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High nitrous oxide (N2O) emissions (2–10% of fertiliser N) were observed previously from acid soils cropped with sugarcane (Saccharum officinarum) in Australia. We assessed the impact of lime, a nitrification inhibitor (NI, as 3,4-dimethylpyrazole phosphate, DMPP), and copper (Cu) on N2O emissions from an acid sugarcane soil in a laboratory experiment using (1) urea (U), (2) U + DMPP, (3) U + CuSO4.5H2O (U + Cu), and (4) U + DMPP + Cu. The treatments were applied to both an un-limed soil (pH 5.1) and a limed soil (pH 6.9) and incubated at 25 °C and 55% water holding capacity (WHC) for 28 d, and then increased to 90% WHC for another 8 d to favour denitrification. At 55% WHC, both the addition of the NI (U + DMPP) and the liming of the acid soil significantly decreased cumulative N2O emissions, due to significantly lower net nitrifications. Liming and DMPP decreased N2O emissions by 79% and 90%, respectively. However, where lime and DMPP were applied together, N2O emissions decreased by 94% compared to those in the un-limed (acid) U-treated soil. In contrast, the addition of Cu and the increase in water content to 90% WHC had no significant effect on N2O emissions. Therefore, the combined use of lime and DMPP provides the best option to decrease N2O emissions from the acid soil. [ABSTRACT FROM AUTHOR]

Soil acidification due to crop removal and the use of acidifying fertilisers reduce land productivity in many agricultural systems worldwide. The most common remedy is to apply lime to the soil surface. An alternative approach is to incorporate lime into the sub‐soil. This is a more expensive option, but it substantially reduces the time required to reduce acidity in the sub‐soil horizons. This paper presents a dynamic optimisation model to determine optimal rates, frequency and methods of lime application for a wheat monoculture system in the northern part of the Western Australian wheatbelt. Results show that optimal application rates depend on rainfall levels and soil‐acidity conditions. The net present value of profit is not sensitive to the frequency of lime application. Incorporating lime into the sub‐soil increases the net present value of profit, but only by a small amount: two to four per cent in most scenarios modelled. In the process, sub‐soil lime application reduces both the optimal lime application rate and the time required for the soil pH to increase to a target level. [ABSTRACT FROM AUTHOR]

Low phosphorus (P) constrains productivity of many of the permanent pastures of south-eastern Australia where wool and meat production are important. Whereas the need for fertilisation with P is indisputable for many soils, the benefits of liming to ameliorate soil acidification are not always clear in terms of forage production or quality. This experiment, by measuring botanical composition and groundcover over 10 years, aimed to address the issue of forage composition and groundcover. Merino wethers were continuously grazed on a permanent pasture under two stocking rates (low and high) following treatments with three rates of surface-applied lime and two rates of P. The lime rates were: nil, and sufficient to raise the pHCaCl2 of the 0–10 cm soil layer to 5.0 and to 5.5. Phosphorus was added as two rates of single superphosphate: 125 kg ha–1 every 2–3 years, and 250 kg ha–1 every year. Two hypotheses were proposed: (i) as lime application rate increased, it would lead to the pasture swards having a higher percentage of species favourable for grazing animal production, and a higher level of sward groundcover would be maintained; and (ii) legume presence would be favoured by a higher level of applied P over the long term. The Millennium Drought (1997–2008), which coincided with this experiment (1998–2008), tended to mask or reduce lime effects; nevertheless, the higher legume content in the sward, as well as the superior groundcover found in the high lime–high P treatments at various times throughout the experiment and at its completion compared with the nil-lime control, indicated positive forage effects of lime application. Moreover, by the termination of the experiment in 2008, groundcover generally tended to be lower under nil lime than in treatments that had received lime. The higher proportion of legume in the sward was closely linked to greater applied P, although this did not occur at the low stocking rate in the absence of lime. By contrast, similar high P–low stocking rate treatments but with applied lime had the highest clover contents. It is proposed that the poor persistence of the treatment without lime may be due to a combination of poor legume seedset, because of excessive competition from accompanying grasses, and aluminium toxicity adversely affecting legume growth. Soil acidity is a serious problem reducing the production of crops and grazing animals, and although lime can reduce acidity, it is expensive because high rates are required. This research follows the effect of lime on the pasture composition of desirable legumes and perennial grasses. The higher legume content in the sward found in high lime–high phosphorus treatments at times throughout the experiment and at its completion compared with the nil-lime control indicated the value of lime application. [ABSTRACT FROM AUTHOR]

