Soil Reserves Research Articles

Input–output nutrient budgets as a diagnostic tool for sustainable forest management

Maintaining, and if possible increasing, soil fertility is a major goal for sustainable forest management, because it determines to a large extent the site's capacity for wood production. As, generally, forest soils are poor, and the demand for wood is still increasing, the boundary of resilience of each ecosystem must be known. Several cases must be identified: the case of natural or native species forests, either planted or not, which are extensively managed and the case of intensively managed plantations. In this paper, input–output budgets are calculated according to temporal and spatial scales. The measurement of the main inputs and outputs is discussed. When all the fluxes entering and leaving the selected compartment are measured, the budget provides a realistic picture of the direction of change in soil fertility. In other cases, the validity of the budget has to be considered according to the proposed hypothesis. A balanced budget means that the element considered is not depleted from the soil. This does not mean that no changes occur in the ecosystem. A positive budget means that the element considered is accumulating in the system, which is not always favorable. A negative budget means the element considered is depleted in the system, but it has to be related to the available soil reserves and to the rate of flux into available pool to be a real index of risk for the ecosystem. Information from several case studies shows the interest of these budgets because (i) they are able to characterize depletion before the direct analysis of the system would be able to indicate it, and (ii) they give useful quantitative data for recommendations applicable to forest management. These budgets have the disadvantage of being labor-intensive and expensive. They are also site-specific and give little direct information for identifying the mechanisms of nutrient tranformations within the ecosystem. The relationships between forest production and nutrient availability are not sufficiently known to be able to quantify the variation in production when nutrient depletion is observed. On account of the difficulty in calculating such a budget, the most efficient strategy could be the following: (i) calculate budgets in a representative network of sites; (ii) relate the individual budgets to more easily available parameters; and (iii) propose more simple indicators for managers. Land classification and the potential impact of forest management is required for giving appropriate recommendations to managers.

Pasture yield responses to phosphorus, sulphur, and potassium applications on North Otago soils, New Zealand

Pasture yield responses to phosphorus (P), sulphur (S), and potassium (K) were measured over four to eight years on different yellow‐grey earth (pallic) soils at three non‐irrigated (Timaru, Kauru, and Claremont soils) and one irrigated (Otiake soil) sites in North Otago. Large pasture yield responses to P at application rates up to 80 kg ha−1 yr−1 occurred on three sites with initial soil Olsen P levels of 6–11 μg ml−1, but only a small response up to this rate was measured on the Timaru soil with a higher initial soil Olsen P level (16 μg ml−1). The relationship between soil Olsen P and relative annual pasture yield was similar and moderate (r2 = 0.57) for the average of the three most responsive sites. The highest pasture yield response to S was measured at application rates up to 80 kg ha−1 yr−1 on an Otiake soil with an initial soil sulphate S level of 3 μg g−1. Smaller pasture yield responses at rates up to 40 kg S ha−1 yr−1 occurred on Kauru and Timaru soils with initial soil sulphate S levels of 8 and 4 μg g−1, respectively. In four of the eight years there was a pasture yield response up to 10 kg S ha−1 yr−1 on the Claremont soil with an initial soil sulphate S level of 9 μg g−1. Soil sulphate S only accounted for a small proportion (27%) of the average variation in relative yield. Three of the four sites had medium to high initial soil quick test (QT) K levels (9–19) and the fourth (Otiake soil) had a low level (4). Over four to eight years, the soil QT K in the nil K treatments declined to 2–7, but there was a pasture yield response only in the last four years at the lowest level, on the Otiake soil. Soil potassium tetra‐phenyl boron levels were increased by K application and showed a lower decline than for no K. There was a moderate to strong relationship measured between relative yield (% of maximum yield) and %P (r2 = 0.58) and %S (r2 = 0.83) in mixed herbage on the Otiake soil but not at the other sites. %P was related to Olsen P (r2 = 0.52–0.69) on the Claremont and Otiake soils and %S was related to soil sulphate S (r2 = 0.51) for the mean of all four sites. Overall, the results show that North Otago yellow‐grey earth soils can be responsive to P, S, and K, and the size of the pasture yield response can be predicted with a reasonable degree of accuracy by the level of available soil P, S, and K, the amount of soil reserve K, and the P, K, and S concentration in mixed herbage.

