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Abstract: Excessive application of fertiliser in agriculture can have detrimental effects, one of which is diffuse contamination with nitrates. An 18-year field study was conducted on a typical rainfed Mediterranean Vertisol to determine the effects of the tillage system, crop rotation and N fertiliser rate on the long-term NO3 −-N content in the soil profile (0–90cm). The experiment was designed as a randomised complete block with a split-split plot arrangement and 3 replications. The main plots tested the effects of the tillage system (no-tillage and conventional tillage); the subplots tested crop rotation, with 2-year rotations (wheat–wheat, wheat–fallow, wheat–chickpea, wheat–faba bean and wheat–sunflower); and the sub-subplots tested the N fertiliser rate (0, 50, 100 and 150kgNha−1). The nitrate content increased with time. The tillage system showed an inconsistent effect on nitrates, although, overall, nitrate levels were higher under conventional tillage than with no-tillage. The wheat–faba bean rotation induced a larger accumulation of soil nitrates. Nitrates usually accumulated to a greater extent in the 30–60-cm depth of soil. As a rule, farmers should know the amount of residual N existing in the soil prior to crop fertilisation in order to avoid over-fertilisation. [Copyright &y& Elsevier]

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: A well-developed root system is crucial for plant growth, especially under dryland farming conditions. A two-year field study (2003–2004 and 2005–2006) was conducted to determine the effects of the tillage system on root growth in chickpea (Cicer arietinum L.) grown in continuous rotation with wheat (Triticum aestivum L.) on a typical Vertisol in southern Spain as part of the long-term “Malagon” experiment begun in 1986. The tillage treatments were either no tillage (NT) or conventional tillage (CT), and the experiment was designed as a randomized complete block with three replications. Both soil cores and a minirhizotron were used to evaluate the root system. Measurements of the root parameters were performed at different depths and included the following: root length, root biomass, root nitrogen and root length density. Root length measurements were performed during five chickpea growth stages. The CT was more favourable than NT for chickpea root development (0.34mmcm−3 versus 0.18mmcm−3), which is one of the factors that induced higher yields during the drier year. The nitrogen content of the roots represented 15% of the total N extracted by the plant. The measured root lengths were larger when using the soil core method than with the minirhizotron (2.5mmcm−3 versus 1.3mmcm−3), which can be attributed to the cracks that occur in Mediterranean Vertisols that can separate the tube from the soil, resulting in the underestimation of the root length. [Copyright &y& Elsevier]

Highlights: [•] No-tillage registered higher water content in the soil at sowing than in conventional tillage. [•] Grain yield improved with no-tillage system. [•] Water use was superior in the no-tillage system than in the conventional tillage. [ABSTRACT FROM AUTHOR]

Abstract: Efficient management of legumes in order to maximize benefits depends on a correct field assessment of N2 fixation. A field experiment was conducted during a 6-year period (2001–2002 to 2006–2007) in Córdoba (Southern Spain) on a rainfed Vertisol within the wheat-chickpea and wheat-faba bean rotation framework of a long-term experiment started in 1986. The aim was to determine the effect of tillage systems [no tillage (NT) and conventional tillage (CT)] on chickpea and faba bean N2 fixation. Fixation was calculated using the 15N isotopic dilution (ID) and 15N natural abundance (NA) methods with the reference being the wheat crop. The strong inter-annual rain variation caused great differences in the behaviour of both leguminous plants with regard to grain yield, nodule biomass and N2 fixation. The NT system showed more nodule biomass than the CT system in both legumes. The ID method was more accurate than the NA method in determining N2 fixation. The average amount of fixed N in faba bean (80kgha−1 year−1) was much greater than that in chickpea (31kgha−1 year−1). The Vertisol under the NT system offered more favourable conditions for the stimulation of the N2 fixation, with fixed N values that were significantly higher than under CT. The N added to the system through N2 fixation was low in faba bean and virtually nonexistent in chickpea, only in terms of above-ground biomass. [Copyright &y& Elsevier]