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Soil acidification is an issue for agriculture that requires effective management, typically in the form of lime (calcium carbonate, CaCO3), application. Mid infrared (MIR) spectroscopy methods offer an alternative to conventional laboratory methods, that may enable cost-effective and improved measurement of soil acidity and responses to liming, including detection of small–scale heterogeneity through the profile. Properties of an acidic soil following lime application were measured using both MIR spectroscopy with Partial Least Squares Regression (MIR-PLSR) and laboratory measurements to (a) compare the ability of each method to detect lime treatment effects on acidic soil, and (b) assess effects of the different treatments on selected soil properties. Soil properties including soil pH (in H2O and CaCl2), Aluminium (Al, exchangeable and extractable), cation exchange capacity (CEC) and organic carbon (OC) were measured at a single field trial receiving lime treatments differing in rate, source and incorporation. Model performance of MIR-PLSR prediction of the soil properties ranged from R2 = 0.582, RMSE = 2.023, RPIQ = 2.921 for Al (extractable) to R2 = 0.881, RMSE = 0.192, RPIQ = 5.729 for OC. MIR-PLSR predictions for pH (in H2O and CaCl2) were R2 = 0.739, RMSE = 0.287, RPIQ = 2.230 and R2 = 0.788, RMSE = 0.311, RPIQ = 1.897 respectively, and could detect a similar treatment effect compared to laboratory measurements. Treatment effects were not detected for MIR-PLSR-predicted values of CEC and both exchangeable and extractable Al. Findings support MIR-PLSR as a method of measuring soil pH to monitor effects of liming treatments on acidic soil to help inform precision agricultural management strategies, but suggests that some nuance and important information about treatment effects of lime on CEC and Al may be lost. Improvements to prediction model performance should be made to realise the full potential of this approach. [ABSTRACT FROM AUTHOR]

Abstract: Nitrous oxide (N2O) is a potent greenhouse gas contributing to global radiative forcing. Grazed legume pasture is one of the major agricultural land uses in southern Australia and no N2O emission studies have been undertaken previously on this system. A study over 1 year has been undertaken measuring N2O emissions from legume pasture at Wagga Wagga, Australia. The study was embedded within a larger on-farm study of the management of acid soils. Sampling involved simultaneous N2O emission measurements on two paddocks each of: acidic soil with pH 4.0; limed soil with soil pH 5.5, and limed soil with addition of 20gNm−2 of animal urine. The average emission of N2O from the acidic legume pasture was 0.35kgNha−1 y−1 with a standard error of 0.03kgNha−1 y−1. Isotope measurements indicated that in aerobic conditions the ratio of N2O emissions to gross mineralisation was 0.01–0.05%. Liming did not make a significant change to the average N2O emissions. The average of daily N2O emissions are: for the acidic plots 0.96±0.07mgNm−2 d−1 and for the limed plots 0.88±0.04mgNm−2 d−1. We conclude that under the conditions experienced at Wagga Wagga, which are typical of many Australian pastures, liming does not change the N2O emissions. Measurements from the urine-treated soil showed that between 0.1 and 0.2% of the nitrogen in the urine was released as N2O. These and a compilation of other emission factors for N2O emissions from urine addition to pasture give a median emission factor of 0.7%, significantly smaller than the two default values of 2% and 1% recommended by the Revised 1996 and the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. [Copyright &y& Elsevier]