Effect of mulch on soil temperature,moisture, weed infestation and yield of groundnut in northern Vietnam

Groundnut (Arachis hypogaea L.) is one of the chief foreign exchange earning crops for Vietnam. However, owing to lack of appropriate management practices, the production and the area under cultivation of groundnut have remained low. Mulches increase the soil temperature, retard the loss of soil moisture, and check the weed growth, which are the key factors contributing to the production of groundnut. On-farm trials were conducted in northern Vietnam to study the impact of mulch treatments and explore economically feasible and eco-friendly mulching options. The effect of three mulching materials (polythene, rice straw and chemical) on weed infestation, soil temperature, soil moisture and pod yield were studied. Polythene and straw mulch were effective in suppressing the weed infestation. Different mulching materials showed different effects on soil temperature. Polythene mulch increased the soil temperature by about 6 °C at 5 cm depth and by 4 °C at 10 cm depth. Mulches prevent soil water evaporation retaining soil moisture. Groundnut plants in polythene and straw mulched plots were generally tall, vigorous and reached early flowering. Use of straw as mulch provides an attractive and an environment friendly option in Vietnam, as it is one of the largest rice growing countries with the least use of rice straw. Besides, it recycles plant nutrients effectively.     

Trace elements in spinach (Spinacia oleracea) cultivated in soil fortified with graded levels of iron

Trace elements in two varieties of spinach cultivated in soil with different levels of added iron were determined. Addition of iron to soil decreased potassium, sodium and magnesium contents in spinach markedly (p<0.05), while the contents of zinc, manganese and copper in spinach were not significantly altered (p>0.05). Differential behaviour of spinach varieties was found in the zinc, manganese and sodium contents.     

花生施钙对红壤旱土酸度及有害金属含量的影响

为探明花生施用钙肥对土壤酸度及有害金属元素铝、锰、镉、铅含量的影响,本研究选取大粒品种湘花2008、中粒品种湘花55、小粒品种蓝山小籽,以典型缺钙瘠薄酸性红壤旱土土柱试验,设置施钙与不施钙两个处理,测定根际土、0~20cm耕层土的pH值和有害金属元素含量。结果表明：各指标整体平均值受钙肥的影响,pH值增高4.93%,铝、镉、锰含量分别降低3.85%、2.13%、1.59%,铅含量升高0.66%。其中根际土,pH增幅远大于耕层土,湘花55＞湘花2008＞蓝山小籽;土壤铝含量降幅为根际土＞耕层土,湘花2008＞湘花55＞蓝山小籽;土壤锰含量降幅在耕层土湘花55＞湘花2008＞蓝山小籽,根际土大、中籽升高,小籽降低;土壤镉含量在耕层土、根际土降幅均以蓝山小籽最大,湘花2008小幅升高,湘花55有降有升;土壤铅含量大、中籽品种在根际土升幅大于耕层土,而蓝山小籽降低。     

Imidacloprid concentrations in paddy rice fields in northern Vietnam: measurement and probabilistic modeling

Paddy and Water Environment - Uncertainties associated with pesticide exposure forecasts arise from many sources such as spatial and temporal variability of factors influencing pesticide behavior,...     

Predicting soil moisture condition in arbitrary agricultural lands using the digital soil map and soil physical properties database

To predict soil moisture condition in arbitral agricultural lands by taking spatial distribution of soil type in a watershed into account, we investigated the possible proper methods of determining the soil hydrological parameters using available soil physical properties database of Japanese soils, “SolphyJ”, and the digital soil map. In this study, simulation of soil moisture was conducted at three neighboring locations, including monitoring sites each in Toyama and Fukui cities. The simulated results of soil moisture appeared to be improved when hydraulic parameters were obtained by fitting water retention data of SolphyJ compared to the parameters estimated by neural network with soil texture and dry bulk density data. It is probably because peculiar soil structure in each field could affect the hydraulic properties more than the soil texture. Simulation results also indicated that soil moistures are much different even if they are located in neighbors (<5 km). We concluded that combination of these two databases is useful for estimating soil hydraulic parameters and to predict soil moisture condition in arbitrary agricultural lands.     

Survey of agricultural reservoirs damaged by the July 2017 torrential rains in northern Kyushu,Japan

Paddy and Water Environment - The torrential rains that hit northern Kyushu, Japan, on July 5–6, 2017, caused serious damage, especially in Asakura City, Fukuoka Prefecture, and in Hita City,...     

