Assessment of the influence of phosphate fertilizers on the microbial activity of pasture soils

The objective of the present work was to examine the effects of phosphate fertilizers on the microbial activity of pasture soils. Various microbial characteristics were measured using soils from an existing long-term phosphate fertilizer field trial and a short-term incubation experiment. The measurements included basal respiration, substrate induced respiration, inhibition of substrate-induced respiration by streptomycin sulphate (fungal activity) and actidione (bacterial activity) and microbial biomass C. The long-term field trials was initiated during 1985 to examine the effectiveness of different sources of phosphate fertilizers (single superphosphate, North Carolina phosphate rock, partially acidulated North Carolina phosphate rock, and diammonium phosphate) on pasture yield. The incubation experiment was conducted for 8 weeks using the same soil and the sources of phosphate fertilizers used in the field trial. In the incubation experiment the fertilizer addition caused an initial decrease in basal and substrate-induced respiration but had no effect on total microbial biomass. The initial decline in basal and substrate-induced respiration with the fertilizer addition was restored within 8 weeks after incubation. In the field experiment the fertilizer addtion had no significant effect on basal respiration but increased substrate-induced respiration and microbial biomass C. The short-term and the long-term effects of phosphate fertilizer addition on the microbial characteristies of the soils are discussed in relation to its effects on pH, salt concentration, and the nutrient status of the soils.     

A simple agro-ecological zonation for fertilizer recommendations in Mozambique

Abstract. A practical and simple agro-ecological zonation of Mozambique is presented to facilitate the identification of production conditions and to serve as a basis for agricultural recommendations. The zonation is based on: FAO Major Soil Groupings, altitude and mean annual rainfall. The rationale of the zonation is evaluated by correlating these criteria with other climatic variables and the maize growth cycle. The effectiveness of the zonation was tested with maize yield data from fertilizer trials.
The results show that FAO Major Soil Groupings explain a significant part of the total variation in N and organic C contents, Olsen P, exchangeable K, pH and CEC. Altitude relates significantly with temperature, maize growth cycle, radiation and rainfall reliability. Mean annual rainfall relates significantly with rainfall reliability and radiation. Grouping the maize fertilizer trials according to the zonation criteria explained 39% of the variation in unfertilized yields and yield responses to NPK fertilization, and 51% of the variation in fertilized (NPK) yields.
The agro-ecological zonation on the basis of soil, altitude and mean annual rainfall proved to be a sound and practical way to identify land areas sufficiently homogeneous to be served by the same fertilizer recommendation.     

Nitrate leaching and pasture yields following the application of dairy shed effluent or ammonium fertilizer under spray or flood irrigation: results of a lysimeter study

Abstract. Nitrate leaching and pasture ( Lolium perenne / Trifolium repens ) yields were measured on monolith lysimeters (80 cm diam. × 120 cm depth) of a Templeton sandy loam soil (Udic Ustochrept), following repeated applications of dairy shed effluent (DSE) or ammonium fertilizer (NH₄Cl), under spray (50 mm/month) or flood (100 mm/month) irrigation. Applications of DSE at 400 kg N/ha per annum resulted in significantly less nitrate leaching (8–25 kg N/ha per yr) compared with NH₄Cl (28–48kg N/ha per yr) ( P < 0.01). Over the two year period, the total mineral N (predominantly nitrate) leached was equivalent to 2.5–3.7% of the total N applied in the DSE and 8.7–9.8% of the N applied in the NH₄Cl. There was a trend of slightly less nitrate leaching under the flood irrigation than under the spray irrigation, probably because of the greater potential for denitrification under the wetter conditions. Average nitrate concentrations in the leachate were generally below the drinking water standard except in the NH₄Cl treatment under spray irrigation where it averaged 10 mg NO₃-N/l over the two year period. DSE was equally as effective as NH₄Cl in stimulating pasture dry matter production. Annual nitrogen uptakes were similar for the DSE (343 kg N/ha) and NH₄Cl (332–344kg N/ha) treatments in the first year but were higher in the DSE (361–412 kg N/ha) than in the NH₄Cl (324–340 kg N/ha) treatments in the second year. Pasture uptakes of phosphorus and sulphur were also higher in the DSE than in the NH₄Cl treatments in the second year. The results emphasize the need to set different regulatory limits for land application of organic wastes of various types and for N fertilizers.     

