Soil Exchangeable Aluminium Research Articles

Assessment of Physicochemical Properties and Heavy Metal Content of Floriculture Soil in Amhara Region of Northwest Ethiopia.

Floriculture is a new and rapidly expanding sector in Ethiopia that aids economic growth but has also come under blame for pollution of the surrounding soil. The purpose of this study was to assess the soil physicochemical properties and heavy metal contents in floriculture in the Amhara Region of Northwest Ethiopia. Soil samples were collected from seven different greenhouses (2ABC, 4DEF, 5ABC, 7DEF, 8ABC, 9DEF, and 11DEF), and a control soil sample was taken on the 15-cm depth from a nearby agricultural area. They were analyzed for soil physicochemical parameters and heavy metal compositions. Soil texture showed a significant difference between the soils sampled from the greenhouses and the control group. The highest average clay, silt, and sand contents were recorded in the control group, 4DEF, and 9DEF, respectively. The lower clay content was at 9 DEF, silt at 11 DEF, and sand in the control group. Clay was positively correlated to soil pH (r = 0.66) and TN (r = 0.38) but showed significant negative correlation with the sand fraction (r = -0.96). The average bulk density (BD) values of the soils from the greenhouses were within acceptable ranges; however, the mean BD value of 7DEF was relatively highest (1.34 g/cm3). There were significant (P < 0.05) changes in soil pH and electrical conductivity, with pH values ranging from 5.8 to 7.17 and EC from 0.08 to 1.72 mScm-1. Soil organic carbon, available phosphorus, total nitrogen, and carbon-to-nitrogen ratio of the soil samples from the greenhouses and the control group were significantly different. There were also significant differences in soil exchangeable aluminum and acidity between greenhouse soil samples and the control group. Soil contents of some of the heavy metals (Pb, Cd, Mn, and Cu) in the floriculture soil were above the permissible limits, while Cr, Zn, and Ni contents were below. The soil in floriculture showed low quality compared to the control group and international standards, indicating the need for improved soil quality management. This study recommends reducing agrochemical use, increasing bio-fertilizers, using botanicals, and transitioning to organic farming. Further studies are needed to assess soil microbial diversity and abundance for soil fixation.

Deep insertion of lime into acid organic soils

Organic (peat) soils are inherently acid in their natural state with soil pH levels that decline from 4.5 – 5.0 in the surface layer of 0 – 75 mm to 4.0 - 4.5 at a depth of 400 mm. Traditionally lime has been surfaceapplied and incorporated into the lower soil layers bycultivation. An alternative method of inserting 3 - 4 t/ha of lime down to 400 mm soil depth was tested on a developing Waikato deep Moanatuatua Organic soil. When two-thirds of the lime was placed within the 300 - 400 mm layer and one-third within the 200 - 300 mm layer in summer 2021, soil pH in the 200 - 300 mm layer decreased from 5.6 in 2021 to 5.3 in 2023 and significantly increased from 4.2 to 4.9 in the 300 – 400 mm layer over the same time period. Reversing the ratio of the lime rate into the two layers resulted in asignificant increase in soil pH from 4.5 to 5.3 in the 200 – 300 mm layer and a non-significant increase from 4.2 to 4.6 in the 300 – 400 mm layer. Generally, there were corresponding decreases in soil exchangeable aluminium (Al) concentration in those layers. The ratioof lime insertion rate had no significant effect on rooting depth between years. There was a moderate correlation between soil pH and exchangeable Al when measured at depths of 0 – 400 mm. These interim results indicate that the deep insertion of lime into an acid Organic soil was effective in increasing soil pH and reducing soil Al concentration in the lower soil layers in the two years after the lime was inserted.

Shallow Incorporation of Lime and Gypsum has Limited Benefit over the Sole-surface Application of Lime for Improving Grain Yield and Water Use Efficiency in the Low Rainfall Region of Western Australia

