Changes in nutrient distribution in forests and soils of Walker Branch watershed,Tennessee, over an eleven-year period

Changes in vegetation, litter, and soil nutrient content were measured in selected plots on Walker Branch watershed, Tennessee, from 1972–73 to 1982. The watershed has been allowed to revert to forest since 1942, before which it consisted of small subsistence farms and woodland pastures. Changes in Ca status were of particular interest because initial nutrient cycling characterizations indicated that net Ca accumulation in vegetation could have caused large decreases in soil exchangeable Ca²⁺ within 20 years.Decreases in forest floor and subsoil (45–60 cm) N, exchangeable Ca²⁺, and Mg²⁺ content were noted in several plots from 1972 to 1982. Surface soils (0–15 cm) showed either no change or, in some cases (e.g., N and exchangeable K⁺ in certain plots), increases over the 11-year period. Reductions in forest floor and subsoil exchangeable Ca²⁺ and exchangeable Mg²⁺ on cherty, upper slope oak-hickory and chestnut oak forests were most striking. The changes in Ca²⁺ are thought to be due primarily to high rates of Ca²⁺ incorporation into woody tissues of oak and hickory species. Reductions in forest floor and subsoil exchangeable Mg²⁺ could not be accounted for by woody increment; leaching may have played a major role in causing these decreases. Changes in P and exchangeable K⁺ were variable, with both increases and decreases.There were significant increases in exchangeable Al³⁺ in both subsoils and surface soils of certain plots, but these were not accompanied by decreases in exchangeable base cations or consistent decreases in pH. Dissolution of interlayer Al from 2:1 clays may be the cause of the exchangeable Al³⁺ increases.These results suggest a general decline in fertility, especially with regard to Ca and Mg in those forests with low soil Ca and Mg supplies. Monitoring of further changes (if any) in these ecosystems will continue as the currently aggrading forests approach steady state.     

Interacting effects of wildfire severity and liming on nutrient cycling in a southern Appalachian wilderness area

Aims

Wilderness and other natural areas are threatened by large-scale disturbances (e.g., wildfire), air pollution, climate change, exotic diseases or pests, and a combination of these stress factors (i.e., stress complexes). Linville Gorge Wilderness (LGW) is one example of a high elevation wilderness in the southern Appalachian region that has been subject to stress complexes including chronic acidic deposition and several wildfires, varying in intensity and extent. Soils in LGW are inherently acidic with low base cation concentrations and decades of acidic deposition have contributed to low pH, based saturation, and Ca:Al ratio. We hypothesized that wildfires that occurred in LGW followed by liming burned areas would accelerate the restoration of acidic, nutrient depleted soils. Because soils at LGW had extremely low concentrations of exchangeable Ca²⁺ and Mg²⁺ dolomitic lime was applied to further boost these cations. We evaluated the effectiveness of dolomitic lime application in restoring exchangeable Ca²⁺ and Mg²⁺ and subsequently increasing pH and Ca:Al ratio of soils and making Ca and Mg available to recovering vegetation.

Methods

Five treatment areas were established: severely burned twice (2000 & 2007) with dolomitic lime application (2xSBL); moderately burned twice with lime application (2xMBL); severely burned twice, unlimed (2xSB); moderately burned once (2000), unlimed (1xMB); and a reference area (REF; unburned, unlimed). In 2008 and 2009, we measured overstory, understory, and ground-layer vegetation; forest floor mass and nutrients; and soil and soil solution chemistry within each treatment area.

Results

All wildfire burned sites experienced substantial overstory mortality. However, understory biomass doubled between sample years on the most recently burned sites due to the rapid regrowth of ericaceous shrubs and prolific sprouting of deciduous trees. Burning followed by lime application (2xSBL and 2xMBL) significantly increased shallow soil solution NO₃-N, but we found no soil solution NO₃-N response to burning alone (2xSB and 1xMB). Surface soil base saturation and exchangeable Ca²⁺ were significantly affected by liming; Ca²⁺ concentrations were greater on 2xMBL and 2xSBL than 2xSB, 1xMB and REF. There was a smaller difference due to moderate burning along with greater soil Ca²⁺ on 1xMB compared to REF, but no difference between 2xSB and REF. Surface and subsurface soil exchangeable Al³⁺ were lower on 2xSBL than 2xSB, 2xMBL, 1xMB, and REF. Liming decreased soil acidity somewhat as surface soil pH was higher on the two burned sites with lime (pH?=?3.8) compared to 2xSB without lime (pH?=?3.6).

