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.     

Susceptibility of soils to physical degradation in Hungary

A simple category system was elaborated by the authors expressing the susceptibility of Hungarian soils to physical degradation, as structure destruction and compaction. The main soil characteristics which were taken into consideration in the category system were as follows: type, subtype and local variant of the soil, parent material, texture, hydro-physical properties, carbonate-, salinity/alkalinity- and organic matter status, and depth of the soil. Based on detailed territorial information on the above mentioned soil characteristics Hungarian soils were classified into 8 physical degradation sensitivity (susceptibility) categories:

• 1.1. Non-susceptible soils;
• 2.2. Slightly susceptible soils;
• 3.3. Moderately susceptible soils;
• 4.4. Soils susceptible to compaction and surface crusting, but not to structure destruction;
• 5.5. Soils susceptible to both structure destruction and compaction;
• 6.6. Soils susceptible to both structure destruction and compaction due to salinity and/or alkalinity;
• 7.7. Organic soils;
• 8.8. Shallow soils (solid rock or cemented layer near to the surface).

The map of these categories was prepared in the scale of 1:500 000.For medium (1:100 000) and large-scale (1:25 000 - 1:10 000) mapping a more detailed category-system (including more categories and subcategories with precise numerical limit values) will be elaborated.     

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.

     

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.     

Restoration of eroded soil with conservation tillage

Eroded Kandhapludult soils occupy more than 40% of the Southern Piedmont region of the USA. The humid-thermic climate associated with the Ultisols permits double crop residue production ranging from 10 to 14 Mg ha⁻¹ yr⁻¹. Long-term conservation tillage into these crop residues is beneficial in ameliorating the effects of soil erosion. During the course of a five-year study, decomposition of these residues increased soil carbon significantly. Restoration processes were initiated by increasing average soil carbon, representing slight, moderate and severe soil erosion classes, from 0.97 to 2.37% in the 0 to 1.5-cm depth. Accompanying soil carbon responses were increases in soil N, water-stable aggregation and infiltration. Runoff coefficients on conservation tilled restored soils was only 6%, compared to 35% for those conventionally tilled. Rill and interrill soil loss rates were also reduced significantly with surface residue provided with conservation tillage.Restoring Ultisol landscapes with variable levels of soil erosion requires differential fertilization. All fertilizer requirements for severely eroded plots were 1.43 to 2.30-fold higher than those of moderately eroded plots. Because biological N fixation by the crimson clover (Trifolium incarnatum L.) cover crop appeared to be retarded on the severely eroded site, observed plant N stress developed on the irrigated/conservation tillage treatment. Cumulative grain yields of severely eroded site, ranged from 15.4 to 30.3 Mg ha⁻¹ 5yr⁻¹, and were statistically equal to or exceeded those of the slightly eroded site. Conservation tillage grain yields were best optimized on the rainfed-moderately eroded site, probably because of the more desirable texture-organic properties of the 13-cm thick Ap horizon. Management of cool-season cover crops with conservation tillage appears essential to restore and sustain crop productivity on eroded Ultisols.     

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.

     

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.     

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.     

不同改良剂与培肥方式对咸灌土壤改良效果的研究

为了探讨改良剂对咸灌土壤的改良效果,采用咸水灌溉下小麦大田种植试验的方法,通过对不同改良剂与培肥方式结合等10个处理的土壤进行采样,分析施用改良剂与培肥方式对咸灌土壤理化性质、养分状况与小麦产量等方面的影响。结果表明,施用改良剂和培肥可降低土壤容重,增大渗透系数和毛管孔隙度,降低土壤pH和全盐含量;增加土壤有机质、速效磷和速效钾含量,而各处理的碱解氮含量低于对照处理;同时可提高小麦产量。因此,在本试验中,T4和T5处理,即改良剂B（醋渣+牛粪+石膏）+有机肥+无机肥和改良剂B+无机肥对改善土壤理化性状、提高土壤养分含量和使小麦增产的效果最好,可作为充分利用咸水资源和盐渍化土壤改良的有效方法。     

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.     

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.     

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).     

Soil compaction and water table effects on soil aeration and corn growth in a greenhouse study

A greenhouse experiment was conducted to study the effects of aeration on growth of corn seedlings. Variable aeration regimes were created by a combination of 3 levels of soil compaction (1.20, 1.37 and 1.56 Mg m⁻³) and 3 water table depths (10-cm, 20-cm and 30-cm). Soil aeration was assessed by measuring the oxygen diffusion rate (ODR) and the gaseous composition of soil air. Samples of soil air were analyzed for concentrations of oxygen, carbon dioxide, ethylene and nitrous oxide.The ODR decreased with increasing soil compaction. The average ODR for the 30 cm water table was 193.5, 89.2 and 15.4 μg O₂ m⁻² s⁻¹ for the three compaction treatments of 1.2, 1.37 and 1.56 Mg m⁻³, respectively. At 40 days after planting, concentration of carbon dioxide in soil air was as high as 0.5% by volume. High concentrations of ethylene and nitrous oxide were also measured in those samples that contained high levels of carbon dioxide. The range of concentration was 2–19 ppm for ethylene and 2–20 ppm for nitrous oxide.The vegetative growth of corn seedlings, as measured by root and shoot weights and plant height, was not significantly affected by the treatments imposed. However, stomatal conductance and photosynthesis significantly differed among treatments.     

