Tillage and crop residue management affect Vertisol properties and grain sorghum growth over seven years in the semi-arid sub-tropics. 2. Changes in soil properties

Six treatments, disc (D), blade (B) or zero (Z) tillage, each with stubble (crop residue) retained (+) or removed (−), were imposed during fallow periods between annual grain sorghum crops from June 1978 to June 1985 on a grey Vertisol in the semi-arid sub-tropics of central Queensland. Plots were neither irrigated nor fertilized. Soil profiles for chemical analysis were sampled post-harvest and pre-plant after fallow. For surface soil (0–0.1 m and sometimes also 0.1–0.2 m) during the 7 years, net decreases were measured for organic and total carbon, total nitrogen, total bicarbonate extractable and calcium chloride extractable phosphorus, total sulphur, total and exchangeable potassium. Net increases were measured for exchangeable sodium, calcium and magnesium. No net changes were found for dispersion ratios and cation exchange capacity. A net decrease in nitrate at 0.6–1.6 m began after 3 years. At 0–1.6 m, changes in pH, electrical conductivity, chloride and ammonium were negligible.

General means at 0–0.1 m decreased annually from June 1978 by 3.9% for organic carbon, 3.1% for total nitrogen, 7.5% for bicarbonate extractable phosphorus and 10.0% for calcium chloride extractable phosphorus. Decreases in organic carbon and total nitrogen had similar trends for each tillage treatment, being greater with stubble removed than with stubble retained. Decreases were least for Z+. After five years the increase in exchangeable sodium was highest for Z−. The pattern for each tillage treatment was for higher exchangeable calcium and magnesium at 0−0.1 m and higer exchangeable potassium at 0–0.02 m with stubble retained than with stubble removed. After 7 years the silt + clay dispersion ratio was lower for Z+ and Z− than for the other treatments.

There was an average net gain of 30 kg ha⁻¹ of nitrate-N at 0–0.6 m during fallow periods followed by a similar loss during cropping periods. Nitrate at the end of the fallow was equally distributed at three depths: 0–0.1, 0.1–0.2 and 0.2–0.6 m. On two occasions after a crop, the pattern was less nitrate (0–0.6 m) with stubble retained than with stubble removed, the difference for each tillage treatment increasing in the order D−1) ranged from 62 kg N ha⁻¹ for Z− to 128 kg N ha⁻¹ for Z+. The decrease for all tillage treatments was greater where stubble was retained than where it was removed. Decreases where stubble was retained were in the order D相似文献   

Tillage and crop residue management affect vertisol properties and grain sorghum growth over seven years in the semi-arid sub-tropics. 1. Crop residue and soil water during fallow periods

The effects of fallow surface management treatments on stubble (crop residue) levels and soil water storage were studied during seven fallow periods between grain sorghum crops on a grey Vertisol near Biloela in central Queensland, Australia. Treatments were disc (D), blade (B) and zero (Z) tillage, each with stubble or residue from preceding crops either retained (+) or removed (-) at the start of the fallow periods, which were of 7–8 months duration.

Where stubble was retained, stubble dry matter levels on the soil surface at the start of the fallow period were mainly influenced by stubble produced by the previous crop, but also by residual stubble on the soil surface before the previous crop. The general order was D +< B +< Z+.

Stubble dry matter and stubble cover on the soil surface declined during the fallow period in all stubble-retained treatments, with the greatest reductions occurring after the initial disc or blade tillage. From the start to end of the fallow, mean reductions in stubble dry matter and stubble cover were, respectively, 60 and 74% in D+, 31 and 57% in B+, and 17 and 24% in Z+. Mean stubble dry matter levels on the soil surface at the end of the fallow period in December–January were 1030, 2030 and 2910 kg ha⁻¹ in D+, B+ and Z+, respectively; corresponding stubble cover levels were 8, 16 and 35%.

Mean plant available water capacity to 1.8 m was 201 mm. Mean fallow soil water accumulation varied between fallow periods from 11 to 102 mm. The corresponding variation in mean fallow water storage efficiency (percentage of rainfall over the fallow stored in the soil) was from 3 to 37%. Fallow soil water accumulation was significantly (P<0.05) higher in Z+ (116 mm) than in Z- (86 mm), D+ (96 mm) and D- (84 mm) in one fallow period.

