Effects of organic and mineral fertilizer inputs on maize yield and soil chemical properties in a maize cropping system in Meru South District, Kenya

Soil nutrient depletion as a result of continuous cultivation of soils without adequate addition of external inputs is a major challenge in the highlands of Kenya. An experiment was set up in Meru South District, Kenya in 2000 to investigate the effects of different soil-incorporated organic (manure, Tithonia diversifolia, Calliandra calothyrsus, Leucaena leucocephala) and mineral fertilizer inputs on maize yield, and soil chemical properties over seven seasons. On average, tithonia treatments (with or without half recommended rate of mineral fertilizer) gave the highest grain yield (5.5 and 5.4 Mg ha⁻¹ respectively) while the control treatment gave the lowest yield (1.5 Mg ha⁻¹). After 2 years of trial implementation, total soil carbon and nitrogen contents were improved with the application of organic residues, and manure in particular improved soil calcium content. Results of the economic analysis indicated that on average across the seven seasons, tithonia with half recommended rate of mineral fertilizer treatment recorded the highest net benefit (USD 787 ha⁻¹) while the control recorded the lowest (USD 272 ha⁻¹). However, returns to labor or benefit-cost ratios were in most cases not significantly improved when organic materials were used.     

Changes in mineral nitrogen, phosphorus availability and salt-extractable aluminium following the application of green manure residues in two weathered soils of South Vietnam

Phosphorus deficiency and aluminium toxicity in weathered soils can be amended by applying organic residues. Nitrogen mineralization, changes in P-availability and changes in salt-extractable Al following the incorporation of residues of various green manures (Flemingia congesta, Mucuna pruriens, Pueraria phaseoloides, Tithonia diversifolia) were quantified in a field core incubation experiment. Dried residues were added at an application rate of 45 kg P ha⁻¹ to two soils representative for the main soil groups of the South Vietnamese uplands, set up in incubation cores in an experimental field near Ho Chi Minh City, Vietnam.Decomposition of the residues proceeded at high rates. Mineralized nitrogen from the residues was recovered mainly as ammonium during the first 2 weeks of incubation. Nitrogen release from Tithonia residues with the highest lignin content and lignin:N ratio occurred more gradually compared to the three legumes. Resin-extractable P was significantly increased by residue treatments. Largest and sustained increases in resin-extractable P (0.67 and 2.06 mg P kg⁻¹ in the two soils) were observed in samples amended with Tithonia, which was related to the large P-content (0.37%) and small C:P ratio (110) of the residues. The P-concentration in the residues, rather than the total amount of P applied through the residues, affected the increase in P-availability. The increase in resin-extractable P was correlated to the P-content (R=0.64) and C:P ratio (R=−0.65) of the residues. Salt-extractable Al-concentrations were considerably reduced by the organic amendments, up to 70 and 50% in the two soils. At the rate of 45 kg P ha⁻¹, no significant differences between the residue treatments to reduce soil acidity were observed.As such, the application of high quality residues that are rich in P, in particular T. diversifolia, may enhance crop production by creating favourable soil conditions during the initial stages of plant development of the main crop.     

箭胡毛杨组培繁殖技术的研究

采用箭胡毛杨幼叶作为外植体进行组织培养,以MS为基本培养基获得了再生植株。从IAA与6-BA间进行的9个正交试验中,选择出适宜脱分化培养基MS+6-BA 0.5 mg/L+IAA 0.1 mg/L,对箭胡毛杨愈伤组织诱导率为90 %;种生长素与6-BA 配比的再分化培养基中,1/2 MS +IAA 0.1 mg/L+6-BA 0.1 mg/L对不定芽的分化诱导率可达到67.1 %;MS+6-BA 0.5 mg/L+NAA 0.01 mg/L的培养基可使单芽直接增殖出5.6个芽。在MS+IAA 0.8 mg/L的生根培养基上,试管苗的生根率可达82.6 %。     

Maize Yields as Affected by Short- and Long-Term Improved Fallows: A Comparative Analysis in the Asian Humid Tropics

Improved short‐ or long‐term fallows are considered suitable low external input technologies for maintaining productivity and sustainability of tropical smallholder upland cropping units, although comparisons on the benefits of this technology are not widely reported. A field study evaluated the impact of improved short (6 months) and long‐term fallow (18 months) using Crotalaria juncea and Tithonia diversifolia, in relation to a natural fallow of the same durations, on the productivity of maize (Zea mays), the most important upland cereal in tropical Asia, over a minor season. The use of improved fallows, especially Tithonia, increased maize yields over the Crotalaria or natural fallow. While the overall yields of maize after a long fallow were greater, the beneficial impact of the green manures was significantly higher in the short fallows. The causal factors for this trend, including biomass production of the improved fallows and possible impact on soils, along with the greater benefits of short‐term fallows for increasing maize yields in the tropics due to lower requirements of unproductive time are presented.     

