Cultivated Plots Research Articles

Dendroecological analysis reveals long-term, positive effects of an introduced understory plant on canopy tree growth

Although the introduction of non-native species can have severe ecological and economic consequences, there is increasing awareness that introduced plants can also provide valuable ecosystem services. Here, we use tree-ring data from 30 sites in the southeastern US to demonstrate that non-native Lespedeza bicolor has long-term, positive effects on the growth of mature Pinus palustris trees. Trees growing near cultivated plots planted with nitrogen-fixing L. bicolor have experienced on average 56 % greater annual growth than trees growing near plots planted with non-nitrogen-fixing Secale cereale. Moreover, this fertilization effect has persisted for 25 years, since the local introduction of L. bicolor. This positive effect of L. bicolor provides evidence that non-native species may alter the growth of overstory trees that play important ecological and economic roles in southeastern forests, and suggests that subsidies from L. bicolor may influence carbon sequestration and change the nature of community dynamics at habitat edges. More generally, our results illustrate that non-native nitrogen-fixing understory plants may have strong, unappreciated effects on canopy tree growth, that the effects of non-native plants may have a distinct spatial extent, and that the net effect of non-native plants depends upon the interplay of ecological costs and benefits that may not be intuitive.

Distribution of Verticillium dahliae through watering systems in widely irrigated olive growing areas in Andalucia (southern Spain)

Verticillium dahliae Kleb. causes Verticillium wilts in many herbaceous and woody species. Many hosts of the pathogen are commonly cultivated in Andalucia (southern Spain), particularly major crops such as cotton, vegetables, almond, peach and, particularly, olive, in which the fungus causes Verticillium wilt of olive. Infective structures of the pathogen (microsclerotia), produced in the late phases of the infection cycle in senescent tissues of the infected plants, can be spread over short or long distances by a number of dispersal methods. Irrigation water is one of the factors implicated in this spread of V. dahliae. Indeed, increasing irrigation dosages in crops or an inadequate irrigation schedule have been identified as cultural practices favouring Verticillium wilt onset and severity in olive and other hosts. Most of the cultivated areas in the Guadalquivir Valley of Andalucia are irrigated by pumping stations using modern infrastructures that supply water to thousands of hectares of farm land, which are usually associated with irrigation communities. This study demonstrates that the pathogen survives in the sediment and particles suspended in water used for irrigation in different facilities of an irrigation community, that were involved in distributing water (main canal and reception tank of a investigated pumping station, irrigation pools and sand from filters). Thus microsclerotia moves from the pumping station to individual plots (olive and cotton cultivated farm) as viable microsclerotia, free or embedded in soil particles and plant debris, suspended in the irrigation water, or deposited in the sludge in piping systems or water storage ponds. We have detected amounts of inoculum in the solid pellet samples in these facilities that ranged from 2.7 to 6.7 microsclerotia per gram. Besides this, water from drippers in cultivated plots released into the soil a variable amount of infective propagules of the pathogen over time that accounted for 3.75 microsclerotia/m3 in some of the recording times. Therefore, irrigation water becomes an important source of inoculum that is very effectively involved in medium and long-distance spread of the pathogen.

Changes on aggregates morphology and roughness induced by different uses of Typical Argiudolls, Buenos Aires province, Argentina

Over the last few years, the increase of agriculture in the Pampean plains has led to a significant degradation of the most fertile soils in the country. The aim of our work is to define the effect of soil use on the stability of aggregates, bulk density and penetration resistance, and, especially, on the morphology and roughness of aggregates for their evaluation as possible soil quality indicators of Typical Argiudolls of south-eastern Buenos Aires. Mollic epipedons of plots with different soil use were analyzed: cultivated, pasture, and natural plots.The results indicated that bulk density values (>1.2g/cm3) and penetration resistance (2–4.4MPa) values were significantly higher (p<0.05) in the cultivated sites when compared to natural soil (1g/cm3 and 1.5–3MPa respectively). Aggregate stability was significantly lower (p<0.05) in the cultivated plots with respect to the natural plot, showing stable aggregates with values of 60–80% (crop intensive) and 85–100% (crop extensive). Moreover, these areas showed a greater percentage of spherical aggregates, and less rough than those in the natural plots. All of the properties were affected by soil use. The morphology and roughness of aggregates are effective indicators to help in the evaluation the quality of Typical Argiudolls of south-eastern Buenos Aires.

