Volume 2 Number 1 & 2 2008
CONTENTS AND ABSTRACTS
Christine H. Stark (Great Britain), Karl G. Richards (Ireland) The Continuing Challenge of Agricultural Nitrogen Loss to the Environment in the Context of Global Change and Advancing Research (pp 1-12)
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Invited Review: Excess nitrogen in soil, aquatic and atmospheric environments is an escalating global problem as a result of technology and human actions increasingly dominating the nitrogen cycle at all environmental scales, which often leads to an accumulation of reactive nitrogen compounds in ecosystems. While sources of environmental nitrogen pollution are diverse and agriculture is not solely responsible, there is growing concern about the large number of identified impacts on water quality and greenhouse gas emissions, which originate from intensified agricultural management with its continually increasing nitrogen fertiliser consumption. Interactions of nitrogen in and with the environment are complex and our understanding of nitrogen cycling continues to be re-defined with the discovery of new nitrogen cycling processes and pathways. There is an increasingly urgent need for interdisciplinary, international studies that holistically investigate measures to control nitrogen losses and reduce agricultural costs while maintaining productivity. This is best achieved by joint actions among researchers, land managers and policy makers by assessing and implementing improved farm management practices that optimise agricultural production, minimise adverse effects on human and animal health and reduce environmental pollution. Similarly promising approaches to enhance environmental and economic sustainability of agricultural production are put forward by recent studies that take advantage of the improved understanding of soil nitrogen processes and plant uptake.
Man-Wah Li, Hon-Ming Lam (China) Searching for Nitrogen Sensing Systems in Higher Plants (pp 13-22)
Invited Review: Nitrogen is an essential element of all life forms. With limited mobility, most plants cannot actively hunt for additional nitrogen resources apart from the substratum they rooted. To efficiently utilize the finite nitrogen resource, plants need to adopt a set of nitrogen sensing systems to manage the nitrogen status from time to time. To cope with diverse situations, different systems were evolved to perceive different form of signals (from inorganic nitrogen to organic nitrogen) at different levels (from intracellular to the whole plant). The integrated effects of these signals ensure efficient uptake, transportation, assimilation, utilization, and storage of important nitrogen resources. Several nitrogen sensing systems were documented in microorganisms and animals. In this review, we summarized the recent progress of similar systems found in plants, including: (i) PII-mediated nitrogen regulatory system; (ii) general amino acid control; (iii) ionotropic glutamate receptors; (iv) cytokinin His-Asp phosphorelay system; and (v) NIT2 system.
Haim Nerson (Israel) Mineral Nutrition of Cucurbit Crops (pp 23-32)
Invited Review: Proper mineral nutrition of crops is in many ways a blend between science and art. Knowledge is the basic pre-requisite for the correct use of fertilizers, but because so many factors (including uncontrolled ones like temperatures and sunlight) are involved in providing proper plant nutrition, a grower’s green finger is also important. The main decisions that one has to make are which fertilizer source to use, when to fertilize (calendar and plant developmental stage) and how much fertilizer to apply (plant requirement and nutrient availability). Adequate fertilization of cucurbits already from the early emergence stage has advantages in terms of uniform, health and seedling vigor, but there is much evidence that plants have efficient mechanisms to repair nutritional stresses. Fertilization under field and protected conditions require different approaches. Fertilization in the field consists of a basic nutrient application (before seeding) and 1-3 side dressings during the growing season, whereas fertilization under protected environments and especially in container-grown crops requires a continuous application of nutrients through the irrigation system. The growing demand over the past decade for cucurbit fruits year-round has shifted a greater part of production from the field to greenhouses and plastic tunnels. Mineral nutrition under expensive protected conditions requires more precise and finely-tuned methods as compared to traditional field-grown crops where soil served as a nutrient reservoir and buffer. A new trend which has been developing over the past few years is the growing interest in environmental conservation and an enlarging movement toward sustainable and organic agriculture. Plant nutrition studies in organic ecosystems are generally long-term and accordingly our present understanding is still in its infancy.
