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The storage of carbon (C) in cultivated soils can be increased with the adoption of different practices. The objective of this study was to determine soil organic carbon (SOC) storage in the 0‐ to 90‐cm depth profile, in four different soil layers (0–15, 15–30, 30–60 and 60–90 cm) in a long‐term (29 years) experiment established in 1986 on a rainfed Mediterranean Vertisol in southern Spain. The treatments studied were: conventional tillage (CT) versus no‐tillage (NT); five 2‐year crop rotations (wheat–chickpea, wheat–sunflower, wheat–bare fallow, wheat–faba bean, and continuous wheat; and nitrogen (N) fertilizer applied to wheat at four rates (0, 50, 100 and 150 kg N ha−1). The SOC accumulation was higher in the 30–60‐cm layer (9.2 Mg ha−1) due to the size of the characteristic cracks of Vertisols under semiarid conditions. Over the 29‐year study period, the SOC in the 0–90‐cm layer increased by 23.6 Mg ha−1 due to the change in residue management. The NT treatment exhibited a higher mean annual rate of organic C accumulation compared with the CT treatment (1.0 and 0.66 Mg ha−1 year−1, respectively) due to the retention of the mulched residue. Additionally, crop rotation influenced the rate of organic C accumulation, with wheat‐faba bean, wheat‐sunflower and continuous wheat exhibiting the highest levels of C storage in comparison to the other treatments. In rainfed Mediterranean agriculture, the selection of no‐tillage along with a rotation with legumes is key to improving soil fertility and increasing C reserves and the rate of C accumulation by soil. Highlights: The SOC increase over the 29‐year study period was 23.6 Mg ha−1 in the 0–90‐cm soil profile.The characteristic cracks of Vertisol increase SOC stocks in deeper soil layers.No tillage accumulated 66.2% more SOC than conventional tillage in the 0–90‐cm profile.The wheat–sunflower rotation had the highest annual rate of C sequestration (1 Mg ha−1 year−1) and wheat–chickpea the lowest (0.6 Mg ha−1 year−1) over 29 years. [ABSTRACT FROM AUTHOR]

Abstract: The application of an adequate rate and splitting of nitrogen (N) is essential for the efficient use of N fertiliser and to maintain the economic sustainability of cropping systems. A 3-year field experiment was conducted on a Vertisol under Mediterranean conditions to determine the effect of tillage systems, crop rotation, and variations in N timing on the grain yield and N recovery of 15N-labelled fertiliser (N R) in hard red spring wheat (Triticum aestivum L.). The experiment was designed as a randomised complete block with a split–split plot arrangement and 3 replications. The main plots were tillage system (no-tillage [NT] and conventional tillage [CT]), and the subplots were the preceding crop with 2-year rotations (wheat–sunflower [WS], wheat–chickpea [WC], and wheat–faba bean [WFB]). Sub-subplots were the N timing (all at the same rate of 100kgNha−1), and the fertiliser was applied 50% at sowing and 50% at stem elongation and 50% at tillering and 50% at stem elongation. The area of each basic plot was 50m2 (5m×10m). The residual NO3–N content (0–90cm) was significantly higher in CT than in NT, the opposite occurring with grain yield. The N R of NT was greater than that of CT. According to the previous crop, the N R was WS>WFB=WC. The soil nitrate content was twice as much when the preceding crop was a legume compared with sunflower and the wheat yields were as follows: WFB>WC>WS. Although the N timing did not have an effect on overall grain yield, the interactions with year, tillage system and previous crop were significant. The average recovery of 15N fertiliser by wheat was 44.6%, with 33.7% obtained in the grain (41% in stem elongation, 32% in tillering and 27% in sowing). The habitual use of high rates of N fertiliser and the frequency of dry years in the agrosystem studied generated a progressive accumulation of residual in the soil profile. This can represent an important source of mineral N for the cereal and can reduce the need to apply N fertiliser to the crop. [Copyright &y& Elsevier]

Abstract: Studies on the growth of faba bean (Vicia faba L.) root systems in Vertisols under Mediterranean climates are practically non-existent. A three-year field study (2003–2004, 2005–2006 and 2006–2007) was conducted on a typical Vertisol (in southern Spain) to determine, using a minirhizotron system, the effects of tillage on root growth in faba bean grown in continuous rotation with wheat (Triticum aestivum L.) as part of the long-term “Malagón” experiment that started in 1986. Tillage treatments were no-tillage (NT) and conventional tillage (CT). The parameters measured were root length (RL), root diameter (RD), root biomass (RB), seed yield and aboveground biomass. Root growth measures with minirhizotron were carried out at six soil depths for five growth stages throughout the faba bean growing season. For the calculation of RB, soil cores were collected during flowering from the same six soil depths. NT was more favorable for the development of the faba bean root system when compared with CT. This can be attributed to improved physical properties of the soil under NT, which improves the water conditions of the soil. [ABSTRACT FROM AUTHOR]

Abstract: The quantification of the below-ground N of legumes is a key to understand its effect on soil N fertility and the N economy of subsequent legume-based rotations. Significant amounts of the N fixed by legumes are incorporated into the soil as fallen leaves and stems. However, the N from roots, nodules and root exudates has rarely been quantified under field conditions, nor have the management effects been evaluated. This study measured the effects of tillage system [no-tillage (NT) and conventional tillage (CT)] on N rhizodeposition in faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) during a 3-year period (2003–2004, 2005–2006 and 2006–2007) in a Vertisol under rainfed Mediterranean conditions. Faba bean and chickpea plants were labelled in situ with 15N using stem feeding and leaf feeding, respectively. NT increased the N derived from rhizodeposition (NdfR) with respect to CT (135 vs. 68kg Nha−1 in faba bean and 115 vs. 97kg Nha−1 in chickpea). Such differences between tillage methods can be attributed to the more favourable conditions for root growth produced by NT. NdfR was significantly influenced by depth; in faba bean, the greatest amount (70%) was found in the 0–30cm layer, whereas in chickpea, 41% of the NdfR was concentrated in the 30–60cm depth. The 54% and 61% of total plant N was NdfR (in faba bean and chickpea, respectively) representing 90% of the below-ground plant N in both crops. Our results show that the N derived from rhizodeposition is an important source for N balance and is a key to soil fertility in rain-fed Mediterranean cropping systems. [ABSTRACT FROM AUTHOR]

Abstract: Roots and the nutrients that they deposit into the soil are a natural source of N for a current crop, or a subsequent crop in the case of rotations. Despite the importance of this process, there are few field studies of rhizodeposition due to methodological difficulties. A two-year field study was conducted on a typical Mediterranean rainfed Vertisol to determine the effects of the tillage system on N rhizodeposition in wheat (Triticum aestivum L.). The tillage treatments were no-tillage (NT) and conventional tillage (CT). Wheat plants were labelled in situ with 15N using a leaf feeding method. The total amount of N that was deposited by the roots in the full soil profile (0–75cm) over two years was an average of 93kgha−1. The N derived from rhizodeposition (NdfR) represented 40% of the total N content and 82% of belowground N for the wheat plant. The NdfR was higher under NT only in the first layer of the soil (0–15cm). Fifty percent of the NdfR in the soil profile was observed within the first 15cm, increasing to 74% within the first 30cm. The amount of NdfR can be important for understanding farming systems and improving their management, especially the application of fertilizers. [Copyright &y& Elsevier]