Soil Reserves Research Articles

Nitrogen and phosphorus limitation of soil microbial respiration in two tropical agroforestry parklands in the south-Sudanese zone of Burkina Faso: The effects of tree canopy and fertilization

We studied nutrient limitation and availability for soil microbial respiration after additions of glucose (C), in combination with nitrogen (N) and phosphorus (P) in soil samples taken from parklands of Vitellaria paradoxa and Faidherbia albida. We hypothesized that in these P-fixing soils: (i) after C addition, respiration will be limited by P, but P-limitation will be lower under tree canopies; and (ii) the maximum respiration rates after adding C will be higher with than without applications of inorganic fertilizer (NPK) in the field. The study site was located in the south-Sudanese zone of Burkina Faso. Microbial respiration was measured as CO 2 evolution from soil samples incubated under laboratory conditions. Two microbial growth peaks were observed after addition of C plus P to the soil samples. When P was added together with C, the initial increase in the microbial respiration rate was higher than when N and C were added, and the maximum respiration rate was also reached earlier. We conclude that P limited the initial rate of respiration. Under the tree canopy the P and N availability, was higher under both F. albida and V. paradoxa trees, than in areas beyond their canopies. NPK fertilization in the field resulted in higher soil reserves of N and P, but these nutrients had low availability in the short term. Results indicated that more P is available in forms that are immediately accessible to microorganisms under tree canopies, than outside the cover of their canopies.

Carbon mitigation by the energy crop, Miscanthus

AbstractBiomass crops mitigate carbon emissions by both fossil fuel substitution and sequestration of carbon in the soil. We grew Miscanthus x giganteus for 16 years at a site in southern Ireland to (i) compare methods of propagation, (ii) compare response to fertilizer application and quantify nutrient offtakes, (iii) measure long‐term annual biomass yields, (iv) estimate carbon sequestration to the soil and (v) quantify the carbon mitigation by the crop. There was no significant difference in the yield between plants established from rhizome cuttings or by micro‐propagation. Annual off‐takes of N and P were easily met by soil reserves, but soil K reserves were low in unfertilized plots. Potassium deficiency was associated with lower harvestable yield. Yields increased for 5 years following establishment but after 10 years showed some decline which could not be accounted for by the climate driven growth model MISCANMOD. Measured yields were normalized to estimate both autumn (at first frost) and spring harvests (15 March of the subsequent year). Average autumn and spring yields over the 15 harvest years were 13.4±1.1 and 9.0±0.7 t DW ha−1 yr−1 respectively. Below ground biomass in February 2002 was 20.6±4.6 t DW ha−1. Miscanthus derived soil organic carbon sequestration detected by a change in 13C signal was 8.9±2.4 t C ha−1 over 15 years. We estimate total carbon mitigation by this crop over 15 years ranged from 5.2 to 7.2 t C ha−1 yr−1 depending on the harvest time.

Towards the digital indexation of USCS classification: Case study in Israel

USCS soil classification is extensively used in different engineering applications. However, being “symbolic and descriptive classification”, it does not allow of an application of numerical methods for map drawing and hence hand drawn soil maps are still subjective to some degree. Application of mathematical extrapolation to soil mapping based on digitization of soil indexes significantly decreases the time taken to complete map drawing and excludes voluntarism from its production. Among other things, both these factors are of paramount importance for preliminary soil reserve estimation. This paper presents the first attempt to find a digital analogy to 17 out of 23 USCS groups (mainly poor graded soils). Examination of digitally and hand drawn vertical sections shows good correspondence between them especially where sharp transition between lithologically distant classification groups is missing from a geological section.

