agronomy Article Dissection of the Contributing Factors to the Variable Response of Crop Yield to Surface Applied Lime in Australia Yvette M. Oliver 1, * , Chris Gazey 2 , James Fisher 3 and Michael Robertson 1   Citation: Oliver, Y.M.; Gazey, C.; Fisher, J.; Robertson, M. Dissection of the Contributing Factors to the Variable Response of Crop Yield to Surface Applied Lime in Australia. Agronomy 2021, 11, 829. https:// doi.org/10.3390/agronomy11050829 Academic Editor: Carlos García-Delgado Received: 31 March 2021 Accepted: 20 April 2021 Published: 23 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Commonwealth Scientific Industrial Research Organisation (CSIRO), Underwood Avenue, Floreat, WA 6014, Australia; Michael.Robertson@csiro.au 2 Department of Primary Industries and Regional Development (DPIRD), East Perth, WA 6004, Australia; chris.gazey@dpird.wa.gov.au 3 Désiree Futures, York, WA 6302, Australia; james@desireefutures.net.au * Correspondence: yvette.oliver@csiro.au Abstract: Modern agricultural farming systems acidify the soil profile due to application of fertilisers with acidifying properties. In most parts of Australia, lime has been used to improve agricultural soil conditions and restore its productive potential. The observed response of crop yield to applied lime often varies with soil type, acidity profile and seasonal conditions, so it is difficult to specify the expected yield response in a given situation. We conducted a meta-analysis of 86 agricultural field trials from Western Australia (WA), New South Wales (NSW) and Victoria (VIC) where various rates of lime had been applied to the soil surface and crop yield (wheat, barley, canola, lupin or field pea) measured for a number of years after the initial application. Information from the meta-analysis was then paired with output from a crop simulation model, where the water-limited yield potential was estimated for both a neutral and acidified soil profile. The average increase in yield to applied lime across all locations and crops was 12%, but the response ranged from 0 to 185%. A trend was observed, where sites with topsoil pH (CaCl 2 ) < 5 and subsoil pH < 4.5 had the greater benefit to liming. Soil type had little effect on the percentage yield increase. Overall, responses to applied lime were most likely when the yield of the trial site was at 50% of water-limited yield potential (or less), the quantity of lime applied was greater than 2.5 t ha -1 and the time since lime had been applied was greater than three years (with the maximum response occurring from four and sometimes up to eight years after liming). Therefore, soil pH measurements, combined with an assessment of actual yield relative to potential yield, provide the best guide to the response to surface applied lime and this response is likely to take more than four years to be realised. Keywords: soil acidity; liming; crop yield; soil constraints 1. Introduction The soil in the wheat belt of Western Australia (WA), New South Wales (NSW) and Victoria (VIC) has many attributes that limit crop production. Most soil is derived from ancient granitic rocks and sediments. Weathering and leaching of these rocks have resulted in predominately sandy textured soil with acidic pH, low nutrient levels and low buffering capacity. The agricultural system has magnified these problems. Processes such as the removal of grain, use of legume crops and pastures, application of fertiliser with acidifying properties, and leaching processes have increased the rate of soil acidification, particularly under more intensive crop production [1,2]. Soil acidification in the agricultural and cropping areas affects an estimated 14.25 million hectares (~80%) in WA [3,4], 16–20 million hectares (~50%) in NSW [5] and 3 million hectares (23%) in VIC [6]. The combined impact of surface and subsurface acidity has been estimated to be responsible for an annual loss of income to the grains and agricultural industry of $500–1600 million in WA [7], $378 million in NSW [8] and $470 million in VIC [8]. Agronomy 2021, 11, 829. https://doi.org/10.3390/agronomy11050829 https://www.mdpi.com/journal/agronomy