Low Soil Nitrogen Research Articles

Combining ability and heterotic patterns of extra-early maturing white maize inbreds with genes from Zea diploperennis under multiple environments

Low soil nitrogen (Low N), Striga hermonthica and recurrent drought are major constraints to maize production and productivity in sub-Saharan Africa (SSA). Only a few extra-early maturing hybrids with combined tolerance to drought, Striga and low N have been commercialized in SSA. The objectives of the study were to determine the general combining ability (GCA) and specific combining ability (SCA) effects of grain yield and other traits, classify the inbreds into heterotic groups using the SCA effects of grain yield, and the heterotic group’s SCA and GCA of grain yield (HSGCA) methods, and examine the performance of hybrids under contrasting environments. Sixty-three extra-early white maize inbred lines containing genes from Zea diploperennis were crossed to four elite testers to obtain 252 single-cross hybrids and evaluated together with four checks at four locations for 2 years under drought, Striga-infested, low N and optimal environments in Nigeria. The GCA and SCA effects were significant (P ≤ 0.01) with preponderance of GCA over SCA effects for all measured traits indicating that additive genetic effects were predominant in the lines under all the contrasting environments. The HSGCA was more efficient than the SCA method in the classification of the inbreds into heterotic groups. The hybrids TZdEEI 74 × TZEEI 13 and TZdEEI 74 × TZEEI 29 were high yielding and most stable across research environments. These hybrids should be further evaluated in on-farm trials to confirm the consistency of performance for commercialization in SSA.

Selection and Bioassay of Azotobacter sp. Isolates to Improve Growth of Chili (Capsicum annum L.) on Entisols in Ambon

Leafy vegetables contributes to the inflation rate in Ambon City due to low productivity in rainy season. Some vegetables are imported from other islands while importantvegetables such as local petsai (Brassica chinensis L.) and chili (Capsicum annum L.) are cultivated in low nitrogen soil, Entisols. Lack of nitrogen could be overcome by using inorganic fertilizeras well as biofertilzer. The soil can be inoculated with rhizobacteria, such as Azotobacter, to increase the nitrogen uptake and improve the quality of vegetables. This research was conducted to isolate and select Azotobacter from rhizosphere of vegetables and to examine the effect of Azotobacter inoculation on chili-seedling growth and nitrogen uptake by using bioassay method. Azotobacter sp. was isolated in nitrogen-free Ashby’s Media. The bioassay was held in the green house with randomized block design experiment, which examined the combination of isolates and population of Azotobacter sp. on chili. Two best isolates which was selected based on pH, nitrogen content and cell viability were s2a10 (from petsai's rhizosphere) and c2a9 (from chili’s rhizosphere). Bioassay showed that Azotobacter inoculation followed by reduced NPK fertilizer doses had no effect on transplant dry weight and nitrogen uptake. All Azotobacter 8 -1inoculation except 10 CFU mL s2a10 maintain soil nitrogen although Azotobacter population in soil was slightly reduced. This showed that Azotobacter sp. potentially reduce the use of inorganic biofertilizer.

Gene action controlling grain yield and other agronomic traits of extra-early quality protein maize under stress and non-stress conditions

Extra-early quality protein maize (QPM) hybrids with combined tolerance to drought and low soil nitrogen (N) are crucial for reduced food insecurity and malnutrition in sub-Saharan Africa (SSA). Ninety six extra-early QPM single-crosses derived from 24 extra-early QPM inbreds using the North Carolina Design II plus four checks were evaluated under stress (drought and low-N) and non-stress environments in Nigeria, 2012 and 2013. The objectives were to (i) determine the gene action for grain yield and other agronomic traits in the QPM inbreds (ii) identify the best inbred testers across environments (iii) classify the inbreds into heterotic groups and (iv) evaluate the performance and stability of the hybrids. General combining ability (GCA) effects contributed more to the total variation among the hybrids for grain yield and most measured traits under each and across environments suggesting that additive gene effects were more important in the inheritance of the traits. The inbreds were classified into three heterotic groups. Inbreds TZEEQI 7 and TZEEQI 134 were the best testers while TZEEQI 7, TZEEQI 60, TZEEQI 61, TZEEQI 8, TZEEQI 11, TZEEQI 137, TZEEQI 63, TZEEQI 66, TZEEQI 44, and TZEEQI 157 possessed favorable alleles for stress tolerance and could be used for population improvement and development of stress tolerant hybrids. The hybrids TZEEQI 183 × TZEEQI 7, TZEEQI 181 × TZEEQI 7 and TZEEQI 144 × TZEEQI 183 were high yielding and the most stable across environments and should be tested extensively in on-farm trials and commercialized in the sub-region.

