Agronomic Terms Research Articles

Sustainable soil management measures: a synthesis of stakeholder recommendations

Soil degradation threatens agricultural production and soil multifunctionality. Efforts for private and public governance are increasingly emerging to leverage sustainable soil management. They require consensus across science, policy, and practice about what sustainable soil management entails. Such agreement does not yet exist to a sufficient extent in agronomic terms; what is lacking is a concise list of soil management measures that enjoy broad support among all stakeholders, and evidence on the question what hampers their implementation by farmers. We therefore screened stakeholder documents from public governance institutions, nongovernmental organizations, the agricultural industry, and conventional and organic farmer associations for recommendations related to agricultural soil management in Germany. Out of 46 recommended measures in total, we compiled a shortlist of the seven most consensual ones: (1) structural landscape elements, (2) organic fertilization, (3) diversified crop rotation, (4) permanent soil cover, (5) conservation tillage, (6) reduced soil loads, and (7) optimized timing of wheeling. Together, these measures support all agricultural soil functions, and address all major soil threats except soil contamination. Implementation barriers were identified with the aid of an online survey among farmers (n = 78). Results showed that a vast majority of farmers (> 80%) approved of all measures. Barriers were mostly considered to be economic and in some cases technological, while missing knowledge or other factors were less relevant. Barriers were stronger for those measures that cannot be implemented in isolation, but require a systemic diversification of the production system. This is especially the case for measures that are simultaneously beneficial to many soil functions (measures 2, 3, and 4). Results confirm the need for a diversification of the agricultural system in order to meet challenges of food security and climate change. The shortlist presents the first integrative compilation of sustainable soil management measures supporting the design of effective public or private governance.

Effect of the Synergetic Use of Sentinel-1, Sentinel-2, LiDAR and Derived Data in Land Cover Classification of a Semiarid Mediterranean Area Using Machine Learning Algorithms

Land cover classification in semiarid areas is a difficult task that has been tackled using different strategies, such as the use of normalized indices, texture metrics, and the combination of images from different dates or different sensors. In this paper we present the results of an experiment using three sensors (Sentinel-1 SAR, Sentinel-2 MSI and LiDAR), four dates and different normalized indices and texture metrics to classify a semiarid area. Three machine learning algorithms were used: Random Forest, Support Vector Machines and Multilayer Perceptron; Maximum Likelihood was used as a baseline classifier. The synergetic use of all these sources resulted in a significant increase in accuracy, Random Forest being the model reaching the highest accuracy. However, the large amount of features (126) advises the use of feature selection to reduce this figure. After using Variance Inflation Factor and Random Forest feature importance, the amount of features was reduced to 62. The final overall accuracy obtained was 0.91 ± 0.005 (α = 0.05) and kappa index 0.898 ± 0.006 (α = 0.05). Most of the observed confusions are easily explicable and do not represent a significant difference in agronomic terms.

Biological mixture of brown algae extracts influences the microbial community of Lobivia arachnacantha, Lobivia aurea, Lobivia jojoiana and Lobivia grandiflora in pot cultivation