Nitrification inhibitor nitrapyrin does not affect yield-scaled nitrous oxide emissions in a tropical grassland

Urea is the most common nitrogen(N)fertilizer used in the tropics but it has the risk of high gaseous nitrogen(N)losses.Use of nitrification inhibitor has been suggested as a potential mitigation measure for gaseous N losses in N fertilizer-applied fields.In a field trial on a tropical Andosol pastureland in Costa Rica,gaseous emissions of ammonia(NH₃)and nitrous oxide(N₂O)and grass yield were quantified from plots treated with urea(U;41.7 kg N ha^-1application^-1)and urea plus the nitrification inhibitor nitrapyrin(U+NI;41.7 kg N ha^-1application^-1and 350 g of nitrapyrin for each 100 kg of N applied)and control plots(without U and NI)over a six-month period(rainy season).Volatilization of NH₃(August to November)in U(7.4%±1.3%of N applied)and U+NI(8.1%±0.9%of N applied)were not significantly different(P>0.05).Emissions of N₂O in U and U+NI from June to November were significantly different(P<0.05)only in October,when N₂O emission in U+NI was higher than that in U.Yield and crude protein production of grass were significantly higher(P<0.05)in U and U+NI than in the control plots,but they were not significantly different between U and U+NI.There was no significant difference in yield-scaled N₂O emission between U(0.31±0.10 g N kg^-1dry matter)and U+NI(0.47±0.10 g N kg^-1dry matter).The results suggest that nitrapyrin is not a viable mitigation option for gaseous N losses under typical N fertilizer application practices of pasturelands at the study site.     

Effects of the nitrification inhibitor nitrapyrin and the plant growth regulator gibberellic acid on yield-scale nitrous oxide emission in maize fields under hot climatic conditions

Nitrification inhibitors are widely used in agriculture to mitigate nitrous oxide(N₂O)emission and increase crop yield.However,no concrete information on their mitigation of N₂O emission is available under soil and environmental conditions as in Pakistan.A field experiment was established using a silt clay loam soil from Peshawar,Pakistan,to study the effect of urea applied in combination with a nitrification inhibitor,nitrapyrin(2-chloro-6-tri-chloromethyl pyridine),and/or a plant growth regulator,gibberellic acid(GA_3),on N₂O emission and the nitrogen(N)uptake efficiency of maize.The experimental design was a randomized complete block with five treatments in four replicates:control with no N(CK),urea(200 kg N ha^-1)alone,urea in combination with nitrapyrin(700 g ha^-1),urea in combination with GA_3(60 g ha^-1),and urea in combination with nitrapyrin and GA_3.The N₂O emission,yield,N response efficiency,and total N uptake were measured during the experimental period.The treatment with urea and nitrapyrin reduced total N₂O emission by 39%–43%and decreased yield-scaled N₂O emission by 47%–52%,relative to the treatment with urea alone.The maize plant biomass,grain yield,and total N uptake increased significantly by 23%,17%,and 15%,respectively,in the treatment with urea and nitrapyrin,relative to the treatment with urea alone,which was possibly due to N saving,lower N loss,and increased N uptake in the form of ammonium;they were further enhanced in the treatment with urea,nitrapyrin,and GA_3 by 27%,36%,and 25%,respectively,probably because of the stimulating effect of GA_3 on plant growth and development and the reduction in biotic and abiotic stresses.These results suggest that applying urea in combination with nitrapyrin and GA_3 has the potential to mitigate N₂O emission,improve N response efficiency,and increase maize yield.     