Assessment of Variability in the Quality of an Acrisol under Different Land Use Systems in Ghana

Three land use types (natural fallow, Leucaena leucocephala woodlot and cultivated plots) on a Ferric Acrisol in a semi-arid tropical zone of Ghana were compared to assess their effects on variability in selected soil properties and plant biomass accumulation. Organic carbon accumulation in the representative natural fallow profile was 22.7 g/kg, followed by 16.5 g/kg for the Leucaena woodlot and lastly 11.8 g/kg for the cultivated site. The mean bulk density of the natural fallow, Leucaena woodlot and cultivated sites were from 1.36 Mg/m3, 0.92 Mg/m3 and 1.33 Mg/m3 with corresponding range in mean weight diameter of 0.5 mm - 1.2 mm, 0.6 mm - 1.2 mm and 1.0 mm - 1.2 mm, respectively. The lower bulk density observed for the woodlot corresponds to increased total porosity, aeration, and root proliferation due to the stronger and extensive rooting system. Significant differences (P 36%). For the surface soils, exchangeable Na was very variable in the natural fallow. Exchangeable Na, Ca and K and total nitrogen were very variable in the Leucaena woodlot and the cultivated sites. Variability in clay content was very high in the cultivated soils only. The order cultivated land > Leucaena woodlot > natural fallow was noted for properties with high variability (CV > 36%). Plant biomass accumulation was 1834 kg/ha (natural fallow) and 830 kg/ha (Leucaena woodlot) indicating that natural fallows do not only maintain soil quality but they also decrease variability in soil properties which is desirable for soil productivity and quality.

Occurrence of Insect Pests in a Tomato Field under a Pesticide-free Dry Season Water-saving Cultivation in Northeast Thailand

The occurrence of insect pests and natural enemies was surveyed in a tomato field subject to watersaving cultivation during the dry season in northeast Thailand. The water-saving cultivation plots were mulched with plastic film or rice straw and watered 5 times during the crop cycle, while the conventional plots were un-mulched and watered 3 times a week. A total of 5 g·m –2 of 12-9-6 liquid fertilizer was applied to each plot. Pesticide was not applied to any of the plots. The tomato yields in the plots covered with plastic film or rice straw mulches were 1205 and 934 g·m –2 , respectively, and that of the conventional plot was 1123 g·m –2 . These values were almost similar to the local average yield of 1190 g·m –2 . The prevalence of various insect pests such as aphid, thrips, whitefly, leaf miner, insects belonging to the Coccidae and Miridae families, and cotton bollworm were observed. The water-saving cultivation had little influence on the occurrence of insect pests compared with conventional cultivation. Apart from some yield loss due to the cotton bollworm, the tomato yield remained nearly intact, and the crops sustained no serious damage.

Organic matter fractionation in aggregates typical Argiudolls southeastern Buenos Aires and its relation to different soil uses: a preliminary study

Organic matter is a fundamental factor in the biogeochemical cycle of carbon; it influences the chemical, physical, and biological properties of the soil. The aim of this paper is to determine the organic fractions in the three predominant morphologies of aggregates found in Typical Argiudolls of the Buenos Aires southeastern area and to link them to different soil uses, as possible indicators of soil quality. The study was carried out in the basin de Los Padres Pound (General Pueyrredon, Buenos Aires). We analyzed the first 5 cm of mollic epipedons of plots with different soil uses: (a) cultivated plots, (b) pine and eucalyptus forests, (c) pastures, and (d) a natural plot in the de Los Padres Pound Reserve as a reference. The percentage of soil organic carbon (SOC), light organic carbon (LOC), fulvic acids (FA), humic acids (HA), and humins (H) in elongated, quadrangular and spherical aggregates were determined. The results show slight variations in SOC (7.2–8.6%) in the spherical aggregates of all the plots and a greater variability in elongated and quadrangular aggregates (5.6–10% and 6.9–13.6%, respectively). HA are minimal in the agroecosystems with extreme values of 0.02% in the spherical aggregates of cultivated plots, and maximal in the elongated and quadrangular aggregates of natural plots (0.3–0.5%). Fulvic acids display a similar behavior, while H decrease slightly with the morphologies and the different practices. The substantial decrease of humic substances in cultivated plots translates into a lower biologic activity; this, in turn, influences the aggregation, thus lowering the structural stability of these plots, which have been under agro-horticultural management for more than 50 years.