Research goal: Based on the information found in the literature, it has been verified that the use of biofertilizing algae can definitely improve plant quality, growth, and blooms. In this work, studies were conducted to evaluate whether the use of algae in the cultivation of ornamental cacti in pots can improve the growth, ornamental qualities and resistance to salt stress of plants that normally grow in environmental conditions different from our latitudes. Materials and Methods: The experiments, started in September 2020, were conducted in the greenhouses of CREA-OF in Pescia (PT), Tuscany, Italy (43°54′N 10°41′E) on Lobivia arachnacantha, Lobivia aurea shaferi, Lobivia jojoiana and Lobivia grandiflora herzogli. The experimental groups were: i) group control, irrigated with water and substrate previously fertilized; ii) group control1, irrigated with water and substrate previously fertilized + 50 mM of NaCl once every 7 days; iii) group with algae, irrigated with water and substrate previously fertilized; iv) group with algae, irrigated with water and substrate previously fertilized + 50 mM of NaCl once every 7 days. On July 28, 2021, plant height and circumference, suckers’ number, number and length of thorns, vegetative and roots weight, flowers number, flowers life, plants dead from salinity stress, substrate microbial count, pH were analysed. Results and Discussion: The test showed a significant increase in agronomic and quality parameters analyzed in plants treated with algae extracts on Lobivia arachnacantha, Lobivia aurea shaferi, Lobivia jojoiana and Lobivia grandiflora herzogli. In fact, the trial showed in agronomic terms an increase in plant height and circumference, number of new suckers, vegetative and roots growth, number and length of thorns and flowers number. In qualitative terms, theses treated with algae extracts have shown a significant increase in the flower’s life and greater resistance to salt stress. The trial also showed an increase in the microorganism’s number in the theses treated with algae and a lowering of the pH in the substrate. The results therefore suggest the presence of additional sources of carbon and energy in particular nitrogen and phosphorus that ensure the increase of microbial populations and influence their behavior. Conclusions: This research paper highlights the potential of biofertilizer technology in terms of cost, environmental sustainability, and saline soil improvement. As in other experiments in the literature, the application of algae not only resulted in significant effects on plant growth but also influenced the development of microbial communities in the soil.

Проблемы передачи и гармонизации терминологии в сфере земледелия в России и за рубежом на примере термина “no-till”

The purpose of the study is to clarify the definition and determine the degree of terminological synonymy of agronomic terms which are conditioned by different approaches in agriculture, using the American term “no-till” and the Russian term «прямой посев» (‘direct seeding’) as examples. The research is carried out on the basis of the material of glossaries and news reviews found on websites of agricultural organisations and the portal eLIBRARY. Scientific novelty of the work is determined by a comparative-contrastive approach, from the standpoint of which a linguistic, statistical and conceptual analysis of the definitions of these terms are conducted, the degree of their synonymy and frequency are identified. As a result, it has been found that Russian agronomic terminology and the American one have common features inherent in this knowledge area.

Allometric models for non-destructive leaf area measurement of stevia: an in depth and complete analysis

ABSTRACT Leaf area measurement is pivotal for plant physiologists. Hence, accurate measurement of their leaf area is incredibly relevant in agronomic terms. The plant Stevia rebaudiana is a sucrose-free plant species that is now vital to the global production of sucrose-free foods. Here, we estimated S. rebaudiana leaf area using a nondestructive methodology comprising allometric equations. Through leaf length (L), leaf width (W), and/or their product (LW) the leaf area was determined. One thousand leaves were sampled from four distinct S. rebaudiana genotypes for model construction. Linear or power models were generated, and the best equation was selected using a statistical criterion. The statistical criteria indicated that the linear models best suited all genotypes tested, included a function of LW, exhibited increased stability, and precisely estimated coefficients. ANOVA revealed that both generalized and combined equations were feasible. Nevertheless, grouping all genotypes into a single model was not possible as the genotype leaf architectures were very dissimilar.

Use of an environmentally oriented organic mineral fertilizer from liquid waste of pig farms in the cultivation of wheat

The article presents the results of a field vegetation experiment in the Rostov region on the cultivation of spring wheat of the “Zlata” variety with the use of an environmentally oriented organic mineral fertilizer from liquid waste of pig farms by the method of split plots with a randomized placement of variants in repetitions, the repetition of the experiment is three-fold. The agrochemical indicators of the soil before and after wheat cultivation at the horizons of 0-20 and 20-40 cm are given. The scheme of carrying out the experiment, including different doses of organic mineral fertilizer application and a plan for cutting plots, is indicated. During the growing season, constant observations of the plants were carried out together with the care. The dynamics of the growth of wheat biomass in different periods of time from planting and its yield are presented. The influence of different doses of ecologically oriented organic mineral fertilizer from pig manure on the yield of spring wheat is estimated. According to the results of experimental data, the effective dose of organic mineral fertilizer application from pig manure was established-2t/ha. The yield of grain crops (wheat) per hectare was determined-49.2 c / ha. The spring wheat variety “Zlata”, which is unusual for the Rostov region, gave a high yield when applying an environmentally oriented fertilizer, which proves its value both in agronomic and ecological terms. The absence of toxic effects on the soil of organic mineral fertilizers for heavy metals (copper, nickel. cadmium, lead), an increase in humus from 5.43% to 5.52%. The assessment of the nutrient reserves in seeds and the effect of organic mineral fertilizer doses on the quality of spring wheat grain of the «Zlata» variety is given. The highest amount of gluten-40.03% - was observed when using the fertilizer at a dose of 2 t / ha.

