DOC and DON from grass-clover - results from a field experiment

The C and N dynamics in perennial grass-clover mixtures are not fully understood although such mixtures dominate temperate grassland. The co-existence of clover and grass involves both competition for and transfer of nutrients between the species. The nutrients that are competed for and transferred may originate from leaky root systems, from a rapid turnover of the fine root systems, or from degradation of more stabile organic material. The aim of the present study was to investigate the origin of dissolved organic C and N in perennial grass-clover mixtures. In an existing grass-clover ley, field mezotrons (cylinders with a diameter 30 cm) were installed in the spring of 2003 to depths of 20, 40 and 60 cm. Suction cups was installed beneath the mezotrons in order to sample the soil solution during the growth season. In late June 2004 cross-labelling of clover and grass populations in the mezotrons was done by leaf labelling (5 days) of either grass or clover using 15N- and 14C-labelled urea. During the following 3 months the percolating soil solution was sampled either after heavy rain or after irrigation of the mezotrons and the content 15N- and 14C-labelled compounds were determined. Leaf material was harvested at tree times during the growth season and at the end of the growth season the mezotrons was excavated and the distribution of 15N and 14C in the plants and soil determined. 14C was detected in the percolating soil solution imediately after leaf-labelling was initiated, with the highest amounts occuring from labelled grass. The peak of 14C reached the depths of 20 and 40 cm between 3-10 and 5-15 days respectively after labelling was initiated while no 14C was detected beneath the 60 cm mezotrons. The majority of 14C in soil solution was identified to be 14CO2 originating either from root respiration or from biomass respiration of 14C-labelled root parts or root exudates. The transfer of 14C was higher from grass to clover than vice versa. This transfer of 14C properly occurs as 14CO2 exchange between the leaves or in the root zone. Transfer of 15N was highest from clover to grass, while the transfer from grass to clover was negligible. These observations confirm previous investigations of 15N transfer between grass and clover. No clear connection was found between the transfer of 14C and 15N. After excavation of the mezotrons 14C was found in higher amounts and at larger depths in the soil for grass compared to clover. The results from this experiment point to that in a grass-clover ley carbon would primarily originate from grass and nitrogen would come from clover. The depths at which 14CO2 is found in the soil solution seem to be somewhat related to the depth of 14C-labelled root material meaning that the rooting profile of a crop influence the deposition of carbon and nitrogen in the soil matrix. These findings add significant new dimensions to our current understanding of processes governing the build up of soil fertility under grass-clover leys

A Vietnam Social Accounting Matrix (SAM) for the Year 2003

This paper documents a Vietnam Social Accounting Matrix (SAM) for the year 2003. The 2003 Vietnam SAM contains 275 accounts including 112 production activity accounts, 112 retail commodity accounts, three transportation margins accounts, three trade margins accounts, 14 primary factor accounts, one enterprise sector account, 16 households group accounts, seven government current budget accounts, two inventory accounts (private and public inventory accounts), three capital accounts (private, public and aggregate capital accounts), one rest of the world account, and one totals accountVietnam, Social Accounting Matrix

On the Choice of Appropriate Development Strategy: Insights from CGE Modelling of the Mozambican Economy

CGE modelling, Development strategy, Mozambique

Trade Liberalization and Spatial Inequality: A Methodological Innovation in Vietnamese Perspective

poverty, trade liberalization, general equilibrium models, Vietnam

Research in sub-saharan African food systems must address post-sustainability challenges and increase developmental returns

The article argue that the livelihood approach is relevant for Research in sub-saharan African food systems, which must address post-sustainability challenges and increase developmental return

Interfirm Linkages and the Vertical Structure and Dynamics of the Danish Trucking and Congress Tourism Industries

This paper questions the overall role of interfirm linkages in industrial dynamics. Studying Danish trucking and congress tourism, the paper addresses a number of particular questions concerning how industry responds to changing conditions. In trucking, the important interfirm linkages are pecuniary and entails nontrivial exchange among multiple dispersed agents, while in congress tourism Inter-organizational linkages are more strategic, with the activities of multiple agents forming together into products, without direct exchange.Industrial dynamics and evolution; inter-organizational linkages; vertical industry structure and division of labor; trucking; tourism

Productivity and quality, competition and facilitation of chicory in ryegrass/legume-based pastures under various nitrogen supply levels