Use of multinutrient soil tests for sulphur determination

The objective of this research was to find a multinutrient extractant that will also work with sulphur (S). The correlation study between methods of soil testing and S‐bioavailability was run in controlled conditions of cultivation of test plants (barley and mustard) in short‐term (21 days) vegetative trials. The following methods were used to evaluate the soil reserve of S: extraction with 0.01 M Ca(H2PO4)2, Mehlich 2, Mehlich 3, extraction by Matula and Pirkl (1988)‐(KVK‐UF method), extraction with 0.01 M CaCl2, the phytoavailability soil test with the PST‐1 resin capsules (UNIBEST, Inc. Bozeman, MT), extraction with water in ratio 1:5 (w/v) and “simulated soil solution”; obtained from water soil paste by centrifugation. These methods were tested on a set of 32 soils taken from plough depth of research plots distributed across the Czech Republic (CzR). The experimental results indicate that the present official method of soil testing used in CzR, Mehlich 2, cannot be successfully employed for estimating the S supplying power of soils. More promising results were found with the KVK‐UF method. The extraction of soils with 0.01 A/CaCl2 was found less useful, mainly due to a greatly dispersed correlation field of phytoavalability in the low S concentration in that extractant. The best results were obtained with extraction of S into a water medium. However, there is a problem with the agronomic interpretation of the other basic nutrients, mainly potassium (K), due to the lack of information about the reservoir of soil nutrients. Only the sink method with the PST‐1 resin capsules was able to successfully provide information about the phytoavailability of S from soil that has a surplus of gypsum. When analyzing the macronutrients in soil testing for fertilizer recommendation, the S concentration can be analyzed by the same KVK‐UF and water 1:5 (w/v) extractants. However, more research is needed to interpret S concentrations in extractants for use in agronomy studies.

Global change and root function

AbstractGlobal change includes land‐use change, elevated CO2 concentrations, increased temperature and increased rainfall variability. All four aspects by themselves and in combination will influence the role of roots in linking below‐ and above‐ground ecosystem function via organic and inorganic resource flows. Root‐mediated ecosystem functions which may be modified by global change include below‐ground resource (water, nutrients) capture, creation and exploitation of spatial heterogeneity, buffering of temporal variations in above‐ground factors, supply and storage of C and nutrients to the below‐ground ecosystem, mobilization of nutrients and C from stored soil reserves, and gas exchange between soil and atmosphere including the emission from soil of greenhouse gases.The theory of a functional equilibrium between root and shoot allocation is used to explore predicted responses to elevated CO2 in relation to water or nutrient supply as limiting root function. The theory predicts no change in root:shoot allocation where water uptake is the limiting root function, but substantial shifts where nutrient uptake is (or becomes) the limiting function. Root turnover will not likely be influenced by elevated CO2, but by changes in regularity of water supply. A number of possible mechanisms for root‐mediated N mineralization is discussed in the light of climate change factors. Rhizovory (root consumption) may increase under global change as the balance between plant chemical defense and adapted root consuming organisms may be modified during biome shifts in response to climate change. Root‐mediated gas exchange allows oxygen to penetrate into soils and methane (CH4) to escape from wetland soils of tundra ecosystems as well as tropical rice production systems. The effect on net greenhouse gas emissions of biome shifts (fens replacing bogs) as well as of agricultural land management will depend partly on aerenchyma in roots.

Management of phosphorus, potassium, and sulfur in intensive, irrigated lowland rice

Management of soil phosphorus (P), potassium (K) and sulfur (S) resources in intensive, irrigated rice systems has received less attention than increasing cropping intensity and yields with new cultivars, irrigation, and fertilizer N. Crop requirements, input-output balance, and soil supplying capacity of P, K and S in irrigated lowland rice are reviewed. Based on projected rice production requirements, we estimate that the total annual nutrient demand for irrigated rice will be about 9 to 13 × 10 6 t N, 9 to 15 × 10 6 t K, 1.2 to 2.4 × 10 6 t P and 0.9 to 1.5 × 10 6 t S in 2025, amounts that represent an increase of 65 to 70% above 1990 requirements. At present, negative K balances are widespread and K deficiency has become a constraint to increasing yields, even on heavy-textured lowland soils with high inherent fertility. Because opportunities are limited for breeding cultivars that acquire more P, K or S from soil or have higher internal nutrient-use efficiencies, long-term management strategies must focus on maintaining adequate nutrient balances in the topsoil layer. Interactions among nutrients have a large influence on physiological and agronomic efficiency that result from nutrient applications. Strategies that only aim at increasing P or K application rates without considering the indigenous supply from soil reserves are inefficient; they may not sustain yield increases to meet rice demand. Little improvement in fertilizer use efficiency can be expected from the present system of providing blanket recommendations for a given production domain. Instead, site-specific nutrient-management approaches will be needed to accommodate the tremendous variability in indigenous nutrient supply found in the irrigated lowlands of Asia.

