An evaluation of the Olsen test as a measure of plant-available phosphorus in grassland soils derived from basalt parent material

Abstract. Anecdotal and circumstantial evidence have suggested that the Olsen test underestimates plant-available phosphorus (P) in basaltic soils in Northern Ireland. Therefore, the ability of this test to predict plant-available P in basaltic (and non-basaltic) soils was investigated by regressing Olsen-P data against herbage P indices calculated from plant tissue test data using the diagnosis and recommendation integrated system. The average Olsen-P concentration for a range of fields situated on basaltic soils was considerably lower than the average Olsen-P concentration for a range of fields situated on non-basaltic soils, and yet mean sward P status, as given by the herbage P indices, was similar for both groups of fields. Herbage P indices were also much better correlated with Olsen-P measurements in non-basaltic soils than in basaltic soils. Furthermore, at low Olsen-P values (≶9mgPL⁻¹) some swards on basaltic soils were genuinely deficient in P, while others were sufficient or even in surplus for this nutrient. The results confirm that Olsen-P is inadequate as a predictor of plant-available P in basaltic soils. It is concluded that an alternative soil test is needed to provide a reliable assessment of plant-available P in basaltic soils, to prevent overuse of fertilizer and manure P and to minimize the amounts of P entering local watercourses.     

Evaluation of two N cycle models for the prediction of N mineralization from grassland soils in the UK

Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization.     

The use of urban organic wastes in the control of erosion in a semiarid Mediterranean soil

Abstract. A two year field experiment was carried out in a semiarid Mediterranean area in order to evaluate, the effect on soil erosion of adding different urban organic wastes: a stabilized municipal waste (compost), an unstabilized municipal waste, and an aerobic sewage sludge. All the treatments significantly reduced soil erosion, compared to the control soil. The soil amended with compost was the most effective treatment, reducing soil loss by 94% and runoff by 54%.     

Effects of 'Agri-SC' soil conditioner on soil structure and erodibility: some further observations

Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.     

上虞海涂实验农场中心试验区排水系统探讨

上虞市海涂实验农场中心试验区的排水系统，能满足十年一遇的年最大２４ｈ降雨，两天内排出的要求。滨海盐土的地下水位高，农田基本建设除用浅、密的排水沟布置外，还应结合平整土地、发展灌溉以及适用的农、林技术等综合措施，才能达到治盐改土的效果。     

超高产水稻产量形成的气候生态特点研究

在云南和湖南异地异季种植，研究了水稻超高产形成的相应气候生态条件，结果表明：超高产水稻具有大穗、多穗、高结实率的特点．云南试区具有日较差大、日照时数多、相对湿度低，平均温度较低的气候特点，故水稻生育期较长，同化物积累多，成穗率高，灌浆强度大．湖南试区阴雨寡照是影响产量的重要因素．     

水稻机械化喷直播技术的应用现状及对策

分析了水稻机械化喷直播技术的特点和技术要求，介绍了水稻机械化喷直播技术的应用现状及其技术推广的制约因素．提出了推广水稻机械化喷直播技术的对策．     

Weeding techniques in transplanted and direct wet-seeded rice in Pakistan

Field studies were undertaken to explore the weed management strategies for transplanted and direct wet-seeded rice in the Dera Ismail Khan district of North-west Frontier Province, Pakistan. The experimental design was a randomized complete block with a split plot arrangement. The main plots consisted of two planting techniques (transplantation and direct seeding), while weed control practises assigned to the subplots included the use of the granular herbicide Sunstar 15WG (ethoxy sulfuron), Machete 60EC (butachlor), conventional hand weeding, and the weedy check (untreated control). Data were recorded on weed dynamics and the agronomic parameters of the rice crop. Economic analyses on the data were also run. The weed density and biomass were lower in the transplantation plots than the direct-seeding plots. The herbicides ethoxy sulfuron and butachlor reduced the density over the weedy check, with a density comparable to hand weeding in 2002, but slightly higher in 2003. As a result of weed management by hand weeding and herbicides, the paddy yield and its components were significantly higher for the transplanted method compared to the direct-seeded method. The comparable yield of herbicides with hand weeding offers an option for the use of herbicides as an alternative management tool. In light of our findings, it is concluded that for good economic returns, rice crops may be transplanted rather than direct-seeded. The herbicides ethoxy sulfuron and butachlor offer a weed control cover comparable with hand weeding under the transplantation method, while butachlor is good for controlling weeds even under the direct-seeded conditions in the agroclimatic conditions of the area.     

Alternative Route of Infection for Bacterial Seedling Blight of Rice Caused by Burkholderia plantarii

Burkholderia plantarii , the pathogen of bacterial seedling blight of rice, was detected in paddy water. Its concentration rose in July and August. The bacterial concentration in the paddy water was always higher along levees than at distances more than 5 m from levees. Confirmed to be released into water when graminaceous weeds were immersed, B. plantarii survived for at least 4 days at 30°C. B. plantarii was splashed at least 30 cm upward by rain splash in the field. Harvested seeds, which had been sprayed with B. plantarii released from graminaceous weeds at the flowering stage, retained the bacteria. Bacterial seedling blight occurred when the seeds were then sown in nursery boxes. These results indicated that graminaceous weeds growing on levees of paddy fields are a source of infection of the disease and that rice seeds are infected through the paddy water. Received 23 May 2002/ Accepted in revised form 1 September 2002