Changes in microrelief and their effects on infiltration and erosion during simulated rainfall

The erosivity of soils under a given rainfall energy appears to vary greatly among soil orders, probably reflecting differences in clay composition and organic matter content. This study was conducted to quantify microrelief, infiltration, and sediment yield changes during three consecutive simulated rain events on a Udic Haploboroll and a Typic Hapludalf from Minnesota, and a Mollic Kandiudalf, and Typic Palehumult from Uganda. Air dry aggregates (< 5 mm) were packed in 19 1 containers tilted to a 5% slope and were subjected to three consecutive high energy rain storms (63 mm h⁻¹) for a duration of 1 h. Runoff and sediment were continuously monitored during a storm. Infiltration was measured by continued weighing of the soil and containers. An automated non-contact laser relief meter was used to measure changes in soil roughness initially and after each storm. Soil surface roughness decreased during the rain events indicating that aggregate breakdown was the dominant process in seal formation. For example, random roughness decreased form 5.9 to 4.0 mm on Barnes loam and from 9.7 to 6.9 mm on Renova silt loam with cumulative rainfall of 0 and 126 mm. These infiltration rates indicated that the Barnes Loam (Haploboroll) and Kabanyolo clay (Kandiudalf) were unstable soils while Kachwekano clay (Palehumult) and Renova silt loam (Hapludalf) were quite stable. Final infiltration rates after 3 consecutive rainfalls on Kachwekano clay (15 mm h⁻¹) and Renova silt loam (13 mm h⁻¹) [the stable aggregate soils] were significantly higher than those of Barnes loam (4 mm h⁻¹) and Kabanyolo clay (3 mm h⁻¹). For the two stable soils a high infiltration rate on a rough surface was maintained until aggregate breakdown occurred and runoff began. Sediment yield from Barnes loam (29 kg m⁻²) and Kabanyolo clay (28 kg m⁻²) was significantly greater than soil loss from Kachwekano clay (0 kg m⁻²) and Renova silt loam (6 kg m⁻²). The microrelief method to quantify aggregate stability is an improvement over wet sieving and other related measurements because of its rapidity and because the statistical quantification can be linked to physical processes.     

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.     

Effects of Reduced Tillage and Fertilization Practices on Soil Characteristics, Plant Water Status, Growth and Yield of Upland Cotton

Three different tillage practices, conventional (mouldboard ploughing at 22–25 cm plus one rotary hoeing at 5–6 cm, CT), minimum (one rotary hoeing at 12–15 cm, MT), and no‐tillage (direct drilling in soil covered by vetch residues, NT), combined with three fertilization treatments, inorganic (50 kg N ha^?1 as ammonium sulphate), cattle manuring (30 t ha^?1), and control (no‐fertilizer), were applied on a cotton crop (Gossypium hirsutum L. cv. Acala SJ‐2) grown on a clay loam soil in the field of the Agricultural University of Athens. Soil (gravimetric water content, bulk density, and penetration resistance in the top 40 cm) and plant parameters (root growth, leaf water potential, leaf area growth and seedcotton yield) were recorded throughout the cultivation period in all treatments. No‐tillage was associated with significantly higher values of soil water throughout the observation period caused by the vetch mulch. Bulk density and penetration resistance were initially higher in the no‐tilled plots, but they became significantly lower after 2–3 months from sowing. These beneficial effects on soil properties favoured root growth, expressed as root surface density, in the NT‐plots at the top soil layer. Similar, although less spectacular, effects were observed in the manured plots. Plant water status, expressed in terms of the water potential index, was significantly and consistently best in the NT‐ and worst in the CT‐plots throughout crop growth. In addition, NT favoured a better foliage growth and resulted in significantly higher yields than the other tillage practices. In general, NT, and in second instance, MT considerably improved plant water status, and hence foliage growth and yield in comparison with CT by maintaining higher levels of soil water and improving root growth. Manuring positively interacted with the reduced tillage practices for most soil and plant parameters.     