Potassium release and fixation as a function of fertilizer application rate and soil parent material

The issue of sustainable soil K management has partly been ignored during the last decades when the potential environmental impact from agricultural use of nitrogen and phosphorus has been considered a more important problem. It has become evident that mixed systems, especially under organic farming practices, commonly suffer from negative K field balances, which may deplete the soil in exchangeable K if release of K from soil minerals does not replace the amount of K that is harvested. In this study, release and fixation rates of K (kg ha − 1 yr − 1 ) were estimated in five long-term field experiments located on varying parent materials in South and Central Sweden, each having an array of K fertilizer application rates. The calculations were based on (i) accumulated K inputs and outputs from the soil during ca 30 yr, and on (ii) changes in topsoil and subsoil exchangeable K. The estimates ranged from ca 65 ± 7 kg ha − 1 yr − 1 of K released from soil reserves, to 85 ± 10 kg ha − 1 yr − 1 of K trapped by fixation. Release and fixation rates were highly dependent on the soil K balance, confirming that these are reversible processes that depend on plant uptake and fertilizer input. When receiving no K fertilizer, a loamy sand soil released 8 ± 10 kg ha − 1 yr − 1 , which was less than the annual net K removal from this soil, 25 ± 4 kg ha − 1 yr − 1 . Soils, with a texture from sandy loam to clay, showed release rates approaching the net K output, when not K fertilized. According to previous results, the pool of K extractable with 2 M HCl (K HCl) consists mainly of a fraction of the K in dioctahedral phyllosilicates. In the present investigation K HCl, corrected for exchangeable K, showed a significant response to soil K balance. More work is needed to yield a precise understanding of the mineralogical nature of this pool and how its measurement might be used to predict potential K release rates in soils.

Long-term K dynamics in organic and conventional mixed cropping systems as related to management and soil properties

The effects of management and soil properties on potassium (K) dynamics and delivery capacity have been investigated in mixed crop rotations that included a period of ley. The study was conducted using three long-term field experiments on sandy loam soils each including a conventional and organic cropping system. Results are based on data collected since the start of the experiment in 1987 up to 2004 which includes three full crop rotations. The mean annual K field balance for the 18 years varied from −21 to −60 kg K ha −1 year −1 in the conventional system and from −22 to −75 kg K ha −1 year −1 in the organic one, depending on site, indicating that present management systems rely to some extent upon K from soil reserves. The K concentration in the ley herbage decreased significantly over time at all sites and both systems, as demonstrated in long-term annual data as well as within individual growing seasons. Exchangeable K (K ex) concentration in the surface soil (0–20 cm) decreased significantly at all sites and systems during the study period, and there was also a decrease in acid-extractable K (K HCl) at two sites. The decrease in the K ex pool (kg ha −1) in the surface soil was smaller than the calculated total deficit of K from the cropping systems based on the accumulated field balances. Thus the crop must have been supplied with K from either deeper soil layers and/or from components of the non-exchangeable K pool. The amounts and distribution of K between different chemically (K ex and K HCl) and mineralogically (phyllosilicates and K-feldspars) defined K pools as well as the root distribution varied considerably between sites, indicating likely site differences in K delivery capacities. The size of the annual K deficit represents between 15 and 40% of the soil K ex pool (0–25 cm) compared to ≤1% of the K present in the phyllosilicate pool. The observed long-term decrease in herbage and soil K concentrations suggests that the current nutrient management plans are not adequate in terms of K. In addition, there is a risk for late season herbage K deficiency through short-term exhaustion of soil K ex. In order to maximise sustainability over the long-term, regionally summarised soil geochemical and mineralogical information could possibly help to improve the predicted long-term K supply from internal soil sources and be a useful compliment to standard soil tests, fertiliser recommendations and nutrient balances.

