Kiriaki L. Kalburtji

Decomposition of dominant plant species litter in a semi-arid grassland

Abstract Dominant plant species in semi-arid environments differ in their effects on litter decomposition. The present study was conducted to investigate the contribution of dominant plant species found in a natural semi-arid grassland to nutrient cycling through their litter decomposition. Aboveground litter (stems and leaves) of Dichanthium ischaemum , Chrysopogon gryllus , Festuca ovina and Trifolium purpureum was placed on the soil for 24 months and chemical characteristics were monitored. The rate of mass loss from stems was significantly lower than that of leaves for all species. The influence of mesh size on the studied parameters for both leaves and stems was similar in most cases for the grass species, Chrysopogon and Festuca (e.g. litter, lignin, TNSC, Energy and Total C, N, K, Ca). Generally, mean decomposition rate ( k ′= k ×10 5 ) had the highest value for Trifolium ( k ′=188), followed by Dichanthium ( k ′=133), Chrysopogon ( k ′=120) and Festuca ( k ′=118). Chrysopogon and Festuca by being the most dominant species in the grassland and having low decomposition rates contribute more organic matter to the soil.

Litter dynamics of low and high tannin sericea lespedeza plants under field conditions

Sericea lespedeza [Lespedeza cuneata (Dum. Cours) G. Don.] is a perennial legume with high polyphenol (tannin) concentration. The decomposition and nutrient release of sericea lespedeza residues with two tannin levels (high = 22% or low = 16%), which were either placed on the soil surface or buried at a depth of 5 cm were studied. An experiment was carried out at two sites for 2 yr. Litter mass loss and nutrient (N, P, K, Ca, Mg, Cu, Fe, Mn, Zn, B, Mo, Co) release were recorded. Litter mass loss was higher for the low-tannin residues and for those buried. From the beginning of the experiments, the C : N ratio was lower than 25 : 1 and N was mineralized for most of the studied cases; this means that N increased in availability to plants. The release of the rest of the studied nutrients was higher at the depth of 5 cm than on the soil surface and higher for low-tannin residues than for high-tannin. The observed accumulation of some nutrients in the first months presumably depended on microbial activity. The rate of release was higher for the macronutrients than for the micronutrients, with the exception of B, which had the same behaviour as the macronutrients.

Nutrient release from decomposing Lotus corniculatus residues in relation to soil pH and nitrogen levels

The rate of biomass decomposition, organic matter loss, and nutrient release from litter of Lotus corniculatus grown with or without N were studied using the litter-bag technique. The experiments were carried out at two sites in northern Greece with soil pH of 7.8 and 5.6, respectively. Applied N increased biomass decomposition and total N release in the neutral soil and decreased organic matter loss and total N release in the acid soil. Nitrogen application increased P, Na and Mg release in the neutral soil and decreased Ca release in the acid soil. Without N application nutrient release was greater in the acid than in the neutral soil. Soil acidity appeared to have important consequences for how elements cycle through litter and soil, probably because of reduced faunal and microbial decomposition and increased levels of organic matter.

Competition between Canada thistle and winter wheat

Abstract This study was conducted to determine the effect of Canada thistle density and the direct and indirect effects of Canada thistle aboveground biomass and N concentration on wheat yield. A 4-yr experiment (1991–1995) with four Canada thistle densities (0, 4, 16, 64 plants m−2) was conducted. Initial statistical analysis showed a significant effect of Canada thistle density on wheat yield. Multiple regression and path analysis showed that the main factor causing wheat yield loss was Canada thistle N concentration. The second factor affecting wheat yield was Canada thistle biomass, and the last was Canada thistle density. Nomenclature: Canada thistle, Cirsium arvense (L.) Scop. CIRAR; winter wheat, Triticum aestivum (L.) Em. Tell. ‘Yecora’.

Maize, soybean and sunflower litter dynamics in two physicochemically different soils.

