Effect of water quality and amendments on the hydraulic properties and erosion from several mediterranean soils

The response of six sandy-loam soils from Portugal and Israel to leaching with sodic and saline water and to simulated rain was studied. The dominant clay mineral in the soils from Portugal was kaolinite, whereas smectite predominates in the soils from Israel. The permeability of the soils depended on the soil texture: it decreased with an increase in the silt and clay content. The response of the soils to sodicity depended on the electrolyte concentration; salt concentrations exceeding 10 mmol_c·L⁻¹ was enough to prevent the deleterious effect of exchangeable sodium (≤20%). When leaching with distilled water (stimulating rain water), the presence of primary minerals and lime determine the susceptibility of the soils to sodicity. The calcareous loess from Israel was the least susceptibility to sodicity.The six soils were susceptible to sealing, high runoff and erosion when exposed to rain. The soil surface was particularly vulnerable to sealing due to both the mechanical impact of raindrops and the low concentration of electrolytes in the rainwater. Seal formation was due to two mechanisms:

• 1.(i) physical disruption of aggregates at the soil surface which depended on the impact energy of raindrops and the inherent aggregate stability; and
• 2.(ii) chemical dispersion which depended on the mineralogy of the clay, the ESP, and the electrolyte concentration.

When the impact of the drops was prevented, or when the anionic polymer was sprayed at the soil surface, physical breakdown of the aggregates was reduced and runoff and erosion were slight. When the electrolyte concentration was high, the chemical dispersion was small and runoff and erosion decreased, compard with the control. The smectite soils from Israel were more susceptible to sealing than the kaolinitic soils from Portugal.     

Management of soil organic matter in the farming systems of the low land humid tropics of West Africa: a review

Soil organic matter is the key to successful and sustained productivity of soils of the tropics. This is because soil organic matter positively affects structure, aggregation, porosity, microbial activity, pore size distribution and water retention capacity of the soil.Furthermore, soil organic matter is the major nutrient storage site for the low-activity-clay soils of the tropics and so affect nutrient retention capacity, availability and mobility of macro- and micro-nutrients. It increases the water use efficiency, and therefore attenuate runoff and erosion and consequently the productivity of the soil.The low land humid tropics is characterised by high temperature, high relative humidity, high rainfall intensity and high microbial activity which all encourage rapid mineralisation, depletion and erosion of organic matter leading to soil deterioration.Many cultural practices and operations encourage rapid depletion of soil organic matter while others are associated with soil organic matter build up. Practices like crop rotation, multiple cropping, mulching, alley cropping, following and farm yard manuring, encourage soil organic matter accretion. However, the effectiveness of these practices in increasing soil organic matter depends on:

• 1.(a) amount and frequency of residue application;
• 2.(b) the nature and C:N ratio of the mulching material, or manure;
• 3.(c) rainfall amounts, intensity and distribution, soil moisture and clay contents.

Land clearing with heavy machinery is associated with removal of biomass from the field, while conventional ploughing and harrowing lead to soil organic matter depletion. These practices should be discouraged or modified to reduce their negative effects on soil organic matter.Effects of green manuring and burning, on soil organic matter are questionable.Research is needed on processes and pathways of crop residue decomposition to provide clues to possible interventions aimed at management of soil organic matter. Work is also needed to improve the efficiency of agro forestry systems in accreting soil organic matter in soils of the low land humid tropics.     

Die kohäsion ungesättigter sandböden und deren beeinglussung durch organische substanz

It is well known in soil science, that organic matter contributes considerably to the stability of soil structure. There are also many methods to determine this stabilizing effect of soil organic matter. But as a matter of fact those methods are mostly developed under chemical or colloido-chemical aspects and do only satisfy the demands of special purposes. The physical and mechanical aspects are often neglected. In this work, however, the mechanical parameter “cohesion of soils” c is selected to describe the stabilizing effect of organic matter on soil structure of sandy soils.Organic matter (black peat) was mixed with a fine sand in gravimetric proportions of 0:100, 1:100, 3:100, 5:100, 8:100. The mixtures were then wetted with distilled water and left undisturbed for a few weeks. A natural sandy soil (Haplo-humod) was also taken, part of the sample was treated with H₂O₂ to destroy the organic matter, so the stabilizing effect of organic matter could be evaluated. The cohesion of all the samples was determined with an annular shearing apparatus under a constant soil water suction between 0 and 300 cm H₂O. Results were calculated using the Coulomb equation τ = c + σ_n tan ϕ⁰, where τ shear strength, c cohesion, σ_n normal stress, and ϕ⁰ friction angle respectively. The results show,

1. 1.1. all samples have no cohesion under saturated conditions (water suction = 0 cm H₂O);
2. 2.2. with all samples the cohesion at first increases with increasing soil water suction, reaches a maximum under a soil water suction of about 40 to 70 cm H₂O, and then decreases with further increasing soil water suction;
3. 3.3. organic matter enhances the cohesion of both the artificial mixtures of sand and organic matter as well as the natural sandy soil, the increase being the higher, the higher the content of organic matter.
4. 4.4. no difference between the artificial mixtures of sand and organic matter and the natural sandy soil was found.