Restoring farmlands for food and nature

Changes in the intensity and extent of farmland have a profound impact on life on Earth. Although nature-rich farmlands have conservation value, their promotion competes with the protection and restoration of natural habitat. Restoring the productive capacity of existing farmland can help maximize opportunities for the restoration of both nature-rich farmlands and natural habitat.

Винос поживних речовин як показник потреби плодових культур у мінеральному живленні

The studies were devoted to determining the parameters of the nitrogen absorption and boom by of pome fruit crops intense in the conditions of Southern Ukraine and to assessing the expediency of these indices using to establish the plants requirements in mineral nutrition and rational fertilizers doses. The size and structure of the nitrogen boom by apple and pear trees, that is, the ratio between the nitrogen boom from pruned trees and fruits proved to depend on the varietal signs level of the crop yield, as well as on the doses, terms and methods of the mineral fertilizers application. However, the average nitrogen boom rates by these crops on the irrigated southern black soil did not exceed 25-52 kg N/ha, and this element absorption rate from mineral fertilizers was no more than 14-22 %. The investigations also showned that, with the maximum doses of the N90-120 fertilizer, the nitrogen boom with pruned trees increased by 11-31 % depending on the crop without significant increase of the orchard yield. In addition, when using nitrogen at doses significantly exceeding its boom, the soil accumulated an excess of nitrate compounds beyond the location of the bulk of the trees root system on vegetative rootstocks. Their amount achieved 17-35 % of the total nitrogen supplied to the soil during the entire fertilizer application period. This can cause both the increase of unproductive nitrogen loss, of environmental stress and the reduction of fertilizer payback, in agrocenoses due to the soil water contamination by nitrates. Considering the above mentioned facts as well as taking into account the ability of fruit crops to re-utilize the nutrients from the vegetative organs, the complex processes of the nitrogenous fund transformation of irrigated southern black soil, in particular, its ability to nitrogen mineralization, and the risk of the environmental contamination with nitrate compounds, the application of nitrogenous fertilizers doses higher than N60 in intense pome orchards in the south of Ukraine are not advisable in agronomic or environmental terms.

EFFICIENCY OF USE OF GREEN-TRANSPORT COMPONENTS BY OPERATING AND ENERGY INDICATORS

In agriculture, the components of production cycles are likely (stochastic) in nature. This is especially true for harvesting. The duration of this period depends on the weather conditions, the biology of plant development, the variety of culture, the composition of the soil, agro technical techniques, etc. In connection with this, there is a need for scientific and production searches for such forms of organization of the harvesting process that would allow harvesting in short agronomic terms and substantially reduce due to this loss. The purpose of the research is to substantiate the structure and composition of the technology of harvesting and transport complexes for different technologies of harvesting cereal crops by operational and energy indicators to reduce the material and energy costs of harvesting. To calculate the comparative estimation of energy costs of complex fuel and operating costs for different harvesting technologies of winter wheat, four technologies are considered: traditional technology - direct harvesting without straw shredding; traditional technology - separate harvesting; zero technology - the use of harvesting equipment of domestic production; Zero technology - the use of harvesting techniques imported production. For these technologies, according to the methodology of the latest scientific research, technological maps for the harvesting of winter wheat have been developed. A comparative analysis of operational and energy costs of harvesting winter wheat indicated that the least cost is zero technology using domestic production technology, and the most expensive is conventional technology with direct combine harvesting. The presented results of researches of various technologies of grain cereal harvesting according to the structure and composition of equipment of harvesting and transportation complexes indicated that reduction of operational and energy expenses is possible due to increase of productivity, reduction of book value and quantity of harvesting equipment in the composition of harvesting - transport complexes at performance of works in optimal agro technical terms with minimal crop losses.

