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• Suberin contributed more to bulk SOC stocks than cutin in topsoil and subsoil. • Of all monomers, suberin monomers were affected most by deep-ploughing. • Effects of deep-ploughing on suberin SOC stocks were not uniform for sandy and silty sites. • Changes in SOC stocks in topsoil and subsoil after deep-ploughing affected input of root-derived C. Roots can add significant amounts of carbon (C) to the subsoil, which improves soil physical properties and can mitigate climate change. About 5% of croplands in Germany have been deep-ploughed (30–120 cm) at least once. This can provide better root access to the subsoil and may increase yields, but little is known on the fate of root-derived C in the subsoil (at depth greater than 30 cm) after deep-ploughing. We hypothesized that five decades after deep-ploughing, root-derived C stocks were higher than conventionally ploughed treatments due to better root development. We analysed suberin and cutin monomers as tracers for root- and shoot-derived C at three former deep-ploughed sites in Northern Germany with different soil textures and deep-ploughing depths. Concentrations of suberin monomers in the soil positively correlated with root biomass; this was most pronounced at one sandy site, but had higher variability at the other two sites due to crops with different root systems in the crop rotation, lower root development, and more favourable conditions for C decomposition. Suberin contributed more to the bulk soil organic carbon (SOC) stocks than cutin throughout the soil profile at all sites. The contribution of suberin monomers to the bulk SOC stock at silty site Banteln and the sandy site Essemühle was 38% higher in the deep-ploughed plots than at the reference plot, respectively, these differences were most visible in the subsoil of Essemühle. We conclude that as C stocks and root development increase, suberin SOC stocks also increase, especially in sandy subsoils with low pH. [ABSTRACT FROM AUTHOR]

[Display omitted] • Topsoil SOC stocks and soil structure recovered 26 years after topsoil removal. • Topsoil buried under the plough layer non-linearly lost 30–50% of SOC in 55 years. • Topsoil SOC recovery and stability of buried SOC was dependent on N fertilisation. Erosion of fertile topsoil means severe land degradation and yield loss. Here, we show that reformation of the fertile topsoil and crop yield increase is possible by good agricultural management within a few decades. Evidence relies on a unique long-term field experiment in NE Germany, where in 1964 the sandy soil (Luvisol) had been excavated to 52 cm and refilled with subsoil material of 52 cm thickness. Undisturbed trials served as controls, these were all combined with either no fertilisation, mineral fertilisation or a combined mineral and organic fertilisation. It took only 26 years until new topsoil had been formed. Its soil organic carbon (SOC) and total N stocks and the aggregate size distributions equalled that of the other treatments; SOC sequestration corresponded to 28 Mg SOC ha−1. The former topsoil buried below the plough layer lost 30–50 percent of its SOC during 5 decades in a non-linear manner. We conclude that our current agricultural tools can restore degraded arable land rather fast and contribute to climate change mitigation through a significant SOC sequestration as well. [ABSTRACT FROM AUTHOR]

Biopores are characterised by high concentrations of plant available nutrients and provide preferential pathways for root growth into the subsoil, thereby potentially enabling plants to access phosphorus (P) resources located in the subsoil. Here, we sampled biopores from a replicated agricultural field trial in Klein-Altendorf, Germany, to analyse their nutrient composition and P speciation as determined by Hedley sequential extraction and X-ray absorption near edge structure (XANES) spectroscopy. In addition, we analysed the oxygen isotopic composition of HCl P (δ 18 O HCl P ) as an indicator of long-term effects of biological P turnover. We found that biopore effects were most pronounced in the subsoil, where the concentration of easily extractable (labile) P tended to be greater in biopores than in bulk soil, as evident in both Hedley sequential extraction and XANES spectroscopy. We assume that these findings result from inputs of organic matter from the topsoil as well as an input of Ca-particles into subsoil biopores by earthworm activity. Biologically cycled P was subsequently precipitated as Ca-P as evident by δ 18 O HCl P values close to equilibrium in biopores even at great depths. When incubating bulk soil samples with 18 O-labelled water, however, we observed a significant increase of δ 18 O HCl P values in the topsoil, but only small if any changes of δ 18 O HCl P values in the subsoil. Thus, biopores present hotspots of P cycling in the subsoil, but the effect of biopores on overall P turnover in the bulk subsoil is limited. [ABSTRACT FROM AUTHOR]

• Model-based estimation of spring wheat root growth, water, N and P uptake reveals importance of subsoil and pre-crops interactions. • Only in years with dry spell, subsoil N uptake by spring wheat was higher after chicory as pre-crop compared to fescue. • Lucerne as pre-crop induced an enhanced P and N uptake from deep soil layers by the following main crop. Water and nutrients in the subsoil are valuable resources in crop production but the availability varies with weather conditions and management, in particular the crop rotation. Moreover, constraints such as mechanical resistance or water stress may impede root growth into deeper soil layers. This study presents a simulation-based stochastic approach to investigate the impact of precrops on spring wheat growth and water and nutrient uptake under varying weather conditions. The effect of the three precrops lucerne, chicory and tall fescue on spring wheat growth was investigated extensively in a field trial. For model calibration and evaluation, we selected a year with a dry spell (2010) and one with abundant precipitation (2012) and used field data on biopore densities in the subsoil, crop development, leaf area index, shoot biomass, grain and straw yield, nitrogen (N) and phosphorus in shoot, grain and straw, root length densities, as well as soil moisture and soil N and P concentrations for several soil depths. The modeling framework consisted of the modeling platform SIMPLACE and the stochastic weather generator LARS-WG to consider climate variability. The weather generator was used to generate a synthetic time-series of daily weather data (100 years) based on observed weather data of the experimental site in order to simulate 100 spring wheat growth periods under recent climate conditions for each precrop. Moreover, a 100 year long time-series with annual dry spells in June was generated to analyze the effect of drought during flowering on crop water and nutrient uptake. During the scenario runs, the model was annually reinitialized at sowing to provide identical initial conditions. The experimental data over two years showed that spring wheat growth as well as total N and P uptake were clearly enhanced after precrop lucerne. This was comfirmed by the simulations over 100 years. The simulation runs also prompt that precrop fescue led to higher spring wheat biomass and enhanced subsoil and total water and N uptake in years with normal precipitation pattern compared to precrop chicory, but in drier years, it was vice versa. Because plants compensate for moderate nutrient or water deficiencies, small differences in grain yield may hide significant differences in total and in subsoil N and P uptake. [ABSTRACT FROM AUTHOR]