Conclusions

Liming resulted in decreased soil Al³⁺ on 2xSBL coupled with increased soil Ca²⁺ on both 2xSBL and 2xMBL, which improved soil Ca/Al ratios. However, the soil Ca/Al ratio response was transitory, as exchangeable Al³⁺ increased and Ca/Al ratio decreased over time. Higher lime application rates may be necessary to obtain a substantial and longer-term improvement of cation-depleted soils at LGW.     

Liming and deep ripping responses for a range of field crops

Grain yields were measured over 2 seasons from a range of field crops following liming and deep ripping an acid and compacted soil in north-eastern Victoria. Lime (2.5 t ha^–1) substantially reduced the level of exchangeable Al and exchangeable Mn whilst raising soil pH by about 1.0 unit. The crops grown were 7 cultivars of wheat and one cultivar each of triticale, oats, barley, rapeseed, safflower, field pea, chick pea and lupins. With the exception of lupin, liming the soil increased (p=0.05) the grain yield of all crops and cultivars. With the wheat cultivars there were 2 distinct groups with different tolerance to soil acidity. Wheat, oats, triticale and lupins had higher absolute yields than the other crops. Safflower and chick pea had very low yields without soil amendment. The magnitude of the lime response did not differ between the wheat cultivars (17%) or between any of the crop species (range 9–29%). Deep ripping the soil to break a hard compacted layer resulted in more yield for all the cereals and safflower. The results demonstrate the importance of using crops with tolerance to acid soil conditions as well as gains that can be obtained with ameliorating identifiable soil problems.     

Effects of P,K, and liming on soil pH,Al, Mn,K, and forage barley dry matter yield and quality for a newly-cleared Cryorthod

Forage barley dry matter yield and quality, as well as soil pH, Al, and Mn were monitored in response to P, K, and lime application on a newly cleared Typic Cryorthod (Orthid Podzol). The overall yearly yield level was affected by precipitation. Without liming soil acidification occurred after three years of production. The liming rate of 2.2 Mg.ha⁻¹ was found optimal for maintaining initial pH levels (5.66) and increasing forage barley yields. It was also found optimum for K and P utilization for these first years of production. Soil pH dropped an average of 0.33 units over the three years on unlimed P plots and 0.46 units over 4 years on K plots. Phosphorus and K fertilization increased N utilization and resulted in decreased soil acidification. Phosphorus availability was greater in the first year of cropping than in subsequent years, this was likely due to the effects of higher available moisture, liming release of native P, and effects of initial fertilization. There was a 148% increase in total dry matter yield and an 85% increase in protein yield of forage barley with P application. Liming increased total forage barley yields an average of 69% and total protein yields 48%. Reduced barley yields in unlimed plots were due to low soil pH. After two years of cultivation, unlimed plots contained exchangeable Al and soluble Mn levels reported toxic for other soils. The higher liming rates of 4.4 and 6.6 Mg.ha⁻¹ reduced soluble Mn to near critically low levels. soil Al and Mn were highly correlated to pH. Soil exchangeable Al, Mn, and soluble Mn along with tissue Al were inversely correlated to percentage yield. The average yield respone to three levels of applied K, increased from zero initially to 67% by the fourth year. Total dry-matter production increased 32% and total protein yield increased an average of 32% and total protein yield increased an average of 15% with K fertilization over four years. About 60% of the yield response occurred between the 0 and 22kg K.ha⁻¹ rates. Initial soil exchangeable K levels were not maintained even at the highest 66kg K.ha⁻¹ treatment. Soil exchangeable Al and soluble Mn were elevated with dropping pH. Soil K reserves and resupply of exchangeable K in these soils over the long term will be an important factor in crop production.     

Soil organic carbon and nutrient status in old-growth montane coniferous forest watersheds,Isla Chiloé, Chile