Species composition is limiting production in >65% of pastures in Tasmania, Australia—a situation not unique to Tasmania. There are many reasons for degradation and poor persistence of improved pastures, with species selection crucial. Selection currently relies on producers making an assessment based on experience, external advice from agronomists and seed merchants, and experimental trial data. This project sought to assess the benefit of using fine-scale soils data and long-term rainfall data to determine the suitability of pasture species at a farm level across >3 Mha of agricultural land in Tasmania. Suitability rules were developed for perennial ryegrass (Lolium perenne L.) and lucerne (Medicago sativa L.) involving growth responses to soil characteristics (pH, soil depth, electrical conductivity, drainage, and coarse fragments) and average annual rainfall. Suitability classes were defined as well suited, suitable, moderately suitable, and unsuitable, with additional subclasses to account for soil limitations that could be mitigated through management. Soil grids were generated using digital soil mapping techniques from ~6500 new and existing site data sources spread across Tasmania. Rainfall data from 539 Bureau of Meteorology rainfall-recording sites were modelled using regression kriging interpolation. Soil pH was found to be a major constraint on lucerne, with 61.3% of the land area having a pH <5.7. Ameliorating the soil with lime could reduce this constraint to 33.5% of the land area. Drainage was another major constraint on lucerne suitability, with 37.8% of land constrained by imperfectly or poorly drained soils. Improving drainage by installing surface or underground drains could reduce the affected area to 22.1%. The mapping showed that perennial ryegrass was constrained by soil pH, with 38.2% of land having a pH <5.5. However, liming could reduce this constraint to just 9.6%. Accurate identification of the likely constraints on pasture production and persistence before sowing and choice of appropriate species and management intervention will result in fewer failed sowings and greater productivity. The feasibility of expanding this approach is being assessed for a larger area of south-eastern Australia and across a wider range of pasture species. Selecting pasture species suitable for particular soil and climate conditions is a critical step in growing productive and persistent pastures. Fine-scale soil and rainfall data were used for spatial evaluation of the suitability of growing perennial ryegrass and lucerne across agricultural land in Tasmania, with soil pH and drainage identified as key constraints. Fine-scale mapping can help to identify constraints and prioritise land suited to amelioration, or support the selection of other pasture species adapted to these conditions. [ABSTRACT FROM AUTHOR]

Applying lime to ameliorate soil acidity has been observed to induce manganese (Mn) deficiency in canola (Brassica napusL.) crops grown on acid sandy soils near Albany and gravelly acid sands of the Great Southern Districts of southwestern Australia. These soils were often Mn-deficient in patches for wheat (Triticum aestivumL.) production when they were newly cleared for agriculture requiring application of Mn fertilizer to ensure grain yields were not reduced by the deficiency. Since then, these soils have acidified and in the 1990s, canola started to be grown on these soils in rotation with wheat and lupins (Lupinus angustifoliusL.). These limed soils may now have become marginal to deficient in Mn for canola production. The effect of liming may change the effectiveness of fertilizer Mn. In addition, the effect of liming on the residual value of Mn fertilizer applied to these soils for canola production is unknown. Therefore, a glasshouse experiment was conducted using Mn deficient sand. Three levels of finely-powdered calcium carbonate were added and incubated in moist soil for 42 days at 22±2°C to produce 3 soils with different pH values [1:5 soil:0.01 M calcium chloride (CaCl2)]: 4.9 (original soil), 6.3, and 7.5. Five Mn levels, as solutions of Mn sulfate, were then added and incubated in moist soil for 0, 50, and 100 days before sowing canola. To estimate the residual value (RV) of incubated Mn for canola production, the effectiveness of the incubated Mn was calculated relative to the effectiveness of Mn applied just before sowing canola (freshly-applied Mn). The RV of the incubated Mn was determined using yield of dried canola shoots, the Mn application level required to produce 90% of the maximum shoot yield, and Mn content in dried shoots (Mn concentration in shoots multiplied by yield of dried shoots). As measured using both yield of dried shoots and Mn content of dried shoots, the residual value of Mn decreased with increasing soil pH and with increasing period of incubation of Mn with moist soil. The critical Mn concentration, for 90% of the total yield of dried canola shoots, was (mg Mn kg−1) ∼17 in youngest mature growth (apex and youngest emerged leaf, YMG), and ∼22 for the rest of dried shoots. These values were similar to current critical values for un-limed soils suggesting critical Mn concentrations remain the same for limed soils. Plant testing of canola is recommended if soils are to be limed to ameliorate soil acidity. When plant tests indicate a high likelihood of Mn deficiency, foliar Mn sprays need to be applied to that crop to ensure Mn deficiency does not reduce grain production that year, and fertilizer Mn needs to be re-applied to the soil when sowing the next crop to reduce the likelihood of Mn deficiency for subsequent crops. [ABSTRACT FROM AUTHOR]