Qualitative Performance Indicators of a Ripping-and-Separating Machine for Soil Cultivation

Pre-­sowing soil cultivation aims at forming such a soil structure, which will allow increasing the yield.(Research purpose)To determine the qualitative indicators of an experimental soil­cultivating ripping­-and-­separating rotary machine for optimizing the ploughed soil layer, modifying the structure and density of the cultivated soil layer in accordance with the agronomic requirements.(Materials and methods)The author has studied physical and mechanical properties of the soil after its spring cultivation in the conditions of bare (black) fallow. Soil structure and aggregate composition depending on the type of cultivation, the density of soil layers at different times, the dynamics of soil moisture changes in the layers for two months after its spring cultivation have been analyzed as well.(Results and discussion)The author has studied the operation of a soil tillage ripping-­and-­separating machine on the soil layer, which is separated after processing into four sublayers: over­-seed, seed, under-­seed and subsurface ones. Soil fragments (lumps) of a size larger than 20 mm have been completely removed from the over-­seed sublayer. The most valuable soil structure in agronomic terms is formed in the seed sublayer, where the size of individual components does not exceed three times the size of seeds, the density of the under-­seed sublayer is up to 1.25 grams per cubic centimeter. The subsurface sublayer has a density of not more than 1.3 grams per cubic centimeter and a hardness of more than 3 MPa in the plow sole, which is provided by the main tillage operations. The information for the study has been obtained as a result of the analysis of literary sources.(Conclusion)The experimental machine for optimizing the agrophysical properties of the ploughed soil layer allows increasing the structural coefficient by about 2.5 times as compared with traditional cultivators. It has been found that soil cultivation with a ripping-­and-­separating tillage machine allows to improve the methods of pre-­sowing cultivation to improve its agrotechnical characteristics, skip pre­-sowing harrowing and cultivation and prepare the soil for sowing in one run.

Solar Radiation Distribution inside a Greenhouse Prototypal with Photovoltaic Mobile Plant and Effects on Flower Growth

The diffusion of renewable energy requires the search for new technologies useful for obtaining good energy and production efficiency. Even if the latter is not always easy to obtain, the integration of photovoltaic panels on the roof of greenhouses intended for floriculture can represent an alternative. The present paper evaluates climatic conditions inside a greenhouse, in which 20% of its roof surface has been replaced with mobile photovoltaic (PV) panels. The PV system implemented in this study can vary the light energy collection surface in relation to the degree of insolation. The aim is to observe the shading effects of the PV system on the growth of several varieties of flowers (iberis, mini-cyclamens and petunias) to ensure the use of solar energy as an income integration deriving from floricultural production. In fact, in agronomic terms, it has ensured: (i) to be able to shade the underlying environment in most lighting conditions; and (ii) to let through more light when it is required for the needs of crop plants or in cloudy weather. Results have described the distribution of solar radiation, variability of temperature and humidity and lighting in a solar year and the observed outcomes on floristic production.

TIPOLOGÍA DE UNIDADES DE PRODUCCIÓN FAMILIAR DEL SISTEMA AGROFORESTALTRADICIONAL CAFÉ- PLÁTANO-CÍTRICOS EN EL MUNICIPIO DE TLAPACOYAN, VERACRUZ

<p>Coffee production is one of the most important activities in the town of Tlapacoyan, Veracruz unfortunately, prices and technologies focused on the monoculture production system have reduced the activity. The study of family production units (FPU), with the construction of a typology and an agronomic characterization of producers, carried out in the traditional agroforestry system of coffee-banana-citrus contributes to further analysis in public policies. This study was conducted in six communities through field work, coffee producers records and open interviews with authorities. A census of 33 individuals was built and questionnaires were applied as a part of the survey, which used multivariate analysis to establish categories of UPF. Each category was described in agronomic terms based on incomes and costs. Three categories were determined according to surface size, labor work and technological level, including diversification of costs of incomes. As a conclusion, this study has contributed to rethink about new supporting strategies for coffee producers, and government policies and supporting programs which will mean a better family income that will take into account differences such as the size varying from 5 to 27 ha. Labor work available varies among categories and technification defines the type and number of vehicles, because it refers to an activity that generates beneficial incomes to producers. We conclude that this heads of the UPF have traditional management of the 3 components, integrating productive practical and the system is dependent on labor.</p>

