Subsurface Acidity Research Articles

Subsoiling Operations Concurrent to the Distribution of Acidity Amendments in the Soil Profile: The Response from Soybeans

In the Brazilian Cerrado region, the soils have significant agricultural potential; however, they are naturally acidic soils due to the constitution of the source material and the high weathering process. Liming has been the main tool for correcting acidity and supplying Ca2+ and Mg2+ to the soil; however, the effect of the corrector is limited to the soil surface. Consequently, the benefits of liming are restricted to the surface layer of the soil and do not solve the subsurface acidity problems. The objective of this work was to evaluate the effect of the subsoiling operation together with the application of a soil acidity corrector on the nutrition and productivity of soybean crops. The experiment was carried out in the experimental area of the Federal University of Jataí in the state of Goias, Brazil. The experimental design was a randomized block design, consisting of six treatments and four replications. The experiment was implemented in 2018, and it utilized the following treatments: T1: control (without subsoiling and liming); T2: the application of superficial limestone, without incorporation at a dose of 1 Mg ha−1; T3: limestone applied through gravity up to 60 centimeters (cm) deep using a subsoiler, with a spacing between the rods of 0.37 meters (m), at a dose of 2.82 Mg ha−1; T4: limestone applied with the same implement used in T3, at the same dose, but with a spacing between the rods of 0.75 m; T5: subsoiling, without the use of liming; and T6: subsoiling and, subsequently, liming on the surface at a dosage of 1 Mg ha−1. The superficial application of the oxide increases the mineral nutrition of plants, the production components, and the productivity of soybeans. There is no agronomic feasibility for using the subsoiler to incorporate limestone.

Evaluation of the influence of surface and subsurface acidity correction methodologies on soil compaction in agropastoral systems under no‐till

AbstractSurface and subsurface acidity and soil compaction restrict root exploration and impair crop yields in agropastoral systems under no‐till. To support the development of surface and subsurface acidity correction methodologies that can decrease soil compaction in agropastoral systems under no‐till, this study tested the following hypotheses: (a) the incorporation of limestone with plowing and harrowing (conventional tillage) for surface and subsurface acidity correction decreases soil compaction in agropastoral systems under no‐till, (b) the subsurface application of hydrated lime with a shank subsoiler‐fertilizer (minimum tillage) for surface and subsurface acidity correction decreases soil compaction in agropastoral systems under no‐till, and (c) the surface application of Ca compounds (no tillage) for surface and subsurface acidity correction increases soil compaction in agropastoral systems under no‐till. In a field experiment in an agropastoral system under no‐till in an Arenic Hapludalf in Brazil, the abilities of three application management methodologies (no tillage, conventional tillage, and minimum tillage) for three Ca compounds (limestone, phosphogypsum, and hydrated lime) to ameliorate acidity in the surface and subsurface layers and decrease soil compaction were evaluated. The experimental design was a randomized complete block with four replications. The results support the following conclusions: (a) the incorporation of limestone with plowing and harrowing does not decrease soil compaction in agropastoral systems under no‐till; (b) the subsurface application of hydrated lime with a shank subsoiler‐fertilizer does not decrease soil compaction in agropastoral systems under no‐till; and (c) the surface application of limestone does not increase soil compaction in agropastoral systems under no‐till.

Strategies to alleviate pH stratification and subsurface acidity in a no‐tillage system

