Long-term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland. VII* Dynamics of nitrogen mineralization potentials and microbial biomass

The dynamics of nitrogen mineralization potential (N0) and mineralization rate constant (k) were studied in six major soils which had been used for cereal cropping for up to 20-70 years. In the top 0.1 m layer of virgin soils, N0 varied from 110 ± 22 mg kg-1 soil (Riverview) to 217 ± 55 mg kg-1 soil (Langlands-Logie), representing about 13% and 11%, respectively, of total N in these soils. Upon cultivation and cropping, N0 declined by 1 7 ± 0.5 mg kg-1 yr-1 (Riverview) to 4.8 ± 2.0 mg kg -1 yr -1 (Billa Billa). This represented 40% clay and k as 0.066 week-1 at 40°C (0.027 week-1 and 0.054 week-1 at 25°C and 35°C, respectively). Organic C and N contained in the 'stabilized' microbial biomass (determined after 30 weeks' pre-incubation) accounted for 1.7-38% of total organic C and 2.0-5.1% of total N in the six soils studied. The microbial biomass C and N declined with cultivation in most soils, biomass N representing 10-23% of the total annual loss of N0. The microbial biomass, urease activity and total N, in addition to a number of other soil properties [e.g. light-fraction (<2 Mg m-3) C, sand-size C, CEC and ESP], were significantly correlated with N0 and k, thus indicating the existence of a myriad of environments for the activity, association and stability of microbial biomass and potentially mineralizable N in soil

Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland. I. Overall changes in soil properties and trends in winter cereal yields

Changes in fertility of some southern Queensland soils resulting from extended periods of cultivation are presented, together with trends in yields of winter cereals on these soils. Six major soils of the cereal-belt, cropped for maximum periods of 20-70 years were examined. These were: Black earths, Waco soil; grey, brown and red clays (brigalow), Langlands-Logie soil; grey, brown and red clays (poplar box), Cecilvale soil; grey, brown and red clays (belah), Billa Billa soil; grey, brown and red clays (coolibah), Thallon soil; red earths, Riverview soil. Organic matter and its constituents, especially total organic C, organic C in the light fraction, total N and mineralizable N, were affected most by cultivation, showing decreases of 19-67% overall. Other soil properties probably associated with organic matter, including bulk density and DTPA (diethylenetriaminepentaacetic acid) extractable manganese, were also significantly affected by cultivation in all soils. Soil properties affected least by cultivation were concentrations of inorganic phosphorus, total and exchangeable potassium, calcium carbonate, and dithionite extractable iron and aluminium. Most other soil properties studied (organic P, total sulfur, pH, exchangeable magnesium and sodium, exchangeable sodium percentage, and oxalate-extractable iron and aluminium) were affected by cultivation in at least four soils. Four factors accounted for 70% of the total variation among the 45 soil properties considered. They appeared to represent organic matter, clay colloids, iron and aluminium oxides, and soluble salts. Dry matter yield and/or N uptake of winter cereal crops (wheat and barley) measured in 1983 showed significant decreasing trends with period of cultivation in all soils

Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland .VII. Dynamics of nitrogen mineralization potentials and microbial biomass

The dynamics of nitrogen mineralization potential (N0) and mineralization rate constant (k) were studied in six major soils which had been used for cereal cropping for up to 20-70 years. In the top 0.1 m layer of virgin soils, N0 varied from 110 ± 22 mg kg-1 soil (Riverview) to 217 ± 55 mg kg-1 soil (Langlands-Logie), representing about 13% and 11%, respectively, of total N in these soils. Upon cultivation and cropping, N0 declined by 1 7 ± 0.5 mg kg-1 yr-1 (Riverview) to 4.8 ± 2.0 mg kg -1 yr -1 (Billa Billa). This represented 40% clay and k as 0.066 week-1 at 40°C (0.027 week-1 and 0.054 week-1 at 25°C and 35°C, respectively). Organic C and N contained in the 'stabilized' microbial biomass (determined after 30 weeks' pre-incubation) accounted for 1.7-38% of total organic C and 2.0-5.1% of total N in the six soils studied. The microbial biomass C and N declined with cultivation in most soils, biomass N representing 10-23% of the total annual loss of N0. The microbial biomass, urease activity and total N, in addition to a number of other soil properties [e.g. light-fraction (<2 Mg m-3) C, sand-size C, CEC and ESP], were significantly correlated with N0 and k, thus indicating the existence of a myriad of environments for the activity, association and stability of microbial biomass and potentially mineralizable N in soil

Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland. I. Overall changes in soil properties and trends in winter cereal yields

