁻¹ because of conservation tillage implement. Moreover, doubled grain yield was obtained from ridging, subsoiling and wing plough (1076, 1044 and 1040 kg ha⁻¹, respectively) compared to traditional tillage which resulted in 540 kg ha⁻¹. Improving water balance and agricultural production in rain‐fed agriculture need to reduce evaporation and surface runoff through improving moisture retention and transpiration. This could be achieved by the adoption of conservation tillage which can improve on‐farm water balance, yields and water productivity among smallholder farmers in Ethiopia. Copyright © 2016 John Wiley & Sons, Ltd.     

Fish assemblages in Atlantic Forest streams: the relative influence of local and catchment environments on taxonomic and functional species

Streams are under environmental pressures acting at different scales that influence the ecological organisation of their fish assemblages. However, the relative influence of the different scale‐related variables on assemblage composition and function is poorly understood. We evaluated the importance of local‐ and catchment‐scale environmental variables, as well as the spatial structure of the sampling sites, in shaping fish assemblages in Atlantic Forest streams. Local‐scale variables were those measured at the sampling sites, describing the local habitat conditions (e.g. depth, substrate type, altitude). Catchment‐scale variables were those integrating the upstream landscape of the sampling sites (e.g. catchment land use). Spatial distances were calculated from watercourse distance using principal coordinates of neighbour matrices. Altogether, 28 local and seven catchment variables were initially subjected to two processes of eliminating co‐linearity. Redundancy analysis was applied to the three matrices (spatial, local and catchment) to quantify the variance in the structure of the fish assemblages explained by each matrix. Local variables explained more variability in both taxonomic and functional assemblage structure, than catchment and spatial variables. Local variables also changed along the longitudinal gradient, which consequently influenced fish assemblage structure. This pattern was also influenced by anthropogenic alteration and non‐native species, which were more abundant in downstream sites. These results highlight the need to assess Atlantic Forest streams under different environmental scales, especially through the use of quantitative local‐scale metrics, and to consider the effects of longitudinal patterns in structuring fish assemblages when developing and implementing monitoring programmes, impact studies and conservation plans.     

Contrasting influence of flow regime on freshwater fishes displaying diadromous and nondiadromous life histories

Flow variability structures freshwater fish community traits and life‐history patterns such as migration patterns between fresh and saltwater (diadromy). Few studies, however, have explored relationships between diadromy and flow regime while accounting for other abiotic covariables. The present paper used canonical ordinations to remove the shared variation between groups of explanatory variables that explain variation in fish communities and examine two objectives with New Zealand fishes: (i) to compare the unique contributions of Hydrological Regime, Climate, Habitat and Spatial‐Seasonal data sets to the variation of diadromous and nondiadromous fishes and (ii) to compare the relative contributions of a Hydrological Variability and Low‐Flow data set to community structure of both life‐history patterns. All explanatory variables explained a total of 20.15% and 29.58% of the variation in diadromous and nondiadromous fishes, respectively. Objective 1 analyses showed that the largest unique component of variation was explained by Hydrological Regime for nondiadromous fishes (12.17%), while Climate uniquely explained the most variation in diadromous fishes (4.3%), followed closely by Hydrological Regime (3.08%). Objective 2 analyses showed that Hydrological Variability uniquely explained five and 11 times more variation than the Low‐Flow data set in diadromous and nondiadromous fishes, respectively. Findings illustrate the importance of hydrological regime to New Zealand freshwater fishes. Specifically, aspects of hydrological variability uniquely account for more variation than aspects of low flow. Differing relative influences of hydrology between life‐history patterns suggest that diadromy may mediate the influence of flow regime. Results outline difficulties for environmental flow settings when biota display differing life histories.     

Carbon and Nitrogen Assimilation and Partitioning in Canola (Brassica Napus L.) In Saline Environment

ABSTRACT

Environmental stress strongly affects the fundamental processes of plant biology. This study was to investigate the growth, yield, carbon (C) and nitrogen (N) assimilation and partitioning of two canola (Brassica napus L.) cultivars (Qinyou 10 and Ningza 1838) under low and high soil salt-ion concentration levels (LSSC and HSSC) of 2.512 and 4.722 g kg^?1, respectively. There was no cultivar effect on agronomic traits other than the 1000-seed weight which was not affected by soil salinity. The increase of soil salt-ion concentration greatly reduced plant height, the numbers of primary branches, pods per plant or per hectare and the resultant seed yield. The C and N accumulations for whole plant and in different organs decreased significantly as soil salinity increased. The suppressive effects of high soil salinity were more strongly on C accumulation than N accumulation, and more obviously in shells and seeds than in roots, stems and leaves. As soil salinity increased, the C and N partitioning in vegetative organs of roots, stems, and leaves was enhanced greatly, while the C partitioning in shells and seeds and the N partitioning in seeds decreased significantly, suggesting an inhibition of C and N transporting from vegetative organs to reproductive organs. Our study revealed the high soil salinity profoundly suppressed canola growth and yield formation, by reducing C and N accumulations in all organs and alleviating C and N partitioning in reproductive organs.     

Throughfall,stemflow and interception loss in a mixed white oak forest (Quercus serrata Thunb.)