Heterotic Patterns of IITA and CIMMYT Early‐Maturing Yellow Maize Inbreds under Contrasting Environments

Drought and low soil nitrogen (low‐N) constitute major constraints to maize (Zea maysL.) production in West Africa (WA). The International Institute of Tropical Agriculture (IITA) and International Center for Maize and Wheat Improvement (CIMMYT) have developed drought and low‐N tolerant inbreds for Africa. Combinations between selected IITA and CIMMYT inbreds could produce outstanding hybrids. Diallel crosses of 12 IITA and five CIMMYT early yellow inbreds plus four checks were evaluated under drought, low‐N and optimal conditions at four locations in Nigeria for 2 yr. The objectives were to examine the combining ability of the inbreds for grain yield and other traits, classify the lines into heterotic groups, identify best testers under the contrasting environments, assess genotype × environment interactions and evaluate the yield performance and stability of single‐cross hybrids. Grouping of the inbred lines was done with heterotic group's specific combining ability (SCA) and general combining ability (GCA) (HSGCA), single nucleotide polymorphism based genetic distance (SNP‐GD) and GCA effects of multiple traits (HGCAMT) methods. The GCA mean squares for all traits were greater than SCA mean squares in all environments. The inbreds were classified into four heterotic groups each across environments by HSGCA and SNP‐GD while HGCAMT method placed them into three groups. HGCAMT was the most efficient followed by HSGCA and then SNP‐GD method. The HGCAMT identified inbreds ENT 17, ENT 15, and ENT 8 as best testers for heterotic Groups 1, 2, and 3. Hybrids TZEI 17 × ENT 15, and TZEI 149 × ENT 15 were outstanding across environments.Core IdeasSeventeen inbreds from CIMMYT and IITA were classified into four heterotic groups each across environments by HSGCA and SNP‐GD while HGCAMT method placed them into three groups.The HGCAMT is the most efficient heterotic grouping method and offers a great opportunity for grouping IITA inbreds that are yet to be grouped.The HGCAMT identified inbreds ENT 17, ENT 15, and ENT 8 as best testers for heterotic Groups 1, 2, and 3, across environments.ENT13, TZEI 17, and TZEI 16 may provide genes for drought and low‐N tolerance for broadening and diversifying genetic base of germplasm and to develop hybrids adapted to sub‐Saharan Africa.Planned crosses involving IITA and CIMMYT inbreds could produce outstanding hybrids for commercialization in SSA.

Estimation of phenotypic variability in symbiotic nitrogen fixation ability of common bean under drought stress using 15N natural abundance in grain.

Common bean (Phaseolus vulgaris L.) is the most important food legume, cultivated by small farmers and is usually exposed to unfavorable conditions with minimum use of inputs. Drought and low soil fertility, especially phosphorus and nitrogen (N) deficiencies, are major limitations to bean yield in smallholder systems. Beans can derive part of their required N from the atmosphere through symbiotic nitrogen fixation (SNF). Drought stress severely limits SNF ability of plants. The main objectives of this study were to: (i) test and validate the use of 15N natural abundance in grain to quantify phenotypic differences in SNF ability for its implementation in breeding programs of common bean with bush growth habit aiming to improve SNF, and (ii) quantify phenotypic differences in SNF under drought to identify superior genotypes that could serve as parents. Field studies were conducted at CIAT-Palmira, Colombia using a set of 36 bean genotypes belonging to the Middle American gene pool for evaluation in two seasons with two levels of water supply (irrigated and drought stress). We used 15N natural abundance method to compare SNF ability estimated from shoot tissue sampled at mid-pod filling growth stage vs. grain tissue sampled at harvest. Our results showed positive and significant correlation between nitrogen derived from the atmosphere (%Ndfa) estimated using shoot tissue at mid-pod filling and %Ndfa estimated using grain tissue at harvest. Both methods showed phenotypic variability in SNF ability under both drought and irrigated conditions and a significant reduction in SNF ability was observed under drought stress. We suggest that the method of estimating Ndfa using grain tissue (Ndfa-G) could be applied in bean breeding programs to improve SNF ability. Using this method of Ndfa-G, we identified four bean lines (RCB 593, SEA 15, NCB 226 and BFS 29) that combine greater SNF ability with greater grain yield under drought stress and these could serve as potential parents to further improve SNF ability of common bean.

