No abstract

The combined long‐term effects of tillage method and crop rotation on crop yield have not been studied in rainfed systems under Mediterranean climates. A field study was conducted from 1988 to 1994 to determine the effects of tillage (TILL), crop rotation and (ROT) N fertilizer on wheat (Triticum aestivum L.) yield in a rainfed Mediterranean region. Tillage treatments include no tillage (NT) and conventional tillage (CT). Crop rotations were wheat‐sunflower (Helianthus annuus L.) (WS), wheat‐chickpea (Cicer arietinum L.) (WCP), wheatfababean (Vicia faba L.) (WFB), wheat‐fallow (WF), and continuous wheat (CW), with N fertilizer rates of 50, 100, and 150 kg N ha−1. A split‐split plot design with four replications was used. Differences in rainfall during the growing season had a marked effect on wheat yield. Amount of rainfall during the vegetative period for wheat (November‐February) was highly correlated with yield because of the high water‐retention capacity of Vertisols (Typic Haploxerert). In dry years, wheat yield was greater under NT than under CT; the opposite was true in wet years. The TILL ✕ ROT interaction was also significant in the drought years; the wheat yield under NT was greater for CW and the WFB and WF rotations than under CT. Wheat yields ranked by crop rotation were: WFB > WF >> WCP > WS >> CW. Wheat did not respond to N fertilizer when rainfall was below 450 mm during the growing season. Using these results strategies can be developed for establishing the N fertilizer rate applied to wheat as a function of rainfall, the preceding crop, and residual N in soil in order to optimize wheat yield and reduce nitrate pollution to groundwater.

No abstract

No abstract

Short rotation willow coppice (SRC) has been investigated for the influence of K, Ca, Mg, Fe and P on is pyrolysis and combustion behaviours. These metals are the typical components that appear in biomass. The willow sample was pre-treated to remove salts and metals by hydrochloric acid, and this demineralised sample was impregnated with each individual metal at the same mol/g biomass (2.4x10 -4 mol g -1 demineralised willow). Characterisation was performed using thermogravimetric analysis, and differential thermal analysis (DTA) for combustion. In pyrolysis, volatile fingerprints were measured by means of pyrolysis -gas chromatography -mass spectrometry (PY-GC-MS). The yields and distribution of pyrolysis products have been influenced by the presence of the catalysts. Most notably, both potassium and phosphorous strongly catalysed the pyrolysis, modifying both the yield and distribution of reaction products. Temperature programmed combustion TGA indicates that combustion of biomass char is catalysed by all the metals, while phosphorus strongly inhibits the char combustion. In this case, combustion rates follow the order for volatile release/combustion: P>K>Fe>Raw>HCl>Mg>Ca, and for char combustionK>Fe>raw>Ca~Mg>HCl>P. The samples impregnated with phosphorus and potassium were also studied for combustion under flame conditions, and the same trend was observed, i.e. both potassium and phosphorus catalyse the volatile release/combustion, while, in char combustion, potassium is a catalyst and phosphorus a strong inhibitor, i.e. Kimpregnated > (faster than) raw > demineralised >> P-impregnated. IntroductionBiomass and energy crops are being considered as serious options for reducing carbon dioxide emissions from electricity production. Biomass includes a vast range of materials including agricultural and forestry residues, lignocellulosic components of wastes, as well as energy crops. In the UK there are financial incentives for using biomass grown specifically for electricity production, i.e. energy crops, and this has started to develop the supply chain for, in particular, short rotation willow coppice and Miscanthus. A number of studies have examined the agronomy and the variability of these and other energy crops, in terms of "fuel quality" attributes, particularly the inorganic content. 1,2 The mix of inorganics affects the ash behaviour during combustion and this has been the subject of a number of reviews.The main plant nutrients needed for energy crop production are nitrogen, phosphorus, and potassium. Other typical metals present in the fuel are Al, Ca, Fe, Mg, Na and Si. Similarly the main inorganic components in SRC bark clonal varieties have been reported to vary in the range 0.09-0.12 wt % P, 0.2-0.5 wt% K, 0.9-1.5 wt% Ca and 0.05-0.16 wt% Mg, while for the stems the ranges reported are lower: 0.04-0.07 wt% P, 0.1-0.2 wt% K, 0.5-0.9 wt% Ca and 0.02-0.05 wt% Mg. 5Pyrolysis temperature, heating rate, and biomass type are important factors influencing the volatilisation of alkali species in the biomass. 6...