Montane temperate forests of the Cordillera de Piuchué Ecosystem Study, Isla Chiloé, Chile, are unaffected by air pollution, timber exploitation and agricultural clearing, and the current floristic assemblage has been relatively stable for the past 7500 years. The apparent absence of major perturbation at this location makes it an appropriate baseline site for ecosystem analysis. We measured soil bulk density, pH, soil organic C (SOC), total N, and NH₄Cl–exchangeable cations (Ca⁺², Mg⁺², K⁺, Na⁺, Al⁺³) in 0–10 and 10–40 cm depth samples from 72 soil profiles representing three vegetation zones: Fitzroya cupressoides Forest, Pilgerodendron uvifera–Tepualia stipularis Forest, and Magellanic Moorland. Fitzroya and Pilgerodendron–Tepualia Forests were indistinguishable for all measured soil characteristics (P > 0.05, Dunn's multiple comparison test on ranked data); these included very high median SOC concentrations (0–10 cm = 49.6%) and correspondingly low bulk density values (0–10 cm = 0.07). Moorland soil median values (0-10 cm) were significantly higher for bulk density (0.12) and lower for SOC (28.5%), but not for total N (Forests = 0.99%, Moorland = 0.95%), resulting in lower median C:N ratios for the moorland (Forests = 44.7; Moorland = 30.3). Across both depths and all three vegetation zones regression analysis indicated that SOC was an excellent predictor (R²; = 0.93, P < 0.001) of (exchangeable Ca⁺² + Mg⁺² + K⁺ + Na⁺). Comparison with other old growth montane environments indicates that the Fitzroya and Pilgerodendron–Tepualia soil profiles are characterized by C:N ratios typical of other relatively unpolluted conifer forest soils (33.0–49.3). Soil profiles of representative polluted montane conifer forests have lower C:N ratios (16.2–23.5). Organic horizons from representative polluted montane conifer forests also retain fewer exchangeable base cations per unit SOC than are retained by organic horizons from the Cordillera de Piuchué forests.     

Simulated effects of atmospheric sulfur deposition on nutrient cycling in a mixed deciduous forest

The effects of three S deposition scenarios — 50% reduction, no change, and 100% increase — on the cycles of N, P, S, K, Ca, and Mg in a mixed deciduous forest at Coweeta, North Carolina, were simulated using the Nutrient Cycling model (NuCM). The purpose of this exercise was to compare NuCM's output to observed soil and streamwater chemical changes and to explore NuCM's response to varying S deposition scenarios. Ecosystem S content and SO₄ ^2– leaching were controlled almost entirely by soil SO₄ ^2– adsorption in the simulations, which was in turn governed by the nature of the Langmuir isotherm set in the model. Both the simulations and the 20-year trends in streamwater SO₄ ^2– concentration suggest that the ecosystem is slowly becoming S saturated. The streamwater data suggest S saturation is occurring at a slower rate than indicated by the simulations, perhaps because of underestimation of organic S retention in the model. Both the simulations and field data indicated substantial declines in exchangeable bases in A and BA soil horizons, primarily due to vegetation uptake. The correspondence of model output with field data in this case was a result of after-the-fact calibration (i.e. setting weathering rates to very low values) rather than prediction, however. Model output suggests that soil exchangeable cation pools change rapidly, undergoing annual cycles and multi-decade fluctuations.Varying S deposition had very little effect upon simulated vegetation growth, nutrient uptake, or N cycling. Varying S deposition strongly affected simulated Ca²⁺. Mg²⁺, K⁺, and P leaching but caused little change in soil exchangeable pools of Ca²⁺ K⁺, or P because soil exchangeable pools were large relative to fluxes. Soil exchangeable Mg²⁺ pools were reduced by high rates of S deposition but remained well above levels sufficient for tree growth. Although the total soil pools of exchangeable Ca²⁺ and K⁺ were only slightly affected by S deposition, there was a redistribution of Ca²⁺ and K⁺ from upper to lower horizons with increasing S deposition, causing increased base saturation in the deepest (BC) horizon. The 100% increased S deposition scenario caused increasing peaks in simulated Al³⁺ concentrations in A horizons after 25 years as a result of large seasonal pulses of SO₄ ^2– and lowered base saturation. Simulated soil solution Al³⁺ concentrations remained well below toxicity thresholds for selected tree species at the site.     

