Effect of organic and inorganic nutrient sources on soil mineral nitrogen and maize yields in central highlands of Kenya

High population pressure in the central highlands of Kenya has led to continuous cultivation of land with minimal additional inputs leading to soil nutrient depletion. Research work has reported positive results from use of manure and biomass from Tithonia, Calliandra, Leucaena, Mucuna and Crotolaria for soil fertility replenishment. An experimental field was set up in Chuka Division to test different soil nutrient replenishment treatments. The experimental design was randomised complete block with 14 treatments replicated three times. At the beginning and end of the experiment, soil was sampled at 0–15 cm depth and analysed for pH, Ca, Mg, K, C, N and P. End of the 2000/2001 short rains (SR) season and 2001 long rains (LR) season, soil samples were taken at 0–30, 30–100 and 100–150 cm for nitrate and ammonium analysis. All the treatments received an equivalent of 60 kg N ha⁻¹, except herbaceous legume treatments, where N was determined by the amount of the biomass harvested and incorporated in soil and control treatment received no inputs. Results indicate soil fertility increased slightly in all treatments (except control) over the 2-year study period. Average maize grain yield across the treatments was 1.1, 5.4, 3.5 and 4.0 Mg ha⁻¹ during the 2000 LR, 2000/2001 SR, 2001 LR and 2001/2002 SR, respectively. The reduced yield in 2000 LR and 2001 LR are attributed to poor rainfall distribution during the two seasons. On average, Tithonia with half recommended rate of inorganic fertilizer recorded the highest (4.8 Mg ha⁻¹) maize yield followed by sole Tithonia (4.7 Mg ha⁻¹). Highest average concentration (144.8 and 115.5 kg N ha⁻¹) of mineral N was recorded at the 30–100 cm soil depth at the end of both 2000/2001 SR and LR, respectively. The lowest average concentration (67.1 kg N ha⁻¹) was recorded in the 100–150 cm soil depth in both seasons, while during the 2001 LR, the 0–30 cm soil depth recorded the lowest concentration (52.3 kg N ha⁻¹). The residual mineral N in the 100–150 cm soil depth doubled at the end of the LR 2001 compared to what was present and the end of the SR 2000/2001 season in all treatments. This shows that there is substantial amount of mineral N that is being leached below the rooting zone of maize in this region.     

两种轮枝菌对15种豆科牧草的致病性

 室内人工接种测定了两种轮枝菌3个菌株对15种豆科牧草的致病性,一个菌株是来自加拿大感病苜蓿上的Verticillium albo-atrum(Vaa),两个V.dahliae菌株中,Vd来自加拿大感病的马铃薯,CVd来自中国的沙打旺。两次试验结果表明,3个菌株对15种豆科牧草表现了不同程度的致病力。沙打旺、鹰嘴黄芪、紫花苜蓿、百脉根、埃及三叶草对3个菌株均感病,每次试验病株率都在50%以上。箭叶三叶草表现中等抗病,而白花草木樨、毛荚野豌豆、长柔毛野豌豆、波斯三叶草、杂三叶草、红三叶草和白三叶草等7种对3个菌株都表现抗病。红豆草对Vaa和CVd两个菌株感病,但抗Vd。山黛豆感染CVd,但抗Vaa和Vd。     

辽宁省凌源市豆科植物资源的开发及其利用

豆科植物抗逆性强,植物生长中与根瘤菌共生形成的根瘤,能将空气中的氮固定成氨,为宿主植物提供大量氮肥,可改良土壤和培肥地力,能创造较高生态和经济效益,实现对有限资源的高效利用和可持续发展。     

Co‐occurrence of organic and inorganic N influences asparagine uptake and amino acid profiles in white clover