Soil acidity is one of the major soil constraints for the grain-growing industry in Australia and around the globe. While surface liming is widely adopted, it has been proven ineffective for the timely amelioration of subsoil acidity. There is a growing interest in finding alternative approaches for the effective amelioration of subsoil acidity, especially for low-rainfall regions. In a controlled environment and a field experiment, we examined whether the combined application of lime and gypsum would be more effective than lime alone under no-till (NT) and shallow strategic tillage (ST) systems for reducing the impact of soil acidity and increasing grain yield. &#x0D; &#x0D; The controlled environment experiment highlighted that lime increased soil pH and decreased the soil exchangeable aluminium concentration (EAC) which resulted in significantly better root growth. In the field experiment, we found that the lime plus gypsum treatment, in most cases, did not significantly affect grain yield, water use efficiency (WUE) or grain quality compared to the lime treatment alone. Lime incorporation with a shallow ST was more effective in increasing soil pH and decreasing EAC at 10&amp;ndash;20 cm depth, compared to the surface application of lime without tillage. However, ST did not affect the grain yield and WUE of wheat in 2017 and 2018 and significantly decreased the grain yield and WUE of canola in 2019 and barley in 2020. We found that measurements of either soil pH or EAC were equivalent in their ability to explain and predict the root growth of major grain crops. The results indicate that soil pH is the simplest indicator for grain growers to measure the improvement of soil acidity with liming and its impact on root growth and crop productivity. We recommend the application of lime as the preferred amendment on acidic sands, while shallow ST should be avoided in the low rainfall region. Further studies involving deep ST are warranted.

Biochar addition to tea garden soils: effects on tea fluoride uptake and accumulation

Long-term consumption of tea with high fluoride (F) content has a potential threat to human health. The application of different amounts of biochar to reduce F accumulation in tea leaves has been little studied. In this study, a pot experiment was conducted to investigate the effect of biochar amounts (0, 0.5%, 2.5%, 5.0%, 8.0%, and 10.0%, w/w) on tea F content during the tea plant growth. Changes in tea quality, soil F fraction, and soil properties caused by biochar and the relationship with tea F accumulation were also considered. The results showed that the application of biochar amendment significantly reduced water-soluble F contents in tea leaves compared to CK (without biochar), especially in the 8.0% treatment (72.55%). Overall, biochar contributed to improving tea polyphenols and caffeine, but had no significant impact on free amino acids and water leachate. Compared with CK, 5.0–10.0% biochar significantly increased soil water-soluble F content due to the substitution of F− with OH− under high pH. Additionally, biochar applied to tea garden soil was effective in decreasing the soil exchangeable aluminum (Ex-Al) content (46.37–91.90%) and increasing the soil exchangeable calcium (Ca2+) content (12.02–129.74%) compared to CK, and correlation analysis showed that this may help reduce F enrichment of tea leaves. In general, the application of 5.0–8.0% biochar can be suggested as an optimal application dose to decrease tea F contents while simultaneously improving tea quality.Graphical

Improving Effects of Different Calcium-Magnesium Conditioners on Latosol

At present, soil acidification seriously restricts the sustainable development of agricultural production. A common method that can be used to improve acidified soils is to apply calcareous materials (conditioners), but there is difference in the improvement effect of the conditioners on the same soil because of the conditioners containing different calcium-magnesium compounds. In order to find suitable conditioners for latosol (acidic red soil), two consecutive soil incubation experiments in laboratory have be done to study the improvement effects of different calcium-magnesium compounds on latosol. The results showed that: (1) Self-made conditioner (CM and it is composed of Mg(OH)2, Ca(OH)2, MgCl2, CaCl2,), CaO, CaCO3 and Mg(OH)2 could rapidly increase the pH and significantly reduce the content of potential acid in latosol. The soil exchangeable acid of Mg(OH)2, CaCO3, CaO and CM treatments than the treatment without conditioner (CK) were reduced by 88, 72, 66 and 34%, respectively, and the soil exchangeable aluminum decreased by 91, 80, 71 and 58%, respectively. (2) The calcium-magnesium compounds can significantly increase the contents of soluble and exchangeable calcium in soil compared with CK. CM and Mg(OH)2 significantly increased the contents of soluble and exchangeable magnesium in latosol. (3) The soil pH buffer capacity of CM is significantly higher than those of other treatments as a result of it has the highest organic matter content and significantly increases the contents of exchangeable calcium and magnesium in the soil. But the soil pH buffer capacity of CaCO3 and Mg(OH)2 are significantly less than that of CK. Because the organic matter and organic acid of CaCO3 and Mg(OH)2 treatments are reduced by the soil pH of them increasing and the functional groups with pH buffer capacity on them may also be destroyed. So the paper suggests that improve acid latosol by applying conditioners with more soluble calcium and magnesium, Mg(OH)2, which can effectively reduce acid ions in soil and improve the pH buffer capacity of soil.