AbstractSome no‐tillage systems necessitate amelioration of subsurface acidity. A 2‐year field trial was conducted on a no‐tillage sandy loam Cambisol, with a pH(KCl) of 4.20 in the 10‐ to 30‐cm depth. The aim was to evaluate one‐time tillage, calcitic lime forms, and lime plus gypsum combinations on soil chemical parameters, and wheat (Triticum aestivum L.) and canola (Brassica napus) production. Incorporation of lime (1.67 Mg ha−1) through one‐time chisel plowing increased soil pH(KCl) and soil exchangeable calcium in the 20‐ to 30‐cm depth by 9.1% and 210.1%, respectively, after 18 months. Conventional one‐time tillage treatments resulted in 15.0%–18.1% reduced wheat seedling establishment in the subsequent season. Surface‐applied hydrated lime (1.56 Mg ha−1) and microfine pelletized lime (1.75 Mg ha−1) both caused over‐liming (pH(KCl) > 6.5) effects in the 0‐ to 5‐cm depth after 6 months, which attenuated from 12 to 18 months. Surface‐applied lime (1.67 Mg ha−1) showed a 2.9% and 5.6% pH(KCl) reduction in the 10‐ to 20‐cm and 20‐ to 30‐cm depths, respectively, after 18 months. While combined surface application of lime (0.55 Mg ha−1) plus gypsum (1.25 Mg ha−1) showed a 3.7% and 0.5% pH(KCl) reduction in the 10‐ to 20‐cm and 20‐ to 30‐cm depths, respectively, after 18 months. Wheat (year 1) and canola (year 2) yield and seed quality parameters were unaffected (p > 0.05) by the treatments. Subsurface acidity amelioration in no‐tillage systems is best achieved through chisel lime incorporation or combined surface application of lime plus gypsum on moderately or highly weathered soils.

Soil and Crop Effects of a Subsurface Fluid Lime Applicator

Highlights Continuous no-tillage with fertilizer deep-banded below the seed can result in stratified soil acidity that cannot be rapidly addressed with surface-applied lime. We modified a tractor-driven sweep implement to inject fluid lime that targets sub-surface soil acidity with minimal disturbance that maintains surface crop residues, and tested it prior to seeding winter peas at 4 liming rates. Soil chemistry, microbiology, and crop growth were monitored over the season. Abstract. Deep-banding ammonia and urea-based nitrogen fertilizers under continuous no-tillage can result in stratified acidification at the fertilizer-injection depth. Currently, producers address this acidification through primary tillage operations that mix the soil and dilute the acidification, but increase the hazard of soil erosion. Typically, lime is required to ameliorate soil acidity; however, surface-applied lime does not immediately address subsurface acidity, and often tillage is used to incorporate lime and correct acidified layers created through deep-banded fertilizer placement under no-tillage. Here, we designed, developed, and tested a subsurface applicator for fluid lime that can target specific soil depths and rates. The liming system was tested in Eastern Washington on a field that had been under continuous no-tillage for 25 years, had stratified soil acidity, and was to be planted to winter pea, a crop known to be sensitive to acid soil conditions. Soil pH and carbon distribution, microbial changes, biomass, and leaf area index (LAI). Results indicated that the lime targeted the seed zone and raised pH significantly; effects on biomass were marginally significant; and effects on LAI and vegetation cover were insignificant. Topography had a significant effect on all variables due to changes in applicator effectiveness with changes in soil mechanics, meaning as-applied rates varied from desired rates. Keywords: Liming, No-tillage, Precision agriculture, Soil acidity, Soil microbiology.

Measurement of lime movement and dissolution in acidic soils using mid-infrared spectroscopy

Acidification of surface and sub-surface soils limits agricultural production globally. Conventional surface application of lime is the most common amelioration approach for surface acidity. However, amelioration of sub-surface acidity is challenging to achieve using this approach. Testing the efficacy of liming to treat acidity through the soil profile via the measurement of lime movement requires high throughput information about soil properties at a high spatial resolution, which can be time consuming and expensive using traditional laboratory analysis. Here, we investigated the potential of Mid Infrared (MIR) spectroscopy as a tool to monitor lime dissolution and vertical movement through soils at high spatial resolution. Soil samples were collected at 2.5 cm intervals to 20 cm depth at three trial sites in South Australia, with various lime treatments applied either 6 years or 1 year prior to sampling. MIR Partial least squares regression (PLSR) predictions were undertaken to measure lime dissolution and alkalinity movement via soil pH, and undissolved lime presence via soil carbonate concentrations. Lime balance calculations were then performed to determine the fate of applied lime and assess efficacy of various rates of lime products applied at the surface only or via incorporation. MIR-PLSR prediction model performance was strong for both soil pH (R2 = 0.923 and RMSE = 0.202) and carbonate (R2 =0.829 and RMSE=0.042 CO3%). Results indicated the movement of alkalinity at all sites was limited, and revealed increased movement at the longer-term (∼6 years) vs shorter-term (∼1 year) sites where lime was surface applied. Lime balance calculations indicated that residual lime remained in the top 7.5 cm of the soil profile while soils remained acidic below this depth. Findings suggest that incorporation of residual lime and additional lime applications may be necessary to remediate sub-surface acidity. A decision tree was developed to inform management of surface and sub-surface soil acidity. The study validates the potential of MIR spectroscopy to measure and monitor the effectiveness and movement of lime with improved resolution in acidic soils.