Background : Direct plant uptake of organic nitrogen (N) may be important for plant N nutrition, but we lack knowledge of how the concentration and form of external N influence organic N uptake and plant N status. Aims : We investigated the uptake of the amino acid asparagine (Asn) in white clover in the presence of different inorganic, organic and total N concentrations. Methods : Actively N₂‐fixing white clover seedlings were for one week exposed to combinations of ${\mathrm{NO}}_3^{-}$ (3–30 µmol N kg^?1 sand DW) and Asn (3–30 µmol N kg^?1 sand DW), whereafter the Asn uptake rate was determined by addition of ¹³C₄‐Asn. Shoot and root amino acid profiles were also analyzed. Results : Increasing ${\mathrm{NO}}_3^{-}$ and total N concentrations decreased ¹³C₄‐Asn uptake rates and internal clover Asn content. In addition, total N and ${\mathrm{NO}}_3^{-}$ also affected amino acid profiles, with Asn, Asp, Glu, Gln, Cys, Gly, Pro, Ser, and Ala being more related to the low N doses, and Thr, Val, Ile, Leu, Phe, Tyr, Trp, and Met being more abundant at increasing N doses. Conclusions : Asn uptake rate in white clover is reduced by increasing inorganic N. Plant amino acid profiles are likely to be a more sensitive indicator of N supply.     

Influence of P Sources and Rhizobium Inoculation on Growth and Yield of Soybean Genotypes on Ferric Lixisols of Northern Guinea Savanna Zone of Ghana

Soybean is becoming an important cash crop in northern Ghana. Yet the yields are low due to use of low yielding varieties and limited use of inputs. Greenhouse and field experiments were carried out to evaluate the effects of two phosphorus (P) sources and Rhizobium inoculation on growth, nodulation, P uptake, and yield of three soybean genotypes on Ferric Lixisols of the Guinea savanna zone of Ghana. The P sources were triple superphosphate (TSP) and Morocco phosphate rock (MPR), while the genotypes were TGx 1448-2E, TGx 1904-6F, and TGx 1955-4F. The greenhouse experiment was conducted at the University of Ghana, Legon in a completely randomized design. The field experiment which was carried out in the Upper East region of Ghana was laid out in a split-split plot design with four replicates. In both the greenhouse and field experiments, application of TSP at 30 kg P ha^?1 resulted in significantly higher growth and P uptake in shoot compared with MPR and control. Soybean genotypes showed significant differences in growth, nutrient uptake, and grain yield in both the greenhouse and the field experiments. Rhizobium inoculation increased nodule number and dry weight but did not increase grain yield. The genotype TGx 1955-4F appears to show greater potential for increasing productivity of soybean in low P soils in northern Ghana.     

Role of sulfur nutrition in plant and seed metabolism of Glycine max L.

The aim of present investigation has been to explore the effect of sulfur application on plant metabolism, seed yield and seed quality in soybean. The sulfur was supplied in different doses ranging as 1, 2, 4, 6 and 8 meq S L^?1. Plant supplied with 4 meq S L^?1 showed optimal growth. Plant growth and dry matter was reduced under sulfur deficiency (1 and 2 meq S L^?1) and toxicity (6 and 8 meq S L^?1). Application of sulfur increases the tissue sulfur and cysteine concentration in both leaves and seeds. The critical concentration for deficiency (CCD) and toxicity (CCT) of sulfur was observed 0.194 to 0.277% dry weight respectively. Pod yield and seed yield was also suppressed in sulfur deficiency and toxicity. In leaves sugar (reducing, non-reducing and total sugar) and starch was found to be accumulated while in seeds both were depleted under sulfur deficiency and toxicty. Seed storage proteins (albumins, globulins, glutelins and prolamins) were also reduced under sulfur stress. Thus, we conclude that sulfur deficiency and toxicity both affects the plant metabolism, yield and seed quality in terms of carbohydrates and storage proteins of soybean.     