Production, nitrogen and carbon balance of maize-based forage systems

Nitrogen (N) and carbon (C) surplus can be used as indicators of an agroecosystems’ ability to maintain soil fertility. Maize is the key crop of intensive forage systems in northern Italy, and large amounts of manure are often supplied to this crop. Different maize-based cropping systems and manure managements were compared in this paper. The following were assessed, using the results of an 11-year experiment: crop production and N uptakes; C and N surpluses; soil C and N contents. The treatments were maize for silage (Ms), maize for grain (Mg), double annual crop rotation maize–Italian ryegrass (Mr), and rotation maize–grass ley (Ml). Five fertilization management systems were adopted: 0N control, and bovine slurry and farmyard manure supplied at two levels, ranging from 215 to 385 kg ha −1 of total N. The dry-matter production of Mr was significantly higher than those of the other systems. The response of maize to fertilization was similar in all the cropping systems, except for Mr, for which the crop showed a high reactivity to N input at both fertilizer levels. Soil reserves were rapidly consumed in the unfertilized treatment of Mr, whereas the high productivity potential of this cropping system was exerted in fertilized plots. The introduction of a ley in rotation with maize reduced the system's DM production, due to the low yield potential of grass compared to that of maize, reduced the system response to fertilization, and diminished the exploitation of organic N at high fertilization rates. Cumulated N surplus caused an enrichment of the soil N pool size: 43% of excess N was retained by the soil. The relationship between the cumulated C surplus and the soil C pool size indicated that 26–27% was retained by the soil. Crop residues of the Mg system were less effective in building up the soil C pool than other C sources. Both slurry and farmyard manure exerted a positive effect on the soil C and N retention. When farmyard manure was used, 18% of C and 45% of surplus N were incorporated into the soil organic matter (SOM). Slurry also built up the SOM content, resulting in 9% of C and 24% of N surplus.

A Micro- and Meso-Level Modeling Study for Assessing Sustainability in Semi-Arid Tropical Agro Ecosystem Using

ABSTRACT Mining of nutrients from soil is a major problem causing soil degradation and threatening long-term food production in developing countries. In this paper an attempt was made for carrying out nutrient audits, which includes the calculation of nutrient balance at micro- (plot/field) and meso-level (farm) and evaluation of trends in nutrient mining/enrichment. A nutrient budget is an account of inputs and outputs of nutrients in an agricultural system. NUTrient MONitoring (NUTMON)isa multiscale approach that assesses the stocks and flows of N, P, and K in a well-defined geographical unit based on the inputs viz., mineral fertilizers, manures, atmospheric deposition and sedimentation and outputs of harvested crop products, residues, leaching, denitrification, and erosion losses. The calculated nutrient balances at crop activity level indicated a negative balance for cereals and pulses, whereas positive for most of the horticultural crops. Similarly the results showed a negative balance for N and K and positive for P at farm level. Soil nutrient pool has to offset the negative balance of N and K, hence there will be an expected mining of nutrients from the soil reserve in the study area. The management options/policy interventions to mitigate this mining by manipulating all inputs and outputs in a judicious way with an integrated system approach are also discussed.

Post-harvest nitrogen cycling in clearcut and alternative silvicultural systems in a montane forest in coastal British Columbia

The MASS (Montane Alternative Silvicultural Systems) trial was established in the coastal mountains of British Columbia to compare clearcut, patch cut, green tree and shelterwood systems. A number of studies were carried out at the MASS trial to determine the extent to which these variable levels of stand retention retained old-growth attributes of N cycling and associated ecological processes. Harvesting led to increases in N mineralization in the forest floor (2×) and mineral soil (10×), and fluxes of N through the upper 25 cm of mineral soil (2× to 3×). However, fluxes of N were not large (< 0.35 kg ha-1per growing season). Nitrogen mineralized was predominantly ammonium and not nitrate in the forest floor (> 95% in all but clearcut, > 75% in clearcut) and upper mineral soil horizon (42–86%). The nitrate component came from heterotrophic decomposition of organic matter, not conversion of ammonium to nitrate by autotrophs, and nitrate increases resulted from decreased gross nitrate consumption with harvesting, rather than increased nitrate production. The increases in soil N availability resulting from harvesting were reflected in only slight increases in seedling foliar N concentrations for two to four years after logging (peak of ~ 2% for western hemlock and ~ 1.6% for amabilis fir) before decreasing to below deficiency thresholds for both species. Overall, estimated losses of N from the rooting zone after harvesting (1 kg ha-1 yr-1) were minimal in comparison to estimated N inputs (4 kg ha-1 yr-1), N exports in logs at harvesting (250 kg ha-1) and soil reserves (11 400 kg ha-1). Although unlikely to affect future site productivity, losses of N could be reduced somewhat through the use of shelterwood harvesting. Key words: alternative silvicultural systems, variable retention harvesting, nitrogen cycling, litterfall, decomposition, nitrification, N mineralization, microbial ecology, leaching, foliar N, Abies amabilis, Tsuga heterophylla, Thuja plicata

