White clover (Trifolium repens L.) is cultivated as a forage crop and planted in various landscapes for soil conservation. There are numerous reports of failed white clover stands each year. A good understanding of the seed germination biology of white clover in relation to environmental factors is essential to achieve successful stand establishment. A series of experiments were conducted to investigate the impacts of light, temperature, planting depth, drought, and salt stress on seed germination and the emergence of white clover. White clover is negatively photoblastic, and seed germination averaged 63 and 66% under light and complete dark conditions 4 weeks after planting (WAP), respectively. Temperature affected the seed germination speed and rate. At 1 WAP, seeds incubated at 15 to 25 °C demonstrated a significantly higher germination rate than the low temperatures at 5 and 10 °C; however, the germination rate did not differ among the temperature treatments at 4 WAP. The results suggest that white clover germination decreases with increasing sowing depths, and the seeds should be sown on the soil surface or shallowly buried at a depth ≤1 cm to achieve an optimal emergence. White clover seeds exhibited high sensitivity to drought and salinity stress. The osmotic potential and NaCl concentration required to inhibit 50% seed germination were −0.19 MPa and 62.4 mM, respectively. Overall, these findings provide quantifiable explanations for inconsistent establishment observed in field conditions. The results obtained in this research can be used to develop effective planting strategies and support the successful establishment of white clover stands.
Daytime energy balance at the surface in cloudy tropical conditions for Ile-Ife; Nigeria (7°33'N, 4°34'E) is investigated based on a series of micrometeorological measurements performed in October/November of 1998. For the humid environment that it is (mixing ratio, 17 -25 g / kg), magnitudes of the latent heat flux were much larger than the values for the sensible heat. Of the morning hours the average value for the Bowen ratio obtained was 0.36, while for the afternoons it was 0.74. As the soil surface became dried up in the afternoons, magnitudes of both sensible heat and ground heat fluxes were found to be comparable.
Fluctuations in the magnitudes of the terms of the surface energy balance correlated well to the cloud amount, degree of soil wetness, air temperature and humidity. But of all these factors, the variation in the amount of cloudiness appeared most dominant.
Decomposition influences carbon and nutrient cycling from crop residues. The nylon-mesh-bag technique was implied to study the decomposition and N-release dynamics from different crop residues under field conditions. The four types of residues were: maize (lower than 50% below the cob), wheat (lower than 25% of wheat stubbles), a whole mung bean residue, and a mixture of wheat + mung bean residue (1:1 ratio) put on the soil surface and in below the sub-surface. Decomposition and N release from both at-surface- and below-surface-placed residues were accurately described by a single-pool first-order exponential decay function as a function of thermal time (based on the accumulative daily mean temperature). The simple first-order exponential model met the criteria of goodness of fit. Throughout the decomposition cycle (one thermal year), the rate of decomposition as measured by a decrease in residue mass and the release of total N were statistically higher from the sub-surface compared to the surface-placed residue, irrespective of the residue type. At the end of the 150-day decomposition cycle, the release of total N was highest in mung bean (32.0 kg N ha−1), followed by maize (31.5 kg N ha−1) > wheat + mung bean (16.1 kg N ha−1), and the minimum (6.54 kg N ha−1) in wheat residue. Crop residues with a wider C/N ratio such as maize and wheat, when applied on the soil surface in conservation agriculture, caused the decomposition to occur at slower rates, thereby providing long-term beneficial effects on the soil thermal regime, soil moisture conservation, and C sequestration in North-West India.
Earlier works on Ramdas Layer were about its certainty, its existence, energy balance on the layer and a matching mathematical model. We, first identified it in Thiruvananthapuram, Kerala, for eight days during a fortnight study on soil heat flux. A lifted minimum in temperature could have implications in agriculture and horticulture and so with a view to finding out a range of height through which Ramdas layer occurs, Ramdas-max, Ramdas-min are identified. On 24 January 1994, Ramdas layer occurred at a maximum height of 0.8m from the surface and the day is labeled as Ramdas-max. On 1 February 1994, it occurred at a lower height of 0.4m from the surface and the day is labeled as Ramdas-min.
The thermal wave at the ground and at 0.05m depth, the range of thermal wave, its relationship with Ramdas layer, the temperature profile, the rate of change of heat in that layer with that at the surface and the subsoil heat flux at the sub-soil surface stratum(surface-0.05m) during R~mdas-max and Ramdas-min are duly compared and discussed.