Response of canola and cereals to amendment of subsurface soil acidity and a hardpan

Context Limitations to crop yield due to subsurface (5–15 cm depth) compaction layers (>2 MPa) and subsurface acidity (pHCa <4.8) have frequently been reported on the non-sodic soils of south-eastern Australia, but amendment studies have been limited in number and inconsistent in the extent and longevity of any response. Aim We tested the hypothesis that amendment of subsurface acidity and compaction would lead to increased grain yield. Method We investigated crop response to the alleviation of these combined subsurface soil constraints by using deep ripping and dry limestone injection to 30 cm depth over 3 years in a canola–cereal sequence. Key results Deep tillage and injection of limestone into the soil both failed to produce significant grain yield responses in any year, despite the reduction of soil strength and increase in pH in subsurface layers. Early vegetative growth sometimes responded to the treatments, but the loss of stored soil water during drier than average seasons appeared to limit grain response. However, we also observed that a proportion of plant roots penetrated these relatively thin constraint layers in unamended soils. Conclusions Amelioration of subsurface acidity and compaction does not necessarily increase grain yield. Implications The effects of subsurface acidity and compaction should be tested on other species and during varying rainfall deciles. Given the potentially large resource requirements for deep amendment of soils, we propose that the selection of tolerant species and cultivars might be more effective in the short term.

New Methodologies for the Surface Application of Limestone and Gypsum in Different Crop Systems

To address the problems of soil acidity (pH values below 4.4) in surface and subsurface soil layers and improve soil chemical fertility, this study evaluated three methodologies for surface application of limestone (LS) (ensuring that calcium (Ca)2+ occupied 70%, 60% or 50% of cation exchange capacity (CEC) at a depth of 0.0–0.2 m) and gypsum (GP, phosphogypsum) (ensuring that Ca2+ occupied 60%, 50% or 40% of effective cation exchange capacity (ECEC) at a depth of 0.2–0.4 m). LS and GP were applied in a conventional pasture system (CPS), no-till system (NTS), and agropastoral system (APS) in an Arenic Hapludult in Brazil. Surface application of LS and GP using these three methodologies corrected surface and subsurface acidity and improved soil chemical fertility. Specifically, Ca2+ content increased in the CPS, NTS, and APS at a depth of 0.0–0.2 m and in the CPS and APS at a depth of 0.2–0.4 m; sulfur (S)-SO42− content and Ca2+/ECEC increased in the CPS, NTS, and APS at a depth of 0.2–0.4 m; base saturation (BS) increased and aluminum (Al)3+ content decreased in the NTS and APS at depths of 0.0–0.2 m and 0.2–0.4 m; and pH, magnesium (Mg)2+ content, CEC, Ca2+/CEC, and Mg2+/CEC increased and total acidity decreased in the NTS and APS at a depth of 0.0–0.2 m.