Functional Role of Bacteria from Invasive Phragmites australis in Promotion of Host Growth.

We hypothesize that bacterial endophytes may enhance the competitiveness and invasiveness of Phragmites australis. To evaluate this hypothesis, endophytic bacteria were isolated from P. australis. The majority of the shoot meristem isolates represent species from phyla Firmicutes, Proteobacteria, and Actinobacteria. We chose one species from each phylum to characterize further and to conduct growth promotion experiments in Phragmites. Bacteria tested include Bacillus amyloliquefaciens A9a, Achromobacter spanius B1, and Microbacterium oxydans B2. Isolates were characterized for known growth promotional traits, including indole acetic acid (IAA) production, secretion of hydrolytic enzymes, phosphate solubilization, and antibiosis activity. Potentially defensive antimicrobial lipopeptides were assayed for through application of co-culturing experiments and mass spectrometer analysis. B. amyloliquefaciens A9a and M. oxydans B2 produced IAA. B. amyloliquefaciens A9a secreted antifungal lipopeptides. Capability to promote growth of P. australis under low nitrogen conditions was evaluated in greenhouse experiments. All three isolates were found to increase the growth of P. australis under low soil nitrogen conditions and showed increased absorption of isotopic nitrogen into plants. This suggests that the Phragmites microbes we evaluated most likely promote growth of Phragmites by enhanced scavenging of nitrogenous compounds from the rhizosphere and transfer to host roots. Collectively, our results support the hypothesis that endophytic bacteria play a role in enhancing growth of P. australis in natural populations. Gaining a better understanding of the precise contributions and mechanisms of endophytes in enabling P. australis to develop high densities rapidly could lead to new symbiosis-based strategies for management and control of the host.

Linking dominant Hawaiian tree species to understory development in recovering pastures via impacts on soils and litter

AbstractLarge areas of tropical forest have been cleared and planted with exotic grass species for use as cattle pasture. These often remain persistent grasslands after grazer removal, which is problematic for restoring native forest communities. It is often hoped that remnant and/or planted trees can jump‐start forest succession; however, there is little mechanistic information on how different canopy species affect community trajectories. To investigate this, I surveyed understory communities, exotic grass biomass, standing litter pools, and soil properties under two dominant canopy trees—Metrosideros polymorpha (‘ōhi‘a) and Acacia koa (koa)—in recovering Hawaiian forests. I then used structural equation models (SEMs) to elucidate direct and indirect effects of trees on native understory. Native understory communities developed under ‘ōhi‘a, which had larger standing litter pools, lower soil nitrogen, and lower exotic grass biomass than koa. This pattern was variable, potentially due to historical site differences and/or distance to intact forest. Koa, in contrast, showed little understory development. Instead, data suggest that increased soil nitrogen under koa leads to high grass biomass that stalls native recruitment. SEMs suggested that indirect effects of trees via litter and soils were as or more important than direct effects for determining native cover. It is suggested that diverse plantings which incorporate species that have high carbon to nitrogen ratios may help ameliorate the negative indirect effects of koa on natural understory regeneration.

Suppression of Phytophthora Blight in Sweet Pepper Depends on Biochar Amendment and Soil Type