Impacts of earthworm species on soil acidification, Al fractions, and base cation release in a subtropical soil from China.

Soil-exchangeable aluminum (Al) has toxic effects on living organisms in acidic soils. Earthworm presence and activity can alter soil pH, which has a significant influence on Al toxicity. However, the effects of earthworms on soil Al toxicity and fractions are still largely unknown. This laboratory study focused on the effects of three earthworm species (endogeics Pontoscolex corethrurus and Amynthas robustus, anecis Amynthas aspergillum) on soil acidification, Al fraction distribution, and base cation release. Three native earthworm species and a soil (latosolic red soil) collected from a botanical garden in South China were incubated under laboratory conditions. After 40days of incubation, six Al fractions in soil, namely exchangeable (AlEx), weakly organically bound (AlOrw), organically bound (AlOr), amorphous (AlAmo), Al occluded in crystalline iron oxides (AlOxi), and amorphous aluminosilicate and gibbsite (AlAag) fractions, were extracted using a sequential procedure. Soil pH; organic carbon; total nitrogen; total Al (AlTotal); exchangeable K, Na, Ca, Mg contents; and CEC were determined as well. Compared to control soil, pH values increased by 0.79, 0.41, and 0.57units in casts in the presence of P. corethrurus, A. robustus, and A. aspergillum, and 0.70, 0.32, and 0.50units in non-ingested soil, respectively. Compared to control soil, the 61.7%, 30.7%, and 36.1% of AlEx contents in casts and 68.5%, 25.9%, and 39.0% of AlEx in non-ingested soil significantly decreased with the addition of P. corethrurus, A. robustus, and A. aspergillum, respectively. Moreover, compared to control soil, the 78.7%, 37.7%, and 40.1% of exchangeable Ca2+ and 12.3%, 24.7%, and 26.8% of exchangeable Mg2+ contents in casts significantly increased with the presence of P. corethrurus, A. robustus, and A. aspergillum, respectively. Soil treated with P. corethrurus had higher soil pH values, exchangeable Ca2+ contents, and lower AlEx than those with A. robustus and A. aspergillum. Results of principal component analyses showed that P. corethrurus, A. robustus, and A. aspergillum casts and non-ingested soil differ for soil pH, Al fractions, and exchangeable base cations release. These results indicate that earthworms, especially P. corethrurus, can reduce soil Al toxicity, increase soil pH, and affect the release of exchangeable base cations.

Effects of soil pH on the root growth of passion fruit and the mechanism of mineral uptake

Acidic soil has recently been reported to be rather preferable for passion fruit growth, although the mechanisms underlying these observations are not known. For these reasons, in the present study the effects of soil pH on the root growth and mineral uptake were examined. The vines and roots of passion fruit plants were pruned in half before transplanting them to 10-L pots filled with soils adjusted to four different pH levels (3.5, 4.5, 5.5, and 6.5). Soil exchangeable cations, leaf and root mineral contents, root length density, vegetative growth, photosynthetic rate, stomatal conductance, and leaf water potential were measured. Soil exchangeable aluminium (Al) as well as Al saturation were higher at the lower pH (pH 3.5, 4.5) than at higher pH (pH 5.5, 6.5), whereas negative effects of neither root elongation nor mineral uptake were observed. On the contrary, the root growth was even the highest of all the treatments at pH 3.5. The root Al content at pH 3.5 was similar to the other treatments, and the leaf Al content was lower than the average concentrations detected in other herbaceous plants. Accordingly, the passion fruit root system seems to use an Al exclusion mechanism, thus resulting tolerant to Al toxicity. Vegetative growth, photosynthetic rate, stomatal conductance, and leaf water potential were lowered at higher pH values of the soils. Insufficient root growth at higher pH caused water deficit in leaves, and the water stress might lead to stomatal closure, which might cause depression of photosynthetic rate. At acidic soil such as pH 3.5, on the contrary, a larger root volume is considered to be advantageous to keep higher leaf water potential and resulted in higher photosynthetic rate with strong vegetative growth.

Deviation from niche optima affects the nature of plant-plant interactions along a soil acidity gradient.

