Phosphorus fertilisation under nitrogen limitation can deplete soil carbon stocks: evidence from Swedish meta-replicated long-term field experiments

Abstract

Abstract. Increasing soil organic carbon (SOC) in agricultural soils can mitigate atmospheric CO 2 concentration and also contribute to increased soil fertility and ecosystem resilience. The role of major nutrients in SOC dynamics is complex, due to simultaneous effects on net primary productivity (NPP) that influence crop residue carbon inputs and in the rate of heterotrophic respiration (carbon outputs). This study investigated the effect on SOC stocks of three different levels of phosphorus and potassium (PK) fertilisation rates in the absence of nitrogen fertilisation and of three different levels of nitrogen fertiliser in the absence of PK fertiliser. This was done by analysing data from 10 metareplicated Swedish long-term field experiments (> 45 years). With N fertilisation, SOC stocks followed yield increases. However, for all PK levels, we found average SOC losses ranging from −0.04 ± 0.09 Mg ha −1 yr −1 (ns) for the lowest to −0.09 ± 0.07 Mg ha −1 yr −1 (p = 0.008) for the highest application rate, while crop yields as a proxy for carbon input increased significantly with PK fertilisation by 1, 10 and 15 %. We conclude that SOC dynamics are mainly outputdriven in the PK-fertilised regime but mostly input-driven in the N-fertilised regime, due to the much more pronounced response of NPP to N than to PK fertilisation. It has been established that P rather than K is the element affecting ecosystem carbon fluxes, where P fertilisation has been shown to (i) stimulate heterotrophic respiration, (ii) reduce the abundance of arbuscular mycorrhizal fungi and (iii) decrease the crop root : shoot ratio, leading to higher root-derived carbon input.The higher export of N in the PK-fertilised plots in this study could (iv) have led to increased N mining and thus mineralisation of organic matter. More integrated experiments are needed to gain a better understanding of the relative importance of each of the above-mentioned mechanisms leading to SOC losses after P addition.

Increasing nitrogen supply to phosphorus-deficient Medicago sativa decreases shoot growth and enhances root exudation of tartrate to discharge surplus carbon dependent on nitrogen form

“…It is likely that, in the present study, in response to N addition, due to reduced C requirement for root biomass, the release of C by roots increased. We did not observe a negative relationship between RMR and P-fertilization in the present study, similar to the results in some previous studies on alfalfa growing in alkaline soils (He et al 2017b;He et al 2021), although often a greater RMR can enhance a plant's P acquisition under P de ciency (Lynch and Ho 2005), and RMR usually declines with P-fertilization (Graciano et al 2006;Poeplau et al 2016). In contrast, RMR of alfalfa increased with P-fertilization in a loess soil, likely due to the plant's response to N-limitation induced by P-fertilization (Zhang et al 2021).…”

Conservation Agriculture Effects on Soil Water Holding Capacity and Water-Saving Varied with Management Practices and Agroecological Conditions: A Review

“…For example, the annual applications of farmyard manure at 35 tons ha −1 increased SOC by 1.8-4.3% year −1 for the whole soil profile in the first 20 years; then, SOC increased by 0.7% for 40-60 years [179]. Similarly, excess long-term application of N, P, and K increased SOC storage by 0.16% year −1 [180]. However, the continuous application of such amounts of organic or inorganic fertilizers tend to be unfeasible under real field conditions.…”

Fate of straw- and root-derived carbon in a Swedish agricultural soil

“…Furthermore, N fertilisation is reported to increase soil C retention due to increased microbial use efficiency (Kirkby et al 2013;Kirkby et al 2014). Under N deficiency, decomposers have been shown to use fresh organic matter as an energy source for the break-up of more recalcitrant, but nutrient rich organic matter (Murphy et al 2015;Poeplau et al 2016a). However, the relevance of each of these mechanisms for SOM dynamics is not sufficiently understood (Poeplau et al 2016a).…”

“…Under N deficiency, decomposers have been shown to use fresh organic matter as an energy source for the break-up of more recalcitrant, but nutrient rich organic matter (Murphy et al 2015;Poeplau et al 2016a). However, the relevance of each of these mechanisms for SOM dynamics is not sufficiently understood (Poeplau et al 2016a). In the Ultuna experiment, a factorial combination of straw and N fertilisation is applied.…”