不同浓度生根粉对胡杨硬枝扦插的影响

通过在数显控温仪调控地温度条件下,ABT1号和ABT2号生根粉不同浓度处理对胡杨硬枝扦插的生根效果影响是显著的,尤其可以显著提高生根率,且在400 mg/kg的浓度处理2 h的生根率最高。2种生根粉处理对成活率影响显著,且ABT1号处理的平均成活率最高,达到42.1%。     

Composted shrub-prunings and other organic manures for smallholder farming systems in southern Rwanda

Organic manures are the primary source of crop nutrients in many African farming systems. The quantity of such materials that are available on farms and their quality are therefore important issues, especially in countries with limited land resources, such as Rwanda. In this study, different types of compost (including composted shrub-prunings) were compared with farmyard manure (FYM) and green manure (Calliandra calothyrsus) using beans (Phaseolus vulgaris) as test crops. The study confirmed the farmers’ general opinion that FYM has high manurial value for crop yields. Composts with P- and Ca-rich Tithonia diversifolia prunings were of similar quality as FYM or dung composts and had a higher fertilizer value than Calliandra ‘green manure’ (biomass transfer). However, the farmers’ perception of trees and shrubs as biomass and nutrient sources is still very low in Rwanda. This revised version was published online in August 2006 with corrections to the Cover Date.     

Allelopathic activity of Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray] in soil under natural field conditions and different moisture conditions

The allelopathic activity of Mexican sunflower [ Tithonia diversifolia (Hemsl.) A. Gray] in soil under natural field conditions and the effect of water stress on the growth and allelopathic activity of this plant were investigated. Seed germination, shoot growth and root growth of tested plant species in soil collected from a field where Mexican sunflower had been grown for 5 years were less than those in soil from an area without the plant. Growth of young leaves, mature leaves, senescent leaves, stem and roots of Mexican sunflower was reduced with decrease in soil moisture level. The allelopathic activity of water extracts (per dry weight of starting material) from each part of the plants grown at low soil moisture levels was greater than that of the water extracts from the same part of the plants grown at high soil moisture levels. The allelopathic activity was found in the soil from the pots previously planted with Mexican sunflower to a similar extent (per plant) at different soil moisture levels. These results suggested that, in the field, under water stress conditions, the growth of Mexican sunflower was reduced but the plants contained a greater amount of allelopathic substance(s) per dry weight than in the absence of water stress. It was considered that allelopathic activity of Mexican sunflower in soil was maintained to a similar extent under various soil moisture conditions in natural fields.     

甘肃河西荒漠区胡杨栽植技术试验

以荒漠地区栽植的3年生胡杨苗木为试验对象,研究了胡杨苗木栽植前对其根系泡水时间、栽植时间、栽植深度、栽植后的修剪、栽植后30d内的浇水间隔时间以及胡杨锈病的防治时段等因素对荒漠区胡杨栽植成活率及保存率的影响。结果表明:栽植前对其根系泡水时间不同,其栽植成活率也不同,泡水时间10~15d,其成活率最高;栽植时间对其成活率也有影响,在试验区最佳栽植时间为4月中旬;栽植深度不同其成活率也不同,最佳栽植深度为苗木根际土低于地表土10~15cm;栽植后的最佳修剪方法是根据苗木大小,在2~2.5m高度处留2~3根枝条,并留2~3个芽短截,其余的枝条要全部清除;栽植后30d内的最合理浇水间隔时段为7d;胡杨锈病防治的最佳时段为5月下旬至8月下旬。     

普洱市入侵植物肿柄菊和本土植物总状山蚂蝗叶表真菌多样性的研究

通过对普洱本土植物总状山蚂蝗和入侵植物肿柄菊叶表真菌混合基因组DNA的提取、18SrRNA片段的扩增、克隆筛选及测序分析等方法,构建了2种植物叶表真菌的系统发育树。结果表明,肿柄菊和不同采集地的总状山蚂蝗叶表均生活着一些属于刺盾炱亚纲和异担子菌亚纲的真菌种类。但相对于独立生长的总状山蚂蝗,与肿柄菊共享小生境的总状山蚂蝗叶表共有真菌种类大多表现出下降的趋势。且肿柄菊和总状山蚂蝗叶表各自生活着一些在种类和功能上均存在差异性的真菌种类,其中生活于肿柄菊叶表的海枣粉座菌可能通过对本土植物的抑制作用来协助肿柄菊的入侵,因此未来研究应深入探索叶表微生物与植物入侵的关系以及相关作用的机制。     

Root and Shoot Growth of Maize (Zea mays) as Affected by Incorporation of Crotalaria juncea and Tithonia diversifolia as Green Manures

Crop establishment, determined by shoot and root growth during early growth is a vital component in procuring desired plant populations and high yields in rainfed tropical smallholder farming systems, where green manures help maintain soil fertility and sustainability. As green manure incorporation could affect early seedling growth, studies were conduced in a plant house using soils from fields, to evaluate the impact of incorporating two popular tropical green manures (Crotalaria juncea and Tithonia diversifolia) into soil under rainfed field conditions over 3 years, on selected physico‐chemical properties of the soils and on establishment and early shoot and root growth of maize (Zea mays), with and without inorganic fertilizers. In a given year, green manure was grown in one season while maize was grown in the other. A soil that did not receive green manures but was left fallow during the period of green manure cultivation was used as the control treatment. The incorporation of green manures over the 3 years showed trends of increasing soil physical properties, and also the available nitrogen, phosphorus and potassium contents. Incorporation of Crotalaria, with its higher nitrogen content, promoted shoot growth, while Tithonia induced the development of an extended root system. The use of inorganic fertilizers stimulated the beneficial impact of the green manures in promoting shoot and root growth. The use of green manures, especially Tithonia, promoted the development of seminal and nodal roots of maize seedlings, both in the form of length and thickness (based on root surface area) and root length densities, which could assist in successful crop establishment and resource utilization, rather than primary roots. The benefits of using green manures, especially Tithonia, in promoting root growth and Crotalaria in shoot development of maize seedlings even without inorganic fertilizers is presented.