Mitsuru Tsubo

Comparisons of radiation use efficiency of mono-/inter-cropping systems with different row orientations

Abstract Intercropping may be helpful to solve future food problem in developing countries. The aim of this study was to compare production efficiency in intercropping with sole cropping in terms of radiant energy use. For analysing crop radiation capture and utilisation, three indices are often used: the fraction of radiation intercepted (F), radiation use efficiency (RUE) and harvest index (HI). Using those indices, maize–bean intercropping was evaluated and compared with maize and bean sole cropping systems. The findings were as follows: the intercrop F was higher than the sole crop F, the sole maize RUE was higher than the others, and there was no difference in HI among cropping systems. From those results, the intercropping may be equivalent to maize sole cropping in the overall efficiency of radiation interception and use. Therefore, when it is considered that both maize and beans would be planted in a given area of land, intercropping has more efficient radiation harvests than sole cropping. No effect of row orientation was found on F, RUE and HI.

A model of radiation interception and use by a maize-bean intercrop canopy

A modelling study on intercropping was carried out to understand the radiation interception and use. The radiation transmission models on both instantaneous and daily bases were described and validated. For testing the model, photosynthetically active radiation was measured above and beneath a maize–bean intercrop canopy in both north–south (NS) and east–west (EW) rows at Bloemfontein, Free State, South Africa. Both models accurately predicted radiation transmitted through the intercrop canopy throughout the vegetative stage. For the instantaneous model, two methods were compared, namely, the geometrical method versus the statistical method. The geometrical method was equal in radiation transmitted per unit row to the statistical method. The daily amount of radiation intercepted and used by each component crop was estimated. Concerning the radiation utilisation, the intercropping was equivalent in growth efficiency of maize to the sole cropping whereas beans had greater radiation use efficiency in intercropping than in sole cropping, which might explain the intercrop yield advantage.

Soil erosion and conservation in Ethiopia: A review

This paper reviews Ethiopia’s experience and research progress in past soil and water conservation (SWC) efforts and suggests possible solutions for improvement. Although indigenous SWC techniques date back to 400 BC, institutionalized SWC activity in Ethiopia became significant only after the 1970s. At least six national SWC-related programs have been initiated since the 1970s and their focus over time has shifted from food relief to land conservation and then to livelihoods. The overall current soil erosion rates are highly variable and large by international standards, and sheet, rill, and gully erosion are the dominant processes. The influence of human activities on the landscape has traditionally been deleterious, but this trend seems to have recently reversed in some parts of the country following the engagement of the communities in land management. The efficiency of SWC measures show mixed results that are influenced by the type of measures and the agro-ecology under which they were implemented; in general, the relative performance of the interventions is better in the drylands as compared with humid areas. Methodological limitations also occur when addressing the economic aspects related to benefits of ecosystem services and other externalities. Although farmers have shown an increased understanding of the soil erosion problem, SWC efforts face a host of barriers related to limited access to capital, limited benefits, land tenure insecurity, limited technology choices and technical support, and poor community participation. In general SWC research in Ethiopia is fragmented and not comprehensive, mainly because of a lack of participatory research, field observations, and adoptable methods to evaluate impacts. A potentially feasible approach to expand and sustain SWC programs is to attract benefits from global carbon markets. Moreover, a dedicated institution responsible for overseeing the research–extension linkage of SWC interventions of the country should be established.

Comprehensive assessment of soil erosion risk for better land use planning in river basins : case study of the Upper Blue Nile River

In the drought-prone Upper Blue Nile River (UBNR) basin of Ethiopia, soil erosion by water results in significant consequences that also affect downstream countries. However, there have been limited comprehensive studies of this and other basins with diverse agroecologies. We analyzed the variability of gross soil loss and sediment yield rates under present and expected future conditions using a newly devised methodological framework. The results showed that the basin generates an average soil loss rate of 27.5tha-1yr-1 and a gross soil loss of ca. 473Mtyr-1, of which, at least 10% comes from gully erosion and 26.7% leaves Ethiopia. In a factor analysis, variation in agroecology (average factor score=1.32) and slope (1.28) were the two factors most responsible for this high spatial variability. About 39% of the basin area is experiencing severe to very severe (>30tha-1yr-1) soil erosion risk, which is strongly linked to population density. Severe or very severe soil erosion affects the largest proportion of land in three subbasins of the UBNR basin: Blue Nile 4 (53.9%), Blue Nile 3 (45.1%), and Jema Shet (42.5%). If appropriate soil and water conservation practices targeted ca. 77.3% of the area with moderate to severe erosion (>15tha-1yr-1), the total soil loss from the basin could be reduced by ca. 52%. Our methodological framework identified the potential risk for soil erosion in large-scale zones, and with a more sophisticated model and input data of higher spatial and temporal resolution, results could be specified locally within these risk zones. Accurate assessment of soil erosion in the UBNR basin would support sustainable use of the basins land resources and possibly open up prospects for cooperation in the Eastern Nile region.

