Nitrogen (N) and Phosphorus (P) deficiencies affect 80% of the soils in western Kenya, but fertilizer use among farmers is limited due to high prices. We studied the use of animal manure and Tithonia diversifolia biomass as potential sources of N and P for maize production along a 100 year cultivation chronosequence. Tithonia is a shrub belonging to the family compositae. It’s biomass contains 3.5 % N, 0.37 %P, 4.1 % K while the animal manure used contained 1.1 % N, 0.4 % P, 6.3% K. These organic materials were applied to supply the equivalent of 25 kg of P per hectare. Similar P fertilizer rates were applied to provide the equivalent inorganic treatment. We monitored inorganic N fluxes using 2.5cm radius field soil cores buried to 10cm and recovered on a monthly basis. Soil samples were extracted for nitrate and ammonium. The difference in total inorganic N min minus N leach provided an estimate of plant N uptake. At time zero, there were no significant differences in the levels of extractable ammonium among the treatments. Recent conversion sites had higher extractable nitrate compared to old conversions for all the treatments. We also observed higher rates of N mineralization on the recently cultivated farms. In addition, we will report agronomic yield responses to all sources of nutrients applied
Tag: soil sciences
Smallholder carbon development projects: linking climate change mitigation with poverty reduction
Louis Verchot, World Agroforestry Centre (ICRAF), explained that Clean Development Mechanism (CDM) projects should generate concrete development and environmental benefits in host countries and that these benefits should be distributed equitably across countries. Stating that smallholder land use and land-use change and forestry (LULUCF) projects can allow some of the poorest people in the world’s poorest countries to enter the carbon market, he lamented that many bottlenecks currently hinder this possibility.
Alternatives to Slash-and-Burn agriculture, symposium ID-6: 15th International Soil Science Congress, Acapulco, Mexico 1994
The fertility capability of soil classification system: interpretation, applicability and modification
This paper summarizes the first five years of testing and evaluation of the Fertility Capability Soil Classification System (FCC) and presents an improved version, examples of interpretation and its applicability. FCC is a technical system for grouping soils according to the kinds of problems they present for agronomic management of their chemical and physical properties. It emphasizes quantifiable topsoil parameters as well as subsoil properties directly relevant to plant growth. FCC-classes indicate the main fertility-related soil constraints, which can be interpreted in relation to specific farming systems or land utilization types. Since its publication in 1975, the FCC has been tested, evaluated and put to use in various countries. As a result, the definitions of several modifiers have been changed and additional modifiers have been introduced. Soil maps can be interpreted and redrawn as FCC-units when the necessary data are available. Portions of the FAO/Unesco (1971, 1974, 1977) Soil Maps of the World have been converted to FCC-units with minor difficulties. The system is directly applicable to FAO’s (1976) Land Evaluation Guidelines.
Diversity of plant-parasitic nematodes and their relationships with some soil physico-chemical charateristics in improved fallows in western Kenya
A survey was conducted in the food crop production area of western Kenya to characterise the nematode communities in different cropping systems and to monitor the effect of improved fallows on the abundance, diversity and community structure of plant-parasitic nematode assemblages. Soil samples were taken from short-term natural fallows (20 years), maize/beans cultivated fields and improved fallows with Crotalaria grahamiana, Sesbania sesban and Tephrosia vogelii. The Shannon diversity index and evenness were used to assess nematode diversity in the different cropping systems. The relationships between plant-parasitic nematodes and the soil physico-chemical properties were investigated with principal component analysis and co-inertia analysis.Planting trees/shrubs as improved fallows in croplands dramatically increased the populations of nematodes in the soil. However, the diversity of plant-parasitic nematodes was reduced. The distribution of plant-parasitic nematodes was correlated with that of some soil physical and chemical properties. Scutellonema spp. were dominant in the improved fallows where the highest values of magnesium and potassium were recorded. The plant-parasitic Dorylaimida (Xiphinema spp. and Paratrichodorus minor) were more abundant in the maize/beans plots and this abundance seemed related to high soil bulk density. Meloidogyne spp. and Rotylenchulusborealis had a strong positive correlation with soil organic matter and clay, and were abundant in the long-term natural fallows.The correlations between soil physico-chemical properties and nematodes indicate that, apart from the direct influence of the host plant, the soil characteristics play an important role in the abundance, distribution and structure of nematode communities. This validates the potential of nematodes as bio-indicator organisms of soil status.
