Initiation of soil formation in weathered sulfidic Cu-Pb-Zn tailings under subtropical and semi-arid climatic conditions

Field evidence has been scarce about soil (or technosol) formation and direct phytostabilization of base metal mine tailings under field conditions. The present study evaluated key attributes of soil formation in weathered and neutral Cu-Pb-Zn tailings subject to organic amendment (WC: woodchips) and colonization of pioneer native plant species (mixed native woody and grass plant species) in a 2.5-year field trial under subtropical and semi-arid climatic conditions. Key soil indicators of engineered soil formation process were characterized, including organic carbon fractions, aggregation, microbial community and key enzymatic activities. The majority (64-87%) of the OC was stabilized in microaggregate or organo-mineral complexes in the amended tailings. The levels of OC and water soluble OC were elevated by 2-3 folds across the treatments, with the highest level in the treatment of WC and plant colonization (WC+P). Specifically, the WC+P treatment increased the proportion of water stable macroaggregates. Plants further contributed to the N rich organic matter in the tailings, favouring organo-mineral interactions and organic stabilization. Besides, the plants played a major role in boosting microbial biomass and activities in the treated tailings. WC and plants enhanced the contents of organic carbon (OC) associated with aggregates (e.g., physically protected OC), formation of water-stable aggregates (e.g., micro and macroaggregates), chemical buffering capacity (e.g., cation exchange capacity). Microbial community and enzymatic activities were also stimulated in the amended tailings. The present results showed that the formation of functional technosol was initiated in the eco-engineered and weathered Cu-Pb-Zn tailings under field conditions for direct phytostabilization

Managing cattle grazing intensity: effects on soil organic matter and soil nitrogen

Extensive cattle grazing is the dominant land use in northern Australia. It has been suggested that grazing intensity and rainfall have profound effects on the dynamics of soil nutrients in northern Australia’s semi-arid rangelands. Previous studies have found positive, neutral and negative effects of grazing pressure on soil nutrients. These inconsistencies could be due to short-term experiments that do not capture the slow dynamics of some soil nutrients and the effects of interannual variability in rainfall. In a long-term cattle grazing trial in northern Australia on Brown Sodosol–Yellow Kandosol complex, we analysed soil organic matter and mineral nitrogen in surface soils (0–10 cm depth) 11, 12 and 16 years after trial establishment on experimental plots representing moderate stocking (stocked at the long-term carrying capacity for the region) and heavy stocking (stocked at twice the long-term carrying capacity). Higher soil organic matter was found under heavy stocking, although grazing treatment had little effect on mineral and total soil nitrogen. Interannual variability had a large effect on soil mineral nitrogen, but not on soil organic matter, suggesting that soil nitrogen levels observed in this soil complex may be affected by other indirect pathways, such as climate. The effect of interannual variability in rainfall and the effects of other soil types need to be explored further

Combining ability analysis for seed yield and component traits in Indian mustard [Brassica juncea (L.) Czern & Coss.]

The present investigation on combining ability analysis for seed yield and itscomponent characters in Indian mustard was carried out under two differentenvironments i.e. timely sown (E1) and late sown (E2) which revealed that both additiveand non-additive variances were present for the expression of all the characters studied inboth the environments and the former playing major role. The study of GCA indicatedthat the genotypes namely RH-9617, RH-9806 RH-9615 and were good combiners forearliness, siliqua length, 1000-seed weight, number of seeds/siliqua, primarybranches/plant and oil content. Hence, these parents could be used in crossingprogrammes for achieving further improvement. The study of SCA indicated that thecross combinations namely RH-9710 x RH-9806 and RH-9707 x RH-9806 should beexploited through heterosis breeding or should be used in recombination breeding forobtaining higher seed yield

Microbial energy and matter transformation in agricultural soils

Low bioavailability of organic carbon (C) and energy are key constraints to microbial biomass and activity. Microbial biomass, biodiversity and activity are all involved in regulating soil ecosystem services such as plant productivity, nutrient cycling and greenhouse gas emissions. A number of agricultural practices, of which tillage and fertiliser application are two examples, can increase the availability of soil organic C (SOC). Such practices often lead to reductions in soil aggregation and increases in SOC loss and greenhouse gas emissions. This review focuses on how the bioavailability of SOC and energy influence the ecology and functioning of microorganisms in agricultural soils. Firstly we consider how management practices affect the bioavailability of SOC and energy at the ecosystem level. Secondly we consider the interaction between SOC bioavailability and ecological principles that shape microbial community composition and function in agricultural systems. Lastly, we discuss and compare several examples of physiological differences that underlie how microbial species respond to C availability and management practices. We present evidence whereby management practices that increase the bioavailability of SOC alter community structure and function to favour microbial species likely to be associated with increased rates of SOC loss compared to natural ecosystems. We argue that efforts to restore stabilised, sequestered SOC stocks and improve ecosystem services in agricultural systems should be directed toward the manipulation of the microbial community composition and function to favour species associated with reduced rates of SOC loss. We conclude with several suggestions regarding where improvements in multi-disciplinary approaches concerning soil microbiology can be made to improve the sustainability of agricultural systems