Water use efficiency in peach trees over a four-years experiment on the effects of irrigation and nitrogen application

The optimization of crop water productivity is a key objective in modern agriculture. Deficit irrigation is a widely used strategy when water and energy are scarce and/or expensive. However, in fruit tree crops, the severity and duration of water stress can affect yield and fruit size, thus imposing severe limitations on the effectiveness of production processes, and on fruit quality and water productivity. Here we analyzed water use efficiency (WUE) of peach trees over four years both in agronomic terms, as water productivity of fruits and biomass (WUEWPy,b), and in physiological terms, as intrinsic and instantaneous leaf WUE (WUEint and WUEins respectively). Our results show a positive and additive effect of water and nitrogen application on WUEWP, reflected by yield enhancement. WUEint and WUEins varied through changes in stomatal conductance and transpiration—two parameters that are determined by plant water status and nitrogen application. Our results suggest that the variation in WUEWPy was caused by complex regulation of plant growth and fruiting, related to water status and nitrogen availability, which both drive plant WUE. In order to evaluate WUE at the canopy scale, we studied δ13C and δ18O in wood. These parameters were found to be related to leaf stomatal conductance and transpiration and also to the effects of irrigation and nitrogen; however, no clear relationship was observed with WUEWPy. Plant water status was also dependent on crop load and vegetative growth and was strongly associated with WUEWPy and WUEWPb. Taken together, our results show that full irrigation and rational nitrogen application can improve WUEWPy, both in agronomic and economic terms. When water deficit conditions are foreseeable, deficit irrigation in fruit growth phase III (GSIII) is a more profitable strategy that when applied in phase II (GSII). In this regard, flexible deficit irrigation in GSIII is an affordable and practical tool to include in strategies aiming to improve water and nitrogen use efficiency in fruit crops when water is scarce.

SPATIAL CORRELATION BETWEEN PHYSICAL PROPERTIES OF SOIL AND WEEDS IN TWO MANAGEMENT SYSTEMS

The spatial correlation between soil properties and weeds is relevant in agronomic and environmental terms. The analysis of this correlation is crucial for the interpretation of its meaning, for influencing factors such as dispersal mechanisms, seed production and survival, and the range of influence of soil management techniques. This study aimed to evaluate the spatial correlation between the physical properties of soil and weeds in no-tillage (NT) and conventional tillage (CT) systems. The following physical properties of soil and weeds were analyzed: soil bulk density, macroporosity, microporosity, total porosity, aeration capacity of soil matrix, soil water content at field capacity, weed shoot biomass, weed density, Commelina benghalensis density, and Bidens pilosa density. Generally, the ranges of the spatial correlations were higher in NT than in CT. The cross-variograms showed that many variables have a structure of combined spatial variation and can therefore be mapped from one another by co-kriging. This combined variation also allows inferences about the physical and biological meanings of the study variables. Results also showed that soil management systems influence the spatial dependence structure significantly.

Diversifier les rotations céréalières notamment avec du pois et du colza – Données récentes d’expérimentations et d’études

Simplification has been a clear trend in the composition of French crop rotations in the past decades, whereas agronomic knowledge proves the interest of diversification in order to benefit from the so called “preceding effects” and “cumulative effects”. It is needed to study the possible input of crops such as rape seed or pea for the cereal-based rotations in agronomic terms but also in economic and environmental terms. The first step is to quantify the impacts specifically due to the change in crop succession composition, and afterwards to allocate an objective economic value to them so that they are easy to integrate into comparisons of production systems. The regional case studies of a current multi-partner project enable to illustrate the economic and environmental evaluation of alternatives to the rotation “Oilseed rape – Wheat – Barley”. In addition, the recent field experiment data of this project (farm tests or experimental trials) provide technical and scientific elements on technical feasibility and the economic performance of the innovative succession “pea before rape seed”, but also on the interest of the introduction of symbiotically fixed nitrogen in crop rotations in order to decrease the negative environmental impacts of mineral fertilisers-based systems. Diversification of crops and nitrogen fixation appear to be two key elements for (i) competitiveness, when at least the agronomic effects are taken into account, and (ii) sustainable systems, when one considers the preservation of farm potential and of the environment.