Throughfall and stemflow measurements in a 60-year-old white oak stand (Quercus serrata Thunb.) were carried out during two periods totalling eleven months, from August to November 1993 and from May to November 1994, in order to clarify the rainfall partitioning of this forest. Troughs and spiral-type stemflow gauges connected to tipping bucket-gauges were used for throughfall and stemflow measurements. Seventy-five storms were analyzed individually. Coefficients of variation for throughfall and stemflow ranged between 5–25% and 20–70% respectively. Partitioning of net rainfall in throughfall and stemflow represent 72% and 10% of the gross rainfall respectively. Multiple regression analyses were carried out to determine the stemflow variability. In was determined that maximum rain intensity was highly correlated with stemflow and this variable explained a further 5.5% of the stemflow variation. Estimates of averaged lag time and drainage after rain cease for stemflow were 290 and 164 min, while estimates for throughfall were 60 and 104 min. respectively. The canopy saturation was estimated from continuous storms and showed a value of 0.6 mm. The trunk storage capacity was estimated at a value of 0.2 mm. The interception loss from the forest canopy was estimated in 18%. Interception loss was heighly correlated with rainfall characteristics such as duration and intensity.     

Physiological and morphological responses to nitrogen limitation in jack pine seedlings: potential implications for drought tolerance

The morphological and physiological responses to nitrogen (N) limitation in jack pine (Pinus banksiana Lamb.) seedlings were studied following the initiation of four different dynamic N treatments for six and 15 weeks. The N treatments produced needle N concentrations from 11 to 31 mg g^-1dry weight, and seven-fold difference in dry weight at 15 weeks. Low-N jack pine seedlings: 1) had an higher root/shoot ratio; 2) extended their tap root more rapidly; 3) were better able to maintain turgor when shoot water potential declined; and 4) had a larger dry weight fraction and apoplasmic fraction than seedlings with higher foliar N concentrations. These responses may contribute collectively to enhance drought tolerance in N-limited plants, thereby affecting seedling quality. Modifying nursery fertilization regimes, other than optimal as usually applied, may thus be needed to produce stock for use on particularly droughty sites. Knowledge of the nature of drought at a particular site could be an important consideration when making decisions related to fertilization.     

Physiological basis of wood production: A review

The theoretical background to wood production is outlined and the factual background is given by reviewing measured rates of wood production. It is recommended that differences in wood production be analysed, not by statistical methods, traditional growth analysis or by comprehensive models, but by using a ‘light use analysis’, where wood production is determined by (1) the amount of light intercepted by the canopy, (2) the light use efficiency, net of respiration, (3) the proportion of assimilates partitioned to wood, and (4) mortality losses. These four components are discussed.     

Plant species influence microbial diversity and carbon allocation in the rhizosphere

Plant species effects on microbial communities are attributed to changes in microbial community composition and biomass, and may depend on plant species specific differences in the quality of resources (carbon) inputs. We examined the idea that plant-soil feedbacks can be explained by a chance effect, which is the probability of a highly productive or keystone plant species is present in the community and will influence the functions more than the number of species per se. A ¹³C pulse labelling technique was applied to three plant species and a species mixture in a greenhouse experiment to examine the carbon flow from plants to soil microbial communities. The ¹³C label was given as CO₂ to shoots of a legume (Lotus corniculatus), a forb (Plantago lanceolata), a grass (Holcus lanatus) and a mixture of the three species. Microbial phospholipid fatty acids (PLFA) was analysed in order to determine the biomass and composition of the soil microbial community. The incorporation of the stable isotope into soil microorganisms was determined through GC-IRMS analyses of the microbial PLFAs. Plant species identity did not influence the microbial biomass when determined as total carbon of microbial phospholipid fatty acids. However, the labelled carbon showed that the grass monoculture (H. lanatus) and the plant mixture allocated more ¹³C into bacteria and actinomycete biomass than the other plant species. H. lanatus monocultures had also the highest amounts of ¹³C allocated to AM-fungi and saprophytic fungi. The carbon allocation from plants to soil microorganisms in a plant species mixture can thus be explained by the presence of a highly productive species that influence soil functions.     

Analysing land-cover changes in relation to environmental variables in Hesse,Germany

Land-use and land-cover changes affect ecological landscape functions and processes. Hence, landscape ecologists have a central interest in a comprehensive understanding of such changes. Our study focuses on the relationships between environmental conditions and agricultural land-cover changes. We present a method to (i) characterise the major spatial-temporal processes of land-cover changes, (ii) identify the correlations between environmental attributes and land-cover changes and (iii) derive potential environmental drivers of land-cover changes in a German marginal rural landscape. The method was applied to study land-cover dynamics from 1945 to 1998 in the districts of Erda, Steinbrücken and Eibelshausen, situated in the marginal rural landscape of the Lahn-Dill Highlands, Germany. We employed land-cover data gained by the interpretation of multi-temporal aerial photographs. Various environmental variables were introduced into the analyses. We identified physical landscape attributes (elevation, slope, aspect, available water capacity and soil texture) and structural landscape dimensions (patch size, patch shape and distance between patch and nearest settlement). With the aid of GIS, K-means partitioning and canonical correspondence analysis, we investigated land-cover trajectory types, land-cover transitions at individual time intervals and their relationships to these environmental variables. Our results show that, between 1945 and 1998, land-cover changes correlated with the physical attributes of the underlying landscape. On the other hand, the structural landscape dimensions correlated with land cover only in periods of minor land-cover changes (1972–98). Greater diversity of physical landscape attributes is correlated with greater land-cover dynamics. Besides the important influence of socio-economic factors, land-cover changes in the study areas took place within the relatively stable physical constraints of the underlying landscape.This revised version was published online in May 2005 with corrections to the Cover Date.