     

Distribution patterns of two bivalve species (Nucula turgida,Tellina fabula) along a frontal system in the Southern North Sea

The distributional patterns of diverse marine soft-bottom invertebrates in the southern North Sea are considered in the light of relevant hydrodynamic and sedimentological conditions, with two species of bivalves, Nucula turgida and Tellina fabula as examples.Four possible mechanisms that may result in spatially differentiated abundances of benthic populations are discussed:

• 1.A. Settling larvae may act like passive suspended particles being deposited on the sea floor at sites where sediments with similar sinking rates would settle.
• 2.B. The upcurrent presence of rich sources of larvae, viz. dense adult populations.
• 3.C. Active habitat selection by settling larvae.
• 4.D. Spatially differentiated survival of larvae, once they have settled.

     

Effects of land reclamation practices on physical properties of an acid,infertile Oxisol

Large areas of soils in tropical rainforests have been damaged by careless mechanical land clearing procedures. The objective of this study was to evaluate the effect on soil physical properties of various management practices to reclaim an acid, infertile Oxisol cleared by bulldozer. Crops would not grow on these soils due to low pH, poor fertility or poor physical properties. Properties in the 0- to 25-cm depth of the Typic Haplorthox soil, measured at the beginning of the study, were: 74% clay, bulk density 1.09 Mg m⁻³, pH 3.66, ECEC 8.9 cmol_c 1⁻¹, and available P 0.4 mg 1⁻¹. Land reclamation treatments included all combinations of six tillage practices and three fertility levels. Tillage practices were: hand hoeing to a depth of 15 cm; hoeing plus applying mulch; hoeing and incorporation of green manure; deep forking, i.e., hand digging to 30 cm with a digging fork; deep forking in alternate 20-cm wide strips; and roto-tilling to the 10-cm depth. Fertility levels were:

• 1.1. no fertilizer or lime added;
• 2.2. addition of lime to maintain an Al saturation near 40% and fertilizer to maintain nutrients just above their critical levels;
• 3.3. lime to neutralize all exchangeable A1 and fertilizer to satisfy the P fixation capacity of the soil and to maintain nutrients at optimum levels.

Soil physical properties monitored periodically while growing five consecutive crops were bulk density, mechanical impedance, and infiltration rate. Macroporosity was evaluated after growing the fifth crop. Deep forking and forking in strips decreased bulk density and mechanical impedance and increased macroporosity and infiltration rate. Deep tillage by forking resulted in the driest soil 10 days after rainfall and the rice crop on this treatment experienced temporary wilting. Increasing the fertility level increased root activity which in turn increased mechanical impedance (the soil was drier) and water infiltration rate. We conclude that the soil physical properties of this soil were damaged very little by the land clearing operation and that the inability of the soil to grow crops was due to other factors.     

Cropping system effects of maize on infiltration,runoff and erosion on loess soils in South-Limbourg (The Netherlands): A comparison of two rainfall events

Two natural rainfall events are compared to evaluate the effects of three cropping systems of silage maize on soil moisture content, infiltration, runoff and erosion. Both rainfall events took place in early summer. One was a low intensity event with 27.6 mm of rain in 9 hours, and the other a high intensity event with 33.4 mm in 42 minutes. Cropping systems were:

• 1.(I) a spring tilled system (conventional),
• 2.(II) an autumn and spring tilled system with summer barley as spring cover crop, and
• 3.(III) an autumn tilled system with winter rye as winter cover crop and direct drilling of silage maize.