The decomposition rates of different plant parts of maize (Zea mays L.; Gramineae), soybean [Glycine max (L.) Merr.; Leguminosae] and sunflower (Helianthus annuus L.; Compositae) were studied in soils with different physicochemical characteristics, and their contribution to nutrient availability was assessed. Litter decomposition rates were affected by plant species, plant part, and soil characteristics. In site A (SiCL soil), loss of litter mass was highest in soybean followed by sunflower and maize. In site B (Loam soil), loss of litter mass for soybean and sunflower was almost the same, while for maize it was lower. Nutrient release was high when their soil concentration was initially low. The higher the initial concentration of a nutrient in a plant part the greater its release rate. Nutrients, especially N, released from maize litter mass will be available to successive crops for a longer period than for soybean and sunflower, and are unaffected by soil texture. Nutrients are easily removed from sunflower and soybeans and are more likely to be lost through leaching than nutrients from maize.

Composting Phragmites australis Cav. plant material and compost effects on soil and tomato (Lycopersicon esculentum Mill.) growth

Composting organic residues is a friendly to the environment alternative to producing fertilizer. This research was carried out to study the process of composting Phragmites australis Cav. plant material alone or with animal manure on a pilot-scale, to evaluate firstly the quality of the composts produced and secondly, using a pot experiment, the effects of their application on soil physicochemical characteristics and tomato plants development. For the compost production a randomized complete block design was used with five treatments (five compost types) and four replications. For the pot experiment, a completely randomized design was used with 17 treatments (plain soil, soil with synthetic fertilizer and the application of five compost types, at three rates each) and five replications. Compost N increased with composting time, while C/N ratio decreased significantly and by the end it ranged from 43.3 for CM to 22.6 for CY. Compost pH became almost neutral, ranging from 6.73 for CY to 7.21 for CM3Y3AM4 by the end. Compost combinations CY7AM3 and CM7AM3 had a more positive influence on the soil physicochemical characteristics than the others. Soil N, P, Ca and Mg concentrations and the reduction of clay dispersion were the highest when CM7AM3 compost was added. The macro-aggregate stability was the highest for CY7AM3, which also sustained plant growth. The latter compost combination improved most of the soil physicochemical characteristics and plant growth especially, when the application rate was 4% (w/w), which equals to 156 Mg ha(-1).

Ecological Threats and Agricultural Opportunities of the Aquatic Cane-Like Grass Phragmites australis in Wetlands

Wetlands are some of the most biologically productive and dynamic natural ecosystems with multiple value for man and nature. Indeed wetlands provide goods and service such as water storing, floodwater trapping, and trapping of sediment and pollutants. Wetlands also affect climate change by absorbing CO2, storing and releasing heat, and harnessing sunlight using a rich variety of vegetation that supports animal life. However wetlands can be polluted by industrial and commercial operations, agricultural runoff and storm water. Wetlands are degraded by filling in and drainage for land development. Wetlands are also degraded by dredging for commercial and recreational water traffic. Dam construction and irrigation roads change the hydrological status of wetlands. Wetlands allow the growth of aquatic macrophytic vegetation such as the emergent Phragmites australis. P. australis is mainly a clonal plant occurring in natural areas. P. australis invasion in wetlands alters the structure and function of the ecosystem by reducing plant and animal biodiversity and changing hydrological regimes and nutrient cycles. This invasion leads to less food or cover for wildlife, decreased use of an area for recreational purposes and decreased availability of drinking and irrigating water. Several methods have been applied in order to control P. australis growth. Control methods include non ecological methods such as burning that releases CO2 in the atmosphere and chemical control with non-specific herbicides. Control methods include also ecological methods such as grazing and removal of above-ground biomass by cutting. Cuttings can in turn be used for on-farm application as green manure or sludge after energy production and compost production. An economic and ecological basis for accepting a beneficial role for P. australis is lacking. This report focuses on the possibility that people living near wetlands could produce compost using plant material from P. australis. Suitable use of compost in agriculture could reduce the fertilizer application and thereby reduce the environmental pollution, improve food security and soil productivity, and increase sustainability in the agroecosystems. It can also play role in the climate change because part of the organic C is released as CO2 in the atmosphere and the rest is consumed by the decomposers.