Solution chemistry profiles of mixed-conifer forests before and after fire

Solution chemistry profiles of mixed-conifer forests in granitic catchments of the Sierra Nevada were measured for three years before (1987–1990) and three years after (1990–1993) prescribed fire. Wet deposition, throughfall and soil solution samplers were installed in both white-fir and giant-sequoia dominated forest stands underlain by poorly developed inceptisols. Stream water chemistry was monitored as part of an ongoing study of catchment outputs. Calcium, NO ₃ ^– and Cl^– were the major ions in precipitation. Canopy leaching increased mean concentrations of all major ions, especially K⁺ and Ca²⁺. Water flux through the soil occurred largely during spring snowmelt. Forest floor leachate represented the most concentrated solutions of major ions. Interaction with the mineral soil decreased mean concentrations of most species and the average composition of soil solutions closely resembled stream water at baseflow. Bicarbonate alkalinity, Ca²⁺, Mg²⁺, and Na⁺ were enriched in stream water relative to precipitation whereas inputs of H⁺, NH ₄ ⁺ , NO ₃ ^– and SO ₄ ^2– were retained within the catchments.Burning of the forest understory and litter layer increased solute concentrations in soil solution and stream water. Mean soil solution Ca²⁺, Mg²⁺ and K⁺ concentrations increased more than 10 fold, but the relative predominance of these cations was not affected by burning. Sulfate concentration, which was very low in soil solutions of undisturbed stands (<25 mmol_c m^–3), increased more than 100 times following fire. Ammonium concentration exhibited a rapid, short-term increase and then a decrease below pre-burn levels. Changes in soil solution chemistry were reflected in catchment outputs.Corresponding author.     

Peanut growth as affected by liming,Ca-Mn interactions,and Cu plus Zn applications to oxidic samoan soils

Effects of coralline lime, in combination with 3 kg Cu ha⁻¹ plus 3 kg Zn ha⁻¹, on yield and nutrient uptake by peanut (Arachis hypogea) were studied at three locations in Western Samoa. Coarse (0–10 mm) coralline lime material containing 31.1% Ca and 1.7% Mg was used as lime at 0, 555, 2222 and 5000 kg ha⁻¹. In the Togitogiga soil, which had the lowest level of exchangeable Ca, peanut yield increased by 6 fold after liming with 555 kg ha⁻¹, relative to the unamended control. This yield increase was associated with reduced Mn toxicity as well as reduced Ca deficiency. The alleviation of Mn toxicity was not likely due to decreased Mn solubility because the lime application (555 kg ha⁻¹) increased soil pH by <0.1 unit. Rather it was the increased Ca availability which reduced the Mn toxicity through a Ca/Mn antagonism. The critical range of exchangeable Ca for peanut growth was found to be about 1.5–1.6 cmol 1/2Ca²⁺ kg⁻¹. A Ca/Mn-ratio >80 was required for a desirable Ca/Mn balance in peanut tissue. On the other two locations (with exchangeable Ca levels of 1.5–1.6 cmol 1/2Ca²⁺ kg⁻¹), liming increased peanut yields by 15–20%. Additions of Cu plus Zn also increased the yields, although the increases were small (7%) and not significant at the 95% probability level. This research was made possible by Grant No. 936-5542-G-SS-9092 from the Program in Science and Technology Cooperation, AID/ST/AGR, U.S. Agency for International Development.     

Effects of liming and boron fertilization on boron uptake of Picea abies

The effects of liming on concentrations of boron and other elements in Norway spruce [Picea abies (L) Karst.] needles and in the mor humus layer were studied in long-term field experiments with and without B fertilizer on podzolic soils in Finland. Liming (2000+4000 kg ha^-1 last applied 12 years before sampling) decreased needle B concentrations in the four youngest needle age classes from 6–10 mg kg^-1 to 5 mg kg^-1. In boron fertilized plots the corresponding concentrations were 23–35 mg kg^-1 in control plots and 21–29 mg kg^-1 in limed plots. Both liming and B fertilizer decreased the Mn concentrations of needles. In the humus layer, total B concentration was increased by both lime and B fertilizer, and Ca and Mg concentrations and pH were still considerably higher in the limed plots than controls. Liming decreased the organic matter concentration in humus layer, whilst B fertilizer increased it.The results about B uptake were confirmed in a pot experiment, in which additionally the roles of increased soil pH and increased soil Ca concentration were separated by means of comparing the effects of CaCO₃ and CaSO₄. Two-year-old bare-rooted Norway spruce seedlings were grown in mor humus during the extension growth of the new shoot. The two doses of lime increased the pH of soil from 4.1 to 5.6 to 6.1, and correspondingly decreased the B concentrations in new needles from 22 to 12 to 9 mg kg^-1. However, CaSO₄ did not affect the pH of the soil or needle B concentrations. Hence the liming effect on boron availability in these soils appeared to be caused by the increased pH rather than increased calcium concentration.     