There is increasing recognition of the importance of niche optima in the shift of plant-plant interactions along environmental stress gradients. Here, we investigate whether deviation from niche optima would affect the outcome of plant-plant interactions along a soil acidity gradient (pH = 3.1, 4.1, 5.5 and 6.1) in a pot experiment. We used the acid-tolerant species Lespedeza formosa Koehne as the neighbouring plant and the acid-tolerant species Indigofera pseudotinctoria Mats. or acid-sensitive species Medicago sativa L. as the target plants. Biomass was used to determine the optimal pH and to calculate the relative interaction index (RII). We found that the relationships between RII and the deviation of soil pH from the target's optimal pH were linear for both target species. Both targets were increasingly promoted by the neighbour as pH values deviated from their optima; neighbours benefitted target plants by promoting soil symbiotic arbuscular mycorrhizal fungi, increasing soil organic matter or reducing soil exchangeable aluminium. Our results suggest that the shape of the curve describing the relationship between soil pH and facilitation/competition depends on the soil pH optima of the particular species.

Phosphorus response and optimum pH ranges of twelve pasture legumes grown in an acid upland New Zealand soil under glasshouse conditions

Pasture legumes provide critical nitrogen inputs but fail to persist in typical acidic low P fertility upland soils. Alternative legume species for these environments are urgently sought. Twelve novel legume species were grown for 42 weeks under glasshouse conditions in an acidic upland New Zealand soil. Phosphorus (P) was applied at eight rates (0, 10, 30, 60, 100, 250, 500, 1500 mg kg-1 soil) or lime (100% CaCO3) at five rates (0, 2, 5, 8, 15 t ha-1 equivalent). Annual species grew on average for 25 weeks, while perennial species grew for 42 weeks. Yield was measured and herbage was analysed for macro and micro elements and soils analysed for pH, exchangeable Al and Olsen P. P responses differed substantially between legume species which were likely driven by genetic adaptations to low phosphorus environments. Critical shoot P concentrations for optimum yield were identified and ranged from 0.23 (tagasaste) to 0.39 % P (falcata lucerne). Arrow leaf, subterranean and balansa clovers had the greatest yield increase at low P inputs (100 mg P kg-1) and show promise as alternatives to white clover. Lime treatments increased the yield of all species to a point beyond which yield decreased with further additions. Increased yield was primarily driven by decreased soil exchangeable aluminium (Al) concentrations and to a lesser extent by increased soil P and molybdenum (Mo) availability, while decreases were driven by lower soil P and boron (B) availability at high pH. Thresholds for soil exchangeable Al differed between legume species. Species with higher Al thresholds (7 - 8 mg Al kg-1) were tagasaste, lotus, persian and gland clovers and falcata lucerne. These species show promise for acid soil environments with soil Al issues and should now be investigated further in field experiments. For many of these legume species this represents new and critical information.

English

Oxisols and ultisols are the major soils of Malawi but the P sorption of these soils has not been studied intensively. As of now, in terms of P fertilizer application these soils are treated &nbsp; the same. This research was conducted to determine the phosphate sorption properties and external P requirements (EPR) of these soils and to derive sorption values from selected soil properties. Physical and chemical analysis showed difference in these soils. Soil exchangeable aluminium, soil pH and soil organic matter is some of the soil properties that affect P sorption and these were different in these two soils. The sorption maxima were 315.5 and 413.0 mg P kg-1 for ultisols and oxisols respectively and EPR values were 37.8 and 52.2 mg P kg-1 of soil for ultisols and oxisols respectively. Exchangeable aluminium, soil pH (H2O), and organic matter found to be highly correlating with sorption maxima. The results from this study showed that, blanket application of phosphate fertilizer may not be a good strategy because ultisols and oxisols demand different amounts of P fertilizer and this blanket application may lead to under-application or over-application of P in some areas. The results also show that farming practices which improve soil organic matter and soil pH should be encouraged.&nbsp; &nbsp; Key words: External P requirement, P-sorption, Langmuir equation, sorption affinity, Malawi, oxisols, ultisols. &nbsp

PH, nitrogen mineralization, and KCl-extractable aluminum as affected by initial soil pH and rate of vetch residue application: results from a laboratory study

