Phosphorus fertilisation causes durable enhancement of phosphorus concentrations in forest soil

The duration of P fertiliser in acid forest soil was investigated in a Norway spruce (Picea abies Karst.) forest in south-central Sweden. The fertilisation of the soil started in 1967, but no P has been applied since 1988. The N fertilisation is still continuing. Totally, 300 kg P per hectare, as superphosphate, and/or 1090 kg N per hectare, as ammonium nitrate, was applied. Concentrations of both 0.05M Na₂SO₄ + 0.02M NaF extractable P and 0.5M H₂SO₄ extractable P in the Of, Oh, E and top B horizons of fertilised soils were elevated compared to the control. The P fractions considered to be extracted are adsorbed and some Al-bound phosphate, in the case of Na₂SO₄ + NaF, and Ca phosphates, in the case of H₂SO₄. 3–4% of the added P was recovered as Na₂SO₄ + NaF extractable P, and 10–22% was recovered as H₂SO₄ extractable P in the soil profile down through the first 5 cm of the B horizon. Still continuing ammonium nitrate fertilisation has decreased the H₂SO₄ extractable P concentration in this soil. Cumulative P fertiliser application of 300 kg P per hectare has counteracted this decrease.     

水稻根系特征与氮吸收利用效率关系的研究进展

植物根系是活跃的物质代谢和吸收器官,对植株生物量积累、养分和水分高效吸收利用具有重要作用。本文主要综述了水稻根系形态、解剖、生理特征与氮吸收利用效率的关系以及不同氮效率品种根系特征的差异,并综述了促进根系生长和提高氮吸收利用效率的栽培调控措施,展望了未来水稻根系的研究方向,为水稻氮肥减施、氮高效栽培管理技术优化和氮高效品种选育提供理论依据。     

Yield and quality components of silage maize in killed and live cover crop sods

In sloping areas with high precipitation, planting maize into live winter cover crop sods may help to alleviate the environmental problems associated with clean-tillage production systems of maize. The present study evaluates the performance of silage maize (Zea mays L.) under several cultivation methods: CC (conventional cropping system, i.e., maize was sown into the bare, autumn-ploughed soil); LGS/CK (maize was planted into a living Italian ryegrass (Lolium multiflorum Lam.) sod which was subsequently herbicidally killed); and LGS/MR (similar to LGS/CK, but the ryegrass was mechanically regulated). The research was conducted in the midlands of Switzerland on a fertile sandy loam under humid conditions during three cropping seasons. With 110 kg N ha⁻¹ (fertilizer nitrogen plus mineral nitrogen of the soil at maize planting), the CC system was much more productive than were the LGS/CK and LGS/MR systems in terms of dry matter and nitrogen yields of maize. Increasing the nitrogen supply to 250 kg N ha⁻¹ considerably reduced the yield advantage of CC over the LGS/CK and LGS/MR systems, indicating that nitrogen was the most limiting factor for maize yield in the mulch seeding systems. With 250 kg N ha⁻¹, the LGS/CK and LGS/MR systems produced greater total yields of digestible organic matter (maize plus ryegrass) than did the CC system, whereas the total nitrogen yield was similar for all cropping systems. The whole-shoot concentrations of nitrogen were highest under CC, irrespective of the level of nitrogen supply. With 110 kg N ha⁻¹, concentrations of phosphorus and magnesium were clearly higher for the mulch seeding systems. There were only minor differences among the cropping methods in the concentrations of potassium and calcium in the whole shoot. When 250 kg N ha⁻¹ were applied, there were no significant variations among the cropping systems in the concentrations of minerals. Changes in the botanical composition of the cover crop sod and in the time and method of cover crop control may help to reduce the competition for nitrogen between maize and the living mulch.     