Traditional perennial ryegrass-white clover mixtures have limitations in combined productivity and quality that herbs like chicory may alleviate. This study examined the consequences on productivity and quality of as well as competition and facilitation after introducing chicory into varies ryegrass-legume-based pastures in a field study over 3 consecutive growing seasons. A cultivar of chicory, suitable for grazing, in pure stand was found to out-yield a pure stand ryegrass in terms of dry matter and nitrogen (N) accumulation but was found to yield similar to mixture of chicory and ryegrass. The inclusion of chicory, increased N accumulation per area unit irrespective of associated leguminous species but had no effect (P>0.05) on the combined dry matter yield of these mixtures as compared to the chicory-ryegrass mixture. Chicory was not found to co-exist well with associated fodder legumes but it co-existed well with perennial ryegrass. Determined by a direct 15N plant labelling technique, chicory transferred little N to associated legumes and under moderate soil N conditions it almost out-competed the white clover whereas lucerne was able to withstand the competition with birdsfoot trefoil as intermediate. Chicory and ryegrass did exchange N amounting to less than 5% of the receiver plants’ N economy whereas the N transfer from the N-rich lucerne constituted 15% of the associated ryegrass’ N economy but less (P<0.05) of the chicory’s N economy. These differences are ascribed to the species’ root morphology and root zonation. Chicory accumulated large amounts of calcium, potassium, sodium and zinc but significant less of magnesium and manganese, irrespective of the N supply. In the case of sodium it was a short-term effect whereas calcium and possibly also sulphur, copper and zinc accumulation increased over time. It is concluded that chicory may improve the management of intensive dairy farms with a large N surplus because of the increase in productivity per unit area and N uptake efficiency and add significant improvements of the quality of the forage

General Equilibrium Measures of Agricultural Policy Bias in Fifteen Developing Countries

A comparative analysis of 15 developing countries shows that, during the 1990s, indirect taxes, tariffs, and exchange rates significantly discriminated against agriculture in only one country (Malawi), was largely neutral in five (Argentina, Brazil, Costa Rica, Indonesia, and Zimbabwe), provided a moderate subsidy to agriculture in four (Mexico, Tanzania, Venezuela, and Zambia), and strongly favored agriculture in five (Egypt, Korea, Morocco, Mozambique, and Tunisia). In contrast to earlier partial equilibrium results, our general equilibrium analysis indicates that exchange rate changes can lead to anything between strongly increasing and strongly decreasing relative agriculture/non-agriculture incentives, depending on relative trade shares and relative tradability of agricultural and non-agricultural commodities. Country-specific circumstances greatly affect the relative impact of trade policies on agriculture and the rest of the economy in a general equilibrium setting. Earlier partial equilibrium measures of policy bias could not adequately incorporate country heterogeneity and are therefore likely to have overstated the bias. In any case, from the empirical results with our sample of countries, we conclude that any incentive bias against agriculture in the 1980s had mostly disappeared by the 1990s.urban bias, food and agricultural policy; general equilibrium modelling

General equilibrium measures of agricultural policy bias in fifteen developing countries

In this paper, we present a comparative analysis of the extent to which indirect taxes, tariffs, and exchange rates affected relative price incentives for agricultural production in a representative sample of 15 developing countries in the 1990s. Empirical studies from the 1980s, using partial equilibrium methodologies, supported the view that policies in many developing countries imparted a major incentive bias against agriculture. Eliminating this bias was one of the goals of policy reform strategies, including structural adjustment programs, supported by the World Bank and others; and many countries undertook such reforms in the 1990s. In our sample, general equilibrium analysis indicates that, in the 1990s, the economywide system of indirect taxes, including tariffs and export taxes, significantly discriminated against agriculture in only one country, was largely neutral in five, provided a moderate subsidy to agriculture in four, and strongly favored agriculture in five. Earlier work assumed that overvaluation of the exchange rate would hurt agriculture, which was assumed to be largely tradable. In a general equilibrium setting, changes in the exchange rate can as demonstrated in this paper lead to anything between strongly increasing and decreasing relative agriculture/non-agriculture incentives, depending on relative trade shares. We conclude that, whatever incentive bias there was in the 1980s, it has mostly disappeared by the 1990s. We also find that it is difficult to generalize-country specific circumstances greatly affect the relative impact of trade policies on agriculture and the rural economy. Authors' Abstract.