Quantity and quality of organic inputs from coppicing leguminous trees influence abundance of soil macrofauna in maize crops in eastern Zambia
Soil invertebrates are the major determinants of soil processes such as organic matter decomposition and nutrient cycling. However, the effect of quantity and quality of organic inputs on soil biota has not been studied in agroforestry systems in southern Africa. Variations in soil macrofauna abundance under maize grown in fallows of Gliricidia sepium, Acacia anguistissima, Leucaena collinsii, Leucaena diversifolia, Leucaena esculenta, Leucaena pallida, Senna siamea, Calliandra calothyrsus and monoculture maize were assessed at three sites with contrasting agro-ecological conditions in eastern Zambia. It was hypothesised that spatial variations in soil macrofauna abundance under maize crops are mediated by heterogeneity in the quality and quantity of organic inputs produced by these legumes. The relationships between the abundance of macrofauna groups and litter, leaf, stump re-sprout and recycled biomass, stump survival and the quality index lignin (L)+polyphenol (P) to nitrogen (N) ratio were assessed using generalised linear models assuming spatial randomness (Poisson distribution) and aggregation (negative binomial distribution). Earthworms, beetles and millipedes showed spatial aggregation, which was partly explained by the heterogeneity in organic resource quantity and quality. Earthworms and beetles were more abundant under legumes that produced high quantities of biomass with low (L + P) to N ratios and species that have high stump survival after coppicing. Millipedes were favoured by species which produced high quantities of biomass with high (L + P) to N ratios. Although ants and termites showed spatial aggregation, their distributions were not influenced by the quantity or quality of biomass produced by the legumes. Centipedes and Arachnida showed spatial randomness, and their distribution was not influenced by any of the organic quality and quantity variables.
Soil biodiversity in rapidly changing tropical landscapes: scaling down and scaling up
Soil has generally been regarded as something of a ‘black box’ by ecologists. The importance of soil is obvious: it provides physical support for plants, and both the living and non-living components contribute to a variety of important environmental functions. Soil is a species-rich habitat, but many questions about the ecological significance of the soil’s biological diversity, and in particular how it affects ecosystem function, have never been asked. The linkages between above-ground ecology, which is rich in ecological theory, and below-ground ecology, where investigation has been restricted by methodological difficulties, have not been made. Technical developments, including isotopic and molecular methods as well as experimental and modelling approaches, have led to a renaissance in soil biodiversity research. The key areas are reflected in this exciting volume which brings together many leading contributors to explore the role and importance of soil biota. A major synthesis focusing explicitly on soil biodiversity and ecosystem function Integrates a vast body of literature on recent theoretical and technological developments in soil ecology and plant-soil relations Provides a strong research basis for both policy development and practical management of soil biodiversity in a changing world
Spectroscopy as a tool for studying swelling soils
This chapter describes the development of spectroscopy from an experimental research instrument toward an operation mapping tool. Integrating spectral based methods with well-established physiochemical methods such as the Atterberg limits, cation exchange capacity(CEC), and coefficient of linear extensibility (COLE) , will bring about a better understanding of expansive soils and results in a better classification. Proper calibrations based on a limited number of samples will enable a user to classify soils of unknown swell potential. Such an approach provides a tool for generalizing results of soil assessments conducted at limited sites, and thereby increasing the efficiency of expensive and time consuming studies. The rapid nature of the environment allows soil variability to be more adequately sampled than with conventional approaches. The spatial characterization of the soil surface in the field provides a coherent framework for linking soil information with remote sensing information for improved spatial prediction of swelling.