Mineralogical budgeting of potassium in soil: A basis for understanding standard measures of reserve potassium

AbstractThe study was conducted to investigate the relationship between some standard measures of soil reserve potassium (K) and soil mineralogy. Eight different agricultural soils from the N temperate and S boreal regions were studied and analyzed both by standard methods (exchangeable K, 2 M HCl‐ and aqua regia–extractable K) and by quantitative mineralogical methods based on X‐ray powder diffraction analysis of spray‐dried bulk soils. Linear regression and multivariate methods were used to assess the relationships between standard measures of soil reserve K and a number of soil chemical, physical, and mineralogical properties. A mineralogical budgeting approach, to estimate total K and its speciation between different mineral phases, is shown to be accurate after validation against total K analyzed geochemically. This approach enabled us to determine that both HCl‐ and aqua regia–extractable K were highly correlated with K in dioctahedral phyllosilicates and extracted 1%–17% and 5%–45% of total K, respectively. Neither extraction showed any obvious relationship to K in feldspar, which is frequently a larger reservoir of K in the soils examined.

Spatial associations of humus, nutrients and soils in mixed dipterocarp forest at Lambir, Sarawak, Malaysian Borneo

Discrete humus layers are common on podzols under temperate coniferous and tropical heath forests, and patchy layers also occur under some temperate broadleaved forests on non-podzolic soils. We used multiple data sets to test the reported association of humus with oligotrophic but non-podzolic soils under non-heath dipterocarp forest at Lambir, Sarawak. We examined the distribution, morphology and nutrient dynamics of necromass on soils derived from sandstone and shale. Concentrations of the main mineral nutrients were lower in fresh litter on the very oligotrophic sandstone soils than on shale. The rates of litterfall were similar, so that annual litterfall fluxes of all nutrients were lower on sandstone. The lower nutrient concentrations and fluxes in the litter on sandstone resulted in slower decomposition, longer residence times and larger standing crops of forest-floor necromass, with lower concentrations of nutrients. The necromass on sandstone sequestered significantly more N, K and Mg but less Ca and Mn than on shale, with no significant difference for P. The variations in necromass nutrient dynamics were associated with morphological differences. There were mats of densely rooted humus under the litter on sandstone, whereas litter lay directly over the mineral topsoil on shale. Spatial associations with soil nutrients were weak for necromass thickness, but clear for humus. The proportions of nutrients in the litterfall and necromass reflected the stoichiometric profiles of the soils. We attribute the differences in necromass nutrient dynamics and their association with soil reserve nutrients to lower rates of nutrient replenishment from the weathering of sandstone than from shale. Necromass characteristics are robust field indicators of multivariate edaphic differences in these and other tropical forests on Acrisols/Ultisols derived from Tertiary clastic sediments.

Sweet and fibre sorghum ( Sorghum bicolor (L.) Moench), energy crops in the frame of environmental protection from excessive nitrogen loads

