Effect of continuous compost application on water-stable soil macroaggregation in a field subjected to double cropping

The influence of continuous application of compost and fertilizer on soil macroaggregation in a field subjected to long-term (ca. 20 years) double cropping (rice and barley) was investigated. Soil samples were collected from 4 different plots: a) No-NF, fertilizer containing P and K but no N; b) F, fertilizer containing N, P, and K; c) F+ LC, fertilizer plus low rate of compost; and d) F+ HC, fertilizer plus high rate of compost. The application of compost and fertilizer increased the degree of macroaggregation (>0.25 mm), the contents of organic C, total N, hydrolyzable carbohydrates, and dithionitecitrate-bicarbonate (DCB) soluble Al, and the hyphal length in the order of No-NF<F<F+LC<F+HC plots. The degree of macroaggregation showed high correlation coefficients (r ≥ 0.95) with the contents of organic and inorganic components or the hyphal length. Most of these properties were strongly intercorrelated among themselves. The results obtained in this study suggest that organic matter including polysaccharides, active Al, and hyphae play an important role together in soil macro aggregation in the field subjected to double cropping under study.     

长期施用生物有机肥对土壤肥力及微生物生物量碳的影响

为了研究施用生物有机肥(EM堆肥,即有效微生物制剂 堆肥)对土壤肥力及微生物生物量碳的影响,进行了7年的施用15t/hm2.a有机肥、施用7.5t/hm2.a有机肥(包括EM堆肥、EM鸡粪肥和传统有机肥)、施用化肥和对照处理的田间试验。结果表明:长期施用生物有机肥的土壤肥力明显提高。随着生物有机肥用量的提高,碱性土壤的pH值逐渐降低,土壤有机质、全N、碱解氮、有效磷、速效钾、微生物生物量碳含量增加,与有机肥施用量呈显著正相关。施用化肥可一定程度提高土壤有机质、全N和有效养分含量,但作用不明显。施肥对土壤肥力和微生物量碳的影响趋势是:EM堆肥>传统堆肥>化肥>对照。土壤微生物量碳与土壤有机质、全N、碱解氮、有效磷、速效钾含量呈显著正相关,可以作为施肥过程中土壤质量变化的生物学指标。     

Uptake of carbon and nitrogen through roots of rice and corn plants,grown in soils treated with 13C and 15N dual-labeled cattle manure compost

Nitrogen and carbon dynamics in paddy and upland soils for rice cultivation and in upland soil for corn cultivation was investigated by using ¹³C and ¹⁵N dual-labeled cattle manure compost (CMC). In a soil with low fertility, paddy and upland rice took up carbon and nitrogen from the CMC at rates ranging from 0.685 to 1.051% of C and 17.6–34.6% of N applied. The ¹³C concentration was much higher in the roots than in the plant top, whereas the ¹⁵N concentration differed slightly between them, indicating that organic carbon taken up preferentially accumulated in roots. The ¹³C recovery in the plant top tended to be higher in upland soil than in paddy soil, whereas ¹⁵N applied was recovered at the same level in both paddy and upland soils. In the experiment with organic farming soil, paddy rice took up C and N from the CMC along with plant growth and the final recovery rates of ¹³C and ¹⁵N were 2.16 and 17.2% of C and N applied. In the corn experiment, a very large amount of carbon from the CMC was absorbed, accounting for at least 7 times value for rice. The final uptake rates of ¹³C and ¹⁵N reached about 13 and 10% of C and N applied, respectively. Carbon emission from the CMC sharply increased by 2 weeks after transplanting and the nitrogen emission was very low. It is concluded that rice and corn can take up an appreciable level of carbon and nitrogen from the CMC through roots.     