Detection of agriculturally relevant lime concentrations in soil using mid-infrared spectroscopy

Globally, surface and subsurface soil acidity pose a serious threat to crop production and require effective management to prevent yield losses. The application of lime (calcium carbonate, CaCO3) is a well-recognised remediation technique for surface soil acidity. However, for subsurface acidity, improved application and detection methods are required to manage acidity due to the stratification of acidic layers. Mid infrared (MIR) spectroscopy has potential as a rapid, cost effective and accurate method of CaCO3 detection in soils. However, for this technology to be valuable in an agricultural context, there is a need to develop MIR spectroscopy methods for the detection of CaCO3 at agriculturally relevant concentrations of <1%, which was the aim of this study. MIR Partial Least Square Regression (PLSR) carbonate prediction models were developed using carbonate-specific spectral regions to predict CaCO3 concentrations in soil. Prediction models were initially developed using a single soil type spiked with reagent grade CaCO3 and were tested further with soils collected from field trials that had been treated with various rates and sources of lime. Prediction models using specific carbonate peak regions were established and compared with models using the entire MIR spectrum to assess the model performance. Models built using a single peak range at 2560–2460 cm−1 gave the best results (highest R2 values and lowest RMSE values) followed by the single peak range at 1840–1760 cm−1. Specifically, model performance was improved when developed with a single soil type and reagent grade CaCO3 in the 2560–2460 cm−1 spectral region, with PLSR R2 of 0.834 and RMSE of 0.030. Performance was reduced but still satisfactory (R2 of 0.735 and RMSE of 0.069) when applied to field trial soils using a range of different lime sources, including dolomitic lime. The MIR method enabled accurate prediction of carbonate concentrations and had a detection limit of 0.05% CaCO3, similar to what can be achieved using a pressure calcimeter. Findings suggest that MIR spectroscopy measurements of agriculturally applied CaCO3 in soils may provide valuable insights into monitoring the movement and efficacy of lime treatments and will enable more informed lime applications in the future. The method may also be used to detect naturally-occurring carbonates at low concentrations and may be useful for rapid isolation of inorganic carbon from organic carbon in soil carbon measurements and carbon accounting.

Forms of lime application and use of phosphogypsum in low acid soil in southern Brazil: soybean-wheat yield and soil chemical properties

Brazil is currently the leading country in no-till (NT) farming, particularly on Ferralsols (Latossolos), the most abundant soil type. These soils are characterized by subsurface acidity that cannot be effectively corrected by surface application of additives. In this situation, the use of phosphogypsum can be advantageous. This study aimed to assess the residual effects of lime and phosphogypsum application on a clayey Ferralsol, and four soybean and two wheat yields in southern Brazil. The area has been cultivated under [...]

Lime and phosphogypsum application management: changes in soil acidity, sulfur availability and crop yield

Oxisols ( Latossolos ) are widely distributed in tropical zones and generally characterized by high levels of surface and subsurface acidity. In Brazil, most Oxisols are managed under no-till conditions with surface application of acidity amendments. This study aimed to evaluate lime application strategies (incorporated and surface) for achieving the desired soil base saturation (BS%) levels (44, 60, 70, and 90 %) and the effect of phosphogypsum + lime application on soil chemical properties as well as wheat and [...]

Slow movement of alkali from surface-applied lime warrants the introduction of strategic tillage for rapid amelioration of subsurface acidity in south-western Australia

Conventional surface-application of agricultural lime takes many years to increase pH deeper in the soil profile, which is a barrier to increased adoption of liming. We conducted a series of experiments to measure the rate of vertical movement of alkali and identify the factors that determine this movement into the subsurface, to evaluate the feasibility of ameliorating acidic subsurface soil using residual (undissolved) lime (CaCO3) at Wongan Hills (30.85°S, 116.74°E) and Merredin (31.48°S, 118.21°E) and to test whether deep tillage and lime incorporation can significantly speed up the amelioration of subsurface soil acidity at Kalannie (30.42°S, 117.29°E). Multiple applications of lime to the surface of the soil at higher rates (total 6–8.5 Mg ha–1) significantly increased subsurface soil pH but only in the 0.10–0.20 m depth by 0.049 pH units per year over 10–24 years. A large proportion of the surface-applied lime was stratified in the top few centimetres of the soil and incorporation of this undissolved lime with a rotary hoe to a depth of 0.25 m significantly increased soil pH (by 0.63 units) within a year in the Wongan Hills field experiment. Deep incorporation of 6 Mg ha–1 lime to a depth of 0.45 m through excavation and spading with a small rotary hoe also increased soil pH by more than a unit and decreased Al concentration to below the toxic level within two months in the Kalannie experiment, allowing wheat (Triticum aestivum L.) plants to produce root systems up to 0.59 m deep compared with 0.26 m for the control. Our soil column leaching experiment indicated that surface incorporation of lime in higher rainfall regions can be useful to treat subsurface soil acidity but that the rate of improvement in subsurface pH was slow. Therefore, deeper incorporation of lime using cost-effective strategic deep tillage is likely to be necessary.