CARBON BUDGET AND SEQUESTRATION POTENTIAL IN A SANDY SOIL TREATED WITH COMPOST

ABSTRACTThe effects of compost application on soil carbon sequestration potential and carbon budget of a tropical sandy soil was studied. Greenhouse gas emissions from soil surface and agricultural inputs (fertiliser and fossil fuel uses) were evaluated. The origin of soil organic carbon was identified by using stable carbon isotope. The CO2, CH4 and N2O emissions from soil were estimated in hill evergreen forest (NF) plot as reference, and in the corn cultivation plots with compost application rate at 30 Mg ha−1 y−1 (LC), and at 50 Mg ha−1 y−1 (HC). The total C emissions from soil surface were 8·54, 10·14 and 9·86 Mg C ha−1 y−1 for NF, HC and LC soils, respectively. Total N2O emissions from HC and LC plots (2·56 and 3·47 kg N2O ha−1 y−1) were significantly higher than from the NF plot (1·47 kg N2O ha−1 y−1). Total CO2 emissions from fuel uses of fertiliser, irrigation and machinery were about 10 per cent of total CO2 emissions. For soil carbon storage, since 1983, it has been increased significantly (12 Mg ha−1) under the application of 50 Mg ha−1 y−1 of compost but not with 30 Mg ha−1 y−1. The net C budget when balancing out carbon inputs and outputs from soil for NF, HC and LC soils were +3·24, −2·50 and +2·07 Mg C ha−1 y−1, respectively. Stable isotope of carbon (δ13C value) indicates that most of the increased soil carbon is derived from the compost inputs and/or corn biomass. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Response of Melon Cultivars to Natural Infection by Diseases in South Western Nigeria

Melon is an important crop in South western, Nigeria. The study evaluated incidence and severity of Anthracnose, mildews, wilt, leaf spot and blight disease of melon cultivars: Serewe, Bara A, Bara B in cultivated plots in South Western Nigeria. Experiment was set in a randomized complete block design with five replicates in the Teaching and Research field of the University of Ibadan, Nigeria. Disease incidence and severity was varied among the melon cultivars. Predominant foliar diseases were Anthracnose and leaf blight with maximum disease incidence index of 82.0–100% across the cultivars. Disease incidence and severity indices for all diseases were high during the early season (27.0-100%) and low during the dry season (19.0-65.0%) except for the downy mildew disease. Fusarium wilt disease incidence was significantly lower than all other diseases encountered. Cultivars were not consistent in their reaction to the diseases and these also varied with the years. The study has given information on the predominant diseases for which control management technology should be developed.

Soil microbial communities are affected more by land use than seasonal variation in restored grassland and cultivated Mollisols in Northeast China