Phytophthora blight has become one of the most serious threats to the vegetable industry. Managing this disease is challenging, because the oomycete pathogen responsible, Phytophthora capsici, can move rapidly through crop fields, has a wide host range, is resistant to many commonly used fungicides, and produces resilient spores that can survive in soil for up to 10 years. Recent studies have demonstrated that biochar amendments can suppress infection by many soil-borne pathogens—indicating that these amendments could have the potential to help control phytophthora blight. In this study, greenhouse trials were conducted to determine whether two commercially available biochar amendments could suppress P. capsici infection in sweet bell pepper (Capsicum annuum) using three naturally infested field soils. Soil biological and chemical assays were conducted to evaluate whether potential changes induced by biochar amendments were correlated with suppressive activity. Amending soil with a biochar product that included a proprietary mix of beneficial microorganisms and enriched substrates resulted in lower soil P. capsici abundance in all soils, and lower percent root infection in two of the soils tested. This product also resulted in higher soil pH, and lower soil nitrogen availability and leaf chlorophyll content. The other biochar product did not suppress P. capsici, and had few effects on soil chemical and biological properties. Results of this study indicate that some commercially available biochar amendments have the potential to help mediate phytophthora blight, but further trials are needed to confirm that suppressive effects will be observed in field trials. Additional research is also recommended to identify the mechanisms regulating biochar-mediated suppression of phytophthora blight to develop products that can reliably suppress soil-borne diseases in the field.

Aboveground insect herbivory increases plant competitive asymmetry, while belowground herbivory mitigates the effect.

Insect herbivores can shift the composition of a plant community, but the mechanism underlying such shifts remains largely unexplored. A possibility is that insects alter the competitive symmetry between plant species. The effect of herbivory on competition likely depends on whether the plants are subjected to aboveground or belowground herbivory or both, and also depends on soil nitrogen levels. It is unclear how these biotic and abiotic factors interactively affect competition. In a greenhouse experiment, we measured competition between two coexisting grass species that respond differently to nitrogen deposition: Dactylis glomerata L., which is competitively favoured by nitrogen addition, and Festuca rubra L., which is competitively favoured on nitrogen-poor soils. We predicted: (1) that aboveground herbivory would reduce competitive asymmetry at high soil nitrogen by reducing the competitive advantage of D. glomerata; and (2), that belowground herbivory would relax competition at low soil nitrogen, by reducing the competitive advantage of F. rubra. Aboveground herbivory caused a 46% decrease in the competitive ability of F. rubra, and a 23% increase in that of D. glomerata, thus increasing competitive asymmetry, independently of soil nitrogen level. Belowground herbivory did not affect competitive symmetry, but the combined influence of above- and belowground herbivory was weaker than predicted from their individual effects. Belowground herbivory thus mitigated the increased competitive asymmetry caused by aboveground herbivory. D. glomerata remained competitively dominant after the cessation of aboveground herbivory, showing that the influence of herbivory continued beyond the feeding period. We showed that insect herbivory can strongly influence plant competitive interactions. In our experimental plant community, aboveground insect herbivory increased the risk of competitive exclusion of F. rubra. Belowground herbivory appeared to mitigate the influence of aboveground herbivory, and this mechanism may play a role for plant species coexistence.

Inoculated Soybean Yields Response to Nitrogen and Phosphorus Application

Inherent low soil nitrogen (N) and phosphorus (P) is one of the major hindrances of increased soybean productivity in Malawian soils. Although, inoculation of legumes with rhizobia, has been advocated for decades as a way of boosting leguminous crops’ productivity through biological nitrogen fixation (BNF), the effectiveness of this strategy, has been low. An experiment was carried out to investigate the effect of the application of small doses of N and P to inoculated soybean. It was laid out in a complete block design (CBD) replicated three times and the treatments included: 1. Soybean only, 2. Inoculated soybean, 3. Inoculated soybean + 30 kg N ha -1 , 4. Inoculated soybean + 30 kg N ha + 25 kg P ha, 5. Inoculated soybean + 30 kg N ha + 35 kg P ha. The soybean in all treatment plots except for treatment 1 was inoculated with 30 kg N ha -1 applied as urea to treatment plots 3, 4 and 5. Phosphorus as TSP was applied to treatment 4 and 5 at the rate of 25 and 35 kg P ha -1 . Data collected included; selected soil physical and chemical properties, Original Research Article Phiri et al.; IJPSS, 10(5): 1-7, 2016; Article no.IJPSS.24905 2 biomass and pod yields. Data obtained were subjected to Analysis of Variance (ANOVA) using the GenStat statistical package and treatment effects tested for significance using the F-test at 5% level of significance. Means were separated using the least significant difference (P<0.05). Results indicate that inoculating soybean with rhizobia and inoculating soybean with rhizobia plus applying 30 kg N ha -1 did not significantly increase biomass yields. However, inoculating soybean plus the combined application of 30 kg N ha and, 25 kg P ha or / and 35 kg P ha increased the soybean biomass yields by 54% and 70% respectively above control. The lack of significant response when N was applied without P points to the significant role played by phosphorus in root development and energy transfer processes within the plant. Effective nodulation, however, was significantly higher (p<0.05) above the control where inoculation was combined with the application of 30 kg N ha and 35 kg P ha, hence underlining the role played by phosphorus in nodule development and the role of starter N in soils low in N.