稻麦两熟制不同耕作方式与秸秆还田土壤肥力的综合评价

该文通过大田小区和网室水泥池微区3年的定位试验,比较研究了稻麦两熟条件下免耕套播秸秆覆盖NTS、免耕套播高茬NT、翻耕秸秆还田CTS、翻耕秸秆不还田CK共4个处理对土壤肥力的影响,并运用数值化方法综合评价土壤肥力。结果表明：免耕和秸秆还田可提高土壤有机质、速效磷、速效钾等土壤养分含量,且主要是0～7 cm增加造成的。土壤肥力数值化综合评价表明,土壤肥力免耕秸秆覆盖好于免耕高茬,翻耕秸秆还田好于翻耕不还田,不同处理养分肥力指标以免耕秸秆覆盖处理最高,翻耕不还田最低;但综合肥力指标却以翻耕秸秆还田最高,免耕高茬最低,主要受土壤容重影响。从不同层次看,综合肥力指标和养分肥力指标均以上层0～7 cm较高,下层14～21 cm较低,尤其免耕秸秆覆盖和免耕高茬处理。     

Impact of long-term N fertilization on the structural composition of spruce litter and mor humus

The aims of this study were to determine the degree of lignin degradation and to investigate changes in the chemical composition of the organic matter in the forest floor in an N fertilized Norway spruce forest soil. Needle litter and mor humus were collected from the field experiment at Skogaby in southern Sweden (56°33′N; 13°13′E). The spruce stand had been fertilized for 11 years with 100 kg N ha⁻¹ yr⁻¹ as (NH₄)₂SO₄. The degree of lignin degradation was determined with alkaline CuO oxidation followed by HPLC analysis. The chemical composition of the organic matter was characterized by CPMAS ¹³C NMR. Tannin was specifically analyzed using dipolar dephasing CPMAS ¹³C NMR and the N distribution was studied by CPMAS ¹⁵N NMR.The C-to-N ratios in the fertilized Oi and Oe layers were significantly lower than in the unfertilized layers (24 compared to 34 and 23 compared to 27, respectively). Neither the sum of the CuO oxidation products (Vanillyls+Syringyls+Cinnamyls expressed as VSC) nor the acid-to-aldehyde ratio ((Ac/Al)_V) showed any significant treatment effects. The content of aromatic C (including phenolic C) was significantly lower in the unfertilized than in the fertilized Oi layer (18 versus 21%). In the unfertilized soil, VSC was positively correlated (r=+0.63, p<0.05) with the C-to-N ratio, whereas the phenolic C content was negatively correlated (r=−0.61, p<0.05). The tannin index showed a tendency of increasing from Oi to Oe layers in both treatments. Most of the organic N was found as amide-N, whereas no heterocyclic N was detected. We have not been able to show any major C structural changes due to N fertilization. We suggest that the significantly higher content of aromatic and phenolic C in the fertilized Oi layer is due to an initial stimulation of the microbial community.     

Effect of chemical composition on the release of nitrogen from agricultural plant materials decomposing in soil under field conditions

Summary In two field experiments, plant materials labelled with ¹⁵N were buried separately within mesh bags in soil, which was subsequently sown with barley. In the first experiment, different parts of white clover (Trifolium repens), red clover (T. pratense), subterranean clover (T. subterraneum), field bean (Vicia faba), and timothy (Phleum pratense) were used, and in the second, parts of subterranean clover of different maturity. The plant materials were analysed for their initial concentrations of total N, ¹⁵N, C, ethanol-soluble compounds, starch, hemicellulose, cellulose, lignin, and ash. After the barley had been harvested, the bags were collected and analysed for their total N and ¹⁵N. In the first experiment the release of N was highest from white clover stems + petioles (86%) and lowest from field bean roots (20%). In stepwise regression analysis, the release of N was explained best by the initial concentrations of lignin, cellulose, hemicellulose, and N (listed according to decreasing partial correlations). Although the C/N ratio of the plant materials varied widely (11–46), statistically the release of N was not significantly correlated with this variable. The results of the second experiment using subterranean clover of different maturity confirmed those of the first experiment.     