The extent, significance and amelioration of subsurface acidity in southern New South Wales, Australia

Soil pH is seldom uniform with depth, rather it is stratified in layers. The soil surface (0–0.02 m) commonly exhibits relatively high pH and overlies a layer of acidic soil of 0.05–0.15 m deep, termed an acidic subsurface layer. Commercial and research sampling methods that rely on depth increments of 0.1 m either fail to detect or under report the presence or magnitude of pH stratification. The occurrence of pH stratification and the presence of acidic subsurface layers may cause the extent of acidity in NSW agricultural land to be underestimated. Though the cause of pH stratification in agricultural systems is well understood, the effect on agricultural production is poorly quantified due in part to inadequate sampling depth intervals resulting in poor identification of acidic subsurface layers. Although liming remains the best method to manage acidic soil, current practices of low pH targets (pHCa 5), inadequate application rates and no or ineffective incorporation have resulted in the continued formation of acidic subsurface layers. Regular monitoring in smaller depth increments (0.05 m), higher pH targets (pHCa &amp;gt; 5.5) and calculation of lime rate requirements that account for application method are required to slow or halt soil degradation by subsurface acidification. If higher pH is not maintained in the topsoil, the acidification of subsurface soils will extend further into the profile and require more expensive operations that mechanically place amendments deep in the soil. Although the use of organic amendments has shown promise to enhance soil acidity amelioration with depth, the longevity of their effect is questionable. Consequently, proactive, preventative management of topsoil pH with lime addition remains the most cost-effective solution for growers.

Impact of novel materials on alkalinity movement down acid soil profiles when combined with lime

Subsurface soil acidity in conjunction with aluminium (Al3+) toxicity is a major limitation to agricultural production globally. The conventional use of surface-applied lime is often insufficient at correcting subsurface acidity; therefore, new practices and ameliorants are required. This 3-month leaching experiment investigated whether animal wastes and other novel ameliorants in combination with lime could improve alkalinity movement, leading to greater amelioration of acid subsurface soil layers compared with lime alone. Five ameliorants (mature dairy compost, vegetable garden compost, poultry litter, potassium humate and gypsum) were added at a rate of 18 mg dry matter g−1 to the topsoil layer either without or with lime (target pH 5.5). All ameliorants with lime improved alkalinity movement below the amended layer (0–10 cm), with pH increases of 0.03–0.10 units at 1 month and 0.02–0.20 units at 3 months. In comparison, the Al3+ concentrations in 10–12-cm and 12–15-cm layers were significantly decreased by 2–5.5 μg g−1. With lime, the improvements in alkalinity movement with ameliorants were in the order of gypsum > vegetable garden compost > potassium humate > poultry litter > mature dairy compost. Without lime, each amendment increased soil pH in the subsoil, with their effectiveness decreasing in the order of poultry litter > vegetable garden compost > mature dairy compost > gypsum > potassium humate. Some organic amendments are effective in addressing subsoil acidity. When combined with lime, their additive effects are limited.

