Diffusive gradients in thin films predicts crop response better than calcium-acetate-lactate extraction

Nutr Cycl Agroecosyst https://doi.org/10.1007/s10705-021-10173-2 (0123456789().,-volV) ( 01234567 89().,-volV) ORIGINAL ARTICLE Diffusive gradients in thin films predicts crop response better than calcium-acetate-lactate extraction Benjamin Hill . Jakob Santner . Heide Spiegel . Markus Puschenreiter . Walter W. Wenzel Received: 22 February 2021 / Accepted: 15 September 2021 Ó The Author(s) 2021 Abstract Soil P testing has been widely used to predict crop yields, P uptake, and fertilizer demands in agriculture. Diffusive gradients in thin films (DGT) provides a zero-sink soil P test which mimics diffusion-controlled plant uptake and has previously been found to predict P availability to crops better than conventional quantity-based P tests in highly weathered Australian, though not in European soils. Here we tested the performance of DGT and the Austrian and German standard P quantity test calcium acetate lactate (CAL) to explain the variation of crop yield and P uptake response of winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.) in long-term P fertilization experiments at four B. Hill  J. Santner  M. Puschenreiter  W. W. Wenzel (&) Department of Forest and Soil Sciences, Institute of Soil Research, University of Natural Resources and Life Sciences Vienna, Konrad-Lorenz-Straße 24, 3430 Tulln an der Donau, Austria e-mail: J. Santner Department of Crop Sciences, Institute of Agronomy, University of Natural Resources and Life Sciences Vienna, Konrad-Lorenz-Straße 24, 3430 Tulln an der Donau, Austria H. Spiegel Department for Soil Health and Plant Nutrition, Institute for Sustainable Plant Production, Austrian Agency for Health and Food Safety, Spargelfeldstraße 191, 1220 Vienna, Austria different sites in eastern Austria. Phosphorus extracted with DGT (P-DGT) and CAL (P-CAL) correlated well in similar soils but not across sites with large variation in soil and site properties such as carbonate equivalent and water availability. The predictive power of DGT for barley (R2 = 0.42) and wheat grain yield (R2 = 0.32), and P uptake in wheat grains (R2 = 0.36) was clearly superior to that of the CAL, and less dependent on soil properties. The better performance of DGT compared to the quantity test is consistent with diffusion-limited P uptake in the water-limited cultivated soils of eastern Austria. The critical values of P deficiency derived from the Mitscherlich-type fits for barley and wheat at 80% relative yield are 64.9 and 26.2 lg L-1, respectively, consistent with differential P demands of the crops. Keywords Diffusive gradients in thin films (DGT)  Phosphorus  Calcium acetate lactate extraction (CAL)  Austria  Long-term field experiment Introduction Phosphorus (P) is a critical component of cell membranes, nucleic acids, and the energy-rich molecule adenosine triphosphate (ATP), and is central in plant metabolism. Plant P status is therefore critical for maintaining agricultural productivity, which is 123 Nutr Cycl Agroecosyst reflected by the large P fertilizer inputs to managed soils worldwide. However, P is characterized by strong fixation and slow diffusion in soils, and therefore is often the limiting nutrient for plant growth. Furthermore, due to the unique chemistry of P, the total amount measured in soils bears little relation to the fraction which may be available for plant uptake. Plant nutrient demands can be expressed either by internal or external requirements. Internal requirements can be defined by the minimum nutrient uptake necessary to obtain a certain yield level or as nutrient concentration in plant tissue that is associated with near maximum yield. External requirements refer to the nutrient availability in the growth medium, i.e., typically soil. The concept of nutrient availability involves four aspects (Fox 1981; Peaslee and Phillips 1981), i.e. (1) capacity, (2) quantity, (3) intensity, and (4) (rate of) resupply and buffering. Capacity refers to the potential of a given soil to store a nutrient in plantavailable (labile) forms, whereas quantity is defined as the realization of this potential, often measured using an extraction method (e.g., Olsen, Mehlich, Bray or CAL) to target this nutrient pool. Intensity has been commonly defined as nutrient concentration in soil solution (Fox 1981). When plants take up nutrients from the soil solution, they deplete the available pool in the rhizosphere. Plant growth/productivity requirements can only be sustained if the rate of resupply, either through desorption from the solid phase and/or diffusion from the bulk soil towards the root surface equals or exceeds nutrient demand. The ability of the soil solid phase to replenish a nutrient has been described by buffer characteristics using the terms buffer power (BP) (Peaslee and Phillips 1981) or distribution coefficient (Kd). The relative performance of P quantity versus intensity tests has been a matter of debate for some time. Mechanistic modelling and related sensitivity analysis suggest that intensity generally determines uptake in plants more than quantity of P in soil (Barber 1995). However, intensive cropping of ryegrass in pot experiments has also shown that P quantity becomes increasingly important during extended cropping periods (Holford and Mattingly 1976). According to Nawara et al. (2017), quantitycontrolled yield response occurs in sites that have low Kd (defined as the ratio between Olsen P and 0.01 M CaCl2-extractable), while intensity better 123 explains yield response at large Kd values. However, this approach does not consider the extent of saturation of the sorption complex as suggested by Cole and Olsen (1959). The kinetics of P release from the solid phase have been found to follow one fast and one subsequent slow reaction, assigned to two labile P pools with differential desorption kinetics (De Jager and Claassens 2005; Lookman et al. 1995; Maguire et al. 2001; MenezesBlackburn 2016; Smolders 2021; Taddesse et al. 2008). A recent experimental and modelling study demonstrates that P desorption rates control P availability to fast growing crops with small specific root area. This is even more relevant in soils with negative P balance as P desorption rates slow down, and may result in decreased P diffusion rates towards plant roots (Smolders et al. 2021). Apart from differences in the concepts and methodologies to assess external P availability, crop response to soil P is further modified by climate and weather conditions, water availability and P mineralization from organic sources. Moreover, plant roots can actively change their soil environment through various root activities, including release of P-solubilizing compounds. Altogether, these factors and processes create additional variation in crop response that cannot be explained by any soil P test. Most conventional tests use equilibrium-type extraction to target the quantity (e.g., Olsen or CAL) or intensity (e.g., water or 0.01 M CaCl2 (...truncated)