Sweet and fibre sorghum ( Sorghum bicolor (L.) Moench) are multipurpose cereals of potential interest for several non-food uses. In order to assess the effects of nitrogen (N) fertilization on crop growth, yield and N budget during crop cycle, field trials were carried out in Northern Italy (44°33′N, 11°21′E) in the years 1997–1999. Sweet and fibre sorghum were grown in combination with three N rates (0, 60, 120 kg ha −1). Both crops depicted a sigmoidal growth-pattern, but fibre sorghum showed an earlier and steeper growth. Sweet sorghum recovered due to a longer cycle, 118 versus 105 days in the 3 years’ average, and attained a similar final yield. Nitrogen fertilization did not affect growth pattern, nor yield partitioning among plant organs: the sweet type allocated more photosynthates to stems (about 75% of total dry weight) compared to the fibre one (55–60%), due to a limited partitioning to panicles. Total dry weight at harvest showed an interaction with years: fibre sorghum yielded significantly more than sweet sorghum in 1997 (23.8 versus 17.7 Mg ha −1), but the opposite happened in 1998 and 1999 (20 versus 24.2 Mg ha −1 as average), when a different sweet hybrid was grown, involving a longer season. When only the stem was considered of potential interest, such as in the case of ethanol production or fibre extraction, fibre sorghum showed a slight advantage in the 1st year (14.4 versus 12 Mg ha −1), whereas the sweet type prevailed in the following 2 years (18.7 versus 11 Mg ha −1). Fertilization did not significantly influence total yield, although interacted with sorghum type in plant N concentration and uptake: fibre sorghum rose in both parameters, due to bulkier panicles acting as a late-season sink for the nutrient, while the sweet type was not affected. Nitrogen budget at harvest was clearly influenced by applied fertilizer and plant uptake, whereas nutrient losses as ammonia volatilization and nitrate leaching and natural supplies along with precipitation played a less relevant role. The expected variations in soil reserves ranged between −216 and +77 kg ha −1 of N, depending also on the plant portion removed from the field (whole plant or stem). A slight decrease in soil reserves, more favourable in environmental terms, is achieved when the whole biomass is removed from the field and when fertilizer rates are tight-suited to crop needs in specific growth conditions.

Changes in agricultural land use and in plant nutrient balances of arable soils in Estonia

The aim of the present study was to assess the impact of changes in agricultural land use and in the plant nutrient balances on the degradation of soils in Estonia. The plant nutrient balances of arable soils in Estonia were calculated at the national level. After the re-establishment of the independence of Estonia, in the transition to market economy, agricultural production has undergone a drastic decline. Agricultural land use has declined most of all in the regions with low soil fertility. Decreased and low-input agricultural production has reduced pressure on the surrounding environment but owing to the inadequate use of fertilizers, the balance of the main plant nutrients is at present negative. In the 1990s, crop production has occurred largely at the expense of soil resources. Current agri-environmental policy should be supplemented with measures for preventing degradation of soils due to the depletion of plant nutrient reserves of arable soils.

Changes in the rate of release of Ca and Mg and normative mineralogy due to weathering along a 5300-year chronosequence of boreal forest soils

Changes in the normative mineralogy and chemical weathering rates (elemental loss) of Ca and Mg from the uppermost mineral soil horizon were determined at five forested sites in the boreal zone forming a chronosequence. The sites were all located on the same glaciofluvial (esker) deposit (well-sorted sand) over a distance of 27 km in the coastal region of the Gulf of Bothnia in Finland and had estimated ages from 339 to 5276 years. Because of isostatic land uplift the region is continually emerging from the sea, the rates of which are known, allowing the age of current surfaces to be dated. Soil profile development progressed from Gleyic Arenosols (youngest and nearest the coast) through Haplic Arenosols to Haplic Podzols (3 oldest and furthest away from the coast). Elemental concentrations of soil (< 2 mm) were determined using XRF and ICP-MS from a hot aqua regia digest. Normative mineralogy was determined using these data and a stoichiometric mineral distribution model. Weathering (elemental loss) rates were calculated using XRF concentrations and normative quartz as the conservative reference component. Quartz was increasingly enriched in the uppermost horizon with soil age, commensurate with the loss of easily weathered minerals. Using quartz as the conservative component, the mass residual fraction remaining in the uppermost soil horizon of the oldest soil was 0.27, 0.35 and 0.57 respectively for biotite, hornblende and anorthite, which are important sources of Ca and Mg. B / E-horizon ratios of hydrous aluminosilicate contents increased from 1 to 14 with soil age clearly indicating the increase in degree of podzolisation. The losses of Ca and Mg increased with soil age but at a decreasing rate. Ca and Mg losses for the youngest soil were respectively 3.3 and 1.8 mol m − 2 ; corresponding values for the oldest soil were 10.6 and 10.5. Mean rates of loss for the youngest soil were 10 and 5 mmol m − 2 yr − 1 for Ca and Mg respectively, and corresponding values for the oldest soil were 2 mmol m − 2 yr − 1 for both Ca and Mg. The loss of these base cations from the soil will have resulted in a lower acid neutralizing capacity and increased sensitivity of these soils to acidic deposition, and represents a reduction in the soil reserve of important plant nutrients.