Alkalinity movement down acid soil columns was faster when lime and plant residues were combined than when either was applied separately

AbstractSubsurface soil acidity is a serious constraint to crop production and is inherently difficult to correct through conventional application of lime. Thus, new approaches to ameliorate subsurface soil acidity are needed. A column leaching experiment was established to determine whether the plant residues, when combined with lime, could facilitate lime dissolution and alkalinity movement down soil columns (10 cm in diameter × 45 cm long) to ameliorate acid subsurface soil layers. Five plant residues from canola (Brassica nappus L.), field pea (Pisum sativum L.), lucerne (Medicago sativa L.), oats (Avena sativa L.) and vetch (Vicia villosa L.) (C/N ratios of 52, 13, 16, 53 and 12, respectively) were mixed with soil (18 g dry matter kg−1) in the top of soil columns (0–10 cm) either limed (target pH 7 in CaCl2) or non‐limed and incubated for 3 months at 25°C. Soil columns were leached six times over the 3‐month incubation period and destructively sampled at 1 and 3 months for chemical analysis. The soil amended with plant residues created favourable pH gradients and facilitated downward movement of alkalinity when lime was added. However, net increases in pH in the 10–12‐cm layer after 3 months were only observed in two non‐legume residue‐amended treatments (canola and oat residues, 0.22–0.43 pH unit increase), but not in three legume residue‐amended treatments (field pea, lucerne and vetch residues), although those treatments had the greatest pH increase in the short term (1 month). In conclusion, surface incorporation of lime in combination with plant residues accelerated the amelioration of subsurface acidity in the immediate zone (10–12 cm) below the amended layer. Canola and oat residues were superior in terms of increased soil pH over a longer term (3 months), possibly due to their higher C/N ratios.Highlights Can plant residues, combined with lime, facilitate alkalinity movement down soil columns? Few studies have examined leaching, alkalinity movement and pH gradients using agricultural soils. Lucerne and vetch had the greatest pH increase (1 month) but canola and oat persisted (3 months). Alkalinity movement was faster when lime and plant residues were combined than when applied alone.

The reaction rate and residual value of particle size fractions of limestone in southern New South Wales

Grain yield is frequently constrained by soil acidity in southern Australia yet limestone crushing plants are few and distant, making the use of limestone costly. The efficient technology of agricultural liming is therefore critical to the continuation of the practice following its adoption during the 1980s. We hypothesise that finer particles are the most effective materials for ameliorating soil acidity even over the longer term, when the residual value of coarser particles might be expected to be greater. Finer particle sizes of limestone, particularly &amp;lt;0.075 mm, initially gave the largest increases in soil pH per tonne of limestone applied. Despite the rapid and large increase in soil pH with finer particles, there was no less residual value in surface soil pH after 7 years or in grain yield in the 7th and 8th growing seasons compared with coarser particles. Most particle size fractions of limestone converged to a similar soil pHca at 0–10 cm depth after about 6 years but the coarsest particle size fraction (2–5 mm) lagged the other five. Finer particles also resulted in better movement of alkali and Ca into the subsurface soil layers below the depth of incorporation (0–10 cm). The measurement of unreacted limestone in the soil showed that the dissolution of limestone took up to 3 years (1807 mm of rainfall) for the 2.5 t/ha rate and up to 6 years (3592 mm) for the 5 t/ha rate. The rapid increase in soil pH in Year 1, the slow ongoing reaction of limestone over 3–6 years as measured by unreacted limestone, the slow but measurable improvement in subsurface acidity, and the sustained residual value to grain yield over in excess of eight seasons, indicate that the use of finer liming materials should remain a viable practice for growers.