Denitrification and nitrogen immobilization as affected by organic matter and different forms of nitrogen added to an anaerobic water-sediment system

The effects of wheat straw and different forms of N on denitrification and N immobilization were studied in an anaerobic water-sediment system. The water-sediment system was supplemented with various combinations of wheat straw and ¹⁵N-labelled and unlabelled (NH₄)₂SO₄ or KNO₃, and incubated anaerobically at 30°C for 10 days. ¹⁵N-labelled and unlabelled NO _inf3 ^sup- , NO _inf2 ^sup- , NH _inf4 ^sup+ , and organic N were determined in the water-sediment system. The gases evolved (N₂, CO₂, N₂O, and CH₄) were analyzed by gas chromatography at regular intervals. Larger quantities of ¹⁵N₂–N and organic ¹⁵N were formed in wheat straw-amended systems than in non-amended systems. Trends in CO₂ production were similar to those of N₂–N evolution. The evolution of N₂O and CH₄ was negligible. Denitrification processes accounted for about 22 and 71% of the added ¹⁵NO _inf3 ^sup- –N in the absence and presence of wheat straw, respectively. The corresponding denitrification rates were 3.4 and 12.4 g ¹⁵Ng^-1 dry sediment day^-1. In systems amended with ¹⁵NO _inf3 ^sup- –N and ¹⁵NO _inf3 ^sup- +NH _inf4 ^sup+ –N without wheat straw, 1.82 and 1.58%, respectively, of the added ¹⁵NH _inf3 ^sup- –N was immobilized. The corresponding figures for the same systems supplemented with wheat straw were 5.08 and 4.10%, respectively. Immobilization of ¹⁵NO _inf4 ^sup+ –N was higher than that of ¹⁵NO _inf3 ^sup- –N. The presence of NO _inf3 ^sup- –N did not stimulate NH _inf4 ^sup+ –N immobilization.     

氮磷钾肥不同施入量对水稻新品种盐粳218产量的影响

采用小区对比试验方法,探讨了氮磷钾肥不同施入量对水稻新品种盐粳218产量的影响。结果表明,氮肥施入量对产量的影响程度最大,各处理比其平均单产增幅-15.3%～8.0%,磷肥各处理比其平均单产增幅-2.9%～1.7%,钾肥各处理比其平均单产增幅-3.3%～1.8%。同时根据氮、磷、钾肥施入量对盐粳218产量影响的函数方程求得与该品种高产高效栽培相配套的氮(N)、磷(P2O5)、钾肥(K2O)适宜施入量为16～20 kg/667 m2、6.5～8.5 kg/667 m2、5.0～7.0 kg/667 m2。在本试验条件下水稻新品种盐粳218可获得598.3～625.0 kg/667 m2的产量。     

稗草影响大豆根瘤固氮的机制研究之一——水分干扰机制

在全自控人工气候室内系统研究了稗草对大豆根瘤固氮的水分干扰机制。稗草在每盆3株的密度下使播后53-63淹水期间及淹水期后1天的大豆单株根瘤固氮速率平均分别比无草对照提高了16.6%和30.0%,在每盆10株的密度下分别使其比无草对照提高了34.2%和67.5%。在不淹水的情况下播后30-70天,稗草在每盆3株和10株的密度下使其所在处理的平均日蒸发蒸腾量分别比无草对照增加了23.8%和50%,削弱了水分对大豆植株的供应水平;而土壤水分供应水平从其田间持水量的80%降低到35%时,大豆根瘤的氧气传导速率从0.38cm/s下降到0.20cm/s,净光合速率从18.81mg/dm#+2/h降低到4.04mg/dm#+2/h,每盆10株稗草对大豆单株结瘤量及根瘤固氮酶活性的抑制率则分别从8.2%和17.8%升高到18.3%和19.6%,其对大豆单株根瘤固氮速率的抑制率也随之从21.5%上升到33.1%。证明通过干扰土壤水分供应水平,首先影响大豆植株的同化物产量及根瘤内的氧气供应,进而影响大豆植株的根瘤形成和根瘤固 氮酶的固氮活性,是稗草影响大豆根瘤固氮的主要机制之一。     

