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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: 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]

Little research has examined the influence of tillage system on root growth in wheat grown on rainfed Vertisols. A 3-year field study (2003, 2004 and 2005) was carried out on a typical Vertisol (southern Spain), to determine the effects of tillage system on root growth in spring wheat ( Triticum aestivum L) grown in continuous rotation with faba bean ( Vicia faba L), within the framework of the long-term “Malagón” experiment started in 1986. Tillage treatments were no-tillage (NT) and conventional tillage (CT), and the experiment was designed as a randomized complete block with three replications. The following parameters were measured: above-ground biomass, grain yield, root length density (RLD), root biomass (RB) and root N content. In the topmost 10 cm of soil, higher values were found under CT than under NT for RLD in the rainiest year (20.2 km m−3 vs. 9.6 km m−3 respectively) and for RB (512 kg ha−1 vs. 261 kg ha−1 respectively) in all study years. In deeper layers, no difference was recorded between the two tillage systems. Greater wheat root development in the upper soil layer under CT may reflect the greater soil penetration resistance found in the topmost 10 cm under NT. Root separation using a sieve with a 0.5 mm mesh screen led to a marked underestimation of RLD and RB, with values up to three times higher when using a 0.2 mm mesh screen. Mean wheat root N content in the topmost 30 cm of soil accounted for over 80% of total root N content. The highest grain yield was observed under NT, since this system provided greater water storage in the soil profile in the mostly dry study years. [ABSTRACT FROM AUTHOR]