Lixin Wang, Jin Wang (China/USA), Jianhui Huang (China) Net Nitrogen Mineralization and Nitrification in Three Subtropical Forests of Southwestern China (pp 33-40)
Original Research Paper: Nitrogen is a limiting nutrient for plant growth in many forest ecosystems; however, information on N mineralization and nitrification in subtropical forests is generally lacking. To determine the effect of forest site on N mineralization and nitrification and the key contributing factors under subtropical climate, we studied the seasonal patterns of soil N mineralization and nitrification with closed in situ core incubation method in a mixed evergreen broadleaf forest, a pure Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) forest, and a pureZhennan (Phoebe zhennan S. Lee et F. N. Wei) forest in Dujiangyan, Sichuan province, southwestern China. Our results indicated that the rates and the seasonal patterns of net N mineralization and nitrification were similar among the three forest sites. The rates of both net N mineralization and nitrification were the highest in the winter season (December 2000 to April 2001), and negligible in spring and summer. The variability in net N mineralization and nitrification and the specific environmental contributing factors, however, varied in different forest sites. The overall similarity in N mineralization and nitrification rates suggests that regional climate condition is the most dominant controlling factor on N mineralization and nitrification. At local scales, however, biodiversity may play an important role in patterns of N mineralization and nitrification; higher biodiversity could lead to higher and more stable N mineralization and nitrification.
Christine H. Stark (Great Britain), Karl G. Richards (Ireland) The Continuing Challenge of Nitrogen Loss to the Environment: Environmental Consequences and Mitigation Strategies (pp 41-55)
Invited Review: In this second part of our review on nitrogen loss to the environment, we discuss the increasing problem of air and water contamination with nitrogenous compounds with a focus on agricultural contributions, water quality standards and legislation and mitigation options available to land managers. Excess nitrogen in soil, aquatic and atmospheric environments is a growing global problem due to human activity increasingly dominating nutrient cycling. While sources of environmental nitrogen pollution are diverse, considerable concern exists regarding the impact of intensified agricultural systems and the effects of increasing rates of fertilisation on water and air quality, which negatively affect human and animal health, increase climate change, ozone depletion and atmospheric nitrogen deposition, and cause the deterioration of aquatic habitats. Over recent decades, regional, national and international legislation has been introduced to control and mitigate nitrogen loss from agricultural sources. While the effects of nitrogen on human and animal health have resulted in the introduction of limits that ensure drinking water quality, the role of nitrogen in aquatic eutrophication has greatly been underestimated in the past and the implementation of new standards and laws has been recommended. In addition, a wide range of mitigation measures, mostly practical farm management solutions, is available to agriculture to reduce nitrogen loss to the biosphere. The involvement of land managers in the decision making and implementation processes is, however, crucial to guarantee the success of measures that optimise agricultural production, minimise adverse effects on human and animal health and reduce environmental pollution. Profitable, environmentally sound and socially acceptable agricultural production has to be achieved through a joint approach by researchers, land managers and policy makers aimed at cost effective, targeted and innovative implementation of mitigation measures to reduce environmental N emissions.
Jardel O. Santos, Ademir S. F. Araújo, Regina L. F. Gomes, Ângela C. A. Lopes, Márcia V. B. Figueiredo (Brazil) Rhizobia–Phaseolus lunatus Symbiosis: Importance and Diversity in Tropical Soils – A Review (pp 56-60)
Invited Mini-Review: Phaseolus lunatus (Lima bean) is the second most economically important species of genus Phaseolus and one of the 12 primary grain legumes. The plant presents great rusticity and has the capacity to resist long dry periods, characteristics that are important for tropical regions. P. lunatus, like other legume plants, can establish a symbiosis with soil rhizobia that leads to the development of legume nodules in response to the appropriate nitrogen-fixing bacteria. These symbioses result in biological nitrogen fixation (BNF), the process by which atmospheric nitrogen (N2) is converted into ammonia (NH3), making it available for legumes plants. The nitrogen-fixing bacteria of the family Rhizobiaceae,including the genera Rhizobium, Sinorhizobium, Mesorhizobium, Allorhizobium, Azorhizobium and Bradyrhizobium, are collectively referred to as rhizobia. In recent years, however other α- and β-proteobacteria have been shown to produce nodules in legumes. However, the rhizobium–P. lunatus symbiosis has scarcely been studied. Recently, some studies have been conducted to evaluate the genetic variability of the rhizobium–P. lunatus symbiosis. These studies have evaluated phenotypic and molecular diversity of rhizobia isolated from soils of several countries. This review describes the main research results in this field.