Responses of maize grain yield to changes in acid soil characteristics after soil amendments

An experiment was conducted from 1997 to 2000 on an acid soil in Cameroon to assess the effectiveness of cultivating acid tolerant maize (Zea mays L.) cultivar and the use of organic and inorganic fertilizers as options for the management of soil acidity. The factors investigated were: phosphorus (0 and 60 kg ha^?1), dolomitic lime (0 and 2 t ha^?1), organic manure (no manure, 4 t ha^?1 poultry manure, and 4 t ha^?1 of leaves of Senna spectabilis), and maize cultivars (ATP-SR-Y – an acid soil-tolerant, and Tuxpeño sequia – an acid susceptible). On acid soil, maize grain yield of ATP-SR-Y was 61% higher than the grain yield of Tuxpeño sequia. Continuous maize cultivation on acid soil further increased soil acidity, which was manifested by a decrease in pH (0.23 unit), exchangeable Ca (31%) and Mg (36%) and by an increase in exchangeable Al (20%). Yearly application of 60 kg ha^?1 of P for 3 years increased soil acidity through increases in exchangeable Al (8%) and H (16%) and a decrease in exchangeable Ca (30%), Mg (11%) and pH (0.07 unit). Lime application increased grain yield of the tolerant (82%) and susceptible (208%) cultivars. The grain yield increases were associated with a mean decrease of 43% in exchangeable Al, and 51% in H, a mean increase of 0.27 unit in pH, 5% in CEC, 154% in exchangeable Ca, and 481% in Mg contents of the soil. Poultry manure was more efficient than leaves of Senna producing 38% higher grain yield. This yield was associated with increases in pH, Ca, Mg and P, and a decrease in Al. The highest mean grain yields were obtained with lime added to poultry manure (4.70 t ha^?1) or leaves of Senna (4.72 t ha^?1). Grain yield increase was more related to the decrease in exchangeable Al (r = ?0.86 to ?0.95, P<0.01) and increase in Ca (r = 0.78–0.94, P<0.01), than to pH (r = ?0.57 (non-significant) to ?0.58 (P<0.05)). Exchangeable Al was the main factor determining pH (r = ?0.88 to ?0.92, P<0.01). The yield advantage of the acid tolerant cultivar was evident even after correcting for soil acidity. Acid soil-tolerant cultivars are capable of bringing unproductive acid soils into cultivation on the short run. The integration of soil amendments together with acid soil-tolerant cultivar offers a sustainable and comprehensive strategy for the management of acid soils in the tropics.     

Effects of forest liming on soil processes

On the basis of a field experiment in Norway spruce with acid irrigation and compensatory liming of the soil surface (Höglwald, S-Bavaria), liming effects are described as lime dissolution rate, transformation of carbonate buffer to exchange buffer, time required for deacidification of soil and drainage water, mobilization of Cu and Pb, changes in soil organisms, humus decomposition, and nitrogen turnover. It was shown that lime dissolution followed an exponentially decreasing curve. 4 t ha^-1 dolomitic lime were dissolved within 6 years. Additional acid irrigation of 4 kmol H⁺ ha^-1 yr^-1 as sulphuric acid speeded up the lime dissolution to about 4 years. After dissolution of lime about 70% of Ca and about 30% of Mg, both originating from lime dissolution, are retained in the surface humus layer, loading the exchange buffer capacity there. Liming acted as a protection against acid irrigation but the extension of soil deacidification downwards proceeded slowly due to the high base neutralizing capacity of protonated functional groups of the organic matter. The main depth effect is caused by Mg translocation. A significant increase of organic Cu complexes occurred due to mobilization of water soluble humus decomposition products. The effect of liming on litter decomposing organisms is demonstrated with microorganisms, collembolae and earthworms regarding the abundance and the structure of dominance. It was shown that liming may induce unusually large changes in biocenoses of forest soils. The decay of surface humus accounted for 7.2 t ha^-1 or 23% of the store within 7 years. Within the same time span, liming caused a loss of about 170 kg N ha^-1 or 14% of the store of the surface humus layer. The nitrate concentration in the drainage water thus increased by about 50 to 60 mg NO₃ ^- L^-1. Site-specific conditions are discussed, which produce such negative liming effects as increased nitrate concentration of seepage, humus decay and heavy metal mobilization. Redistribution of tree roots, induction of boron deficiency and root rot are also considered. It is indicated that liming may aggravate the increasing problem of nitrate contamination of forest ground water resources which is associated with deposition of atmogenous nitrogen compounds. Some recommendations are given regarding forest practice.     