During the low intensity event, soil moisture content of the top 5 cm rose to field capacity on all three cropping systems. No runoff was generated. During the high intensity event, soil moisture content rose to field capacity on the two spring tilled cropping systems but was only slightly raised in the direct drill system, in spite of 17.7 mm of infiltrated rain. Runoff coefficients of the high intensity event were 41.7% (conventional system), 14.9% (autumn and spring tilled system) and 47.0% (direct drill system). The direct drill system showed a severely slaked soil surface in early summer, caused by winter rain.The response to rainfall of soil moisture content is ascribed to:

• 1.(I) a predominance of matrix infiltration on all cropping systems during the low intensity event and on the spring tilled systems during the high intensity event, and
• 2.(II) a predominance of infiltration via continuous macropores, open to the surface (of biologic origin), by-passing the soil matrix, on the direct drill system during the high intensity event.

The presence of continuous, vertical macropores on the direct drill system explains its surprisingly high infiltration capacity, considering its strongly slaked appearance. The smooth soil surface of the direct drill cropping system may have delayed infiltration during the flooded stage of the high intensity event by not providing vent points for the escape of soil air. Soil loss from the direct drill system during the high intensity event was only 15.6% of that from the conventional system. This is ascribed to low detachment rates of soil material by drop impact and/or overland flow, due to the presence of winter rye remains and, especially, the relatively high soil surface shear strength of the direct drill cropping system in early summer.     

Size-differential control of phytoplankton and the structure of plankton communities

We provide evidence and discuss the possibility that the main factors determining food web structure in oligotrophic and eutrophic marine environments are:

• 1.-1. Small algae are better competitors for light and nutrients than larger algae.
• 2.-2. The potentially high reproduction rate of their predators makes the smaller algae more susceptible to grazing control by microzooplankton than larger algae.
• 3.-3. Larger algae escape from microzooplankton grazing, due to their size, but experience losses through sedimentation.
• 4.-4. Microzooplankton is an important food source for mesozooplankton in oligotrophic areas.

Basically, the maintenance system (also known as the retention or regenerative system), which consists of pico- and nano-algae, microzooplankton, carnivorous mesozooplankton and in which bacteria and heterotrophic nanoflagellates act as decomposers and mineralisers, is typical in consuming most fixed energy within the photic zone. The overflow response, being an extension of the maintenance system with larger micro- and macro-algae and herbi-/omnivorous copepods, shows extended export of fixed energy out of the photic zone through sedimentation. The maintenance system is present in all marine environments, whether light- and/or nutrient-controlled, well-mixed or stratified, and oligotrophic or eutrophic. Typical overflow response is observed during an upward shift of the import of the controlling factor, which is either light or nutrients.In agreement with the hypothesis of size-differential control it was found that light-controlled phytoplankton consisted mainly of small flagellates (<8 μm) during winter in the well-mixed central North Sea.The dominance of large diatoms during the early spring bloom in the Marsdiep area (The Netherlands) was not necessarily caused by their growth characteristics, but was due to their escape from size-selective microzooplankton grazing.     

Facies analysis of Nile delta continental shelf sediments off Egypt

This study evaluates the texture and coarse fraction composition of 108 bottom samples from the Nile delta continental shelf. In total 19 petrological variables were considered for each of the samples, and Q-mode factor analysis of the textural and mineralogical variables yielded 4 factors (facies groups):

• 1.Facies I. Fine and very fine sands, light minerals, heavy minerals and ‘glauconite’, extending from the shoreline to the inner shelf and decreasing away from the shoreline.
• 2.Facies II. Silty sand rich in biogenic components occupies the entire outer shelf and its contiguous lower terraces.
• 3.Facies III. Mud (silt plus clay), mica and ‘glauconite’, covering the middle shelf and the upper terraces.
• 4.Facies IV. Fine to coarse-grained sediments and ‘glauconite’, locally distributed along the coast off lake ldku, Burullus headland, and Damietta promontory and El Gamil.

The configuration patterns of facies I (delta-front), facies III (prodelta) and facies IV (distributary mouth bar or progradational coastal sand) help identify delta lobes related to former distributary branches of the Nile river (Canopic, Saitic, Sebennitic, Atribic and Mendisian). The 4 facies-forming shelf sediments have resulted from sediment dynamics, sea-level fluctuation and differences in sediment input and provenance.     

Risques d'erosion au tiers monde: le point de vue de l'utilisateur

Recent studies of failed soil and water conservation programmes in the Third World have revealed, amongst others, serious flaws in the process of identification of the causes and consequences of land degradation. These flaws are not caused by an erroneous scientific analysis, but originate in a theoretical framework which is not targetted at the user of the land.The authors propose an alternative approach to the analysis of land degradation problems. The method is based upon the identification of the social, political and economic environment of the land user and can be divided into two parts:

• 1.(i) a study of the relationship between land degradation and development and
• 2.(ii) a study of productivity decline caused by erosion.