N-fluxes and N-turnover in a mixed beech–pine forest under low N-inputs

Within the framework of the International Cooperative Programme on Integrated Monitoring (ICP IM), nitrogen pools and fluxes and their balance were determined for the German Integrated Monitoring (IM) site, Neuglobsow, characterized by very low soil nitrogen. From 1998 to 2013, total nitrogen (N) deposition in form of ammonium and nitrate was 6.80 ± 1.36 and 6.46 ± 1.09 kg N ha−1 year−1, respectively (in total 13.26 ± 2.01 kg N ha−1 year−1). Meanwhile, the average gaseous loss was 0.7 kg N ha−1 year−1 and the leaching loss was 2.38 kg N ha−1 year−1. Since the remaining atmospheric net N-inputs (10.18 kg N ha−1 year−1) exceeds plant uptake (8.36 kg N ha−1 year−1), there is a nitrogen surplus of 1.82 kg N ha−1 year−1. This surplus and the accelerated mineralization of the soil organic matter which was stored during the decades before the study began when temperatures were slightly cooler, combined with low leaching rates, explain the high nitrogen supply found in the leaves and needles. However, with decreasing nitrogen deposition, biomass export and with air temperatures rises expected the ecosystem N-supply will likely decline in the long run.

Effects of NPK Single Fertilizers on Relative Growth Performances of Two Cycles of Maize (Zea mays L.) Grown in a Degraded Soil of Southwest Nigeria

A B S T R A C T The balanced use of inorganic amendments to enhance effective crop production for developing world economies like Nigeria is paramount to achieve her Millennium Development Goals (MDGs) for its teeming population. Thus this study was carried out to assess the relative growth performances of a major food crop under different regimes of fertilizer application. Field and Green House experiments were carried out to assess the relative growth performances of two Cycles of Zea mays L. (LNTP-W C0 and C3) used as test crops for the amendment of degraded soil using N, P and K single fertilizers. The single fertilizers (treatments) used were Urea, Single Super Phosphate (SSP) and Muriate of Potash and the study was carried out in the Department of Botany, University of Ibadan, Nigeria. The experiment consisted of 4 treatments applied at 2 levels (C0 and C3) and replicated three times in a Completely Randomized Design (CRD) to give a total of 48 experimental units. The application of Nitrogen (N) was done at four levels (0, 30, 60 and 90 kg haG 1 ), while the Phosphorous (P 2 O 5 ) and Potassium (K) were applied at a constant rate of about 60 kg haG 1 for all the pots except for the experimental control pots. The design was adopted for both Green House and Field experiments. The results from the study showed that C3 performed better than C0 in Field and Green House experiments with respect to their relative performances of the growth parameters; plant height (cm), stem diameter (mm), number of leaves, leaf length (cm) and leaf width (cm) measured within the Pre-flowering period of 8 weeks. The treatment combination of 90 kg haG 1 N, 60 kg haG 1 P and 60 kg haG 1 K gave the best performance in this study. The study also revealed that the growth rate of the maize plant was directly proportional to the level of N applied with constant levels of P and K providing the basis for developing optimum NPK fertilizer level for the amendment of degraded soil for higher productivity using maize with tolerance to low soil Nitrogen. The study showed that more derelict soils can be put to good use with the appropriate level of NPK Fertilizer application optimum for the right crop, thus aiding the use of hitherto abandoned degraded land and putting more land under cultivation.

Functional role of an endophytic Bacillus amyloliquefaciens in enhancing growth and disease protection of invasive English ivy (Hedera helix L.)