Mabiletswane P. Siele, Tabo Mubyana-John, Mpaphi C. Bonyongo (Botswana) The Effects of Soil Cover on Soil Respiration and Microbial Population in the Mopane (Colophospermum mopane) Woodland of North Western Botswana (pp 61-68)
Original Research Paper: Soil cover influences soil biological and chemical processes in various ways. The effects of soil cover (bare soil without litter, litter cover, Mopane tree canopy and grass cover) on soil respiration and microbial population at four sites in the Mopane woodland of north western Botswana were investigated. Soil respiration rates were measured using an infrared gas analyzer. Nitrifying bacterial populations were quantified by MPN on ammonium and nitrite calcium carbonate media, oligotrophs on 1% nutrient agar, actinomycetes on starch casein agar, bacteriovorous protozoans by MPN on sodium chloride agar baited with Enterobacter, and fungal biomass carbon using buried slides were also determined. Soil respiration in different habitats was significantly influenced by type of cover, diurnal temperature variations and soil moisture. Soils under cover showed significantly higher soil respiration than the bare soils. Autochthonous bacterial populations in the Mopane woodland soils consisted mostly of oligotrophs which varied insignificantly between seasons. Fungi were the most dominant microorganisms in all the Mopane woodland soils, with biomass of 162.05 to 282.14 mg C/g soil in the wet season and 11.84 to 44.16 mg C/g soil in the dry season. Microscopic observation of buried slides revealed that fungi play a vital role in holding soil particles together in these soils. The results showed a strong positive relationship between changes in fungal biomass and fluctuation of soil respiration. However, no clear correlation was observed between the variation of soil respiration and other microbial populations (oligotrophic bacteria, actinomycetes, and nitrifying bacteria). Overall these results indicate that in soils under Mopane tree canopy, fungi contribute significantly to soil structure and soil respiration. Other microbial populations consist mostly of oligotrophs which show minimal seasonal variations. Soil moisture significantly influences seasonal fluctuation in soil respiration.
Rosario Nicoletti, Angela Carella, Eugenio Cozzolino (Italy) Investigation on Fungal Antagonists of Root Rot Agents from the Rhizosphere of White Lupin (Lupinus albus) (pp 69-72) Ipublish™ What is Ipublish?
Original Research Paper: Crown and root rot of white lupin (Lupinus albus) is quite complex in aetiology as several soil-borne fungal pathogens, such as Pythium ultimum, Rhizoctonia solani and Fusarium spp., are usually recovered from infected plants. A severe outburst of the disease compromised the crop outcome in a farm located in Campania, southern Italy; notwithstanding, some more or less extended patches of unaffected plants were visible amidst the decaying areas. The presence of fungal antagonists was investigated in the rhizosphere of both healthy and infected plants to verify which species had been stimulated in the presence of a massive inoculum of several pathogens, and if any eventually prevailed in the unaffected patches. The ability of the strains isolated to establish mycoparasitic relationships and/or to inhibit mycelial growth of the above-mentioned pathogens was investigated in vitro. Besides Trichoderma spp. and Clonostachys rosea, whose active development was particularly evident on the outer surface of the roots of the infected plants, most species were recovered from both sources. Penicillium restrictum stood out for its prevalence in the rhizosphere of healthy plants, and showed a conspicuous mycoparasitic aptitude that is described for the first time in the present study. The occurrence of two rare Penicillium species, P. glaucolanosum and P. sajarovii, is also reported.