Evaluation of three organic wastes for reclaiming burnt soils: Improvement in the recovery of vegetation cover and soil fertility in pot experiments

The efficacy of three abundant organic wastes: poultry manure (PM), cattle slurry (CS) and sewage sludge (SS) for the reclamation of burnt soils was evaluated. A forest soil, previously furnace-heated in order to simulate exposure to a high-intensity wildfire, was labelled with nitrogen-15 (15N) to evaluate the contribution of N derived from the organic waste to the burnt soil and vegetation. Four treatments were performed with the heated 15N-labelled soil: an unamended control soil (S) and three waste amended soils (S+PM, S+CS and S+SS) at a dose waste of 167mg total N kg–1 soil. Lolium perenne was grown in all the pots for 3 months. In each treatment the phytomass produced and its N content decreased significantly in the following order of treatments: S+PM \(\) S+CS > S+SS \(\) S. The percentage of plant N derived from the waste was similar in the S+PM (22.8%) and S+CS (24.0%) treatments, but significantly lower in the S+SS treatment (16.5%). At the end of the 3 month experimental period, the available N reserves (phytomass N+soil inorganic N) in the control soil accounted for 51.5–71.5% of those in the S+PM, S+CS and S+SS treatments, whereas the yield of the plants was only 13.4–29.8% of that in the manured soils. These results demonstrated the importance of the addition of organic wastes, particularly PM, for the recovery of the vegetation cover and for the stabilization of the soil ash layer. They also showed that the level of N was not the main controlling factor of plant growth in the control soil, which, moreover, did not show evidence of a shortage of macronutrients, i.e. phosphorus, potassium, calcium or magnesium. It is hypothesized that, as occurs in heat-sterilized soils, phytomass production in the control-heated soil could have been inhibited by the heat-induced production of phytotoxic compounds, their negative effects being microbially or chemically suppressed by the addition of organic wastes.

The role of long-term site productivity in maintaining healthy ecosystems: A prerequisite of ecosystem management

Forest health is a central issue across North America. Most definitions imply that forest health is a condition of the forest ecosystem which sustains complexity or diversity while still providing for human needs. Imbedded in this definition is the need to maintain the productive capacity of managed sites. Although site productivity is largely a function of climate, soil properties, and the biotic potential of the vegetation occupying the site, forest management can also play an influential role in altering site productivity.In terms of site productivity, different concerns exist when managing different ecosites. Based on a recently-conducted expert opinion survey, the major concerns when harvesting black spruce from shallow-soil, upland sites were: 1) harvest-related nutrient removals, and 2) loss of organic matter. In contrast to these ecosites, the major concerns for organic sites (including wet, mineral soils) were: 1) altered hydrology, and 2) rutting. The water table on these sites is typically near the surface for a significant portion of the frost-free season, minimizing organic matter decomposition and associated nutrient release. Any forest management practice which exacerbates this situation would have a negative impact on site productivity. Tree nutrient cycling studies conducted on shallow-soil sites in northwestern Ontario were presented to show that calculated nutrient replacement times, with the exception of K, did not exceed current rotation periods. However, the forest floor nutrient pool represented a major component of the soil reserves. Based on the importance of this nutrient pool, best practices designed to protect and allow for the rebuilding of this active soil pool are essential if long-term site productivity is to be maintained.This paper outlines a series of steps to evaluate and correct management-induced changes in long-term site productivity. These steps included: 1) the development of "best practice" guidelines, 2) the development of a set of "criteria and indicators", and 3) the establishment of long-term experimental field trials. The results of this third step should, in turn, be used to refine the "best practice" guidelines and suggest alternative "criteria and indicators" that should be incorporated into a monitoring program of forest sustainability. Key words: forest health, ecosystem management, site productivity, nutrient cycling