Initial soil pH determines the direction and magnitude of pH change after residue addition. This study aimed to evaluate the relative importance of initial soil pH and rate of residue application in determining subsequent pH change, nitrogen (N) mineralization, and soil-exchangeable aluminum (Al). An incubation experiment was conducted for 102 days on a Plinthudult soil and a Paleudalf soil, where pH gradients were produced after application of direct current (DC). Rates of vetch applications were 0, 5, 15, 30, and 50 g kg−1 soil. Increasing rates of vetch application caused greater increases in soil pH, but no consistent increase in soil pH at higher initial pH range (4.40∼6.74), because of nitrification. There was a positive correlation between alkalinity production and the initial soil pH at day 14, while correlations became negative at days 56 and 102. Mineral N accumulated as NH4 +–N in low pH soils, due to limited nitrification, while NO3 −–N dominated in higher pH soils. Application of vetch decreased KCl-extractable Al, probably because of complexation of Al by organic matter and precipitation of Al as a result of increased pH, reductions in Al concentration increased with increasing rates of vetch application. However, this amelioration effect on Al concentration weakened with time in higher pH soils. Application of vetch residue can significantly increase soil pH and concentrations of mineral N and reduce exchangeable Al. These amelioration effects are enhanced with increased rate of vetch addition and vary with time depending on the initial pH of the soil.

Medium-term soil pH and exchangeable aluminium response to liming at three high country locations

Acid soil conditions and associated aluminium (Al) toxicity pose a serious impediment to legume establishment, persistence and productivity in high country. However, data that report soil exchangeable Al concentrations in response to lime applications are scarce. Three historical (3-8-year-old) lime trial soils were sampled for soil pH and exchangeable aluminium (Al). Soil pH ranged from 4.8 to 7.5, with exchangeable Al concentrations (CaCl2 extraction) of 0.2 to 24 mg Al/ kg. Soil pH and exchangeable Al changed significantly when lime was applied, but the shape of the response differed between the three site locations. The soil pH changes (0-7.5 cm horizon) were 0.16, 0.10 and 0.20 pH units/t lime applied. Critical research needs to be conducted to investigate the key soil factors and mechanisms that result in Al toxicity in high country soils to enable development of mitigation strategies. On-farm decisions on lime rates and legume species suitability need to be based on soil pH and Al testing from individual farm blocks rather than using "rule of thumb" approaches. Keywords: soil pH, soil exchangeable aluminium, lime, pasture legumes

Cadmium, Lead, Copper, Zinc, and Nickel in Lettuce and Dry Beans as Related to Mehlich-3 Extraction in Three Brazilian Latossols

ABSTRACT Lettuce (Lactuca sativa L.) and dry beans (Phaseolus vulgaris L.) were grown in three Brazilian Red-Yellow Latossols (Oxisols) in greenhouse conditions with cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), and nickel (Ni) applied to soils in treatments arranged as a randomized complete block design. Plant metals were analyzed in lettuce shoots and dry beans roots, stems, leaves, and seeds. After plant growth, soil samples from the pots were extracted with Mehlich-3 (M-3) for metal availability evaluation. The release of Ni in the M-3 extraction was dependent on the soil exchangeable aluminum (Al3 +). Mehlich-3 was efficient for determination of availability of Cd, Pb, Cu, Zn, and Ni for dry beans and availability of Cd and Ni for lettuce. The dry bean leaves Cd, Pb, Cu, Zn, and Ni were highly correlated with their recovering from soils with M-3. The same was observed for Cd and Ni in lettuce shoots and the M-3 recovered metals from soils.

Soil and pasture responses to lime on dry hill country in central Hawke's Bay, New Zealand