Changes in fertility of some southern Queensland soils resulting from extended periods of cultivation are presented, together with trends in yields of winter cereals on these soils. Six major soils of the cereal-belt, cropped for maximum periods of 20-70 years were examined. These were: Black earths, Waco soil; grey, brown and red clays (brigalow), Langlands-Logie soil; grey, brown and red clays (poplar box), Cecilvale soil; grey, brown and red clays (belah), Billa Billa soil; grey, brown and red clays (coolibah), Thallon soil; red earths, Riverview soil. Organic matter and its constituents, especially total organic C, organic C in the light fraction, total N and mineralizable N, were affected most by cultivation, showing decreases of 19-67% overall. Other soil properties probably associated with organic matter, including bulk density and DTPA (diethylenetriaminepentaacetic acid) extractable manganese, were also significantly affected by cultivation in all soils. Soil properties affected least by cultivation were concentrations of inorganic phosphorus, total and exchangeable potassium, calcium carbonate, and dithionite extractable iron and aluminium. Most other soil properties studied (organic P, total sulfur, pH, exchangeable magnesium and sodium, exchangeable sodium percentage, and oxalate-extractable iron and aluminium) were affected by cultivation in at least four soils. Four factors accounted for 70% of the total variation among the 45 soil properties considered. They appeared to represent organic matter, clay colloids, iron and aluminium oxides, and soluble salts. Dry matter yield and/or N uptake of winter cereal crops (wheat and barley) measured in 1983 showed significant decreasing trends with period of cultivation in all soils

Long-term trends in fertility of soils under continuous cultivation and cereal cropping in southern queensland. iii* Distribution and kinetics of soil organic carbon in particle-size fractions

Distribution of soil organic carbon in sand-, silt- and clay-size fractions during cultivation for periods ranging from 20 to 70 years was studied in six major soils used for cereal cropping in southern Queensland. Particle-size fractions were obtained by dispersion in water using cation exchange resin, sieving and sedimentation. In the soils' virgin state no single particle-size fraction was found to be consistently enriched as compared to the whole soil in organic C in all six soils, although the largest proportion (48%) of organic C was in the clay-size fraction; silt and sand-size fractions contained remaining organic C in equal amounts. Upon cultivation, the amounts of organic C declined from all particle-size fractions in most soils, although the loss rates differed considerably among different fractions and from the whole soil. The proportion of the sand-size fraction declined rapidly (from 26% to 12% overall), whereas that of the clay-size fraction increased from 48% to 61% overall. The proportion of silt-size organic C was least affected by cultivation in most soils. It was inferred, therefore, that the sand-size organic matter is rapidly lost from soil, through mineralization as well as disintegration into silt-size and clay-size fractions, and that the clay fraction provides protection for the soil organic matter against microbial and enzymic degradation

Nucleophilicity of Glutathione: A Link to Michael Acceptor Reactivities

Deprotonated glutathione is among the most potent biological nucleophiles and plays an important physiological role in cellular detoxification by forming covalent conjugates with Michael acceptors. The electrophilicity E of various Michael acceptors was characterized recently according to the Patz–Mayr relation lg k2=sN(N+E). We now determined the nucleophilic reactivity (N, sN) of glutathione (GSH) in aqueous solution at 20 °C to connect published GSH reactivities (kGSH) with Mayr's electrophilicity scale (E). In this way, electrophilicities E of more than 70 Michael acceptors could be estimated, which can now be used to systematically predict novel reactions with the multitude of nucleophiles whose nucleophilicity parameters N/sN are known

Effects of a nitrogen-based supplement on intake, live weight and body energy reserves in breeding Bos indicus cross cows

Breeding cows grazing seasonally dry rangelands usually lose substantial live weight (LW) during the dry season, when in late pregnancy. An experiment investigated the effects of feeding a N-based supplement to cows in late pregnancy on voluntary intake, total live weight (T-LW), body condition score (CS) and estimated body net energy content (Body-NE), as well as carry-over effects during lactation. In Phase A for 139 days from mid-pregnancy, mature Bos indicus cross breeders [initially 438 kg T-LW and 5.7 CS units (9-point scale)] were fed in pens on low quality tropical grass hay alone (Control) or with a N supplement (Supplemented). Most (17/22) of the cows calved during this interval. Voluntary hay intake averaged 6.74 g DM/kg T-LW/d in Control cows, and was increased by 35% (P<0.001) when supplement was fed. As a result, feeding supplement reduced loss in conceptus-free live weight (CF-LW) by 30% (from 1.11 kg/d to 0.78 kg/d; P<0.001) and in Body-NE by 20% (from 26.6 to 21.2 MJ NE/d; P = 0.007). Control cows mobilized 24% of maternal LW and 32% of body energy when fed low quality hay during late pregnancy, and these losses were substantially reduced when a N-based supplement was fed. During Phase B, when the lactating cows with their calves grazed a high quality rainy season grass-Stylosanthes pasture, the previously supplemented cows produced more milk (P = 0.065) and their calves grew faster (P = 0.077) in early lactation than Control cows. In addition, during early lactation Control cows exhibited compensatory LW gain relative to the Supplemented cows (0.80 vs. 0.43 kg/d, respectively; P<0.001) and there was no discernable weight difference between the groups by 205 days of lactation. In conclusion the losses in LW and body energy reserves by late pregnant cows fed low quality tropical grass hay were substantially reduced by a N supplement, but the differences were not maintained when the cows subsequently grazed high quality pasture