Soil nutrient dynamics in response to irrigation of a Panamanian tropical moist forest

We measured concentrations of soil nutrients (0–15 and 30–35 cm depths) before and after the dry season in control and dry-season irrigated plots of mature tropical moist forest on Barro Colorado Island (BCI) in central Panama to determine how soil moisture affects availability of plant nutrients. Dry-season irrigation (January through April in 1986, 1987, and 1988) enhanced gravimetric soil water contents to wet-season levels (ca. 400 g kg^–1 but did not cause leaching beyond 0.8 m depth in the soil. Irrigation increased concentrations of exchangeable base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), but it had little effect on concentrations of inorganic N (NH₄ ^+C, NO₃ ^– and S (SO₄ ^2–). These BCI soils had particularly low concentrations of extractable P especially at the end of the dry season in April, and concentrations increased in response to irrigation and the onset of the rainy season. We also measured the response of soil processes (nitrification and S mineralization) to irrigation and found that they responded positively to increased soil moisture in laboratory incubations, but irrigation had little effect on rates in the field. Other processes (plant uptake, soil organic matter dynamics) must compensate in the field and keep soil nutrient concentrations at relatively low levels.     

Effect of millipede Parafontaria tonominea Attems (Diplopoda: Xystodesmidae) adults on soil biological activities: A microcosm experiment

Effects of high density adult millipede populations on soil ecosystem properties were investigated using laboratory and field microcosm methods in a deciduous broad-leaved forest in western Japan. The density of Parafontaria tonominea adults was 25.6–72.0 individuals m^–2 on 15 September 1996, then the density declined to 0–5.4 m^–2 on 22 October 1996. Addition of millipedes to the laboratory microcosm enhanced soil respiration and decreased soil microbial biomass. Soil microcosms with and without millipedes (one and two pairs of adults) were set on a forest floor, and soil respiration, dissolved ion concentration in leacheate water were observed for 8 weeks. The millipedes ingested both leaf litter and soil, which increased soil respiration, leaching of Ca²⁺, Mg²⁺, and nitrate from the soil, whereas the soil microbial biomass was not changed at 8 weeks after introduction of the animals. Millipede feeding on soil enhanced microbial activity and nutrient leaching from the forest soil.     

Efficiency of soil and fertilizer nitrogen of a sod–potato system in the humid,acid and cool environment

It was hypothesized that soil N variability, and fertilization and cropping management affect potato (Solanum tuberosum L.) growth and fertilizer N efficiency. Following a 20-year sod breakup on a loamy soil in eastern Quebec, Canada (46°37 N, 71°47 W), we conducted a 3-year (1993–1995) study to investigate the effects of soil pool N and fertilizer N management on non-irrigated potato (cv. Superior) tuber yield, fertilizer N recovery (NRE), and residual N distribution in soils under humid, cool and acid pedoclimatic conditions. The fertilizer N treatments consisted of a control, side-dress at rates of 70, 105 and 140 kg ha^–1, and split applications (at seeding and bloom) at rates of 70+70, 105+70 and 140+70 kg ha^–1, respectively. Soil acidity was corrected with limestone following the plow down of the sod. Years of cropping, main effect of N treatment, and year and fertilizer N interaction were significant on total and marketable tuber yields and N uptake, which were significantly related to soil N, and root growth. Apparent NRE ranged between 29 and 70%, depending on years and N rates. Total tuber yield, N uptake, soil N use and NRE were significantly higher in the first (sod–potato) year, but decreased by 41.8, 22.7, 21.4 and 14.7%, respectively, in the third (sod–potato–potato–potato) year. Initial soil N pool was declined by 75% following the 3-year cropping. In 2–3 years, the side-dress N (140 kg ha^–1) increased significantly tuber yields (11.4–19.8%) compared to the split N (70+70 kg ha^–1). Higher split N had no effect on tuber yield and N uptake but increased residual N at harvest. Unused fertilizer N was strongly linked (R ²=0.98) to fertilizer N rates. Time factor and N treatment had significant effects (P<0.0001) on loss of N to below the root zone. Smaller scale rate and timing of split N need to be further determined. Increasing fertilizer N use efficiency could be expected with sod breakup and 75% of regional recommendation rate under humid, cool and acid pedoclimatic conditions.     