Denitrification losses from puddled rice soils in the tropics

Summary Although denitrification has long been considered a major loss mechanism for N fertilizer applied to lowland rice (Oryza sativa L.) soils, direct field measurements of denitrification losses from puddled rice soils in the tropics have only been made recently. This paper summarizes the results of direct measurement and indirect estimation of denitrification losses from puddled rice fields and reviews the status of research methodology for measurement of denitrification in rice fields. The direct recovery of (N₂+N₂O)-¹⁵N from ¹⁵N-enriched urea has recently been measured at sites in the Philippines, Thailand, and Indonesia. In all 12 studies, recoveries of (N₂+N₂O)-¹⁵N ranged from less than 0.1 to 2.2% of the applied N. Total gaseous N losses, estimated by the ¹⁵N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-N. Denitrification was limited by the nitrate supply rather than by available C, as indicated by the values for water-soluble soil organic C, floodwater (nitrate+nitrite)-N, and evolved (N₂+N₂O)-¹⁵N from added nitrate. In the absence of runoff and leaching losses, the amount of (N₂+N₂O)-¹⁵N evolved from ¹⁵N-labeled nitrate was consistently less than the unrecovered ¹⁵N in ¹⁵N balances with labeled nitrate, which presumably represented total denitrification losses. This finding indicates that the measured recoveries of (N₂+N₂O)-¹⁵N had underestimated the denitrification losses from urea. Even with a probable two-or threefold underestimation, direct measurements of (N₂+N₂O)-¹⁵N failed to confirm the appreciable denitrification losses often estimated by the indirect difference method. This method, which determines denitrification losses by the difference between total ¹⁵N loss and determined ammonia loss, is prone to high variability. Measurements of nitrate disappearance and ¹⁵N-balance studies suggest that nitrification-denitrification occurs under alternate soil drying and wetting conditions both during the rice cropping period and between rice crops. Research is needed to determine the magnitude of denitrification losses when soils are flooded and puddled for production of rice.     

稻茬过晚播扬麦25产量形成与氮素积累利用特征

为明确过晚播种(较适播期晚30 d左右)对小麦产量及氮素积累与利用的影响,2018-2020年以长江中下游地区主栽品种扬麦25为供试材料,在11月1日(适期播)和12月1日(过晚播)条件下设置225×104株·hm-2和375×104株·hm-2两种种植密度,分析过晚播和适期播小麦产量、氮素积累与分配和氮素利用效率的差...     

黄淮海平原水氮耦合对小麦产量和蛋白质含量的影响

根据水氮耦合试验,小麦单产随着施氮水平和浇水次数的增加而提高,当施氮肥量达到337.5 kg/hm2时,小麦产量最高,以后随着施氮量的增加,单产下降.一水产量是5 092.5 kg/hm2,二水产量比一水提高14.6%,三水产量比一水提高了10.5%.小麦子粒中蛋白质含量随施氮量的增加而略有下降;随着浇水次数的增加,蛋白质含量也下降.     

不同氮效率型苜蓿氮素吸收差异与根系形态的关系及其对氮的响应

以高效型苜蓿（‘龙牧806’‘肇东苜蓿’）和低效型苜蓿（‘公农1号’‘陇东苜蓿’）为试验材料,采用营养液砂培法,在4个供氮量下（2.1,21,210和420 mg·L^-1）,研究紫花苜蓿苗期氮素吸收、分配的氮效率型差异及其与根系形态之间的关系。结果表明高效型苜蓿品种的株高、地上生物量、根重、总根长和根体积均显著高于低效型品种（P<0.05）;供氮量较低时（2.1和21 mg·L^-1）,高效型向根系分配了较大比例的氮素,而低效型则向地上部分配了较大比例的氮素,根系形态参数与总氮量呈显著正相关（P<0.05）,且根重对氮素吸收的直接作用较大,直接通径系数是1.230和1.102。因此,在氮胁迫下,根系形态对氮吸收效率起重要作用,尤其是根系形态中的根重对其影响较大。