Effect of gypsum rates and lime with different reactivity on soil acidity and crop grain yields in a subtropical Oxisol under no-tillage

The low solubility of lime (CaCO3) and the absence of soil disturbance in fields under no-tillage (NT) may diminish the effectiveness of surface liming to reduce exchangeable Al3+ (toxic to plants) and increase the base saturation in deep soil layers. However, the effects of subsurface soil acidity can be attenuated by applying agricultural gypsum (CaSO4⋅2H2O), which is more soluble than lime, and thus, can leached bases (exchangeable Ca2+, Mg2+ and K+) and S-SO42− to deeper soil layers as well as decrease Al3+ toxicity to plants. Therefore, gypsum can be applied individually or in combination with lime. Herein, we conducted a field experiment aiming to evaluate short- (1 year) and long-term (11 years) effects of surface liming and gypsum application on the chemical properties of the 0.00–0.10, 0.10–0.20, 0.20–0.40 and 0.40–0.60 m soil layers and also on crop yield of 22 crop seasons (i.e., 10 soybean, 3 maize, 4 white oat, 3 wheat and 2 barley crops). The study was performed in a clayey Typic Hapludox of moderate acidity managed under NT for more than 25 years in Guarapuava, Paraná State, southern Brazil. Three soil surface-applied lime strategies were tested in order to raise base saturation to 70%, namely: (a) 4.62 Mg ha–1 rate of lime of low effective calcium carbonate equivalent (ECCE = 75%); (b) 3.47 Mg ha–1 rate of lime with a high ECCE value (101%); and (c) the same rate of high-ECCE lime split in three applications (i.e., 1/3 at the start of experiment; 1/3 after 1 year and 1/3 after 2 years). A control treatment without liming was also conducted. The liming strategies were combined with four rates of agricultural gypsum (i.e., 0, 3, 6 and 9 Mg ha–1) applied at the start of the experiment. Our findings did not reveal synergistic effect of lime and gypsum on soil chemical properties nor on crop yield. Gypsum resulted in very slight gains in grain yield (4% on average) and limited to just 25% of cereal (corn and winter cereals) crop seasons. On the other hand, liming increased soybean yields by 14% in 40% of crop seasons. Gypsum was more efficient than lime in raising exchangeable Ca2+ levels up to −0.60 m in the short term; however, lime promoted greater reduction of soil acidity and had a more marked residual effect on exchangeable Ca2+ contents than gypsum. The liming strategies did no promote substantial differences in crop yield, but low-ECCE lime sustained better soil chemical condition to plant growth for a longer period. Surface liming efficiently reduced subsurface acidity in a moderately acidic Oxisol managed under NT even in the short-term, promoting increments on soybean crop yields. In this case, the application of gypsum rates did not bring additional benefits to soil or plant yield.

Crop Response to Gypsum Application to Subtropical Soils Under No-Till in Brazil: a Systematic Review

ABSTRACT The use of gypsum to improve the root environment in tropical soils in the southeastern and central-western regions of Brazil is a widespread practice with well-established recommendation criteria. However, only recently gypsum began to be used on subtropical soils in South of Brazil, so available knowledge of its effect on crop yield is incipient and mainly for soils under no-till (NT) systems. Avaiable studies span a wide range of responses, from a substantial increase to a slight reduction in crop yield. Also, the specific conditions leading to a favorable effect of gypsum application on crop yield are yet to be accurately identified. The primary objectives of this study were to examine previously reported results to assess the likelihood of a crop response to gypsum and to develop useful recommendation criteria for gypsum application to subtropical soils under NT in Brazil. For this purpose, we examined the results of a total of 73 growing seasons, reported in 20 different scientific publications that assessed grain yield as a function of gypsum rates. Four different scenarios were examined, by the occurrence or not of high subsurface acidity (viz., Al saturation >20 % and/or exchangeable Ca 3 cmolc dm-3) failed to increase crop yield, irrespective of the soil water status. Under these conditions, high gypsum rates (6-15 Mg ha−1) may even reduce grain yield, possibly by inducing K and Mg deficiency. On the other hand, applying gypsum to soils with high subsurface acidity increased yield by 16 % in corn (87 % of cases) and by 19 % in winter cereals (83 % of cases), whether or not the soil was water-deficient. By contrast, soybean yield was only increased by gypsum applied in the simultaneous presence of high soil subsurface acidity and water deficiency (average increase 27 %, 100 % of cases).