The effects of lime and phosphorus on the function of wheat roots in acid top soils and subsoils

Two wheat varieties with differing aluminium tolerance were grown in pots of acid soil. Liming did not change significantly the amounts of chemically extractable P and K, but caused improved vegetative growth, increased inflow of P and K and reduced uptake of Al. Without lime, roots had a higher content and concentration of P than shoots; liming reversed this. Without lime the sensitive variety with a shorter root length had an Al inflow ten times that of the tolerant one: tolerance involves a mechanism for exlcuding Al. The inflow of P per unit inflow of Al (mol ratio) without lime was three times greater for the tolerant variety which therefore has more P to counteract the effects of Al. The same varieties were grown in two-layer soil columns, with a low P status and a limed topsoil and acid subsoil. Liming the subsoil improved plant growth but this was still restricted by low P availability. Addition of P to the topsoil caused good growth regardless of subsoil acidity: root growth increased in both layers and P (labelled with³²P) taken up from the topsoil was translocated to roots in the subsoil. This P inactivated root Al and allowed the roots to grow and take up more P from the acid subsoil with however a reduction in inflow. The sensitive variety was affected more by the acid subsoil and low P availability, had a similar ability to translocate P to subsoil roots but could not attain the growth rate of the tolerant wheat even with P and lime.     

The role of <Emphasis Type="Italic">Calamagrostis</Emphasis> communities in preventing soil acidification and base cation losses in a deforested mountain area affected by acid deposition

The effects of grass growth and N deposition on the leaching of nutrients from forest soil were studied in a lysimeter experiment performed in the Moravian-Silesian Beskydy Mts. (the Czech Republic). It was assumed that the grass sward formed on sites deforested due to forest decline would improve the soil environment. Lysimeters with growing acidophilous grasses (Calamagrostis arundinacea and C. villosa), common on clear-cut areas, and with unplanted bare forest soil were installed in the deforested area affected by air pollution. Wet bulk deposition of sulphur in SO₄^2– corresponded to 21.6–40.1 kg ha^–1 and nitrogen in NH₄⁺ and NO₃^– to 8.9–17.4 kg N ha^–1, with a rain water pH of 4.39–4.59 and conductivity of 18.6–36.4 S cm^–1 during the growing seasons 1997–1999. In addition, the lysimeters were treated with 50 kg N ha^–1 yr^–1 as ammonium nitrate during the 3 years of the experiment. Rapid growth of planted grasses resulted in a very fast formation of both above- and below-ground biomass and a large accumulation of nitrogen in the tissue of growing grasses. The greatest differences in N accumulation in aboveground biomass were observed at the end of the third growing season; in C. villosa and C. arundinacea, respectively, 2.66 and 3.44 g N m^–2 after addition of nitrogen and 1.34 and 2.39 g N m^–2 in control. Greater amounts of nitrogen were assessed in below-ground plant parts (9.93–12.97 g N m^–2 in C. villosa and 4.29–4.39 g N m^–2 in C. arundinacea). During the second and third year of experiment, the following effects were the most pronounced: the presence of growing grasses resulted in a decrease of both the acidity and conductivity of lysimetric water and in a lower amount of leached nitrogen, especially of nitrates. Leaching of base cations (Ca²⁺ and Mg²⁺) was two to three times lower than from bare soil without grasses. An excess of labile Al³⁺ was substantially eliminated in treatments with grasses. Enhanced N input increased significantly the acidity and losses of nutrients only in unplanted lysimeters. The leaching of N from treatments with grasses (3.9–5.6 kg N ha^–1) was 31–46% of the amount of N in wet deposition. However, the amount of leached N (4.2–6.0 kg N ha^–1) after N application was only 7.1–8.9% of total N input. After a short three year period, the features of soil with planted grasses indicated a slight improvement: higher pH values and Ca²⁺ and Mg²⁺ contents. The ability of these grass stands to reduce the excess nitrogen in soil is the principal mechanism modifying the negative impact on sites deforested by acid depositions. Thus it is suggested that grass sward formation partly eliminates negative processes associated with soil acidification and has a positive effect on the reduction of nutrient losses from the soil.     

The effect of lime on phosphorus adsorption and barley growth in three acid soils

For three acid soils from Santa Catarina, Brazil, lime application and time of incubation with lime had little effect on the adsorption of added phosphorus. In two soils with high contents of exchangeable aluminium, solution P and isotopically exchangeable P were decreased by incubating with lime for 1 month: phosphorus was probably adsorbing on freshly precipitated aluminium hydrous oxides. In one soil with less exchangeable aluminium, P in solution was increased by liming. After 23 months lime increased solution and exchangeable P possibly due to crystallization of aluminium hydrous oxides reducing the number of sites for P adsorption. All these changes were however small. In a pot experiment, lime and phosphorus markedly increased barley shoot and root dry matter and P uptake. Although liming reduced P availability measured by solution P, isotopically exchangeable P and resin extractable P, it increased phosphorus uptake by reducing aluminium toxicity and promoting better root growth. The soil aluminium saturation was reduced by liming, but the concentration of aluminium in roots changed only slightly. The roots accumulated aluminium without apparently being damaged.     

