Field trials under rain-fed conditions at the International Center for Tropical Agriculture (CIAT) in Colombia were conducted to study the comparative leaf photosynthesis, growth, yield, and nutrient use efficiency in two groups of cassava cultivars representing tall (large leaf canopy and shoot biomass) and short (small leaf canopy and shoot biomass) plant types. Using the standard plant density (10,000 plants ha-1), tall cultivars produced higher shoot biomass, larger seasonal leaf area indices (LAIs) and greater final storage root yields than the short cultivars. At six months after planting, yields were similar in both plant types with the short ones tending to form and fill storage roots at a much earlier time in their growth stage. Root yield, shoot and total biomass in all cultivars were significantly correlated with seasonal average LAI. Short cultivars maintained lower than optimal LAI for yield. Seasonal PN, across cultivars, was 12% greater in short types, with maximum values obtained in Brazilian genotypes. This difference in PN was attributed to nonstomatal factors (i.e., anatomical/biochemical mesophyll characteristics). Compared with tall cultivars, short ones had 14 to 24 % greater nutrient use efficiency (NUE) in terms of storage root production. The lesser NUE in tall plants was attributed mainly to more total nutrient uptake than in short cultivars. It was concluded that short-stemmed cultivars are superior in producing dry matter in their storage roots per unit nutrient absorbed, making them advantageous for soil fertility conservation while their yields approach those in tall types. It was recommended that breeding programs should focus on selection for more efficient short- to medium-stemmed genotypes since resource-limited cassava farmers rarely apply agrochemicals nor recycle residual parts of the crop back to the soil. Such improved short types were expected to surpass tall types in yields when grown at higher than standard plant population densities (>10,000 plants ha-1) in order to maximize irradiance interception. Below a certain population density (<10,000 plants ha-1), tall cultivars should be planted. Findings were discussed in relation to cultivation and cropping systems strategies for water and nutrient conservation and use efficiencies under stressful environments as well as under predicted water deficits in the tropics caused by trends in global climate change. Cassava is expected to play a major role in food and biofuel production due to its high photosynthetic capacity and its ability to conserve water as compared to major cereal grain crops. The interdisciplinary/interinstitutions research reported here, including, an associated release of a drought-tolerant, short-stem cultivar that was eagerly accepted by cassava farmers, reflects well on the productivity of the CIAT international research in Cali, Colombia., and M. A. El-Sharkawy, S. M. de Tafur
In this study the compressive strength and durability of soft clay soil stabilized with halloysite nanotubes are investigated. Halloysite nanotubes are novel 1D natural nanomaterials which are widely used in reinforcing polymer, pollution remediation, and as nanoreactors for biocatalyst. The wide use of halloysite nanotubes is due to their high aspect ratio, appropriate mechanical strength, high thermal stability, nature-friendly and cost-effectiveness. However, the use of halloysite nanotubes as a stabilizing agent for improving the durability of soil is not clear. In this research, halloysite nanotubes was used in the amounts of 2%, 5% and 10% by the weight of dried soil. Unconfined compressive strength, wet/dry cycles and freeze/thaw cycles tests were performed to evaluate the strength and durability of stabilized soft clay soil. Experimental results showed that halloysite nanotubes considerably improves the compressive strength and durability of soft clay soil. The optimum amount of halloysite nanotubes for soil stabilizing in terms of compressive strength and durability was 5%. The compressive strength of soft clay increased as much as 129% by applying 5% halloysite nanotubes. Also, the specimen containing 5% halloysite nanotubes showed the least strength loss after wet/dry and freeze/thaw cycles. The soil sample containing 5% halloysite nanotubes lost 20% of its initial compressive strength after 8 cycles of freezing and thawing, while the soil sample without any halloysite content lost 100% of its compressive strength after the same number of freezing and thawing. Based on the obtained results, the use of halloysite nanotubes in order to enhance the strength and durability of soft clay is strongly recommended., Tavakolipour Masoud, Salemi Niloofar., and Obsahuje bibliografické odkazy
Příspěvek se zabývá a) vztahem pravěkého osídlení k půdám na území dnešních Čech, b) vztahem mezi obilninami pěstovanými v pravěku a vybranými parametry přírodního prostředí, zejména půdní produktivity, na území celé České republiky. Vztahy archeologických období a půdních typů se dají na úrovni makroregionu rozdělit do čtyř skupin, které v zásadě odpovídají vývoji pravěkého orebního zemědělství. Všechny zemědělské kultury přednostně využívaly oblasti kvalitních půd, ale byly schopné hospodařit i na půdách s nižší kvalitou. Silná vazba osídlení a nejlepších orebně zemědělských půd přestává platit v průběhu mladší fáze starší doby bronzové, ale opět se projevuje v závěru pravěku zejména v době stěhování národů. Nejdůležitější environmentální proměnnou, která ovlivňuje složení pravěkých souborů pěstovaných obilnin je kvalita půdy. To je nejvíce patrné na poměru pěstovaných pšenic a ječmene: s klesající půdní kvalitou stoupá podíl ječmene a klesá podíl pšenic. Ačkoliv ekologické nároky pravěkých obilnin nejsou známy, ukazuje se, že prospívaly za podobných podmínek jako dnešní odrůdy a strategie pravěkého zemědělství byla podobná dnešním neindustriálním zemědělským komunitám, to znamená dosažení stabilní úrody pomocí vhodného výběru optimálních plodin vzhledem k lokálním podmínkám. and The study deals with: a) the relationship between prehistoric settlement and soil within the territory of today’s Bohemia, b) the relationship between cereals grown in prehistory and selected parameters of the environment, specifically the soil productivity, throughout the territory of the whole Czech Republic. The relations between archaeological periods/cultures and soil types on the level of macro-region can be divided into four groups generally corresponding the development of prehistoric arable agriculture. All prehistoric cultures using arable farming as the main subsistence strategy settled preferentially high-quality soil regions. However, they were able to farm on lower quality soils, too. The strong bond between settlement and the best arable soils ceased to apply during the later phase of the Early Bronze Age but it reappeared at the end of prehistory, especially during the Migration period. The most important environmental variable influencing the composition of cereals preserved within prehistoric macroremains assemblages is the quality of soil. This is manifested by the proportional representation of cultivated wheat and barley: as the soil quality goes down, the ratio of barley increases, while wheat decreases. Though the environmental demands of prehistoric cereals are not known, it turns out, that they thrived under similar conditions as current varieties and, moreover, the strategy of prehistoric arable farming was similar to present-day non-industrial farming communities, e.g. the stable yield was achieved through adequate choice of optimal crops corresponding local conditions.