桐油包膜尿素养分释放机理的研究

以桐油为包膜材料,采用土壤盆栽试验和水中静置试验,对控释肥料养分释放动态进行了研究。结果表明,以桐油为包膜材料的包膜尿素,在土壤中养分初期溶出率为12.6%,在水中养分初期溶出率为20.1%,是比较理想的包膜材料。在水中与土壤中养分释放期为1∶1.2;N素的释放可用LOGISTIC动力学方程描述,释放常数k值可用来判断控释尿素的N素释放速率大小。     

施用涂层尿素对水田土壤氮去向及其利用率的影响

采用水稻盆栽试验方法,研究施用涂层尿素对水田土壤氮的挥发、土壤残留、水稻吸收三个去向及其氮素利用率的影响。研究结果表明:施用涂层尿素可显著抑制NH3和NOX挥发损失,NH3和NOX挥发量之和的减少幅度为22.1%~24.8%;使土壤中全氮含量增加,增加幅度为1.9%~2.1%。等氮用量条件下,施用涂层尿素可极显著提高氮素利用率,其提高幅度随施用量增大而减小;使水稻经济产量显著增加,中用量和高用量水平处理经济产量增加幅度分别为21.8%和21.5%。说明施用涂层尿素不仅能提高水田土壤氮素利用率,而且可减轻生态环境污染。     

日本北海道农村生态系统中N循环研究

This study of Mikasa City in 2001, which analyzed N flow between N production and N load in seven agricultural and settlement subsystems, i.e., paddy, onion, wheat, vegetable, dairy, chicken, and citizen subsystems, aimed to compare N flow in each subsystem, to determine the main sources of the N load, and to evaluate the influence of agricultural production and food consumption on N cycling in a rural area. The results showed that in Mikasa city, 38.5% of the N load came from point sources and the remainder from non-point sources with intensive vegetable farming imparting a serious N load. Because of the internal N cycling in the dairy subsystem, chemical fertilizer application was reduced by 70.2%, and 23.72 Mg manure N was recycled to the field; therefore, the N utilization efficiency was raised from 18.1% to 35.1%. If all the manure N in the chicken subsystem was recycled, chemical fertilizer application would be reduced by 8.1% from the present level, and the point sources of N pollution would be reduced by 20.8%.     

Immobilization of nitrogen from urea and plant residues in a ferrallitic soil: Laboratory experiments and study by size-fractionation

Summary The fate of N when incorporated in a ferrallitic soil was investigated during a 3-month incubation, using either ¹⁵N-labelled urea or ¹⁵N-labelled crop residues (sugarcane roots and leaves). The organic matter was characterized by particle-size fractionation. The urea-derived organic ¹⁵N was mainly found in the clay-sized fractions and was ascribed to biological activity. The plant-derived ¹⁵N was observed both in the sand-sized and in the clay-sized fractions; the former pool was ascribed to the persistence of crops residues, the latter to biological immobilization. The relative proportions of organic ¹⁵N recovered in the various clay fractions (coarse, fine, and very fine) were similar, irrespective of the nature of the added ¹⁵N. The very fine clay fraction (F<0.05 m) showed the highest isotopic excess, and thus gave rise to the highest turnover rate.     

树脂包膜尿素在稻田中的释放特征及与积温的关系

为了缓解农村劳动力短缺和适应农业机械化耕作的需要,水稻一次性施肥技术显得十分重要。该文采用埋袋法研究了一种用于一次性基施的树脂包膜尿素在水稻生长期内的释放规律,并对其释放与温度关系建立了数学模型。结果表明该树脂包膜尿素在稻田中释放80%的养分所需时间比标注的长。在水稻整个生育期内,其累计释放率可达到69%~83%。该树脂包膜尿素在田间的释放过程不存在明显的迟滞期,可分为快速释放阶段和缓慢释放阶段,且日均释放率为0.5%。其累计释放率与水稻移栽天数可用二次项方程描述。尽管试验地土壤相对含水率存在差异(60%~100%),但养分的累计释放率与气温积温和15 cm深处土壤积温显著相关(R~2=0.964和0.983)。这可为在不同气候条件下确定控释肥的施用量并掌握其释放情况提供一定的参考。