Patterns and mechanisms of soil acidification in the conversion of grasslands to forests

Grassland to forest conversions currently affect some of the world's most productive regions and have the potential to modify many soil properties. We used afforestation of native temperate humid grassland in the Pampas with eucalypts as an experimental system to 1) isolate forest and grassland imprints on soil acidity and base cation cycling and 2) evaluate the mechanisms of soil acidification. We characterized soil changes with afforestation using ten paired stands of native grasslands and Eucalyptus plantations (10–100 years of age). Compared to grasslands, afforested stands had lower soil pH (4.6 vs.5.6, p < 0.0001) and 40% lower exchangeable Ca (p < 0.001) in the top 20 cm of the soil. At three afforested stands where we further characterized soil changes to one meter depth, soil became increasingly acidic from 5 to 35 cm depth but more alkaline below 60 cm compared to adjacent grasslands, with few differences observed between 35 and 60 cm. These changes corresponded with gains of exchangeable acidity and Na in intermediate and deeper soil layers. Inferred ecosystem cation balances (biomass + forest floor + first meter of mineral soil) revealed substantial vertical redistributions of Ca and Mn and a tripling of Na pools within the mineral soil after afforestation. Soil exchangeable acidity increased 0.5–1.2 kmol_c.Ha^–1.yr^–1 across afforested stands, although no aboveground acidic inputs were detected in wet + dry deposition, throughfall and forest floor leachates. Our results suggest that cation cycling and redistribution by trees, rather than cation leaching by organic acids or enhanced carbonic acid production in the soil, is the dominant mechanism of acidification in this system. The magnitude of soil changes that we observed within half a century of tree establishment in the Pampas emphasizes the rapid influence of vegetation on soil formation and suggests that massive afforestation of grasslands for carbon sequestration could have important consequences for soil fertility and base cation cycles.     

A field comparison of lime requirement indices for maize

Due, in part, to the relative paucity of published comparisons based on field generated data, there is still poor agreement regarding the relative merits of lime requirement indices based on exchangeable Al and those based on pH. The objective of this study was to compare such indices using results obtained from long-term field experiments. Data were obtained over 22 site-years from lime trials conducted on clay (Typic Haplorthox) and sandy loam (Plinthic Paleudult) soils differing widely in organic carbon content. Relative maize (Zea mays L.) yields were used to compare the prognostic value of soil pH with indices obtained using exchangeable Al and exchangeable acidity (Al+H). Both within and across soils, pH proved to be markedly inferior to Al based indices. Exchangeable acid saturation of the effective cation exchange capacity, a readily obtained and popular index of lime requirement in some countries, proved as effective as less easily acquired indices based on exchangeable Al per se. The findings reported are consistent with those of many glasshouse studies and support the viewpoint that indices based on Al or acid saturation should replace pH as a measure of lime requirement.     

Water use efficiency of a maize/cowpea intercrop on a highly acidic tropical soil as affected by liming and fertilizer application

Due to global warming, there is a need to increase the water use efficiency of crops under rainfed agriculture, particularly in semi-arid regions. Therefore, the effect of NPK fertilizer application (with or without liming) on the water use efficiency of a maize/cowpea intercropping system was investigated in the semi-arid part of Brazil. The crops were grown on a strongly acidic, sandy soil with three treatments: (i) Complete NPK fertilizer application with lime (Compl), (ii) Complete NPK fertilizer application without lime (Compl-L) and (iii) Control. On the average, dry matter production was 2.6 times higher with the Compl treatment than in the Control and 1.6 times higher than in the Compl-L treatment. The soil water balance was calculated with two different model approaches (HILLFLOW and EPICSEAR). When checked against measured soil water content during the growing period, both models produced accurate results, but only EPICSEAR was sensitive to the effects of liming and fertilizer application on soil water balance and dry matter production at this site. Comparison between the Compl and the Compl-L treatments shows that the increase in transpirational water use efficiency (WUE_T) (+63 and +80%, respectively) is mainly due to the application of NPK. Although the site is highly acid, liming was of minor importance for increasing the WUE_T. However, observations and simulations demonstrate that, through the additional application of lime, the gross water use efficiency (WUE_C) in a maize/cowpea intercropping system can be increased by 60% compared to sole application of NPK and by more than 160% compared to the control. Abbreviations: EPIC – erosion productivity impact calculator; EPICSEAR – erosion productivity impact calculator for semi-arid regions; TDR – time domain reflectometry; WUE – water use efficiency.