Small plot trials were established with four combinations of aspect and slope (north‐easy, north‐steep, south‐easy, south‐steep) with initial soil pH 5.6, 5.4, 5.6, and 5.4, respectively) on hill country under low annual average rainfall (800 mm yr–1) near Waipawa in central Hawke's Bay. At each site, lime at 0, 0.5, 1.0, 2.0, 4.0, and 8.0 t ha–1 was applied once in November 2000 to increase soil pH to 5.4–5.6, 5.5–5.8, 5.7–5.9, 5.7–6.0, and 6.0–6.4, respectively for each rate of lime after 1 year. Soil exchangeable aluminium (Al) levels measured in November 2003 were above the critical level of 3 μg g–1, where root growth is restricted, on the north‐steep and south‐steep sites (4.48 and 5.23 μg g–1), just above on the south‐easy site (3.02 μg g–1) and below on the north‐easy site (1.45 μg g–1). At the north‐steep and south‐steep sites, soil Al was reduced below the critical level at rates of 0.5 and 1.0 t lime ha–1 and higher, respectively. There was no significant response in dry matter (DM) yield to lime measured at any site in Year 1 (December 2000‐November 2001), or for the north‐easy and north‐steep sites in Year 2 (December 2001‐November 2002) or Year 3 (December 2002‐November 2003). Lime had no significant effect on legume cover (19–61% in any one year) on the north‐easy site. Lime increased legume cover in years 2 and 3 (14–56%) on the north‐steep site. In Years 2 and 3, there was a significant DM yield response levelling off at 1.0 t lime ha–1 on both the south‐easy and south‐steep sites. On the south‐easy site, there was a significant response in legume cover to 0.5 t lime ha–1 and greater in Year 2, and 4.0t lime ha–1 and greater in Year 3 while on the south‐steep site there was a significant response in Year 2 to 1 t lime ha–1 and greater and in Year 3 to 2 t lime ha–1 and greater. Where a south aspect and easy slope favours legume growth in dry hill country, low rates of lime (1t ha–1) can result in a worthwhile pasture yield response, especially where soil Al levels are greater than 3 μg g–1.

Corrigendum to: Dung decomposition in temperate dairy pastures. I. Changes in soil chemical properties

The effect of dung from cows grazing low and high input systems (2 cows/ha, 35 kg P/ha; 4 cows/ha, 140 kg P/ha) on soil chemical properties in temperate dairy pastures was investigated. Dung was used to create pads, and their effect on soil at 2 depths compared with control areas to which nothing was applied. Most dung had decomposed after 40 days in autumn, and was completely degraded by Day 60 in this temperate environment. Large quantities of the nutrients P, K, Ca, Na, Mg, and S were applied to the soil in these dung pads. The mechanism of movement of these nutrients from the pads into soil appeared to be based on their solubility in water. Phosphorus did not leach from the pads but was incorporated into the soil with the decomposing pad. Calcium, Mg, and S concentrations declined slowly in the decomposing pads. On the other hand, K and Na appeared to leach from the pads, as significant decreases in concentrations occurred during decomposition. Soil pH (1:20 soil:water) decreased under dung pads, although the effect did not last beyond 60 days and was linked to the observed increase in soil EC with depth. Extractable P and K increased considerably in soil under dung pads, but only in the upper 0–5 cm layer. Soil exchangeable aluminium and total organic P were not affected by the presence of dung pads. These results are discussed in relation to nutrient cycling in temperate Australian dairy pasture soils.

Dung decomposition in temperate dairy pastures. I. Changes in soil chemical properties

The effect of dung from cows grazing low and high input systems (2 cows/ha, 35 kg P/ha; 4 cows/ha, 140 kg P/ha) on soil chemical properties in temperate dairy pastures was investigated. Dung was used to create pads, and their effect on soil at 2 depths compared with control areas to which nothing was applied. Most dung had decomposed after 40 days in autumn, and was completely degraded by Day 60 in this temperate environment. Large quantities of the nutrients P, K, Ca, Na, Mg, and S were applied to the soil in these dung pads. The mechanism of movement of these nutrients from the pads into soil appeared to be based on their solubility in water. Phosphorus did not leach from the pads but was incorporated into the soil with the decomposing pad. Calcium, Mg, and S concentrations declined slowly in the decomposing pads. On the other hand, K and Na appeared to leach from the pads, as significant decreases in concentrations occurred during decomposition. Soil pH (1:20 soil:water) decreased under dung pads, although the effect did not last beyond 60 days and was linked to the observed increase in soil EC with depth. Extractable P and K increased considerably in soil under dung pads, but only in the upper 0–5 cm layer. Soil exchangeable aluminium and total organic P were not affected by the presence of dung pads. These results are discussed in relation to nutrient cycling in temperate Australian dairy pasture soils.

