黑龙江西部旱作玉米水肥生产潜力试验研究

以氮肥、磷肥、补水量为试验因子,以玉米产量为指标,利用MINITAB15统计分析软件进行试验设计和数据分析,通过响应曲面法建立水肥相互作用对玉米产量影响的二次多项数学模型。利用模型的等值线图对影响玉米产量的关键因子及其相互作用进行了探讨,以玉米产量为响应值优化得出玉米生产潜力田间试验值的条件:氮肥为241.1 kg/hm2,磷肥为173.1 kg/hm2,补水量为108.3 m3/hm2,玉米田区生产潜力试验值为12 224 kg/hm2。     

鸭梨不同施氮期肥料氮的平衡及其效应

以3年生初结果的鸭梨/杜梨为试材,用~(15)N示踪技术探讨了秋施、春施及夏施肥料氮在土壤-植物中的平衡及其效应。结果表明,肥料氮损失量与植株吸收量之比表现为夏施>秋施>春施;肥料氮利用率以春施最高,秋施次之,夏施最低。肥料氮在植株体内的分配基本上随生长中心的转移而转移,无果中、短枝有优先累积肥料氮的效应。以秋施肥料氮的分配与植株生长节奏最吻合,并能刺激生长势弱的植株吸收利用肥料氮。显示出秋施氮对植株的效应最好。     

土壤微生物量和土壤固定态铵的变化及水稻对残留N的利用

在小麦盆栽试验后的^15N标记土壤上,研究了水稻生长过程中土壤微生物量C、N和土壤固定态铵的变化及其有机无机肥料残留N的有效性,结果表明,土壤微生物量C随着水稻生长而逐渐增加,到收获时达到1378．6－1790．5mg/kg土;土壤微生物量N的变化与水稻吸收N素有关,开始时由于淹水使得土壤微生物N有所下降,但随后又有所增加;随着水稻的N的吸收增加,生物量N又下降,直到水稻成熟期又有所恢复。在整个水稻生长季节中,土壤固定态铵的含量变化不大,但其中的一些^15N仍与外界土壤中矿质N发生了交换,表明 些固定态铵对水稻仍有较高的有效性。     

A yield-independent, 15N-isotope dilution method to estimate legume symbiotic dependence without a non-N2-fixing reference plant

The proportional contribution of atmospheric N₂ to the N nutrition of lupin (P _atm) was estimated in a field experiment following addition of NH₄Cl of KNO₃ to unconfined microplots (1.5 m²) at 2.5 g N m^-2 (10 atom% ¹⁵N). The integrated ¹⁵N enrichment, or mean pool abundance, of nitrate extracted from 0- to 15-cm samples taken under the lupin crop on eight occasion between 28 and 190 days after sowing was used as the reference criterion to estimate P _atm by the ¹⁵N-isotope dilution technique. Estimates of P _atm were similar to those obtained using canola as a non-fixing reference plant, but were higher than estimates obtained using a yield-dependent model. Use of mean pool abundance obviates the need for a non-fixing reference plant, and the frequent sampling and isotope-ratio analysis of the legume biomass required with the yield-dependent model is unnecessary. However, further work is needed to validate a sampling strategy commensurate with the growth of the legume roots.     

Evolution of dinitrogen and nitrous oxide from the soil to the atmosphere through rice plants

Summary It is commonly assumed that a large fraction of fertilizer N applied to a rice (Oryza sativa L.) field is lost from the soil-water-plant system as a result of denitrification. Direct evidence to support this view, however, is limited. The few direct field, denitrification gas measurements that have been made indicate less N loss than that determined by ¹⁵N balance after the growing season. One explanation for this discrepancy is that the N₂ produced during denitrification in a flooded soil remains trapped in the soil system and does not evolve to the atmosphere until the soil dries or is otherwise disturbed. It seems likely, however, that N₂ produced in the soil uses the rice plants as a conduit to the atmosphere, as does methane. Methane evolution from a rice field has been demonstrated to occur almost exclusively through the rice plants themselves. A field study in Cuttack, India, and a greenhouse study in Fort Collins, Colorado, were conducted to determine the influence of rice plants on the transport of N₂ and N₂O from the soil to the atmosphere. In these studies, plots were fertilized with 75 or 99 atom % ¹⁵N-urea and ¹⁵N techniques were used to monitor the daily evolution of N₂ and N₂O. At weekly intervals the amount of N₂+N₂O trapped in the flooded soil and the total-N and fertilized-N content of the soil and plants were measured in the greenhouse plots. Direct measurement of N₂+N₂O emission from field and greenhouse plots indicated that the young rice plant facilitates the efflux of N₂ and N₂O from the soil to the atmosphere. Little N gas was trapped in the rice-planted soils while large quantities were trapped in the unplanted soils. N losses due to denitrification accounted for only up to 10% of the loss of added N in planted soils in the field or greenhouse. The major losses of fertilizer N from both the field and greenhouse soils appear to have been the result of NH₃ volatilization.     