Dynamics and hotspots of soil erosion and management scenarios of the Central Rift Valley of Ethiopia

Most of the lowland in the central rift valley of Ethiopia is arid or semiarid and in degradation, with frequent occurrence of droughts. Soil erosion by water during the rainy season is a serious problem in the region, leading to declining agricultural production, decreased food security, and a sedimentation risk for water bodies. However, there has been no systematic study of this problem or of possible management solutions. To meet this need, we analyzed soil erosion rates from 1973 to 2006, identified erosion hotspots, and proposed possible soil conservation scenarios. We assessed the soil loss dynamicity using the universal soil-loss equation and geographical information system software, considering the land use change at the following three periods: 1973, 1985 and 2006. We characterized the watershed in terms of the erosion severity, topography, and land use to identify hotspots and proposed, modeled, and evaluated various watershed management scenarios to mitigate the problem. Soil erosion increased markedly from 1973 to 2006, with annual rates of 31, 38, and 56 t ha−1 in 1973, 1985, and 2006, respectively, as a result of vegetation degradation and particularly the conversion of thousands of hectares of forest or woodland into cropland. The observed soil erosion rates are far from the tolerable rate of soil loss of the country and hence require urgent soil conservation interventions, especially in the hotspot areas. We proposed eight scenarios for reducing soil losses and evaluated their effectiveness. Rehabilitating degraded land (using exclosures and planted vegetation) and installing stone erosion-control structures (stone bund) in cropland reduced the total soil loss by 12.6% and 63.8%, respectively. Treating hotspot areas with annual soil loss of more than 20 t ha−1 by integrated management (erosion-control structures and exclosures) was the most effective approach, reducing soil loss by 87.8%.

Spatial variations in water availability, soil fertility and grain yield in rainfed lowland rice: a case study from Savannakhet province, Lao PDR.

Abstract Rice is the single most important food crop in Laos. Savannakhet province, the largest area of rainfed lowland rice of any single province in the country was selected for the present case study to quantify the spatial distribution of two major limiting factors, water availability and soil fertility, and rice productivity in rainfed lowlands. Field water availability, fertilizer application and other crop management practices, and grain yield information were collected from over 100 farmers to provide basic information relating to rainfed lowland rice productivity and potential bio-physical constraints in this province over two rice cropping seasons. Poor soil fertility is identified as a major yield constraint with yield responding strongly to fertilizer application rate. The results also show that rainfall distribution pattern, soil type and position of rice fields on a sloping land, affect paddy water availability, and this in turn influences sowing time and is also expected to have effect on grain yield. To improve the productivity of rainfed lowland rice, combination of appropriate crop phenology, increased fertilizer use that is matched with water availability, and an understanding of soil water condition for the rice growing environment, is required. In a long term increasing soil fertility is required, and a significant improvement in rice productivity cannot be achieved by improved water availability alone, in a situation where the majority of paddy soils have low levels of fertility.

Effects of Soil Clay Content on Water Balance and Productivity in Rainfed Lowland Rice Ecosystem in Northeast Thailand

Abstract Water availability is one of the determinants of productivity of rainfed lowland rice (Oryza sativa L.). Quantifying water losses from a paddy field, such as deep percolation and lateral seepage, assists estimation of water availability to the rice crop and development of appropriate water management in the lowlands. The main objective of this study was to evaluate paddy water availability and productivity across various soils in Northeast Thailand. The daily rate of downward water flow from standing water in the field (D) varied between 0 and 3 mm day-1 from clayey to sandy soils when the standing water was connected to groundwater table. However, when the standing water was separated from groundwater table, D increased up to 5 mm day-1 on soils with very low clay content in the topsoil. Daily net lateral water flow from the field (L) averaged over the season varied between 5 and 24 mm day-1 for the outflow and between 3 and 16 mm day-1 for the inflow. Both the inflow and outflow tended to be associated negatively with the soil clay content. The seasonal water loss through D plus L during the growing season in the lowlands was also negatively related to the soil clay content. The yield of a major rainfed lowland rice cultivar in Northeast Thailand (KDML105) varied from 2 to 4 t ha-1 across the region, and the water productivity (the ratio of grain yield to cumulative rainfall from transplanting/seedling establishment to maturity) ranged from 3 to 9 kg ha-1 mm-1. High clay soils could provide good standing water until late in the growing season, so the high production efficiency was measured on such soils.