Evaluation of Two Industrial By-products as Soil Conditioners for Reducing Potential Aluminium Toxicity and Acidity in a Palexerult of Western Spain

A field experiment evaluated the effects of surface applications of two industrial by-products (sugar foam and phosphogypsum) to an acidic Ultisol of the temperate zone in Spain to ameliorate topsoil and subsurface acidity and potential aluminium (Al) toxicity. The by-products were applied in single and combined amendments and at two different rates. Two years after their application, it was determined that applications at a low rate of sugar foam and sugar foam + phosphogypsum increased the pH and the exchangeable calcium (Ca) and reduced the exchangeable Al in the surface horizon of the soil while only a significant reduction of exchangeable Al was obtained in the subsurface horizon. Long-term amelioration of acidity and potential Al toxicity were only achieved upon the addition of these treatments at high rate. The addition of sugar foam at a high rate provides an effective practice for long-term acidity amelioration from the surface downward.

Biological amelioration of subsoil acidity through managing nitrate uptake by wheat crops

Subsoil acidity occurs in many agricultural lands in the world, and is considered to be an irreversible constraint due to amelioration difficulties. This field study aimed to develop a biological method to ameliorate subsoil acidity through the root-induced alkalisation resulting from nitrate uptake. Aluminium (Al)-tolerant wheat variety Diamondbird and Al-sensitive variety Janz (Triticum aestivum L.) were grown at two contrasting field sites with mild and severe subsurface acidity, respectively, and were supplied with either Ca(NO3)2 at the soil surface, Ca(NO3)2 at 10 cm depth or urea at 10 cm depth. Application of nitrate increased rhizosphere pH up to 0.5 units and bulk soil pH to 0.3 units, and to a depth >30 cm in the Kandosol. The placement of nitrate at 10 cm increased subsoil pH more than the surface application. Nitrate application increased nitrate concentration in soil profiles as expected, whereas urea application increased NH 4 + concentration which in turn favored acidification processes. Diamondbird generally produced more tillers and shoot biomass at anthesis but the two varieties did not differ in grain yield or rhizosphere alkalisation. Similar grain yields were achieved under supply of nitrate and urea. The results suggest that biological amelioration through managing nitrate uptake is possible as part of an integrated approach to combat subsoil acidity in farming systems.

A financial analysis of lime application in a long-term agronomic experiment on the south-western slopes of New South Wales

Management of Acid Soils Through Efficient Rotations (MASTER) is a long-term agronomic experiment commenced in 1992. There were 3 fundamental treatment contrasts in this experiment: (a) annual systems v. perennial systems; (b) limed v. unlimed treatments; and (c) permanent pastures v. pasture–crop rotations. The soil was acidic to depth with pH (in CaCl2) below 4.5 and exchangeable Al above 40% at 0.10–0.20 m when the experiment started. Lime was applied every 6 years to maintain soil pHCa at 5.5 in the 0–0.10 m soil depth. A financial analysis was undertaken to estimate potential benefits and costs involved in liming acid soils on the south-western slopes of New South Wales, based on data from the MASTER experiment. The most important finding from the current study is that liming pastures on soils that have a subsurface acidity problem is profitable over the long-term for productive livestock enterprises. The pay-back period for liming pastures, grazed by Merino wethers, was 14 years for both annual and perennial pastures. More profitable livestock enterprises, such as prime lambs or growing-out steers, were estimated to reduce the pay-back period. This gives farmers confidence to invest in a long-term liming program to manage highly acid soils in the traditional permanent pasture region of the high-rainfall zone (550–800 mm) of south-eastern Australia. Results from the current study also confirmed that the total financial return from liming is greater if the land is suitable for operation of a pasture–crop rotation system. The positive cash flows generated from cropping in a relatively short time can significantly shorten the pay-back period for the investment in lime. But cropping without liming on soils with subsurface acidity was worse than grazing animals. Crop choice is crucial for the perennial pasture–crop rotation. Inclusion of high-value cash crops, such as canola or a wheat variety with high protein, would lead to a rise in the aggregate benefits over time as the soil fertility improved and soil acidity was gradually ameliorated.