Dinámica de población de plantas de Arachis pintoi CIAT 17434, asociada a gramas nativas en pastoreo, en el trópico húmedo de México

The objectives were to identify the survival resources of Arachis pintoi associated to native grasses under grazing. The experiment was performed in the north-central region of Veracruz State, Mexico, from March 2001 to March 2002. Two and a half ha of an associated pasture were used, with a stocking rate (animal units/ha) of 3.2 in the rainy season and two for the remaining of the year, with one day of grazing and 20 d of resting. Flowering, soil seed reserve, stolon density, and plant and seedling survival were evaluated. Analyses of variance and regression procedures were performed as well as the fitting of curves that best described data behavior. June 2001 showed the highest flowering value (851 flowers/m2), while the minimal value occurred on January 2002 (3 flowers/m2). Soil seed reserves on three assessments were of 1,671, 1,388 and 3,029 kg/ha, respectively. Stolon density (stolons/m2) showed an initial downward trend, followed by an increase from September 2001 to March 2002. Mortality of seedlings was higher (more than 40 %) during the first two weeks. It can be concluded that drought and winter affected flowering, while trampling increased plant mortality, however, these effects were counteracted by seed soil reserve and high stolon density.

Induction and Inhibition of Striga hermonthica (Del.) Benth. Germination by Extracts of Traditional Chinese Medicinal Herbs

Striga hermonthica (Del.) Benth. is a root parasitic weed that reduces the yield of many important cereals in the semiarid tropics in Africa. Yield losses from damage by the parasite are often significant, and complete crop failure is not uncommon. The prolonged use of nonhost plants that produce S. hermonthica germination stimulants may reduce seed reserves in soil over time. The production of high‐value medicinal herbs with S. hermonthica germination induction properties in soils infested with S. hermonthica seed would offer growers an alternative crop as well as potentially reducing S. hermonthica seed reserves. We screened the extracts of 383 traditional Chinese medicinal herbs to test their ability to induce or inhibit the germination of S. hermonthica seeds. Distilled water and methanolic extracts of over 20 herbs induced S. hermonthica germination. Herb extracts that induced S. hermonthica germination rates greater than 50% were Acorus gramineus Soland., Agrimonia pilosa Ledeb. var. japonica (Miq.) Nakai, Areca catechu L., Citrus tangerina Hort. et Tanaka, Cudrania cochinchinensis (Lour.) Kudo et Masam., Nardostachys chinensis Batal., Oldenlandia diffusa (Wild.) Roxb., Portulaca oleracea L., Scrophularia ningpoensis Hemsl., and Semiaquilegia adoxoides (DC.) Mak. Water extracts from 27 herbs inhibited S. hermonthica germination. The undiluted extract from Curcuma longa L. completely inhibited S. hermonthica germination. Undiluted extracts from 15 other herbs reduced germination by more than 50% compared with the positive control. The results from this study indicate that metabolites produced by some traditional medicinal herbs may have the potential to be used as bioherbicides to control S. hermonthica.