We hypothesize that invasive English ivy (Hedera helix) harbors endophytic microbes that promote plant growth and survival. To evaluate this hypothesis, we examined endophytic bacteria in English ivy and evaluated effects on the host plant. Endophytic bacteria were isolated from multiple populations of English ivy in New Brunswick, NJ. Bacteria were identified as a single species Bacillus amyloliquefaciens. One strain of B. amyloliquefaciens, strain C6c, was characterized for indoleacetic acid (IAA) production, secretion of hydrolytic enzymes, phosphate solubilization, and antibiosis against pathogens. PCR was used to amplify lipopeptide genes and their secretion into culture media was detected by MALDI-TOF mass spectrometry. Capability to promote growth of English ivy was evaluated in greenhouse experiments. The capacity of C6c to protect plants from disease was evaluated by exposing B+ (bacterium inoculated) and B− (non-inoculated) plants to the necrotrophic pathogen Alternaria tenuissima. B. amyloliquefaciens C6c systemically colonized leaves, petioles, and seeds of English ivy. C6c synthesized IAA and inhibited plant pathogens. MALDI-TOF mass spectrometry analysis revealed secretion of antifungal lipopeptides surfactin, iturin, bacillomycin, and fengycin. C6c promoted the growth of English ivy in low and high soil nitrogen conditions. This endophytic bacterium efficiently controlled disease caused by Alternaria tenuissima. This study suggests that B. amyloliquefaciens plays an important role in enhancing growth and disease protection of English ivy.

Microbial activity is not always limited by nitrogen in Arctic tundra soils

Both primary productivity and decomposition appear to be limited by low soil nitrogen (N) availability throughout much of the Arctic tundra active growing season, making these ecosystems among the most N-limited in the world. Climate warming may potentially stimulate microbial activities such as N mineralization, which could have cascading long-term effects on Arctic tundra ecosystems. Despite previous evidence of N limitation to microbial decomposition in Arctic tundra, N may not limit microbial activity throughout the entire active season. Labile carbon (C) may be co-limiting for portions of the active season when there is relatively high inorganic N and/or low labile C availability. To assess seasonal variation in the controls on microbial activity, we conducted a series of laboratory incubations with soils collected at the beginning and peak of the active season in two years to examine intra-seasonal and annual variability of soil microbial N limitation in an Arctic moist acidic tundra (MAT) soil. The soil incubations were set-up in a factorial design with treatments of added N or DI water as a control and incubation temperatures of 5 °C and 15 °C. We measured chloroform-labile C and N (as a proxy for microbial biomass), extractable nutrients, C-mineralization and potential enzyme activities. In contrast to previous studies, we found that these metrics of microbial activity were not consistently stimulated by N additions; rather, added N was primarily immobilized by microbes resulting in decreased chloroform-labile C:N ratios. Stimulation of C mineralization by N addition was short-lived and variable between our two sampling dates within a single active season. Additionally, there were differences in temperature sensitivities of C mineralization and contrasting effects of N amendment on enzyme activities between the two study years. These findings suggest that, at times, other factors co-limit microbial activities in MAT soils. The current dogma of universal N-limitation to microbial activity may need to be refined in light of these results, to more accurately predict the fate of the large amounts of C currently sequestered in Arctic tundra soils.

Carbon allocation, nodulation, and biological nitrogen fixation of black locust (Robinia pseudoacacia L.) under soil water limitation

The pioneer tree black locust (Robinia pseudoacacia L.) is a drought-resistant tree and, in symbiosis with Rhizobium, able to fix dinitrogen from the atmosphere. It is, therefore, an interesting species for marginal lands where soil amelioration is sought in addition to economic gain. However, the interaction between soil water availability, carbon allocation and nitrogen fixation is important for a successful establishment of trees on marginal lands and has not yet been investigated for black locust. Twoyear-old trees were grown under various soil water conditions and drought cycles. The stable isotopic composition of C (δ 13C) and N (δ 15N) of the leaves was used to identify i) the effective drought condition of the treatments and ii) the portion N accrued from the atmosphere by the biological nitrogen fixation. Drought-stressed plants significantly reduced their total aboveground biomass production, which was linearly linked to tree transpiration. The shoot:root ratio values changed from 2.2 for the drought-stressed to 4.3 for the well-watered plants. Our investigation shows that drought stress increases the nodule biomass of black locust in order to maintain biological nitrogen fixation and to counteract the lower soil nitrogen availability. The biological nitrogen fixation of drought-stressed trees could be maintained at relatively higher values compared to the well-watered trees. The average leaf nitrogen content varied between 2.8% and 3.0% and was not influenced by the drought stress. Carbon fixation, carbon allocation, and biological nitrogen fixation are to some extent balanced at low irrigation and allow Robinia to cope with long-term water constraints. The combination of black locust’s ecophysiological and morphological plasticity make it interesting as a biomass source for bioenergy and timber production, even in nutrient-limited and drought-affected areas of Europe.