Anantha Naik Tulajappa, Earanna Ninganna, Narayanaswamy Papanna, Luke Simon (India) Molecular Characterization of Azotobacter chroococcum Strains Isolated from Different Agro-climatic Zones of Karnataka, India (pp 73-76)
Original Research Paper: Azotobacter chroococcum is an aerobic, free-living bacterium capable of synthesizing various plant growth-promoting substances and is useful in crop improvement for biological nitrogen-fixing activity. Ten A. chroococcum strains were isolated and purified from different agro-climatic zones of Karnataka, India by Waksman No. 77 N-free agar by a serial dilution plate technique. Molecular diversity of the isolates was estimated by using ten selected RAPD primers. A total of 103 bands were scored out of which 87 were found to be polymorphic (84.97%). A dendrogram divided the isolates into two groups separated by 37 linkage distances and the dissimilarity matrix showed a maximum difference of 64% between the isolates of the North eastern transition zone and the Central dry zone and a minimum difference of 18% between the isolates of the Eastern dry zone and the Hilly zone. The isolate from zone 4 was clustered separately from the group. Thus, RAPD markers analysis proved to be a quick, simple and significant testing method to assess genetic diversity among A. chroococcum isolates.
Natchimuthu Karmegam, Thilagavathy Daniel (India) Effect of Vermicompost and Chemical Fertilizer on Growth and Yield of Hyacinth Bean, Lablab purpureus (L.) Sweet. (pp 77-81)
Original Research Paper: A 180-day field trial (Randomized Block Design) was carried out with 14 different treatments, using vermicomposts of Polyalthia longifolia leaf litter + cowdung (1:1, VC-PL), pearl millet cobs + cowdung (1:1, VC-PT) and a weed, Rottboellia exaltata + cowdung (1:1, VC-RE), chemical fertilizer and combination of vermicompost and chemical fertilizer with Lablab purpureus (L.) Sweet. The results of the study showed that all the growth and yield parameters i.e. leaf area index, total chlorophyll content of leaves, dry matter production, number of primary branches per plant, day of first flower appearance, length of fruits, dry weight of 100 seeds, yield (fruit) per plant, yield per plot and yield per hectare were significantly higher in the plots which received vermicompost, chemical fertilizer and vermicompost + chemical fertilizer mixture than in the control plots (P<0.05). The highest fruit yield (fresh weight) of 109 tonnes ha-1 was recorded in the treatment which received 2.5 tonnes of vermicompost (VC-RE prepared using Perionyx ceylanensis) + ½ dose of recommended NPK ha-1, while it was 61.9 tonnes ha-1 in control plots without vermicompost and/or chemical fertilizer. The available soil nutrients (nitrogen, phosphorus and potassium) were higher in the plots which received vermicompost than in the plots that received chemical fertilizer and those that received chemical fertilizer + vermicompost mixture. The uptake of nutrients by the plants was high in the plots which received chemical fertilizer + vermicompost mixture over the plots which received chemical fertilizer and vermicompost. The available NPK after harvest in soil collected from the plots treated with chemical fertilizers were 244, 32.9 and 100 kg ha-1 which were higher than in the control plots and lower than in the plots that received chemical fertilizer + vermicompost mixture. The available NPK values in soil which received VC-RE prepared using P. ceylanensis + ½ dose of recommended NPK ha-1 were 262, 45.2 and 110 kg ha-1, respectively.
Adônis Moreira, Nand K. Fageria (Brazil) Potential of Brazilian Amazon Soils for Food and Fiber Production (pp 82-88)
Mini-Review: The Amazon region has the world’s largest tropical forest. Its conservation is of high importance to maintain the balance of climatic conditions and the diversity of the flora and fauna of this still largely unexploited region. In view of the increasing concern for the environment and growing world demand for food and fiber, and since this regions represents one of the last agricultural frontiers, there is a need for sustainable management to produce food and fiber. The objective of this review is to discuss the region’s potential and the problems related to the use of these areas caused by anthropogenic activities. Brazilian environmental laws permit the use of Amazon up to 20% of its total territory. The Amazon region contains extensive savanna areas, with eutrophic soils, and 6.0 million hectares floodplains. However, the majority of soils are characterized by high acidity and low nutrient availability (0.4 billion ha – 86% of the area), and in the primary forest the dynamic of organic matter is responsible for recycling nutrients. Unfavorable climate conditions in the humid tropical part, with periods of intense rainfall and flooding, restricting cultivation of annual crops, is another problem of the region. In the more elevated upland regions, where the climate is more favorable, the planting of exotic and native tropical fruit species in combination or monoculture has great productive potential.