MANAGEMENT SYSTEM BY SATELLITE IMAGES FOR GUAVA (PSIDIUM GUAJAVA L.) ORCHARDS ON YIELD ESTIMATES BASED ON THE CHARACTERIZATION OF GUAVA TREES BY PHENOTYPIC STAGE

The management system which is based on handling GIS database files and remotely sensed imageries on Geographical Information System (GIS) environment is an essential tool to guide and regulate the production systems and marketing activities of product chains. In the case of guava, the management system has to be fed with a specific and structured field database and its metadata to verify the phenotypic status of guava trees and to characterize the production system applied by the producer in agronomic terms (coordinate data, planting frame, vigor, health etc). This data is useful to determine agronomic conditions to be incorporated as a field test in a supervised classification process on SPOT satellite images (PAN and MS) which is used as a mean to scale the punctual field observation data. As a numerical value, the raster structure of satellite images and the numeric value for each cell represents guava photosynthetic activity rate. Along with this, the isolation of guava's phenotypic signature in DN units will feed the supervised classification procedure allowing the user to generate thematic maps per class. On GIS environment, a multi-assessment analysis is applied in order to assign a weight to each component on the project. The analysis is based on spatial analysis vicinity functions applied to guava orchard locations, proximity to collecting centers, roads, and highways. The visual immediacy on thematic maps will allow the decision makers to implement their own criteria analysis to plan the market destination of guava production volume weeks after harvest (fresh market or industry) in Calvillo County.

Nutrient losses by surface run-off following the application of organic manures to arable land. 1. Nitrogen

Research was conducted on nitrogen (N) surface run-off losses following organic manure applications to land, utilising a purpose-built facility on a sloping site in Herefordshire under arable tillage. Different rates and timing of cattle slurry, farmyard manure and inorganic N and phosphorus (P) fertiliser were compared, over a 4-year period (1993–97). P losses from the same studies are reported in a separate paper. The application of cattle slurries to the silty clay loam soil increased the loss of solids and NH 4 +-N in surface water flow compared to control plots receiving inorganic fertiliser only, or no treatment, but had little effect on NO 3 −-N losses by this route. Results were consistent with other observations that rainfall events immediately after manure applications are particularly likely to be associated with nutrient run-off losses. Losses via subsurface flow (30 cm interflow) were consistently much lower than via surface water movement and were generally unaffected by treatment. Increasing slurry application rate and, in particular, slurry solids loading, increased solids and NH 4 +-N losses via surface run-off. The threshold, above which the risk of losses via surface run-off appeared to be greatly increased, was ca. 2.5–3.0 t/ha slurry solids, which approximates to the 50 m 3/ha limit suggested for slurry within UK ‘good agricultural practice’. Sealing of the soil surface by slurry solids appears to be a possible mechanism by which polluting surface run-off may occur following slurry application on susceptible soils. Total losses of NH 4 +-N and NO 3 −-N during the 4-year monitoring period were insignificant in agronomic terms, but average soluble N concentrations (NH 4 +-N+NO 3 −-N) in run-off, ranging from ca. 2.0 mg/l, up to 14.0 mg/l for the higher rate slurry treatments. Peak concentrations of NH 4 +-N>30 mg/l, are such as to be of concern in sensitive catchments, in terms of the potential for contribution to accelerated eutrophication and adverse effects on freshwater biota.