Seasonal variations of soil microbial communities in a cultivated black soil (0–20 cm) with different fertilizing treatments [no fertilizer (NoF), chemical fertilizer (CF) and chemical fertilizer plus manure (CFM)] and in a neighboring plot of natural restoration (NR) in Northeast China were studied over a period of two years. The cultivated soils were plowed and had a rotation of maize–soybean–wheat. The NR plot was revegetated naturally with grasses since 1985. The soil microbial biomass C content across the five sampling times was 102, 89, and 53% larger in NR plot than that in NoF, CF, and CFM plots, respectively. Dominant members of bacterial and fungal communities as assessed by DGGE banding patterns of partial PCR products of bacterial 16S rDNA and fungal rDNA ITS were different between cultivated plots and NR plot but not between cultivated plots, and less influenced among seasonal sampling times. These findings indicate that land use was a major factor in influencing dominant members of microbial communities in black soils in Northeast China and that they were little affected by fertilization and very stable over time despite the distinct seasonal fluctuations in temperature and rainfall. Sequence analysis of several excised DGGE bands indicated that bacterial phyla of Proteobacteria and Actinobacteria, and fungal phyla of Ascomycetes and Basidiomycetes contributed to the dominant microbial community members in black soils in Northeast China.

Impact of Long-Term Alfalfa Cropping on Soil Potassium Content and Clay Minerals in a Semi-Arid Loess Soil in China

Alfalfa cropping has been considered an efficient method of increasing soil fertility. Usually nitrogen increase in root nodules is considered to be the major beneficial effect. A 21-year time series (five sampling periods) of alfalfa cultivation plots on a loess soil, initially containing illite and chlorite, in Lanzhou of northwestern China was selected to investigate the relationships among alfalfa cropping, soil potassium (K) content and soil clay minerals. The results indicated that soil K significantly accumulated after cropping, with a peak value at about 15 years, and decreased afterwards. The accumulated K was associated with the K increase in the well-crystallized illite, which was not extracted by the traditional laboratory K extraction methods in assessing bioavailability. The steep decline in soil K content after 15-year cropping was in accord with the observed fertility loss in the alfalfa soil. Plant biomass productivity peaked at near 9 years of culture, whereas soil K and clay minerals continued to increase until cropping for 15 years. This suggested that K increased in the topsoil came from the deep root zone. Thus alfalfa continued to store K in clays even after peak production occurred. Nitrogen did not follow these trends, showing a general decline compared with the native prairie soils that had not been cropped. Therefore, the traditional alfalfa cropping can increase K content in the topsoil.

A fuzzy quality index for the environmental assessment of a restored wetland

This paper describes the feasibility study for the restoration of agricultural land with a tendency to become waterlogged into a natural wetland, conceived to mitigate floods and to remove nutrients from the water drained from the cultivated plots. The wetland model, developed in aquatox, includes the nutrient dynamics both in the water and in the sediment, and the vegetation that is expected to develop as a consequence of flooding. The model inputs were synthesized from historical time series of rainfall and chemical data collected over the last decade. The model outputs are used to compute a synthetic fuzzy quality index (FQI) to assess the removal efficiency of the wetland. This FQI is based on three main variables describing the ecosystem quality: chlorophyll-a, dissolved oxygen and total suspended solids. This index has the merit of being simple enough to be immediately grasped by non-technical people, like managers and stakeholders, to whom the restoration project is proposed. The simulations, performed under five differing loading scenarios demonstrate the feasibility of this solution, which is robust enough to accommodate a 50% increase in either nitrogen, phosphorous or organic matter.

Bio-concentration of chromium—an in situ phytoremediation study at South Kaliapani chromite mining area of Orissa, India

Mine waste water at South Kaliapani usually contains toxic levels of hexavalent Cr(VI). The present in situ study was conducted at South Kaliapani chromite mine area in Orissa state, India, to assess the phytoremediation ability of three plants, namely, rice (Oryza sativa L.), paragrass (Brachiaria mutica), and an aquatic weed (Eichhornia crassipes), in attenuating Cr(VI) from mine waste water and to correlate the bio-concentration factors (BCF) of Cr. Water hyacinth (E. crassipes) showed 24% to 54% reduction whereas paragrass (B. mutica) was able to reduce 18% to 33% of Cr(VI) from mine water. This reduction was studied over a period of 100 days of plant growth. The reduction was observed through a passage of a sum total of 2,000 sq. ft. cultivated plots and ponds separately. Reduction in Cr(VI) content in mine water varies with plant age as well as with the distance of passage. Cr accumulation and BCF values increased with high soil Cr levels as well as the age of plants. High BCF and transportation index (Ti) values, i.e., 10,924 and 32.09, respectively, were noted for water hyacinth. The Ti values indicated that the root-to-shoot translocation of Cr was very high after 100 days of growth. The total accumulation rate was maximum (8.29 mg Cr kg dry biomass(-1) day (-1)) in paragrass. The BCF values for roots were noted to be higher than those of leaves, stems, and grains of the 125-day-old plants. Hence, paragrass and water hyacinth may be used as tools of phytoremediation to combat the problem of in situ Cr contamination.