Influence of paddy rice terraces on soil erosion of a small watershed in a hilly area of Northern Vietnam

Soil erosion is the main cause of soil degradation in northern Vietnam. In this study, soil erosion was measured in 2 m² field plots, a 19.1-ha sub-watershed, and a 248.9-ha main watershed in Tam Quan commune, Tam Duong district, northern Vietnam during 2 years, i.e., 2004–2005. The main watershed includes lowland paddy fields, and is representative for watersheds in the northern Vietnamese landscape. Soil erosion was measured for eight events, at all the three scales to increase our understanding of erosional processes and to assess the effects of paddy fields within the main watershed. The results show that total discharge and sediment yield in both sub-watershed and main watershed were much lower than those in the field plots. Total discharge per unit area in the main watershed was higher than in the sub-watershed, because during the growing season, the paddies are filled with water and any rainfall on them therefore becomes runoff. Sediment yield in the main watershed fluctuated, depending on the soil erosion contribution from many sub-watersheds. Annual rainfalls in 2004 and 2005 were 1,172 and 1,560 mm, respectively, resulting in corresponding total discharges of 54 and 332 mm and total soil losses of 163 and 1,722 kg ha^?1 year^?1. High runoff volumes occurred in July, August, and September, but April, June, the last 10 days of September and October, were the susceptible periods for soil erosion in the study area because of low plant cover and many agricultural activities during these periods.     

Individual lift irrigation: a case study in the Cau Son irrigation and drainage area, Red River Basin, Vietnam

The irrigation trend in Asia has been characterised as a shift from gravity to lift irrigation, but the importance of individual lift irrigation using surface water remains to be documented. Surveys on field water application by farmers using lift were undertaken in three sites and across the 44,600 ha Cau Son irrigation and drainage area in the spring crop season. Lift irrigation was found to be practised by 82 % of households. The main lift technology was mechanical pump (petrol and electric), followed by traditional swing and long-handle baskets. The main source for lifting was on-farm canals. Although gravity irrigation was the dominant field application method, the area solely irrigated by individual lift ranged from 25 to 52 % of the irrigated areas. Scaling up from the sites, individual lift accounted for 29 % by irrigation area and volume, with 17 and 12 % attributed to mechanical and manual lift. The application of mechanical pumps was a response to locally high-field elevations and significantly increased with the distance of water delivery from the main canal. The impact of mechanical pumping on flexibility and reliability was significant and positive. Petrol driven pumps had relatively high operational and investment costs, but farmers gained higher flexibility and reliability and compensated by applying less water. Farmers using electric pumps applied significantly more water and thereby wasted electric energy as a compensation for uncertain electric power supply. The importance of individual lift irrigation suggests that it should be explicitly considered in irrigation management policies and performance assessments.     

Heavy metal contamination of agricultural soil and countermeasures in Japan

Many heavy metals exist in minute amounts in natural agricultural soil. However, when their amounts exceed a certain level due to pollutants brought from outside, soil contamination occurs and agricultural products become contaminated. There have been many cases in Japan of heavy metal contamination originating from old mines and smelters, and soil contamination of agricultural land has become a social issue. In particular, cadmium (Cd) is one of the most harmful heavy metals. If agricultural products absorb an excessive amount of Cd, they may adversely affect people’s health, and therefore allowable concentrations are regulated by law. If agricultural land has become contaminated with Cd, measures for minimizing the absorption of Cd by agricultural crops are necessary; these include: (1) soil dressing, (2) water management (paddy field), (3) chemical cleaning of soil, (4) phytoextraction, and (5) use of different varieties and rootstock. Other heavy metals such as arsenic, lead, copper, zinc, and mercury also sometimes cause contamination of agricultural soil.     

农产品及产地环境中微量元素检测研究进展

农产品及产地环境中微量元素高效、准确检测是农产品政府监管、保障消费安全、促进粮油产业高质量发展的重要手段。本文评述了近几年农产品及产地环境中微量元素的检测技术,比较分析了光谱、质谱、色谱和电化学等方法的原理和特点,及其在微量元素检测实际应用中的优缺点,以期为农产品及产地环境中微量元素检测技术研究提供参考,为粮油产业高质量发展与农产品质量安全提供技术支撑。     

Effect of nitrogen fertilization on net nitrogen mineralization in a grassland soil,northern China