The effect of chloride and sulphate application to soil on changes in nutrient content in barley shoot biomass at an early phase of growth

In this study experiments primarily aimed at the needs of specification of an adequate soil reserve of labile sulphur were extended by investigations of the impact on interactions in nutrient uptake by a test barley plant. Vegetation (18-day) experiments under controlled conditions of cultivation were conducted on a diverse set of 48 soils from agricultural lands. Before barley sowing the experimental set of soils was divided into two variants: A &amp;ndash; control (with NH&lt;sub&gt;4&lt;/sub&gt;Cl application) and B &amp;ndash; response variant [with (NH&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt; application], and a uniform dose of 26 mg N/kg soil was used. After the experiment terminated, concentrations of N, N-NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;&amp;ndash;&lt;/sup&gt;, S, S-SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2&amp;ndash;&lt;/sup&gt;, P, K, Mg, Ca, Na, Mn and B were determined. Paired t-test revealed significant differences between the sets of data on variants A and B in barley yield and concentrations of sulphur, sulphate, nitrate, phosphorus and boron in barley plants. Sulphate variant (B) had higher yield of barley, higher concentrations of sulphur, sulphate and boron and lower concentrations of nitrate and phosphorus compared to variant A. The lower concentrations of nitrate and phosphorus could not be reasoned by the effect of dilution resulting from the higher barley yield. A substantial decrease in nitrate concentration was related to better utilisation of plant nitrogen after the nutrient status of soil was adjusted with sulphur. Phosphorus concentration in barley adequately corresponded to the soil reserve of labile phosphorus, but only after the phosphorus concentration in barley markedly decreased to the lower level in (sulphate) variant B. Higher concentration of boron in barley could potentially be related to the depression of phosphorus uptake after sulphate application.

Barley response to the soil reserve of sulphur and ammonium sulphate in short-term experiments under controlled conditions of cultivation

The objective of the paper was to determine an appropriate concentration of available sulphur in soil for the initial growth of plants. Based on previous researches two methods of soil extraction were used to acquire information on the soil reserve: water extraction (H&lt;sub&gt;2&lt;/sub&gt;O 1:5, w/v) and extraction in 0.5M ammonium acetate with addition of NH&lt;sub&gt;4&lt;/sub&gt;F (KVK-UF soil test). Spring barley was used as a test crop to determine the soil reserve of sulphur and its response to sulphur addition to the soil. A collection of 48 samples of topsoil from agriculturally important localities in the CR was made up for this purpose and the parameters of the nutrient status of the soil were remarkably different. A set of soils was used to establish short-time vegetation experiments in a plant growth chamber according to the scheme: A) control &amp;ndash; without sulphur application and B) response variant with application of 30 mg S/kg of soil in the form of (NH)&lt;sub&gt;4&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;; nitrogen in variant A was adjusted by application of NH&lt;sub&gt;4&lt;/sub&gt;Cl. Index of nutrient efficiency (IE = Y/N where Y = yield and N = nutrient concentration in the plant) and boundary lines of the point field were used to evaluate the efficiency of barley nutrition with sulphur. The efficient soil reserve of sulphur for the soil test H&lt;sub&gt;2&lt;/sub&gt;O (1:5) when the ICP analytical technique was used was indicated in the range of 8&amp;ndash;11 mg S/kg; 6&amp;ndash;10 mg S/kg for sulphate detection on a SKALAR analyser. The efficient utilisation of sulphur by barley plants for the KVK-UF soil test was in the range of 7&amp;ndash;12 mg S/kg. The conversion of the KVK-UF S-test to the index of soil reserve of sulphur by adding up a variable portion of the CEC value to the value of sulphur determined by the soil test (0.0167CEC + 9.1667) improved the closeness of the relationship between soil and plant.

Effects of intensive monocropping of bananas on properties of volcanic soils in the uplands of the French West Indies