Nutrient losses by surface run-off following the application of organic manures to arable land. 2. Phosphorus

Phosphorus (P) surface run-off losses were studied following organic manure applications to land, utilising a purpose-built facility on a sloping site in Herefordshire under arable tillage. Different rates and timing of cattle slurry, farm yard manure (FYM) and inorganic nitrogen (N) and P fertiliser were compared, over a 4-year period (1993–97). N losses from the same studies are reported in a separate paper. The application of cattle FYM and, especially slurry, to the silty clay loam soil increased both particulate and soluble P loss in surface water flow. Losses via subsurface flow (30 cm interflow) were consistently much lower than via surface water movement and were generally unaffected by treatment. Increased application of slurry solids increased all forms of P loss via surface run-off; the results suggested that a threshold for greatly increased risk of P losses via this route, as for N, occurred at ca. 2.5–3.0 t/ha solids loading. This approximates to the 50 m 3/ha application rate limit suggested for slurry within UK ‘good agricultural practice’. The studies also provided circumstantial evidence of the sealing of the soil surface by slurry solids as the major mechanism by which polluting surface run-off may occur following slurry application on susceptible soils. Losses of total and soluble P, recorded for each of the 4 years of experiments, reached a maximum of only up to 2 kg/ha total P (TP), even after slurry applications initiating run-off. Whilst these losses are insignificant in agronomic terms, peak concentrations of P (up to 30,000 μg/l TP) in surface water during a run-off event, could be of considerable concern in sensitive catchments. Losses of slurry P via surface run-off could make a significant contribution to accelerated eutrophication on entry to enclosed waters, particularly when combined with high concentrations of NO 3 −-N. Restricting slurry application rates to those consistent with good agronomic practice, and within the limits specified in existing guidelines on good agricultural practice, offers the simplest and most effective control measure against this potentially important source of diffuse pollution.

Nitrogen fixation in endophytic and associative symbiosis

N-balance, 15N isotope dilution and 15N natural abundance studies provide strong evidence that some tropical grasses, especially sugar cane ( Saccharum spp.), wetland rice ( Oryza sativa) and kallar grass ( Leptochloa fusca) can obtain at least part of their N-needs from biological nitrogen (N 2) fixation. However, these studies have not provided conclusive evidence that these plants are engaged in symbiotic partnerships with any bacteria, as the techniques used do not distinguish between “symbiotic” N 2 fixation on the one hand, and N 2 fixation inputs from free-living heterotrophs and cyanobacteria on the other. Large and diverse populations of heterotrophic diazotrophs can be isolated from the surfaces and rhizospheres of sugar cane, wetland rice and kallar grass, and also from surface-sterilized plants. While the latter suggests that these organisms are living intimately within the plant tissues and hence may be fixing N 2 in symbiotic partnerships with their hosts, “endophytic diazotrophs” have been observed only within the intercellular spaces, vascular tissue, aerenchyma and dead cells of their hosts, not in their living cells. Recent studies have also shown expression by diazotrophs of genes encoding for nitrogenase (e.g., nifA, nifH), in situ expression of the nitrogenase enzyme proteins, and nitrogenase (acetylene reduction) activity in association with their host plants, but have yet to determine whether the bacteria transfer the products of N 2 fixation to the plants. Earlier studies used 15N 2 gas incorporation to show transfer of fixed N in sugar cane, rice, maize ( Zea mays), sorghum ( Sorghum bicolor) and various forage grasses. However, the long exposure times often used in these studies could mean that the fixed N may have been transferred principally by the death and mineralization of asymbiotic diazotrophs, rather than through direct and rapid transfer as occurs in legume nodules. To demonstrate that N 2-fixing symbioses are present, future 15N 2 experiments should utilize short exposure times (hours), and compare plants inoculated with wild type diazotrophs and nif mutants. Only an integrated and multidisciplinary approach can determine if (a) N 2-fixing symbioses with Gramineae really exist, and (b) if they are effective in agronomic terms.

Agroecological Implications of the System of Rice Intensification (SRI) in Madagascar

A system of plant, soil, water and nutrient management for irrigated rice developed in Madagascar has been yielding 5, 10, even 15 t ha−1 on farmers' fields where previous yields averaged around 2 t ha−1. This is achieved using whatever variety of rice the farmer is already using and without having to utilize chemical fertilizer or other purchased inputs. This system, known as SRI, shows that alternative management practices, creating optimal growing conditions for plants, can bring out previously untapped genetic potential. It also shows that the practices farmers have used for centuries may not always be the best in agronomic terms.