Nutrient resources for crop production in the tropics

For the foreseeable future a majority of the population, and almost all the mal– and under–nourished, will continue to be found in the tropics and subtropics. Food security in these parts of the world will have to be met largely from local resources. The productivity of the land is to a large extent determined by the fertlity of the soil, which in turn is mostly determined by its organic matter content and stored nutrients. Soil organic matter is readily lost when organic matter inputs are reduced upon cultivation and more so upon intensification. The concomitant loss of topsoil and possible exposure of subsoil acidity may cause further soil degradation. Plant nutrients to replenish what is yearly taken from the soil to meet the demands for food and fibre amount to 230 million tonnes (Mt). Current fertilizer consumption stands at about 130 Mt of N, P 2 O 5 ,and K 2 O, supplemented by an estimated 90 Mt of N from biological nitrogen fixation worldwide. Although 80 per cent of the population lives in the developing world, only half the world's fertilizer is consumed there. Yet, as much as 50% of the increase in agricultural productivity in the developing world is due to the adoption of fertilizers. World population growth will cause a doubling in these nutrients requirements for the developing world by 2020, which, in the likely case of inadequate production, will need to be met from soil reserves. Because expansion of the cultivable land area is reaching its limits, the reliance on nutrient inputs and their efficient use is bound to grow. With current urban expansion, nutrients in harvested products are increasingly lost from the rural environment as a whole. Estimates of soil nutrient depletion rates for sub–Saharan Africa (SSA) are alarmingly high. The situation may be more favourable in Latin America and Asia where fertilizer inputs are tenfold those of SSA. Closing the nutrient cycle at a community level in rural areas may be tedious; on an inter–regional level it is associated with considerable costs of collection, detoxification and transportation to the farms. Yet, at the rate at which some of the non–renewable resources such as phosphorus and potassium are being exploited, recycling of these nutrients will soon be required.

Fuzzy mapping of soil fertility — a case study on irrigated riceland in the Philippines

Intensive irrigated rice production technologies have changed the input-output balance of many soil nutrients in tropical Asia, but their impact on soil fertility has not been studied adequately at regional scales. To assess the current soil fertility status in irrigated riceland of Nueva Ecija, Philippines, soil samples were collected from 384 farmers' fields in a 19,176 ha area. Block-kriged maps of topsoil properties (0–20 cm depth) were produced. Yields and nutrient uptake were measured for a subset of 63 farmers during the 1994 dry and wet seasons. Logical Boolean and fuzzy membership models for land classification with or without Monte Carlo simulation were compared. Crisp Boolean classification underestimated the potential area with severe soil fertility constraints to high rice yields by 0.2–5.2%. A combination of fuzzy membership functions with Monte Carlo simulation was used to produce maps of membership values for three soil fertility classes and two multivariate soil fertility qualities. Most of the area investigated had a high inherent fertility potential and was rated suitable for intensive rice production, but 97% of the land had limitations due to low soil status of one or more nutrients. Low available K, P, and Zn occurred on 54%, 64% and 63% of the land, respectively, whereas low S status was only found in minor areas. The average P balance in farmers' fields was positive, but both under- and overfertilization with P occurred. Long-term irrigated rice-rice monoculture has led to a significant depletion of soil K reserves in soils of Nueva Ecija. Although K uptake was larger than N uptake in both seasons, most farmers applied little or no K fertilizer. Average net K loss was 38 kg K ha −1 crop −1 and K is now one of the most important constraints to sustaining and increasing rice yields.

Responses of productive and unproductive kikuyu pastures to top‐dressed nitrogen and phosphorus fertiliser

In South Africa there is widespread reliance on kikuyu grass as a source of summer forage for intensive dairy, beef and sheep enterprises. There is, however, a dearth of reliable information on the fertility requirements of kikuyu pastures. Responses of previously productive and unproductive kikuyu pastures in the Mistbelt and Highland Sourveld of KwaZulu‐Natal to top‐dressed nitrogen (N) and phosphorus (P) fertilizers were studied infield cutting trials conducted during two consecutive seasons. Significant dry matter (DM) yield responses accompanied incremental N applications of up to 500 kg ha−1. First‐season DM yields of previously productive pastures at zero applied N were in the range 6 to 9 t ha−1, while yields of previously unproductive pastures at zero N were 0 to 2 t ha−1. By the second season, yields at zero N were uniformly low on the various pastures, reflecting the limited extent of plant‐available N reserves in soils under productive kikuyu. In both the Mistbelt and Highland Sourveld, efficiency of response to applied N in seasons when rainfall was similar to the long‐term mean was approximately 30 kg DM per kg N over the N application range of 0 to 250 kg N ha−1. When rainfall was substantially below average, N efficiencies decreased markedly. Application of N in six rather than three dressings during the growing season resulted in the N efficiency increasing by 3.5 kg DM per kg N. In contrast to the enormous responses to N, there was little or no response to P in the various trials. An optimum P test (NH4 HCO3 / NH4F / EDTA) for high clay content (>50% clay) Mistbelt soils of approximately 10 mg L−1 is suggested from yield‐soil test calibrations. Data highlighting the impact of soil sampling depth on P test values are presented, and this information serves to underline the importance of standardizing sampling procedures in the soil testing of pastures for fertility purposes.