Impact of very low crop residues cover on wind erosion in the Sahel

In the Sahel, with average annual precipitation in the order of 500 mm yr − 1 , wind erosion occurs mainly on cultivated millet fields whose surfaces are only partially covered by crop residues. The impact of these residues on wind erosion was not clearly established. The objective of this study is thus to quantify the actual amount of crop residues in traditional Sahelian fields and to determine their impacts on wind erosion by reference to a bare surface throughout the seasonal cycle over several years. At the beginning of the year during dry season, Sahelian farmers use to “clean” their fields, i.e. cut and lay flat on the soil surface any millet stalks still standing and yearly sprouts of shrubs. After this clearing, the crop residues cover (CRC) regularly decreases passing from 12% to less than 2% four months later. On traditional cultivated plot, crop residues efficiently prevent soil losses by wind erosion during the dry season and considerably reduce erosion fluxes at the beginning of the rainy season. However, for CRC lower than 2%, wind velocities were sufficient to produce important erosion even during dry season. A minimal cover rate of about 2% (100 kg ha − 1 ) thus appears as critical to reduce wind erosion. This reduction is driven by the higher aerodynamic roughness length which increases the wind erosion threshold velocity. If field clearing is made in January, as currently done, the CRC just after clearing should be about 800 kg ha − 1 to maintain CRC above 2% at beginning of the rainy season when wind velocities are the highest and wind erosion the most intense. Our results also demonstrate that during the second part of rainy season wind erosion is reduced, not so much due to vegetation development but rather to a decrease in the number and the intensity of high winds events. ► Below a threshold of 2% of crop residues cover, Z0 decreases dramatically fields. ► Crop residues cover of 2% corresponds to a residues density of 100 kg ha − 1 . ► Above this threshold, potential wind erosion is reduced by at least a factor of 3. ► Meteorological changes explain the end of erosion by mid July in the Sahel.

Using 7Be to Trace Temporal Variation of Interrill and Rill Erosion on Slopes

Understanding the processes of erosion-transport-deposition of sediments is necessary to develop more effective soil erosion prediction models. In this study, Beryllium-7 (7Be) was used as a tracer to describe the dynamics of soil erosion during a simulated rainfall event on outdoor cultivated plots. The quantitative results of interrill and rill erosion on slopes are discussed in this paper. And the calculated results using 7Be tracer are in good agreement with the measured ones. Therefore, 7Be tracer could accurately quantify the processes of erosion on the cultivated slope.

The implications of land preparation, crop establishment method and weed management on rice yield variation in the rice–wheat system in the Indo-Gangetic plains