It is believed that this methodology permits the design of soil and water conservation programmes which take into account the knowledge, present day conditions and prospects of the land user and the society which supports him/her, hence be more likely to succeed.     

Iso-erodent map of Zambia: Part I: The calculation of erosivity indices from a rainfall data bank

The first stage in the establishment of an iso-erodent map of Zambia is the development of a Zambian rainfall data bank, the calculation and discussion of three erosivity indices and correlating the erosivity indices with rainfall amount.The data bank is made up of 10 years of data from eight different meteorological stations representing the different rainfall zones in Zambia. The data bank includes

• 1.1. total rainfall amounts split into component rainfall amounts with constant intensity
• 2.2. kinetic energy calculations
• 3.3. the erosivity indices.

Three erosivity indices have been calculated: E130 (WISCHMEIER 1959), KE (KINNELL 1981) and ΣN_pI_p (LAL 1976). Daily amount of rainfall explained 96, 95, and 89% of the variation in those indices respectively.Although the three indices are of comparable value, advantages and disadvantages of each of them are discussed.This work will be the basis for modelling the monthly erosivity and finally for making the iso-erodent map of Zambia (see part II, this volume).     

Application of fiber optic techniques in underground observations

Two major procedures involving the use of a fiber optic borescope were established for the purpose of:

• 1.in situ root growth monitoring and
• 2.iron ochre inspection in subsurface drainpipes.

The root image obtained was used to calculate root length using the Newman grid method. The effects of groundwater levels on root growth of silage corn were clearly indicated by the calculated root intensities (length per unit area). Further quantification of root intensities could be achieved using photographic images in a video digitizing process. Iron ochre in a subsurface drainage system was visually inspected. The severity of ochre occurrence was easily estimated from photographic images. The results suggest that permanent observation holes for routine maintenance purposes may be beneficial in future drainage system design.     

Potential use of the scheduler plant stress monitor in soybean

Much of work relating plant temperature to plant water stress has been done in arid regions. In 1989–1990, investigations were carried out verifying the validity of the Scheduler Plant Stress Monitor made by the Standard Oil Engineering Materials Company of the United States, in irrigation timing, under Hungary's changeable weather conditions.Three different water treatments were used:

• 1.⊎ natural rainfall only (control),
• 2.⊎ lysimeter study, where the water supply is in accordance with the water demand of plants,
• 3.⊎ irrigation according to the instructions of the Scheduler.

The monitor compares plant and air temperature differences to calculate stress index and irrigation timing. The measured indices were corrected for wind speed.Taking the varied water levels into account, the highest grain yield occurred in canopies watered by using the Scheduler instructions. In 1989, the yield increase was more moderate (16.5%) than that of the yield surplus in dry 1990 (38.1%), comparing to the results of non-irrigated control.The water-use efficiency in plant stands grown by the Scheduler control fell between the results of non-irrigated control and lysimeter study, independent of weather conditions.Use of the Scheduler may be recommended mainly in arid growing seasons, where yield increase is high enough to compensate for the additional cost of irrigation water. In Hungary, where the weather is very changeable it cannot be stated with complete confidence that the Scheduler is always an effective tool in irrigation planning. To clarify this problem further work is needed.     

How the food supply harvestable by waders in the Wadden Sea depends on the variation in energy density,body weight,biomass, burying depth and behaviour of tidal-flat invertebrates

For several reasons, waders in the Wadden Sea face a large seasonal and annual variation in their food supply. Observations on a tidal flat in the Dutch Wadden Sea have shown that:

• 1.- (1) The average energy density of ten invertebrate prey species varies between 21 and 23 kJ·g⁻¹ AFDW. In Scrobicularia plana and Mya arenaria, but not in Macoma balthica, the energy density is 10% lower in winter than in summer.
• 2.- (2) Depending on the species, body weights of prey of similar size are 30 to 60% lower in winter than in summer.
• 3.- (3) The year-to-year fluctuation in standing-crop biomass is larger in some species than in others, the difference depending mainly on the frequency of successful recruitment. The overall biomass of the macrobenthos in winter is half of that in summer, but the timing of the peak biomass differs per species.
• 4.- (4) The burying depth varies per species: Cerastoderma edule live just beneath the surface, while M. balthica, S. plana, M. arenaria, Arenicola marina and Nereis diversicolor bury more deeply and the majority of these prey live out of reach of the bird's bill. In all six species, burying depth increases with size. There is no seasonal variation in depth of C. edule and M. arenaria, but the four other species live at most shallow depth in early summer and most deeply in midwinter. Burying depths in winter vary from year to year, but are unrelated to temperature. Neither has temperature any effect on depth within months. For knot Calidris canutus feeding on M. balthica, the fluctuation in the accessible fraction was the main source of variation in the biomass of prey that is actually harvestable, i.e. the biomass of prey of suitable size that is accessible.Accordingly, the paper reviews the available data on the temporal variations in accessibility, detectability, ingestibility, digestibility and profitability of prey for waders. Only a small part of the prey is harvestable since many accessible prey are ignored because of their low profitability, while many profitable prey are inaccessible. The profitability of prey depends on their size and weight but also on their depth in the mud, since handling time increases with burying depth. A simple biomechanical rule explains why the handling time of small prey increases with bill length and why large, long-billed waders ignore a disproportionately larger part of the small prey. The fraction detectable for visually feeding waders is usually very low, especially when the temperature of the substrate is below 3–6°C. Waders vary their prey choice over the year in response to the changes in the availability and profitability of their different prey species. The food supply harvestable by waders is much lower in winter than in summer. For waders wintering in the Wadden Sea, the food supply may be characterized as unpredictable and usually meagre. Waders wintering in NW Europe are concentrated in coastal sites where the average surface temperature is above 3°C. This probably cannot be explained by a greater burying depth, and only partly by a lower body condition, of prey in colder areas. Yet the harvestable fraction is lower in colder sites, especially for sight-feeding waders, as invertebrates are less active at low temperatures. However, the lower energetic cost of living and reduced chances of the prey being covered by ice may also contribute to the waders' preference for warmer sites.

     

Selection of carrots for carotene content

1. 1.
   It was still questionable if the soil moisture content affected colouring of the carrot root directly or indirectly via the soil temperature.     
   
   

Factors influencing the occurrence of clubroot in semi-resistant populations of Brassica oleracea L.

1. 1.
   In breeding for resistanceto clubroot the plants have to be exposed to infection as long as possible. The clubbing of a susceptible variety forms an unreliable measure of the efficiency of the clubroot test.     
   
   

Internal tipburn in white cabbage I. Variety trials

1. 1.
   In a number of variety trials with white cabbage observations on the occurrence of tipburn were made. The various varieties showed different degrees of susceptibility. Of the Dutch autumn varieties, Succes and Glory of Enkhuizen were little susceptible, whereas Langedijker Autumn White was highly susceptible. Between the strains of the latter variety there were clear differences in this respect.     
   
   

Scab resistance in progenies of varieties of the cultivated pear

1. 1.
   Several selections from progenies from crosses between pear varieties were found to be free from scab (Venturia pirina) in one locality but susceptible when tested at another location. It is suggested that biotypes of the fungus are sharply restricted in their range of distribution at any given time.     
   
   

Selection of carrots for carotene content

1. 1.
   The influence of the oxygen content of the soil on the total carotenoid content of carrots was studied in pot cultures. Two methods were used.     
   
   

The selection of pulses in suriname

The selection of pulses in Suriname can be distinguished according as the objective is aiming at breeding for sandy soils or for heavy clay soils. The selection for sandy soils is mainly related to groundnuts for local consumption. This article deals with selection for heavy clay soils where pulses are grown in rotation with rice and are destined mainly for the world market. The crops are soybeans, cowpeas, blackeye peas, mungbeans and some other, minor crops. The existing local varieties were partly superseded by varieties from Indonesia or the Philippines, partly by lines selected from local varieties. The results of the investigations led to the following conclusions.

1. 1.
   Any country wishing to raise varieties that surpass its own local varicties can start with simple line selection.     
   
   

Juvenile phase and growth of apple and pear seedlings

It was investigated whether and to what extent the duration of the juvenile phase of pear and apple seedlings is related to their vegetative growth. The juvenile phase was defined as the period in years that the seedling remains vegetative; the trunk diameter served as a measure of vegetative vigour. The following observations were made:

1. 1)

   A significant negative correlation exists between the duration of the juvenile phase and the vigour of the seedling (as measured by trunk diameter).

2. 2)

   Environmental conditions with respect to weather, soil and cultural practices which promote or restrict growth, tend to shorten or lengthen the juvenile phase accordingly by their influence on the time required for the attainment of a certain minimum size which at least partly determines the attainment of the flowering condition.

3. 3)

   The weak rootstock M. IX significantly accelerated the onset of flowering of apple seedlings by about 1 1/2 years; this rootstock appears to combine a retarding effect on growth with a specific influence on flowering.