Release of complexing organic acids by rhizosphere fungi as a factor in Norway spruce yellowing in acidic soils

A field experiment in the Vosges (a low mountain range in north-eastern France) had shown that a CaMg amendment of an acidic forest soil reduced the total number of fungal propagules per gramme dry soil, while the number of species considerably increased. Some rhizosphere fungi isolated from the amended and/or control plots were grown in three media with ammonium or nitrate as the sole source of nitrogen, and with or without aluminium. Complexing organic acids released by the fungi and likely to interfere with tree nutrition were analyzed in the culture medium after fourteen days incubation. The largest amounts of complexing organic acids are released by fungi isolated from the acid control plot. These rhizospheric fungi take part in soil acidification, which results in the long-term decrease of soil mineral reserves in a forest soil subjected to permanent leaching. Therefore, we conclude from this work that fungi might contribute to the deficient mineral nutrition of the Norway spruce on acidic soils, by impoverishment of the root environment in essential cations. However, among the causes of the Norway spruce yellowing, rhizosphere deleterious fungi act as secondary agents or contributing factors rather than primary causes of decline.

Nutrient dynamics of chestnut tree ( Castanea sativa Mill.) coppice stands

A chronosequence of chestnut coppice stands was used to study nutrient dynamics in an ecosystem during stand development. The strategy of the ecosystem was demonstrated in this study: to achieve a large biomass production under conditions of limited nutrient availability. Contrary to what is generally expected, forest production has high nutrient requirements. Perennial vegetation fulfilled half its requirements of N, P and K from internal translocation of nutrients that were reused when physiological activity ceased; the remaining part was taken up from available soil reserves. Half of the uptake returned to the soil, mainly as litterfall. As a result, overal immobilization was low. As a consequence, decreasing the rotation length will enhance the depletion of forest soil nutrients, as will harvesting a larger part of the forest biomass and hence the smaller biomass compartments, which contain most of the nutrients in the vegetation. Dynamics of biological fluxes clearly show the importance of tree vegetation on soil mineral functions, especially by continuously returning organic matter and nutrients back to the soil surface.

Forest floor carbon pools and fluxes along a regional climate gradient in Maine, USA

Global carbon (C) reserves in soil are large compared with atmospheric stocks (in the form of CO2 and methane), so small changes in soil C storage will have a significant effect on atmospheric CO2 concentrations. In order to better understand the consequences of global climate change, it is essential that we define how soil C storage is influenced by changes in temperature and moisture that are expected as a result of global climate change. Forest floor carbon pools and fluxes were evaluated at 16 northern hardwood sites located within four distinct climate regions (Northern, Central, Southern and Coastal) in Maine. Mean annual air temperature at the sites ranged from 2.0°C in the Northern region to 6.2°C in the Coastal region and average annual precipitation ranged from 90 cm in the Northern region to 140 cm in the Coastal region.Leaf litter mass and leaf litter C flux were not correlated with temperature indices and did not vary among regions. However, they were positively correlated with annual precipitation, suggesting that litter production was controlled, in part at least, by precipitation but not by temperature.Northern sites stored more C in the forest floor than Coastal sites, and they experienced slower decomposition rates. Because soil and vegetation characteristics of these sites were similar, we attribute these trends to differences in climate. Indeed, C turnover time was correlated with latitude and temperature indices. Slower decomposition in the Northern region was attributed to a combination of lower specific activity at temperatures below 13°C, cooler average temperatures and a shorter frost-free season.Soil respiration at each site was positively correlated with temperature and the slope of the relationship increased with latitude, indicating that the ability of the soil biota to respire C varied with climate. A predictive equation is presented that accounts for the change in slope with latitude.Because C loss through soil respiration was more sensitive to temperature than C inputs from litter, any regional warming in the next century may lead to a decrease in forest floor carbon storage. However, if precipitation increases with temperature, then litter C flux may increase and offset the increase in soil respiration.