Effect of successive cuttings on uptake and partitioning of 15N among plant parts of Leucaena leucocephala

Summary We studied the effect of three successive cuttings on N uptake and fixation and N distribution in Leucaena leucocephala. Two isolines, uninoculated or inoculated with three different Rhizobium strains, were grown for 36 weeks and cut every 12 weeks. The soil was labelled with 50 ppm KNO₃ enriched with 10 atom % ¹⁵N excess soon after the first cutting. Except for the atom % ¹⁵N excess in branches of K28 at the second cutting, both the L. leucocephala isolines showed similar patterns of total N, fixed N₂, and N from fertilizer distribution in different parts of the plant at each cutting. The Rhizobium strain did not influence the partitioning of ¹⁵N among the different plant parts. Significant differences in ¹⁵N enrichment occurred in different parts. Live nodules of both isolines showed the lowest atom % ¹⁵N excess values (0.087), followed by leaves (0.492), branches (0.552), stems (0.591), and roots (0.857). The roots contained about 60% of the total plant N and about 70% of the total N derived from fertilizer over the successive cuttings. The total N₂ fixed in the roots was about 60% of that fixed in the whole plant, while the shoots contained only 20% of the fixed N₂. We conclude that N reserves in roots and nodules constitute another N source that must be taken into account when estimating fixed N₂ or the N balance after pruning or cutting plants. ¹⁵N enrichment declined up to about fivefold in the reference and the N₂-fixing plants over 24 weeks following the ¹⁵N application. The proportion and the amounts of N derived from fertilizer decreased, while the amount derived from N₂ fixation increased with time although its proportion remained constant.     

C and N turnover in structurally intact soils of different texture

The turnover of native and applied C and N in undisturbed soil samples of different texture but similar mineralogical composition, origin and cropping history was evaluated at −10 kPa water potential. Cores of structurally intact soil with 108, 224 and 337 g clay kg⁻¹ were horizontially sliced and ¹⁵N-labelled sheep faeces was placed between the two halves of the intact core. The cores together with unamended treatments were incubated in the dark at 20 °C and the evolution of CO₂-C determined continuously for 177 d. Inorganic and microbial biomass N and ¹⁵N were determined periodically. Net nitrification was less in soil amended with faeces compared with unamended soil. When adjusted for the NO₃-N present in soil before faeces was applied, net nitrification became negative indicating that NO₃-N had been immobilized or denitrified. The soil most rich in clay nitrified least N and ¹⁵N. The amounts of N retained in the microbial biomass in unamended soils increased with clay content. A maximum of 13% of the faeces ¹⁵N was recovered in the microbial biomass in the amended soils. CO₂-C evolution increased with clay content in amended and unamended soils. CO₂-C evolution from the most sandy soil was reduced due to a low content of potentially mineralizable native soil C whereas the rate constant of C mineralization rate peaked in this soil. When the pool of potentially mineralizable native soil C was assumed proportional to volumetric water content, the three soils contained similar proportions of potentially mineralizable native soil C but the rate constant of C mineralization remained highest in the soil with least clay. Thus although a similar availability of water in the three soils was ensured by their identical matric potential, the actual volume of water seemed to determine the proportion of total C that was potentially mineralizable. The proportion of mineralizable C in the faeces was similar in the three soils (70% of total C), again with a higher rate constant of C mineralization in the soil with least clay. It is hypothesized that the pool of potentially mineralizable C and C rate constants fluctuate with the soil water content.     

Inter‐specific variability in organic nitrogen uptake of three temperate grassland species

We tested the inter‐specific variability in the ability of three dominant grasses of temperate grasslands to take up organic nitrogen (N) in the form of amino acids in soils of differing fertility. Amino acid uptake was determined by injecting dual labeled glycine‐2‐¹³C‐¹⁵N into the soil, and then measuring the enrichment of both ¹³C and ¹⁵N in plant tissue after 50 hours. We found enrichment of both ¹³C and ¹⁵N in root and shoot material of all species in both soils, providing first evidence for direct uptake of glycine. We show that there was considerable inter‐specific variability in amino acid uptake in the low fertility soil. Here, direct uptake of amino acid was greater in the grass Agrostis capillaris, which typically dominates low fertility grassland, than Lolium perenne, which inhabits more fertile sites. Direct uptake of amino acid for Holcus lanatus. was intermediate between the above two species. Unlike in the low fertility soil, there was no difference in uptake of either ¹³C or ¹⁵N by grasses in the high fertility soil, where uptake of mineral N is thought to be the major mechanism of N uptake of these grasses. Overall, our findings may contribute to our understanding of differences in competitive interactions between grasses in soils of different fertility status.     

施用控释尿素对大豆吸氮量及产量的影响研究

试验研究施用控释尿素对大豆吸N量及其产量与品质的影响结果表明 ,控释尿素比普通尿素N肥利用效率提高 3 0 6 %～ 1 1 93% ,沙土中尿素N残留量增加 1 2 5 %～ 1 5 89% ,大豆产量提高 2 1 6 9%～ 4 9 2 2 % ,且改善大豆品质。     

水稻对氮素的吸收、分配及其在组织中的挥发损失

应用¹⁵N示踪技术研究了水稻不同生育期吸收的¹⁵N在各器官中的分配,以及后期植物组织中的挥发损失。结果发现,水稻在分蘖期吸收的氮量少于在幼穗分化期吸收的氮量;在分蘖期吸收的¹⁵N,标记结束时氮素主要分配于水稻的叶片中,至成熟期¹⁵N有39%转运至水稻子粒中;水稻在幼穗分化期吸收的¹⁵N,标记结束时氮素主要分配在水稻茎和叶鞘中,至成熟期¹⁵N有46%转运至水稻的子粒中;水稻在分蘖期和幼穗分化期吸收的氮素在后期可以通过植株组织挥发损失,至成熟期损失的比例分别达16.7%和13.4%。