Nitrogen (N) applications can have a significant effect on soil N availability. The effect of 3 years of N fertilization on soil net N mineralization during the growing season (May–September) was studied in 2005 and 2006 in grassland of northern China. The experimental design was a randomized complete block with four replications of five rates of N addition as urea (0, 2, 4, 8 and 16 g N m^?2 year^?1). Results indicated that net N mineralization rate varied seasonally and between years, ranging from ?0.04 to 0.52 μg g^?1 d^?1 in 2005 and from ?0.09 to 0.39 μg g^?1 d^?1 in 2006. Mean N mineralization and nitrification rates were highest in July, in 2005 and 2006, whereas highest ammonification rates occurred in September. Rainfall was significantly correlated with net nitrification. In comparison with the untreated control, N mineralization increased sharply when N fertilization increased from 2 to 8 g N m^?2 year^?1. Mobile soil NO₃^? accumulated late in the growing season for the 16 g N m^?2 year^?1 treatment, suggesting the potential for NO₃ and associated cation leaching. These results suggest that N fertilization of 8 g N m^?2 year^?1 (80 kg N ha^?1) is suitable for the management of grassland ecosystems of Inner Mongolia.     

北方无公害优质水稻栽培管理技术

承德市具有良好的无公害水稻自然环境和区位优势,通过选用优质、高产、高抗品种,在整个水稻生长过程中实行规范化栽培技术管理,可提供无公害、优质、水稻产品。     

Optimal gate operation of a main drainage canal in a flat,low-lying,agricultural area using a tank model

Chiyoda basin is located in Saga Prefecture in Kyushu Island, Japan, and lies next to the tidal compartment of the Chikugo River to which the excess water in the basin is drained away. Chiyoda basin has a total area of about 1,100 ha and is a typical flat and low-lying paddy-cultivated area. The main problem in this basin is the appropriate operation of drainage structures during and after flood events in order to minimize the inundation damages for crop yield and to fulfill the irrigation requirement in the irrigation period. This paper presents a mathematical model of a drainage system in Chiyoda basin for calculating the flood inundation and optimizing the operation of gates in a main drainage canal. First, the algorithm of gate operation was simulated and the drainage model was then evaluated by comparing the simulated water levels with those observed during an actual rainfall event. The results show that the observed and simulated water levels are in good agreement, indicating that the proposed model is applicable for drainage and inundation analyses in flat, low-lying paddy-cultivated areas. Second, the optimization of gate operation was investigated by trial and error method using a stochastic rainfall time series with a return period of 30 years and the tidal conditions of spring and neap tides in the Chikugo River. Comparing a total inundation time, a total inundation area and maximum inundation depth in the paddy tanks at the upstream and the downstream ends, it was concluded that the present operation based on the gate operators’ experience was almost the optimal one, and the sooner start of opening operation and the later start of closing operation within the operationality of check gates were recommended to minimize the inundation damage. The present operation could be able to minimize the total inundation time, the total inundation area and the maximum inundation depths in paddy tanks and to meet fully both the drainage and the irrigation requirements.     

Numerical prediction of suspended sediment concentrations in the Ariake Sea, Japan, using a time-dependent sediment resuspension and deposition model

The Ariake Sea, a typical semi-closed bay located in Kyushu Island, western Japan, has a maximum tidal range of 6 m in spring tide, and its vast tidal flats are composed of both sandy bottom areas and muddy bottom areas. In this study, two-dimensional depth-averaged finite difference numerical models have been developed for predicting the tidal flow velocity and suspended sediment concentration in the Ariake Sea. In the suspended sediment transportation model, a time-dependent sediment resuspension and deposition process was modeled as a response to the tidal flow by considering the presence of cohesive bottom sediment. The shifting-particles method, known as an operator-splitting technique, was used for time integration of the convective-dispersion equation. The model results were compared with in situ measurements of suspended sediment concentration and tidal flow velocity at several points in Isahaya Bay—located at the western part of the Ariake Sea—and also with the estimated suspended sediment concentration distribution via a Landsat Thematic Mapper image. The results indicated that the models were able to predict the measured values for suspended sediment concentration and tidal flow velocity, as well as the spatial distribution pattern of the suspended sediment concentration as estimated by the Landsat Thematic Mapper image.     