双季连作晚稻免耕抛秧氮钾肥施用技术的研究

研究了不同氮钾施用量对免耕抛秧双季连作晚稻的产量效应。研究表明,增施氮肥可以促进分蘖的发生和叶面积的扩展,增加单位面积的有效穗数,但成穗率下降;增施钾肥可适当提高单位面积的有效穗数和成穗率;各施氮处理水稻根系活力和剑叶叶绿素含量均明显高于无氮处理;随着氮肥用量的增加,水稻干物质的积累量增加,而收获指数减少;等氮条件,增施钾肥对水稻干物质的积累基本没有影响,但提高了氮肥的吸收利用率;氮肥的吸收利用率开始随着施氮量的增加而提高,至中氮处理达最大值,氮肥的生理利用率和农学利用率均随施氮量的增加而降低;氮(N)、钾(K2O)肥用量分别为150 kg/hm2和160 kg/hm2时,免耕抛秧稻的效果最佳。     

Soil microbial biomass and organic matter composition in soils under cultivation

To determine whether there is a relationship between the composition of soil organic matter and the activity of the soil microbial biomass, the composition of the organic matter in 12 typical arable soils in Northwest Germany was investigated by wet chemical analysis and CPMAS cross polarization magic angle spinning ¹³C-NMR spectroscopy. The data were correlated with the microbial biomass as estimated by substrate-induced respiration. A strong correlation between the microbial biomass and alkylic C compounds was observed (r=-0.960^***). Recalcitrant substances were enriched in this fraction, which were classified as humic acids according to the wet chemical procedure. The microbial decomposition of these humic acids is probably retarded, due to their chemical structure and/or physical bonding, when the soil microbial biomass activity is limited.     

Rhizodeposition of C and N in peas and oats after C-N double labelling under field conditions

Compounds released by plant roots during growth can make up a high proportion of below-ground plant (BGP) carbon and nitrogen, and therefore influence soil organic matter turnover and plant nutrient availability by stimulating the soil microorganisms. The present study was conducted to examine the amount and fate of C (CdfR) and N rhizodeposits (NdfR), in this study defined as root-derived C or N present in the soil after removal of roots and root fragments, released during reproductive growth. BGP biomass of peas (Pisum sativum L.) and oats (Avena sativa L.) was successfully labelled in situ with a ¹³C-glucose-¹⁵N-urea mixture under field conditions using a stem feeding method. Pea plants were labelled at the beginning of flowering and harvested 36 and 52 days after labelling at pod filling (P_P) and maturity (P_M), respectively. Oat plants were labelled at grain filling and harvested 42 days after labelling at maturity (O_M). CdfR was 24.2% (P_P), 29.6% (P_M) and 30.8% (O_M) of total recovered plant C. NdfR was 32.1% (P_P), 36.4% (P_M) and 30.0% (O_M) of total plant N. Due to higher N assimilation, amounts of NdfR were four times higher in peas in comparison with oats. The results for NdfR in peas were higher than results from other studies. The C-to-N ratio of rhizodeposits was lower under peas (17.3) than under oats (41.9) at maturity. At maturity, microbial CdfR at 0-30 cm soil depth was 37% of the microbial biomass C in peas and 59% in oats. Microbial NdfR was 15% of microbial N in peas and 5% in oats. Furthermore, inorganic NdfR was 34% in peas and 9% in oats at 0-30 cm at maturity. These results show that rhizodeposits of peas provide a more easily available substrate to soil microorganisms, which are incorporated to a greater extent and turned over faster in comparison with oats. Beside the higher amounts of N released from pea roots, this process contributes to the higher N-availability for subsequent crops.     