The implications of adopting alternative seeding methods for rice and wheat establishment were examined at three geographically separate sites in the rice–wheat system of the Indo-Gangetic plains, across northern India. Rice yields in cultivated plots, established by either wet or dry seeding methods, were evaluated in comparison to yields from zero-tillage plots and under conventional transplanting methods. In the same trials, the effects of crop establishment methods in wheat were assessed both on wheat yields and rice yields. Rice crop establishment methods markedly influenced the emerging weed flora and attainable yields were measured in relation to intensity of weed management. Over four years, average rice grain yields in the absence of weed competition were greatest (6.56 t ha −1) under wet seeding (sowing pre-germinated rice seed on puddled soil), and similar to those from transplanted rice (6.17 t ha −1) into puddled soil, and dry seeded rice after dry soil tillage (6.15 t ha −1). Lowest yields were observed from dry seeded rice sown without tillage (5.44 t ha −1). Rice yield losses due to uncontrolled weed growth were least in transplanted rice (12%) but otherwise large (c. 85%) where rice had been sown to dry cultivated fields or to puddled soil, rising to 98% in dry seeded rice sown without soil tillage. Weed competition reduced multiple rice yield components, and weed biomass in wet seeded rice was six-fold greater that in rice transplanted into puddled soil and twice as much again in dry seeded rice sown either after dry tillage or without tillage. Wheat grain yields were significantly higher from crops sown into tilled soil (3.89 t ha −1) than those sown without tillage (3.51 t ha −1), and also were elevated (5% on average) where the soil had been dry cultivated in preparation for the previous rice crops rather than puddled. The method of wheat cultivation did not influence rice yield. Soil infiltration rates in the wheat season were least where the land had been puddled for rice (1.52 mm h −1), and greater where the soil had been dry-tilled (2.63 mm h −1) and greatest after zero-tillage (3.54 mm h −1). These studies demonstrated at research managed sites across a wide geographic area, and on farmers’ fields, that yields of dry seeded rice sown after dry cultivation of soil were broadly comparable with those of transplanted rice, providing weed competition was absent. These results support the proposition that direct seeding of rice could provide an alternative to the conventional practice of transplanting, and help address rising costs and threats to sustainability in the rice–wheat rotation. Further, analysis of patterns of long-term rainfall data indicated that farmers reliant on monsoon rainfall could prepare fields for dry direct seeded rice some 30 days before they could prepare fields for either transplanting or seeding with pre-germinated seed. Dry, direct seeding of rice contributes a valuable component of an adaptive strategy to address monsoonal variability that also may advance the time of wheat establishment and yield. Whilst the results illustrate the robustness, feasibility and significant potential of direct seeded rice, they also highlight the critical nature of effective weed control in successful implementation of direct seeding systems for rice.

Eco-sanitation and its benefits: an experimental demonstration program to raise awareness in central Nepal

This study focuses on awareness and an experimental demonstration about the use of human urine and wood ash as a fertilizer. This study was conducted in Chanauta, central Nepal, from November 2009 to February 2010. The villagers (N = 27) were asked about their awareness of eco-sanitation and fertilizer value of urine and ash. All the participants agreed that the use of urine and ash was a good idea. In the experimental study, the fertilizer value of urine+ash was compared with animal manure and no-fertilizer in the cultivation of radish, potato, broadleaf mustard, cauliflower, and cabbage. Different plants cultivated plots received 54–81 kgN/ha with urine+ash or manure fertilizer. The urine+ash fertilizer produced significantly (p < 0.05) higher broadleaf mustard biomass than obtained from animal manure and without fertilization. Urine+ash-fertilized plots growing radish, potato, cauliflower, and cabbage produced similar or slightly higher yields biomass compared to those achieved with manure fertilization. This might be because of high P, K as well as greater availability of N in applied urine compared to manure. It is concluded that urine+ash fertilizer can be used instead of animal manure; in this study, a dose of 4 L of urine was equal to 1 kg of dry cattle manure and produced a similar or greater yield of vegetable biomass than manure fertilization. To be able to generalize this conclusion, it is important to conduct these kinds of experiments with different seasonal crops and in other parts of the world.

About Sr isotopes in coffee ‘Bourbon Pointu’ of the Réunion Island

Demonstration of the regional source of a high-quality product is nowadays essential to protect it from commercial transactions and cheatings. In this study, Sr isotopes are proposed as a tool to identify the regional source of a vegetable, on the basis of a combined geochemical investigation on a Coffea Arabica var. Laurina cultivation plot located on th Réunion Island. The Sr isotopic composition (87Sr/86Sr) of the produced coffee beans (called Pointed Bourbon) and of their growing environment, including soils, parent rocks, waters and fertilizers are determined. Flux of Sr in coffee beans is mainly dominated by soil solutions that can be influenced by Sr-rich fertilizers. This influence is however low enough to detect the cultivation soils’ Sr isotopic ratio in the vegetable product, even after roasting. It also allows discrimination of coffees produced on varied geological areas. Measurements performed on the same variety of coffee beans produced in New Caledonia strengthen the demonstration.