Heterotic responses among crosses of IITA and CIMMYT early white maize inbred lines under multiple stress environments

Two major constraints militating against the achievement of food security in West Africa (WA) are recurrent drought and poor soil fertility. Seventeen early maturing maize inbreds from IITA and CIMMYT were used as parents to produce 136 diallel crosses which were evaluated along with four checks in contrasting environments at four locations for 2 year in Nigeria. The objectives of the study were to (i) examine the combining ability of the lines under drought, low soil nitrogen (low N), optimal and across environments; (ii) classify the inbreds into heterotic groups using the specific combining ability (SCA) effects of grain yield, heterotic group’s specific and general combining ability (HSGCA), the heterotic grouping based on general combining ability (GCA) of multiple traits (HGCAMT) and the molecular-based genetic distance methods; (iii) compare the efficiencies of the four heterotic grouping methods in classifying the inbreds and identifying the best testers; and (iv) examine the performance of the inbreds in hybrid combinations across environments. Sum of squares for GCA of inbreds for grain yield and other measured traits were larger than those of the SCA in all environments. The relative importance of GCA to SCA effects for grain yield and other traits increased from stress to nonstress environments with the additive genetic effects accounting for the major portion of the total genetic variation under all research environments. The HSGCA method classified the lines into three groups and was the most efficient because it had the highest breeding efficiency (40 %) in the test environments followed by the HGCAMT, SNP marker-based and the SCA effects of grain yield methods. Inbred TZEI 19 was identified as the best tester across research environments based on HSGCA method. Hybrids ENT 11 × TZEI 19 and TZEI 1 × TZEI 19 were the most outstanding and should be tested extensively in on-farm trials and commercialized.

Gains in Grain Yield of Early Maize Cultivars Developed During Three Breeding Eras under Multiple Environments

ABSTRACTMaize (Zea maysL.), an important staple crop in West and Central Africa (WCA), has enormous potential to reduce food insecurity in this subregion. Research covering three periods or eras of breeding has been conducted to develop cultivars resistant/tolerant to three maize stress factors:Strigaparasitism, drought, and low soil nitrogen. A study was conducted under optimal or natural growing environments at 35 locations in WCA for 2 yr to determine genetic improvement in grain yield of the maize cultivars developed during the three breeding periods: 1988–2000 (period 1), 2001–2006 (period 2), and 2007–2010 (period 3). The average rate of increase in grain yield under optimum growing conditions was 40 kg ha−1yr−1with a genetic gain of 1.3% yr−1, which was slightly higher than the gain of 30 kg ha−1yr−1, an annual genetic gain of 1.2% across 16 stress environments. It was concluded that substantial improvement in the yield potential of early maize under relatively nonstress environmental conditions has been made in this subregion by breeding for stress tolerance during the past three decades. The varieties EV DT‐W 2008 STR, 2009 DTE‐Y STR Syn, and TZE‐W DT C2 STR, all from the latest era of improvement, were identified as the highest yielding and most stable cultivars and should be promoted to contribute to food security in this subregion.

Genetic Analysis of Grain Yield of IITA and CIMMYT Early‐Maturing Maize Inbreds underStriga‐Infested and Low–Soil‐Nitrogen Environments

ABSTRACTBreeding maize (Zea maysL.) hybrids resistant toStrigaand tolerant to low soil nitrogen (low‐N) will reduce grain yield losses due to stresses in West Africa (WA). Studies were conducted to determine if selection forStrigaresistance and/or drought tolerance in early‐maturing maize populations improved low‐N tolerance in hybrids derived from selected inbreds from International Institute of Tropical Agriculture (IITA) and International Centre for Maize and Wheat Improvement (CIMMYT) underStriga‐infested, low‐N and optimum environments in Nigeria. One hundred and fifty hybrids developed from crosses involving 30 lines using North Carolina Design II plus six checks were evaluated at two locations each under low‐N, artificialStrigainfestation, and optimum environments for 2 yr. Lines with combined resistance or tolerance toStrigaas well as low‐N were identified.Striga‐resistant– as well as low‐N–tolerant hybrids with outstanding performance under both stress environments could be obtained through the accumulation of favorable alleles for resistance or tolerance in both parental lines. Although selection forStrigaresistance and/or drought tolerance resulted in improved performance of genotypes under low‐N, it is important to test genotypes under low‐N to identify those with outstanding performance under the target stress. ENT 11 × TZEI 4 and TZEI 65 × ENT 11 were identified as the most stable and high‐yielding hybrids.