烤烟连作对耕层土壤酶活性及微生物区系的影响

以烤烟品种"龙江911"为材料,在大田试验条件下分别测定了连作1年和5年的烤烟耕层土壤酶活性及微生物区系变化。结果表明:烤烟连作1年的耕层土壤酸性磷酸酶与脲酶活性高于正茬(大豆-小麦-烤烟),而烤烟连作5年的土壤酸性磷酸酶与脲酶活性低于连作1年。在0~10 cm土层内,烤烟连作1年和连作5年的土壤过氧化氢酶活性均比正茬低,且连作5年土壤比连作1年土壤降低了35.47%。10~20 cm土层内,烤烟连作1年和5年的土壤蔗糖酶活性分别比正茬降低了30.27%和52.14%。烤烟连作减少了土壤细菌和放线菌数量,增加了真菌数量,细菌主要以土壤氨化细菌、好气性自生固氮菌和好气性纤维素分解菌降低为主。因此,烤烟连作破坏了微生物种群的平衡及降低土壤酶活性可能是引起烤烟连作障碍的主要原因之一。     

连作栽培对当归光合参数日变化的影响

利用CI-310 便携式光合作用系统, 测定正茬(连作0 年)、迎茬(隔年连作)、重茬(连作2 年)3 种种植方式下当归叶片的光合参数, 研究其日变化特征。结果表明: 3 种种植方式下当归叶片净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)和胞间CO₂ 浓度(Ci)的日变化均呈“双峰”曲线, 12:00 时存在明显“午休”现象, 但不同茬口Pn、Tr、Gs 和Ci 高峰和低谷出现的时刻和值不同; 根据Pn、Ci 和Gs 的变化方向, 推测当归叶片的光合“午休”受气孔因素影响; 重茬和迎茬极显著(P<0.01)降低当归叶片叶绿素含量; 正茬种植方式下当归叶片Pn、Gs、Ci 和Tr 的日均值均极显著(P<0.01)和显著(P<0.05)高于重茬。由此得出, 连作栽培显著降低当归叶片的叶绿素含量、Gs、Ci、Pn 和Tr, 进而影响产量形成。     

Use of 13C and 15N natural abundance techniques to characterize carbon and nitrogen dynamics in composting and in compost-amended soils

Isotope fractionation during composting may produce organic materials with a more homogenous δ¹³C and δ¹⁵N signature allowing study of their fate in soil. To verify this, C, N, δ¹³C and δ¹⁵N content were monitored during nine months covered (thermophilic; >40 °C) composting of corn silage (CSC). The C concentration reduced from 10.34 to 1.73 g C (g ash)⁻¹, or 83.3%, during composting. Nitrogen losses comprised 28.4% of initial N content. Compost δ¹³C values became slightly depleted and increasingly uniform (from −12.8±0.6‰ to −14.1±0.0‰) with composting. Compost δ¹⁵N values (0.3±1.3 to 8.2±0.4‰) increased with a similar reduced isotope variability.The fate of C and N of diverse composts in soil was subsequently examined. C, N, δ¹³C, δ¹⁵N content of whole soil (0-5 cm), light (<1.7 g cm⁻³) and heavy (>1.7 g cm⁻³) fraction, and (250-2000 μm; 53-250 μm and <53 μm) size separates, were characterized. Measurements took place one and two years following surface application of CSC, dairy manure compost (DMC), sewage sludge compost (SSLC), and liquid dairy manure (DM) to a temperate (C₃) grassland soil. The δ¹³C values and total C applied (Mg C ha⁻¹) were DM (−27.3‰; 2.9); DMC (−26.6‰; 10.0); SSLC (−25.9‰; 10.9) and CSC (−14.0‰; 4.6 and 9.2). The δ¹³C of un-amended soil exhibited low spatial (−28.0‰±0.2; n=96) and temporal (±0.1‰) variability. All C₄ (CSC) and C₃ (DMC; SSLC) composts, except C₃ manure (DM), significantly modified bulk soil δ¹³C and δ¹⁵N. Estimates of retention of compost C in soil by carbon balance were less sensitive than those calculated by C isotope techniques. One and two years after application, 95 and 89% (CSC), 75 and 63% (SSLC) and 88 and 42% (DMC) of applied compost C remained in the soil, with the majority (80-90%) found in particulate (>53 μm) and light fractions. However, C₄ compost (CSC) was readily detectable (12% of compost C remaining) in mineral (<53 μm) fractions. The δ¹⁵N-enriched N of compost supported interpretation of δ¹³C data. We can conclude that composts are highly recalcitrant with prolonged C storage in non-mineral soil fractions. The sensitivity of the natural abundance tracer technique to characterize their fate in soil improves during composting, as a more homogeneous C isotope signature develops, in addition to the relatively large amounts of stable C applied in composts.     