Effect of shifting cultivation on distribution of nutrient elements and carbohydrates within water-stable aggregates in northern Iran

This study attempts to evaluate the nutrient element and carbohydrate distribution within Water-Stable Aggregates (WSA) of two natural ecosystems, native forest and pasturelands, under different land uses. Soil samples were collected from depths of (0-20) cm in Typic Haploxeroll soils. The overall pattern indicated that Mean Weight Diameter (MWD) and WSA were greater in the pasture and forest soils compared with the adjacent cultivated soils and aggregates of > 1.0 mm size were dominant in the uncultivated soils, whereas the cultivated soils comprised aggregates of the size < or = 0.5 mm. Distribution of organic carbon, nitrogen, phosphorus and carbohydrates within the WSA showed preferential enrichment of these parameters in the macroaggregate fraction (4.75-1.0 mm) for the uncultivated soils and microaggregate fraction (> 0.25 mm) for the cultivated soils. Average distribution of total exchangeable bases within WSA showed that cultivation of forest pastureland soils significantly led to reduce in these nutrient in the 4.75-2.0 mm fraction and increase in concentration of these cations in < 0.25 mm fraction. Since smaller aggregates are preferentially removed by erosion, this study emphasizes the need for sustainable soil management practices that they will minimize nutrient loss when forest or pastures lands are converted to cropland.     

Fate of phosphate and nitrate in waters of an intensive agricultural area in the dry zone of Sri Lanka

The chemistry of surface waters and groundwater draining agricultural catchments in the north-central and northwestern areas of Sri Lanka is described. Hydrochemical data from 296 water samples are used to evaluate water quality and to identify the processes that control nitrate and phosphate concentrations in the water. The results indicate that nutrient concentrations in the groundwaters are greater than those in the surface waters. Increased nutrient levels were observed in groundwater in a selected area in the fortnight following fertilizer application. Detailed geochemical investigations of selected groundwater samples reveal a gradual rise of nitrate–N and other solutes along the horizontal flow direction. Compared to the application rates of fertilizer in the area, the average nutrient concentrations in all waters are relatively low (1.5 mg/l nitrate and 0.5 mg/l phosphate) and stable. The results suggest that prevailing reducing conditions, iron-rich overburden soil cover and manmade canal networks control nutrient accumulation in the groundwater.     

生物炭改良土壤机理及其在我国热区应用前景综述

近年来,生物炭在农业废弃物的有效利用、土壤改良、环境修复等方面发挥着重要作用,日益受到国内外研究者的关注。众多研究结果表明：生物炭可以通过改善土壤结构,提高土壤pH和有机质含量,增加土壤养分有效性,提高土壤酶活性,调控土壤微生物环境,进而改良土壤,促进作物生长。本文从生物炭对土壤物理、化学性质、土壤养分、酶活性和土壤微生物的影响等方面,综述生物炭改良土壤的机理。同时结合我国热带亚热带农业生产现状,从原材料供应和土壤环境条件等方面,分析生物炭在我国热带亚热带地区的应用前景,为生物炭的广泛利用及热带亚热带地区土壤改良提供理论参考和借鉴。     

红壤旱地春大豆品种的产量,品质及矿质营养的基因差异

在江西红壤旱地底施氮磷钾肥条件下,６个不同生育期品种的产量均可达到１５００ｋｇ／ｈｍ＾２以上,在气候条件较好的１９９７年,分别达到１７００－２３５０ｋｇ／ｈｍ＾２,产量高低及主要经济性状随品种生育期长短而异,与对照相比,增产率为２．５４％－３５．５３％,主要农艺性状亦存在差异;生育期长的品种比生育期短的品种蛋白质含量低、油分含量高,但蛋白质,油分之和均超过６５％。早熟品种８９０５－１不但产量高出中     

Operation of the Ba Lai irrigation system in the Mekong Delta, Vietnam

Ba Lai Irrigation Project is located at coastal area in the Mekong Delta. In dry season when the flow rate decreases and the strong east wind blows into the delta, the salinity intrusion increases and seriously affects agricultural and domestic water use. Intakes of Ba Lai system have to be closed for 1–3 months depending on their locations, and no water supply during this period often causes water pollution in the project area. In order to solve such problems, this study aims to seek gate operation procedures for salinity control and water environment improvement. A numerical model is developed to simulate water movement, salinity concentration and duration of remaining water (water age) within the system under three scenarios: (1) without control structures, (2) with available control structures, (3) with the full control structures. Through the numerical simulations, control structures are confirmed to be an effective measure for the salinity control and suitable gate operation schedules are proposed to improve the water environment in the project.