Evaluation of Different Improved Upland Rice Varieties for Low Soil Nitrogen Adaptability

Scarcity of nitrogen fertilizer is a major constraint to rice production particularly in developing countries. Low soil fertility prevalent in farmer’s fields has led to low rice yields and the ever escalating fertilizer prices have made this important input unaffordable to most smallholder farmers who have limited resources for purchasing the required inputs. The Mwea Upland rice (MWUR) varieties were bred under low fertilizer input environment while other authors have indicated that the New Rice for Africa (NERICA) gives high yields under low input conditions. There is therefore need to identify the superior rice varieties that are adaptable to low nitrogen levels. Thus, the objective of this study was to investigate the effects of different rates of nitrogen fertilizer on improved upland rice varieties and identify the low input adaptable varieties. Field studies were conducted at Alupe in Western Kenya under rainfed upland conditions between August 2012 and April 2013. The experiment layout was split plot factorial in a Randomized Complete Block Design with three replicates. The main plot treatments were four rates of nitrogen fertilizer levels which were; 0 (control), 40, 80 and 120 kg ha-1 applied as calcium ammonium nitrate (26% N) in two equal splits; 21 days after sowing (DAS) and at panicle initiation (46 DAS). Sub-plots consisted of Original Research Article Sikuku et al; IJPSS, 5(1): 40-49, 2015; Article no.IJPSS.2015.058 41 four MWUR varieties namely MWUR 1, MWUR 2, MWUR 3, MWUR 4; and four NERICA varieties namely NERICA 1, NERICA 4, NERICA 10 and NERICA 11. The parameters measured included plant height, tiller number, filled grain ratio percentage and yield components. In the study, nitrogen treatment showed significant effect on plant growth and the measured parameters increased significantly with increase in nitrogen level. MWUR varieties studied were more adaptable to low nitrogen conditions as compared to NERICA varieties. The NERICA varieties recorded higher yield at high nitrogen levels as compared to MWUR varieties. However, NERICA 4 gave higher yield as compared to other NERICA varieties regardless of the nitrogen level. Results from our study suggest that MWUR 1 and 2 and NERICA 4 were more tolerant to low nitrogen as compared to MWUR 3 and 4 and NERICA 1, 10 and 11, because of higher height, more tiller number, higher filled grain ratio percentage and higher yield component as compared to the other studied varieties and may be suitable for soils low in nitrogen.

Post-wildfire soil and plant foliar nutrient ratios and soil fungi : bacterial ratios in alpine meadows on the southeastern Qinghai-Tibet Plateau

Wildfire is increasingly considered as a common ecological phenomenon in grassland. However, little is known about its effects on soil and plant nutrient ratios, especially in alpine ecosystems where wildfires are common. In the present study, nutrient ratios of the post-wildfire surface soil (0–5 cm) and nine dominant plant species leaves, in addition to soil fungi : bacterial ratios (F : B ratios), were investigated in the alpine meadows on the south-eastern Qinghai-Tibet Plateau, approximately 20 months after a high-severity wildfire. The results indicated that the burned sites had lower soil nitrogen : phosphorus (N : P) and nitrogen : potassium (N : K) ratios compared with unburned sites. Moreover, foliar N concentrations were lower on burned than unburned sites, but foliar N : P ratios were not different. Compared with the unburned sites, greater foliar K concentrations and lower N : K ratios were observed in burned sites. The idiosyncratic responses of foliar nutrient ratios to wildfire varied greatly, especially N and related nutrient ratios with plant species. Soil F : B ratios were positively correlated with soil C : N and C : P ratios, whereas they were negatively correlated with soil N : P and N : K ratios. The results of the present study suggest that there is reduced supply capacity of soil N for plants relative to soil P and K in the post-fire alpine meadow, which could have potential ecological implications in this region.