Abstract
The bioavailability and fractionation of Cu reflect its deliverability in soil. Little research has investigated Cu supply to crops in soil under long-term rotation and fertilisation on the Loess Plateau. A field experiment was conducted in randomized complete block design to determine the bioavailability and distribution of Cu fractions in a Heilu soil (Calcaric Regosol) after 18 years of rotation and fertilisation. The experiment started in 1984, including five cropping systems (fallow control, alfalfa cropping, maize cropping, winter wheat cropping, and grain-legume rotation of pea/winter wheat/winter wheat + millet) and five fertiliser treatments (unfertilised control, N, P, N + P, and N + P + manure). Soil samples were collected in 2002 for chemical analysis. Available Cu was assessed by diethylene triamine pentaacetic acid (DTPA) extraction, and Cu was fractionated by sequential extraction. Results showed that DTPA-Cu was lower in cropping systems compared with fallow control. Application of fertilisers resulted in no remarkable changes in DTPA-Cu compared with unfertilised control. Correlation and path analyses revealed that soil pH and CaCO3 directly affected Cu bioavailability, whereas available P indirectly affected Cu bioavailability. The concentrations of Cu fractions (carbonate and Fe/Al oxides) in the plough layer were lower in cropping systems, while the values in the plough sole were higher under grain-legume rotation relative to fallow control. Manure with NP fertiliser increased Cu fractions bound to organic matter and minerals in the plough layer, and its effects in the plough sole varied with cropping systems. The direct sources (organic-matter-bound fraction and carbonate-bound fraction) of available Cu contributed much to Cu bioavailability. The mineral-bound fraction of Cu acted as an indicator of Cu supply potential in the soil.
Highlights
Copper (Cu) is an essential micronutrient in crop production
A comparison of different systems revealed that diethylene triamine pentaacetic acid (DTPA)-Cu concentrations were lower in the cropping systems compared with fallow control (FW) (Fig 1)
DTPA-Cu in the plough layer was lower in AC-Ctrl than in FW, while no difference occurred in the plough sole
Summary
The bioavailability of Cu in soil is regulated by its adsorption, desorption and solubility [1, 2]. The adsorption and desorption processes of Cu strongly depend on the soil microenvironment and chemical properties, such as pH, CaCO3, organic matter, and available phosphorous (P) levels [2,3,4,5]. Cropping systems and fertilisation practices affect the bioavailability of Cu in soil [6,7,8]. A 9-year fertilisation study found that manure accelerated the depletion of available Cu in a purple paddy soil in southwest China [9]. Investigators have approached the problem of Cu in soil by sequential extractions, with a view to characterizing various available forms of Cu [12]. The water-soluble, exchangeable, and organicallycomplexed Cu forms are available to plants, whereas Cu occluded in oxides of iron (Fe), aluminium (Al) and manganese (Mn) as well as primary and secondary minerals are not readily available [13, 14]
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