Effect of colonizing tree species on soil nutrient availability in a clay soil of the boreal mixedwood

Soil nutrient availability was assessed around stems of trembling aspen (Populustremuloides Michx.), white spruce (Piceaglauca (Moench) Voss), and paper birch (Betulapapyrifera Marsh.) that regenerated after fire 49, 77, and 123 years ago on a clayey soil of the southern boreal forest. For all stand ages, forest floor pH was greater by 0.5 unit under aspen than under other species, while the accumulation of organic matter and nutrients was generally greater in the forest floor of spruce. With time since fire, forest floor pH and mineral soil reserves of nitrogen (N) and exchangeable calcium declined significantly, while the C/N ratio increased, perhaps as a result of nutrient immobilization in the aggrading biomass. Net N mineralization and nitrification, measured by aerobic laboratory incubations, were higher under birch and aspen than under spruce in the forest floor and the mineral soil of the youngest stand (49 years old). However, in older stands, these parameters were significantly lower, and no significant differences were found between soils of deciduous and coniferous species. These results suggest that a decrease in N availability with time since fire was caused by factors other than the generally assumed succession to coniferous trees.

Comparison of The Efficiencies of Urea Nitrogen and Phosphoryl Triamide Nitrogen forLolium Multiflorumand Their Influence on the Soil Nitrogen Reserve

Abstract 15N-Labelled phosphoryl triamide (PTA) was synthesized. Experiments with Lolium multiflorum plants in vegetation pots have shown that there are important differences between urea and PTA treatments. At high N rates, uptake of N by plants increased in both treatments and N uptake from the soil reserve decreased. The coefficient of N utilization by plants was higher in the urea than in the PTA treatments. However, at the highest N rate, the coefficient of N utilization by plants was higher in the PTA than in the urea treatment. A strong negative correlation was found between the rates applied and the decrease of N content in the soil reserve.

In vitro weathering of phlogopite by ectomycorrhizal fungi

The ways in which ectomycorrhizal fungi benefit tree growth and nutrition have not been fully elucidated. Whilst it is most probably due to improved soil colonization, it is also likely that ectomycorrhizal fungi could be directly involved in nutrient cycling of soil reserves. This study assessed access by two species of ectomycorrhizal fungi to soil nonexchangeable K+ reserves. The incubation of ectomycorrhizal fungi in bi-compartment Petri dishes with phlogopite led to cation exchange reactions and to crystal lattice weathering. Paxillus involutus COU led to irreversible phlogopite transformations, while Pisolithus tinctorius 441 led to reversible ones. Simultaneous depletion in K+ and Mg2+ led to an enhanced weathering of phlogopite by P. tinctorius 441. The observation of phlogopite evolution shows that some specific Al3+ immobilization occurred under P. tinctorius 441. The data suggest that these bio-weathering mechanisms could be related to the release of fungal organic acids or other complex forming molecules.

Nutrient budgets and status in three pairs of conventional and alternative mixed cropping farms in Canterbury, New Zealand

The major inputs of nitrogen (N), phosphorus (P) and sulphur (S) as fertilizer and biological N 2 fixation, and the major removals of these nutrients in harvested products (grain, meat and wool) for each year of the rotation of three pairs of farms were calculated. The farms were under a mixed cropping system of farming, common to the study area, in which grazed grass/white clover pasture and/or grass and white clover seed crops are grown in rotation with arable crops. One of each pair of farms was managed conventionally and the other was under an alternative organic or biodynamic system. The nutrient status of soils, harvested grain and pasture herbage were also measured along with the organic matter content and enzyme activities of the soils. Nutrient budgets (inputs minus outputs) for N, P and S on the conventional farms were generally balanced or positive so that the supply of these nutrients is unlikely to be limiting production. Nitrogen budgets were positive at all three alternative farms with biological N 2 fixation accounting for most or all of the N input. One alternative farm had positive P and S budgets because of additions of compost, phosphate rock and elemental S. By contrast, at the other two alternative farms, net removal of P, and in one case S, occurred. In the other case, the S budget was balanced by one application (per rotation) of S fertilizer to the pasture. At these two sites, concentrations of grain N, P and S were lower than those at conventional sites and pasture herbage P and S concentrations were below recommended critical concentrations. Levels of total S and P and available P in soils were also lower on the alternative than conventional farms. Production on these alternative farms is relying on soil reserves of P and S, and additions of P and S will be required in the future to sustain current production levels. Organic C content and arylphosphatase, arylsulphatase and urease activities tended to be higher under alternative than conventional pastoral management. This was attributed to the longer pastoral phase under alternative (3–4 year) than conventional (1–2 year) management resulting in a small build up of organic matter. However, organic C content and enzyme activities were similar under conventional and alternative systems during the arable phase suggesting that conventional management had no adverse effect on soil biological activity.