Distribution of arbuscular mycorrhizal fungi spores in soils of smallholder agroforestry and monocultural coffee systems in southwestern Ethiopia

Arbuscular mycorrhizal fungi (AMF) are associated with the root system of coffee (Coffea arabica L.) plants, but their distribution in smallholder agroforestry and monocultural coffee systems is not well known. This study investigates the spatial distribution of AMF spores in a field study in southwestern Ethiopia. Soil samples from different depths (0–50 cm) were collected under the tree canopies of Acacia abyssinica, Albizia gummifera, Ficus sur, Ficus vasta and randomly selected unshaded coffee plants at different sampling points (canopy base, radius, edge and outside canopy). Significantly higher AMF spore densities were recorded at canopy bases and at 0–30 cm soil depth. Spore populations were found to belong to five genera: Acaulospora, Entrophospora, Glomus, Gigaspora and Scutellospora, with Glomus and Acaulospora dominating. Sampling points, sites and depths, shade tree species and shade tree/coffee plant age affected AMF spore density. Agroforestry practices including the use of leguminous shade trees effectively maintained AMF numbers in soils even at depth compared with unshaded coffee plants (monocultures).     

新育牧草茎秆收获期力学特性与显微结构

为分析缠结牧草茎秆力学性能与显微结构的相互关系,进而指导牧草品种优育和设计开发新机具、新工艺提供理论依据,该文以2种新育品系低纤维苜蓿、直立型小冠花和对照品种甘农三号苜蓿、匍匐型小冠花结荚期底部茎秆为研究对象,在500 N微机控制电子万能试验机上测试了茎秆的拉伸和剪切应力-应变规律;试验观察了茎秆的微观组织结构,得到了茎秆扫描电镜下的解剖构造图像。研究表明：牧草茎秆是一种典型的多相、筛状、不连续、不均匀和各向异性的复合材料;同一品系不同品种牧草茎秆生物力学特性不同,其强度和刚度主要取决于各自机械组织的厚度、维管束的数量以及各组织及其细胞之间的连接形式和连接强度。4种牧草结荚期拉伸试验测得平均弹性模量分别是1427.3、673.0、1377.5、441.7 Mpa;30°滑切试验测得平均最大剪切力分别是96.24、60.9、124.1、84.4 N,2种新品系牧草结荚期茎秆均比对照品种刚度大,柔韧性小,需剪切力小,更易机械化收获。     

Impact of crop rotations on microbial biomass,faunal populations,and plant C and N in a Gray Luvisol (Typic Cryoboralf)

We studied the impact of continous barley and a 4-year rotation consisting of fababean, barley after fababean, barley intercropped with field pea, and barley after the intercrop on the soil biological properties of a Gray Luvisol. The crop rotations were estabilshed in 1988 and fertilizer N was not applied to any plots. The plots were sampled five times over the growing season in 1990. The average size of microbial N over the growing season was 20% greater when barley followed fababean or intercropping than in the fababean and intercropped plots. It was 14.9% greater when barley followed fababean or intercropping than in the continuous barley plots. Protozoa populations were greater when barley followed intercropping than in the continuous barley plots, but an inverse trend was found for nematode populations. Average size of the mineral N over the growing season in the 4-year rotation plots was 32% greater than in the continuous barley plots. It was also 23% greater when barley followed fababean or intercropping than in the fababean and intercropped plots. Plant N in the latter plots was significantly greater than in the former and in continuous barley plots; therefore legumes contributed N to the crop rotation through biological N fixation and addition of N-rich crop residues. Significantly higher mineral N and microbial N in the barley of rotation plots than in continuous barley plots indicate that rotation systems with annual legumes alter soil biological properties and N availability.     

四川攀西地区豆科蔬菜丛枝菌根真菌的初步研究

用湿筛倾析-蔗糖离心法分离土样中丛枝菌根真菌的孢子,并用形态学方法对其进行种类鉴定。研究结果显示,攀西地区的豆科蔬菜中共分离出2属9种丛枝菌根真菌,球囊霉属(Glomus)8种,G.luteum、G.mosseae、G.aggregatum、G.lamellosum、G.claroideum、G.etunicatum、G.intraradices、G.occultum;无梗囊霉属(Acaulospora)1种,A.delicata。丛枝菌根真菌与攀西豆科蔬菜的共生性良好,其种类较多,种群结构丰富。