Annual crop rotation of tropical pastures with no-till soil as affected by lime surface application

Soil acidity and low natural fertility are the main limiting factors for grain production in tropical regions such as the Brazilian Cerrado. The application of lime to the surface of no-till soil can improve plant nutrition, dry matter production, crop yields and revenue. The present study, conducted at the Lageado Experimental Farm in Botucatu, State of São Paulo, Brazil, is part of an ongoing research project initiated in 2002 to evaluate the long-term effects of the surface application of lime on the soil’s chemical attributes, nutrition and kernel/grain yield of peanut (Arachis hypogaea), white oat (Avena sativa L.) and maize (Zea mays L.) intercropped with palisade grass (Urochloa brizantha cv. Marandu), as well as the forage dry matter yield of palisade grass in winter/spring, its crude protein concentration, estimated meat production, and revenue in a tropical region with a dry winter during four growing seasons. The experiment was designed in randomized blocks with four replications. The treatments consisted of four rates of lime application (0, 1000, 2000 and 4000 kg ha⁻¹), performed in November 2004. The surface application of limestone to the studied tropical no-till soil was efficient in reducing soil acidity from the surface down to a depth of 0.60 m and resulted in greater availability of P and K at the soil surface. Ca and Mg availability in the soil also increased with the lime application rate, up to a depth of 0.60 m. Nutrient absorption was enhanced with liming, especially regarding the nutrient uptake of K, Ca and Mg by plants. Significant increases in the yield components and kernel/grain yields of peanut, white oat and maize were obtained through the surface application of limestone. The lime rates estimated to achieve the maximum grain yield, especially in white oat and maize, were very close to the rates necessary to increase the base saturation of a soil sample collected at a depth of 0–0.20 m to 70%, indicating that the surface liming of 2000 kg ha⁻¹ is effective for the studied tropical no-till soil. This lime rate also increases the forage dry matter yield, crude protein concentration and estimated meat production during winter/spring in the maize-palisade grass intercropping, provides the highest total and mean net profit during the four growing seasons, and can improve the long-term sustainability of tropical agriculture in the Brazilian Cerrado.     

Modellversuche zur Aufnahme von Boden- und Dünger-Stickstoff aus verschiedenen Tiefen durch Sommerweizen*

Model trials on the uptake of soil and fertilizer nitrogen from various depths by spring wheat The uptake of ammonium nitrogen by spring wheat mixed into various soil depths was investigated in a pot trial using 1-m high soil columns. At the same time a nitrification inhibitor (NI) was used in some of the variants in order to study the utilization of fertilizer N under the conditions of a temporary inhibition of nitrification. In order to monitor the interrelationships of soil and fertilizer N, ¹⁵ N-labelled ammonium sulphate was used. The following results were obtained.

• 1 The various depths at which the N was located were not found to affect yields; nor did the use of the NI have any influence.
• 2 There was a statistically significant increase in the N content of the grains as the N was mixed with deeper layers of the soil; this was at a lower level in the series with NI. In straw no change was observed in the series without NI, there being a decrease of the N content in the series with NI.
• 3 The utilization of fertilizer N according to the “difference method” was between 76 % and 84 % in the series without NI with an increasing tendency of the nitrogen located at deeper levels. In the series with NI there was a reverse tendency of 74 % to 69 %. According to the 15N method only 54–62 % of the fertilizer N was used by the plants. The NI scarcely changed the utilization. Overall there was not a significant higher use of the nitrogen in the deeper layers.
• 4 In the fertilized series more soil N was mobilized and taken up by the plants than in the control. This effect was more pronounced in the series with no NI.
• 5 The mobilization of soil N by fertilizer N (“priming effect”) contrasted with a more vigorous immobilization of fertilizer N. This resulted in an overall positive soil N balance.
• 6 A total of about 30 % of the fertilizer N remained in the soil. Most of it was to be found in the incorporation layer. However, displacement into the neighbouring layers did take place, this being more pronounced in the acropetal direction in the case of the N in the deeper layers than in the basipetal direction in the case of the N introduced into the top layer.

     

The Effect of Fertilizer Type and Level of N Fertilization Before and After Grassland Renewal on N Leaching Losses

When grassland is ploughed and reseeded this results in an increased mineralization of organically bound nitrogen (N) in the soil. Greater amounts of nitrate in autumn are at risk of being leached during the winter half of the year. In two field experiments, nitrate leaching was measured over 2 years after reseeding of a 9‐year‐old grassland field in spring on a sandy soil in northwest Germany. During the experiments, major management factors that can influence the intensity of mineralization were varied: Type of fertilizer, mineral N fertilizer or organic manure, and the level of fertilization, 0, 160 or 320 kg N ha⁻¹ a⁻¹, before renewal of the grassland, and level of fertilization, 0, 160 or 320 kg N ha⁻¹ a⁻¹ in mineral form, after renewal of the grassland. The type of fertilization as well as the level of N fertilization before ploughing had no significant effect on the soil mineral nitrogen content (SMN) in autumn and N leaching in the year following the grassland renewal. N fertilizer level after sward renovation had a significant effect on the nitrate leaching losses in the two following years. Fertilization at a rate of 320 kg N ha⁻¹ resulted in leaching losses of 7 and 61 kg N ha⁻¹ in the first and second subsequent years, respectively. At fertilizer rates of 0 and 160 kg N ha⁻¹ leaching losses were lower than 5 kg N ha⁻¹. It is concluded that for mown grassland no restriction of the N fertilization before the renovation of the sward is necessary to reduce the nitrate leaching risk as long as the amount of N fertilized does not exceed the N‐uptake by the crop. Similarly, the N fertilization after the sward renewal does not bear a particular leaching risk.     

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.