Persistence and productivity of perennial ryegrass in sheep pastures in south-western Victoria: a review

Loss of perennial ryegrass (Lolium perenne L.) from the pasture within several years of sowing is a common problem in the higher rainfall (550–750 mm annual rainfall), summer-dry regions of south-eastern Australia. This pasture grass came to Australia from northern Europe, where it mostly grows from spring to autumn under mild climatic conditions. In contrast, the summers are generally much drier and hotter in this region of south-eastern Australia. This ‘mismatch’ between genotype and environment may be the fundamental reason for the poor persistence. There is hope that the recently released cultivars, Fitzroy and Avalon, selected and developed from naturalised ryegrass pastures in south-eastern Australia for improved winter growth and persistence will improve the performance of perennial ryegrass in the region. Soon-to-be released cultivars, developed from Mediterranean germplasm, may also bridge the climatic gap between where perennial ryegrass originated and where it is grown in south-eastern Australia. Other factors that influence perennial ryegrass persistence and productivity can be managed to some extent by the landholder. Nutrient status of the soil is important since perennial ryegrass performance improves relative to many other pasture species with increasing nitrogen and phosphorus supply. It appears that high soil exchangeable aluminium levels are also reducing ryegrass performance in parts of the region. The use of lime may resolve problems with high aluminium levels. Weeds that compete with perennial ryegrass become prevalent where bare patches occur in the pasture; they have the opportunity to invade pastures at the opening rains each year. Maintaining some herbage cover over summer and autumn should reduce weed establishment. Diseases of ryegrass are best managed by using resistant cultivars. Insect pests may be best managed by understanding and monitoring their biology to ensure timely application of pesticides and by manipulating herbage mass to alter feed sources and habitat. Grazing management has potential to improve perennial ryegrass performance as frequency and intensity of defoliation affect dry matter production and have been linked to ryegrass persistence, particularly under moisture deficit and high temperature stress. There is some disagreement as to the merit of rotational stocking with sheep, since the results of grazing experiments vary markedly depending on the rotational strategy used, climate, timing of the opening rains, stock class and supplementary feeding policy. We conclude that flexibility of grazing management strategies is important. These strategies should be able to be varied during the year depending on climatic conditions, herbage mass, and plant physiology and stock requirements. Two grazing strategies that show potential are a short rest from grazing the pasture at the opening rains until the pasture has gained some leaf area, in years when the opening rains are late. The second strategy is to allow ryegrass to flower late in the season, preventing new vegetative growth, and perhaps allowing for tiller buds to be preserved in a dormant state over the summer. An extension of this strategy would be to delay grazing until after the ryegrass seed heads have matured and seed has shed from the inflorescences. This has the potential to increase ryegrass density in the following growing season from seedling recruitment. A number of research opportunities have been identified from this review for improving ryegrass persistence. One area would be to investigate the potential for using grazing management to allow late development of ryegrass seed heads to preserve tiller buds in a dormant state over the summer. Another option is to investigate the potential, and subsequently develop grazing procedures, to allow seed maturation and recruitment of ryegrass seedlings after the autumn rains.

A comparative analysis of aluminum biogeochemistry in a northeastern and a southeastern forested watershed

This comparative biogeochemical analysis focused on the patterns and processes of aluminum cycling in two small watersheds, one in the west‐central Adirondacks of New York and the other on Cumberland Plateau of eastern Tennessee. Despite shared similarities in soil acidity, soil exchangeable aluminum concentrations, and elevated inputs of acidic deposition, the northern and southern sites exhibited strong differences in aqueous aluminum chemistry and transport. Soil and stream drainage waters in the northern watershed were more acidic, and contained higher concentrations of base cations, sulfate, nitrate, and organic carbon than waters in the southern ecosystem. Mean concentrations of biologically active labile inorganic aluminum, Ali, ranged from 17 to 46 μmol L−1 in soil solutions and stream water in the northern drainage basin, and from 0 to 2 μmol L−1 in the southern system. The major differences in aluminum chemistry and transport between the two watersheds were related to different patterns of alkalinity generation and mobile anion transport in these contrasting systems. In the northern watershed, atmospheric inputs of acidity were partially neutralized through the release of mixed cations (Ca, Al, Mg, K, and Na) from soils and detritus. Because of the high mobility of sulfate and nitrate in the northern watershed, there was significant transport of Al through the soil profile and into stream water. At the southern watershed, soil sulfate adsorption, biological retention of nitrate, and base cation release were the major sources of acid neutralizing capacity for soil drainage waters and surface waters. Because these processes resulted in both the release of alkalinity and the removal of mobile strong acid anions, concentrations of labile Al remained low throughout most of the drainage profile in the southern watershed. At the ecosystem level, results indicated that aluminum cycling at the southern site was controlled more by biotic transfers (e.g., plant uptake and litterfall), while solution transfers (e.g., soil leaching) dominated aluminum cycling at the northern site.