Growth and nutrient accumulation by Pinus caribaea on three savanna sites in northern Nigeria

Growth and nutrient accumulation by a 14 year old stand of Pinus caribaea var. hondurensis (Barr. and Golf.) on three different savanna sites in northern Nigeria were determined. There were differences in the rate and magnitude of productivity and nutrient accumulation between the stands growing on the different sites. These differences were attributed to contrasts in soil characteristics, altitude and mean annual rainfall. Growth was higher and nutrient use efficiency better on sites where soil and climatic factors were more favourable. Comparison of the amounts of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) held in the tree biomass with the inventory of the corresponding soil reserves of plant ‘available’ nutrients showed that the amounts of N, Ca and Mg immobilised in the above-ground tree layer were small. In contrast a much greater proportion of each of P and K was held in the biomass. The fraction of plant ‘available’ soil P immobilised in the biomass varied between 72% and 176%; the respective K fractions were 64% and 92%. Based on these data, the estimates of nutrient loss that might accompany different intensities of biomass utilisation were calculated. The estimates indicated potential problems of P and K nutrition in future rotations. This prediction was qualified in view of the fact that precise data on some of the nutrient fluxes of the ecosystems were lacking. It was concluded that savanna sites with inherently low nutrient quality were at a risk of nutrient depletion.

The biogeochemical cycle in a healthy and highly productive Norway spruce (Piceaabies) ecosystem in the Vosges, France

The biogechemical cycle in a highly productive and healthy Norway spruce (Piceaabies (L.) Karst.) stand was studied in the west part of the Vosges Mountains, France. The plot, an 85-year-old plantation established on an acidic brown soil, was considered the healthy control of a series of stands in varying stages of decline in this area. The nutrient reserves were evaluated in the soil and in the living biomass. A classical design was set up and monitored for 3 years to measure the total atmospheric input and the transfer of solution through the ecosystem using tensionless lysimeters. The current soil functioning was dominated by the nitrogen cycle (nitrification) and the occurrence of large amounts of Al in the solution. Nitrification, essentially endogenous, was the main acidifying factor. Nitrates contribute to the leaching of large amounts of Ca and Mg. The mean annual losses in the seepage water at a depth of 60 cm were 17.2 kg•ha−1 of N, 10.2 kg•ha−1 of Ca, and 6 kg•ha−1 of Mg. The mean annual input-output budget of these elements was always negative (−6.3 kg•ha−1 for N; −4.7 kg•ha−1 for Ca; −2 kg•ha−1 for Mg). The seasonal budgets show that the atmospheric input is only helpful to the stand if it occurs during the growing period. The question of the perenniality of the current ecosystem productivity is of paramount interest, even if at present the available soil reserves and the nutrient content of solutions (absolute values and ratios between elements like Ca/Al and Mg/Al) indicate that tree nutrition is not a limiting factor.

Nitrogen and dry matter partitioning of barley grown in a dryland environment

Abstract Fifty‐eight spring malting barley crops (Hordeum vulgare L. ‘Triumph') were monitored in the Rangitikei district, New Zealand (40°20'S), over three seasons beginning 1987/88 and covering a wide variation in soil moisture conditions during grain filling but small deficits before anthesis. The objectives were to: (1) document the range of variability of grain yield among locations and years; (2) determine if systematic patterns occurred in the dry matter (DM) accumulation and nitrogen (N) uptake; and (3) evaluate the effects these processes have on the partitioning of DM and N between the grain and the rest of the plant. Mean yearly grain yields (14% moisture) were 6.85, 5.12, and 5.07 t/ha, respectively. Grain number/m2 accounted for 79% of the variation in grain yield. On average, 63% of the N in the above ground crop was derived from soil reserves, and 87% of the total N uptake occurred before anthesis. Pre‐anthesis processes had a major effect on crop characteristics at maturity. For example, t...