During the fallow period, B+ and Z+ generally resulted in higher plant available water than other treatments at mean values of 50–100 mm. However, these effects were not present at higher plant available water levels (mean of 128–164 mm), as occurred at the end of six fallow periods. The main treatment effect at the end of the fallow was for significantly (P<0.05) lower plant available water in Z-.     

THE EFFECT OF AGE ON RESISTANCE OF CATTLE TO BABESIA BOVIS

SUMMARY Susceptible Hereford cattle of different ages were inoculated with 2 times 10⁸Babesia bovis organisms. Experiment 1 consisted of cows aged 6 to 7 years, steers aged 17 to 18 months and calves aged 5 to 6 months, while experiment 2 consisted of cows aged 6.5 to 7.5 years, steers aged 23 to 24 months and yearlings aged 11 to 12 months. Daily measurements of temperature, parasitsemia and packed cell volume were made in order to determine susceptibility of the different ages. Twenty-four of the 36 animals in experiment 1, which included all 12 cows, required treatment. One cow died as a result of an enlarged ruptured spleen, and 2 steers and 1 calf died with classical babesiosis symptoms. No treatment was given to experiment 11 animals, and 5 of the 12 cows died, but the steers and yearlings underwent relatively mild reactions. Statistical analysis confirmed the high susceptibility to B. bovis of the aged cows in both experiments, and the innate resistance of 5 to 6 month old calves in experiment 1. The reaction of the 18-month-old steers in experiment 1 was significantly greater than that of the calves, but significantly less severe than that of the aged cows. Two-year-old steers and yearlings in experiment 2 underwent similar mild reactions, suggesting that innate immunity may persist for longer periods when compared to aged cows. Age groups showing reduced susceptibility were found to reach peak parasitaemia, temperature and anaemia before the more susceptible age groups. Heterologous challenge of the remaining experiment 1 and experiment 2 animals at 6 and 8 months respectively after primary inoculation, revealed all animals of all ages had a solid resistance to B. bovis.     

Tillage and crop residue management affect Vertisol properties and grain sorghum growth over seven years in the semi-arid sub-tropics. 3. Crop growth, water use and nutrient balance

The effects of fallow surface management treatments on subsequent growth and yield of grain sorghum were studied during seven cropping periods on a grey Vertisol near Biloela in central Queensland, Australia. Treatments were disc (D), blade (B) and zero (Z) tillage, each with stubble or residue from previous crops either retained ( + ) or removed ( − ) at the start of the fallow period. Treatments were planted to grain sorghum between December and February, following a 7–8 month fallow period.

Plant establishment was significantly (P<0.05) lower in Z than in D and B treatments in five of the seven crops. Average plant establishment over 7 years was about 20% lower in Z treatments. Early crop growth was generally more vigorous in D and B than in Z treatments, but this trend became less pronounced at later stages of growth. Surface cover (stubble+crop) ranged from 46% in Z + to 26% in Z− 5 weeks after planting and from 68% to 57% at anthesis and 62% to 46% at maturity in these same treatments. For the seven crops, annual mean grain yields over all treatments ranged from 1650 to 4490 kg ha⁻¹. Z− had a significantly (P<0.05) lower mean grain yield over the seven crops than all other treatments, which did not differ significantly (P>0.05). Where stubble was retained, yields of D+ and B+ never differed significantly. However, yields from Z+ were significantly higher in three crops than those from D+ and B+ and lower in three other crops. Stubble retention consistently resulted in significantly higher yields than stubble removal in the Z treatment. Crop water use was consistently lower in Z− than in all other treatments. Of the total roots to a depth of 1.6 m, a mean of 28% were found at 0–0.1 m. At 0.1–0.2 m and in deeper 0.2 m increments, the mean ranged from 6 to 11%.

Over 7 years, decreases in soil organic carbon at 0–0.1 m with stubble retained were less than with stubble removed. The differences corresponded to 4.1, 10.0 and 6.2% of stubble carbon inputs in D, B and Z treatments, respectively. Nitrogen removal in grain and stubble, expressed as a fraction of soil total nitrogen at 0–0.2 m plus nitrate-nitrogen at 0–1.6 m, ranged from 43% for D+ to 82% for Z+. Decreases of bicarbonate- and acid-extractable phosphorus at 0–0.1 m each corresponded to between 31 and 50% of the phosphorus removal in grain and stubble.