Viruses Infecting Tomato in València, Spain: Occurrence, Distribution and Effect of Seed Origin

AbstractViral diseases are a serious limitation to the tomato crop in the region of València, Spain. A survey of tomato viruses in open field cultivation plots was made in the three provinces of this region. A total of 228 plots classified according to the origin of the seed (farmer seed plots or commercial seed plots) were surveyed, from which 1300 individual plants were sampled and tested for Cucumber mosaic virus (CMV), Pepino mosaic virus (PepMV), Parietaria mottle virus (PMoV), Potato virus Y (PVY), Tomato mosaic virus (ToMV), Tomato spotted wilt virus (TSWV) and for the tomato yellow leaf curl disease (TYLCD). Virus infection was detected in 58.9% of the plants sampled and in 86.0% of the plots surveyed. All these viruses were detected, and the most prevalent were ToMV and PVY (34.1% and 27.1% of infected plants, respectively), but PMoV and TYLCD were the less prevalent (1.2% and 1.3% of infected plants, respectively). Differences among provinces and seed origin were found for most of the viruses studied. In particular, both ToMV and PVY had a higher level of infection in plants from farmer seed plots than in commercial seed plots, which accounts for the higher percentage of virus‐infected plants in the former (64.2%) when compared to the latter (49.1%). Single and multiple infections were found in 42.38% and 16.54% of the samples, respectively. The most common multiple infection was of ToMV, PVY or both. These results show that the percentage of infected plants and plots in open field cultivation is very high in this region and the origin of the seed is an important factor in the incidence of virus infection. In this respect, preventive measures, including virus‐free seed, resistant cultivars and improved cultural practices, could reduce the incidence of virus infection.

Do abiotic factors cause a gradual yield decline under continuous aerobic rice cultivation? A pot experiment with affected field soils

Aerobic rice is a water-saving technology in which rice grows in non-puddled and non-saturated (aerobic) soil without ponded water. A gradual decline in rice yield was found in field plots at the farm of the International Rice Research Institute, Los Baños, Philippines, where rice has been cultivated continuously for 10 cropping seasons under aerobic rice conditions. We investigated whether abiotic soil factors lead to the observed yield decline. An aerobic rice pot experiment was conducted using field soils from flooded rice plots and from the 10-season-long aerobic rice cultivated plots (referred to as 1st-season and 11th-season aerobic rice, respectively). Subtreatments consisted of soil sterilization by oven heating (at 95°C or higher for 24 h) and a control treatment. The above-ground biomass of 1st-season aerobic rice was significantly greater than that of 11th-season aerobic rice in both the oven-heating and control treatments. Oven heating increased soil N availability and above-ground biomass accumulation over the control in both 1st-season and 11th-season aerobic rice, but the above-ground biomass in the oven-heated 11th-season aerobic rice was still significantly lower than that of the oven-heated and even the untreated (control) 1st-season aerobic rice. These results suggest that abiotic factors contribute to the gradual yield decline observed in the field plots.

Vegetation recolonisation of abandoned agricultural terraces on Antikythera, Greece

Antikythera is a small, relatively remote Mediterranean island, lying 35 km north-west of Crete, and its few contemporary inhabitants live mainly in the small village at the only port. However, an extensive network of terraces across the island bears witness to the past importance of farming on the island, although the intensity of use of these cultivated plots has changed according to fluctuating population levels. Most recently, the rural population and intensity of cultivation have dramatically declined. Our aim is to understand the recolonisation process of agricultural land by plants after terraces are no longer used for the cultivation of crops. The results demonstrate a relatively quick pace of vegetative recolonisation, with abandoned farm land covered by dense scrub within 20 to 60 years. The archaeological implications are that, following even relatively short periods of abandonment, the landscape would have required arduous reinvestment in the removal of scrub growth, as well as the repair and construction of stone terraces, to allow cultivation once again.