Estimating Percolation and Lateral Water Flow on Sloping Land in Rainfed Lowland Rice Ecosystem

Abstract Quantifying water losses in paddy fields assists estimation of water availability in rainfed lowland rice ecosystem. Little information is available on water balance in different toposequence positions of sloped rainfed lowland. Therefore, the aim of this work was to quantify percolation and the lateral water flow with special reference to the toposequential variation. Data used for the analysis was collected in Laos and northeast Thailand. Percolation and water tables were measured on a daily basis using a steel cylindrical tube with a lid and perforated PVC tubes, respectively. Percolation rate was determined using linear regression analysis of cumulative percolation. Assuming that the total amount of evaporation and transpiration was equivalent to potential evapotranspiration, the lateral water flow was estimated using the water balance equation. Separate perched water and groundwater tables were observed in paddy fields on coarse-textured soils. The percolation rate varied between 0 and 3 mm/day across locations, and the maximum water loss by lateral movement was more than 20 mm/day. Our results are in agreement with the previously reported findings, and the methodology of estimating water balance components appears reasonably acceptable. With regard to the toposequential variation, the higher the position in the topoesquence, the greater potential for water loss because of higher percolation and lateral flow rates.

Index-based assessment of agricultural drought in a semi-arid region of Inner Mongolia, China

Agricultural drought is a type of natural disaster that seriously impacts food security. Because the relationships among short-term rainfall, soil moisture, and crop growth are complex, accurate identification of a drought situation is difficult. In this study, using a conceptual model based on the relationship between water deficit and crop yield reduction, we evaluated the drought process in a typical rainfed agricultural region, Hailar county in Inner Mongolia autonomous region, China. To quantify drought, we used the precipitation-based Standardized Precipitation Index (SPI), the soil moisture-based Crop Moisture Index (CMI), as well as the Normalized Difference Vegetation Index (NDVI). Correlation analysis was conducted to examine the relationships between dekad-scale drought indices during the growing season (May-September) and final yield, according to data collection from 2000 to 2010. The results show that crop yield has positive relationships with CMI from mid-June to mid-July and with the NDVI anomaly throughout July, but no correlation with SPI. Further analysis of the relationship between the two drought indices shows that the NDVI anomaly responds to CMI with a lag of 1 dekad, particularly in July. To examine the feasibility of employing these indices for monitoring the drought process at a dekad time scale, a detailed drought assessment was carried out for selected drought years. The results confirm that the soil moisture-based vegetation indices in the late vegetative to early reproductive growth stages can be used to detect agricultural drought in the study area. Therefore, the framework of the conceptual model developed for drought monitoring can be employed to support drought mitigation in the rainfed agricultural region of Northern China.

Effects of land-cover type and topography on soil organic carbon storage on Northern Loess Plateau, China

Abstract Changes in land cover from cropland to conservation can sequester carbon in soil. On the Loess Plateau of China, vast areas of sloping cropland were converted into forest and grassland to control soil erosion. The northern plateau is a topographically heterogeneous, semi-arid region. A good understanding of the change of soil organic carbon (SOC) storage on the plateau in the process of land-cover change is important for assessing environmental changes and planning future land cover. We selected four land-cover types (cropland, planted grassland, abandoned orchard, and secondary grassland), and two vegetation covers (Stipa bungeana and Caragana korshinskii) on shady and sunny slopes, to analyse the effects of land cover and slope aspect on SOC storage. Soil C in the top 100 cm was significantly (P<0.05) greater in artificial grassland (2.49 kg m−2) and secondary grassland (2.98 kg m−2) than in cropland (1.69 kg m−2). The SOC pool in the surface soil and throughout the 1-m profile followed the order secondary grassland>artificial grassland>abandoned orchards>cropland. Sequestration extended to deep soil (80–100 cm). Slope aspect affected SOC concentration: wind erosion of the shady slope marginally reduced surface SOC relative to the sunny slope. In deep soil, responses of SOC concentration to slope aspect differed between vegetation covers: under C. korshinskii, SOC concentration was significantly greater on the shady slope (P<0.05), but no difference was found under S. bungeana.