There is global interest in enhancing the ecosystem services provided by landscapes and catchments dominated by plantation (monoculture) forestry. Partial reversion of plantations to locally native species (reforestation) is one option. However, the ecological outcomes of this kind of plantation reversion are poorly known. The partial reforestation of a pine plantation (Pinus radiata D. Don 1836) in the Australian Capital Territory with native species following a wildfire provides a rare case study of the environmental consequences of such a reversion. We estimated changes in landscape functionality by measuring indices of water infiltration, nutrient cycling, and soil surface stability across five landscape-scale treatments after the 2003 Lower Cotter Catchment bushfire: (1) natural regeneration of a native forest burned in 2003, (2) burned pine plantation replanted to pines, (3) burned plantation replanted to native trees and shrubs, (4) burned plantation allowed to naturally regenerate, and (5) forest roads rehabilitated by planting native trees and shrubs. At 14 years after the fire, we found that the regenerating native forest had the highest indices of water infiltration, nutrient cycling, and soil surface stability. The burned pine plantation that was replanted to pines in 2005 had indices of functionality that were higher than the burned plantation areas that were either allowed to naturally regenerate to native eucalypt forest or were planted with native forest species. These two types of native forest rehabilitation treatments had only minor differences in functionality. The rehabilitated closed roads were the least functional. We found that a pine plantation at the closed canopy stage can supply regulating services of water infiltration, nutrient cycling, and soil surface stability comparable to a native forest at a similar stage postfire; however, a significant limitation of the plantation was its low ecosystem resilience. It required massive soil disturbance to replant postfire and long-term maintenance of an extensive unpaved road network. The active or passive rehabilitation of native forest is justified to improve the natural resilience to wildfire. However, this rehabilitation of a native forest following use as a pine plantation is a multidecade process in this relatively low-rainfall environment.
The 2003 Canberra bushfire destroyed the entire pine plantation at Lower Cotter Catchment, a water catchment in Australian Capital Territory, but also provided an opportunity to examine and quantify changes in ecosystem functions with different restoration treatments. Landscape Function Analysis, including three indices (water infiltration, nutrient cycling, and soil surface stability), was used in this study. Findings suggest that both native eucalyptus forests and pine plantations recovered to relatively high levels of functionality within just 15 years after the bushfire, compared with all other restoration treatments, but plantations of Pinus radiata are not resilient to wildfire from a commercial perspective. These results help to justify the controversial decision to restore the majority of the catchment with native species in 2005. However, long-term monitoring is needed to determine how long it will take for the replanted and natural regeneration treatments to approach the functionality of the native forest.
The substitution of native vegetation in agricultural systems can cause several changes in the chemical and physical soil attributes, and in the dynamics of soil organic carbon. This study aimed to evaluate changes in soil physical attributes and carbon stock in soil organic matter fractions in irrigated sugarcane crops, as a function of land use and straw management practices over time, in the North of Minas Gerais State, Brazil. Four sugarcane fields with different ages and management systems were studied: Cane 6, Cane 7, Cane 8, and Cane 10. The data obtained were compared with a native vegetation area located near the sugarcane fields, and used as reference for unmanaged soil. In each system, soil samples were collected in the 0-10, 10-20, and 20-30 cm depth layers, to determine the physical attributes, the total organic carbon, and the physical fractions of the soil organic matter. We found that the sugarcane management with the maintenance of a part of the straw on the soil surface contributes to the preservation of the soil structure and the most stable fractions of organic carbon over time. However, in the regions with high annual mean temperature and in the irrigated systems, the soil tillage for the renewal of the sugarcane fields significantly decreases the total soil organic carbon.
AbstractThe potential for a Trichoderma-based compost activator was tested for in-situ rice straw decomposition, under both laboratory and field conditions. Inoculation of Trichoderma caused a 50% reduction in the indigenous fungal population after 2 weeks of incubation for both laboratory and field experiments. However, the Trichoderma population declined during the latter part of the incubation. Despite the significant reduction in fungal population during the first 2 weeks of incubation, inoculated samples were found to have higher indigenous and total fungal population at the end of the experiments with as much as a 300% increase in the laboratory experiment and 50% during day-21 and day-28 samplings in the field experiment. The laboratory incubation experiment revealed that inoculated samples released an average of 16% higher amounts of CO2 compared to uninoculated straw in sterile soil samples. Unsterile soil inoculated with Trichoderma released the highest amount of CO2 in the laboratory experiment. In the field experiment, improved decomposition was observed in samples inoculated with Trichoderma and placed below ground (WTBG). From the initial value of around 35%, the C content in WTBG was down to 28.63% after 42 days of incubation and was the lowest among treatments. This is significantly lower compared with NTBG (No Trichoderma placed below ground, 31.1% C), WTSS (With Trichoderma placed on soil surface, 33.83% C), and NTSS (No Trichoderma placed on soil surface, 34.30% carbon). The WTBG treatment also had the highest N content of 1.1%. The C:N ratio of WTBG was only 26.27, 39.51% lower than the C:N ratio of NTBG, which is 43.43. These results prove that the Trichoderma-based inoculant has the potential to hasten the decomposition of incorporated rice straw.