Abstract. On the volcanic soils of the uplands of the French West Indies, banana monocropping has been practised since about 1980, mostly with large inputs of chemicals and replanting every three to five years after ploughing. However, in Guadeloupe less intensive cropping systems with only few added chemicals are still being used. The effects of the intensive practices on the physical, chemical and biological attributes of soils were evaluated on 34 farmed fields, which were selected to include the diverse soils and management practices found in the uplands of South Basse‐Terre. Management was classified into four groups to differentiate effects of fertilizers, nematicides and tillage over at least 10 years. The population of the parasitic nematode Radopholus similis was, on average, greater 3 months after the application of nematicides. Thus, the use of nematicides increases the dependency of yield on nematicides. Ploughing decreased soil organic matter in the 0–10 cm layer as well as microbial respiration and earthworm biomass, but increased banana root infestation by R. similis. Ploughing was also associated with a change in soil structure, as revealed by the decrease in soil water content at −1 kPa potential and the increased infiltration rate of water into the 0–10 cm layer. The use of fertilizers has advantages for the maintenance or increase of soil reserves of K. However, due to the decreasing of negative electrical charges in the lower layers of andosols, where pH remains low, the majority of the cations supplied by fertilizers, mainly potassium, are prone to leaching.

Nitrogen management in Eucalyptus nitens plantations

Low nitrogen (N) availability commonly limits the growth of Eucalyptus nitens plantations on ex-forest sites in Tasmania, Australia. We summarise here a decade of mechanistic and empirical research that has improved the basis for N management of these plantations. Twenty-two fertiliser experiments were used to define relationships between tree growth and methods of N fertilisation, i.e. timing, frequency, form, rate and placement. Pools and fluxes of mineral N were monitored at five sites. Potential deficiencies of N between planting and 10 years of age were indicated by the concentrations of soil NH 4, NO 3, total N and total phosphorus (P). Appropriate timing of N fertilisation depended on when N demand started to exceed supply from soil reserves, and was indicated by soil total N. Plantations on low-N sites experienced N deficiency during the first few years of growth, but others experienced it later or not at all. High cumulative rates of N fertilisation (at least 500 kg N ha −1) were needed to maximise growth at many sites, but there is no evidence to suggest that any individual application in excess of 200 kg N ha −1 is warranted. Hence, multiple applications will be needed to maximise growth. Urea was the preferred form of N, because it was relatively cheap and at least as effective as other N forms. Limiting N application to the crown drip line of 6-year-old trees with small crowns did not increase growth compared to a totally broadcast application. Soil N availability increased for 1–2 years following most N-fertiliser applications. Tree growth rates increased significantly for the same period followed by several years of less significant responses during which re-applications promoted a more sustained response in growth. This research has fostered an increase in the use of N fertilisers to increase productivity, and it should improve the basis for evaluating the economics of options for N fertilisation. Although applications of N fertilisers at rates up to 200 kg N ha −1 and at intervals of several years are unlikely to be a threat to water quality, especially if urea is used, research is needed to determine the environmental risks associated with long-term and higher intensity uses.

Major element fluxes from a coniferous catchment in central Ontario, 1983–1999

Acid deposition over time scales of decades may deplete essential base cation (BC) reserves in soils to the extent that forest health may be affected. In order to assess the nutrient status of soils in central Ontario, input–output budgets for calcium (Ca), magnesium (Mg), potassium (K) and nitrogen (N) were calculated over a 17-year period (1983–1999) for a coniferous catchment in the Muskoka-Haliburton region. Inputs through deposition and weathering (BCs only), were compared with outputs through stream export and net accumulation in forest biomass. Despite a lack of forest growth at PC1, annual NO3–N concentrations in the stream were low (<0.1 mg/l) over the 17-year period, and over 80% of the atmospheric N input was retained in the catchment, indicating this catchment has not reached N-saturation. Stream export of Mg, and in particular Ca, exceeded input of these elements through deposition and weathering, indicating a net loss from the catchment over the 17-year period. Mass balance calculations indicated there was no net loss of K from the catchment. Soil re-sampling measurements confirmed large losses of Ca, but not Mg, and there were significant decreases in both NaCl-exchangeable Ca concentrations and soil pH between 1983 and 1999. The measured decline in soil Ca concentration amounted to a loss of approximately 85 kg/ha Ca from the exchangeable pool over the 17-year period. Similarly, input–output budget calculations indicated a net loss of Ca from the catchment in the range of 76 to 88 kg/ha between 1983 and 1999. Although the magnitude of Ca export decreased over the 17-year period, current stream export continues to exceed Ca input through deposition and weathering.