Savanna-derived organic matter remaining in arable soils of the South African Highveld long-term mixed cropping: Evidence from C and N natural abundance

Sustainable agriculture requires the formation of new humus from the crops. We utilized ¹³C and ¹⁵N signatures of soil organic matter to assess how rapidly wheat/maize cropping contributed to the humus formation in coarse-textured savanna soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) cropped for lengths of time varying from 0 to 98 years, after conversion from native grassland savanna (C4). We performed natural ¹³C and ¹⁵N abundance measurements on bulk and particle-size fractions. The bulk soil δ¹³C values steadily decreased from −14.6 in (C4 dominated) grassland to −16.5‰ after 90 years of arable cropping. This δ¹³C shift was attributable to increasing replacement of savanna-derived C by wheat crop (C3) C which dominated over maize (C4) inputs. After calculating the annual C input from the crop yields and the output from literature data, by using a stepwise C replacement model, we were able to correct the soil δ¹³C data for the irregular maize inputs for a period of about one century. Within 90 years of cropping 41-89% of the remaining soil organic matter was crop-derived in the three studied agroecosystems. The surface soil C stocks after 90 years of the wheat/maize crop rotation could accurately be described with the Rothamsted Carbon Model, but modelled C inputs to the soil were very low. The coarse sand fraction reflected temporal fluctuations in ¹³C of the last C₃ or C₄ cropping and the silt fraction evidenced selective erosion loss of old savanna-derived C. Bulk soil ¹⁵N did not change with increasing cropping length. Decreasing δ¹⁵N values caused by fertilizer N inputs with prolonged arable cropping were only detected for the coarse sand fraction. This indicated that the present N fertilization was not retained in stable soil C pool. Clearly, conventional cropping practices on the South African highlands neither contribute to the preservation of old savanna C and N, nor the effective humus reformation by the crops.     

Fate of residual 15N-labeled fertilizer in dryland farming systems on soils of contrasting fertility

Abstract

Up to 50% of nitrogen (N) fertilizer can remain in soil after crop harvest in dryland farming. Understanding the fate of this residual fertilizer N in soil is important for evaluating its overall use efficiency and environmental effect. Nitrogen-15 (¹⁵N)-labeled urea (165 kg N ha^?1) was applied to winter wheat (Triticum aestivum L.) growing in three different fertilized soils (no fertilizer, No-F; inorganic nitrogen, phosphorus and potassium fertilization, NPK; and manure plus inorganic NPK fertilization, MNPK) from a long-term trial (19 years) on the south of the Loess Plateau, China. The fate of residual fertilizer N in soils over summer fallow and the second winter wheat growing season was examined. The amount of the residual fertilizer N was highest in the No-F soil (116 kg ha^?1), and next was NPK soil (60 kg ha^?1), then the MNPK soil (43 kg ha^?1) after the first winter wheat harvest. The residual fertilizer N in the No-F soil was mainly in mineral form (43% of the residual ¹⁵N), and for the NPK and MNPK soils, it was mainly in organic form. The loss rate of residual ¹⁵N in No-F soil over summer fallow was as high as 48%, and significantly (P < 0.05) higher than that in the NPK soil (22%) and MNPK soil (19%). The residual ¹⁵N use efficiency (RNUE) by the second winter wheat was 13% in the No-F soil, 6% in the NPK soil and 8% in the MNPK soil. These were equivalent to 9.0, 2.0 and 2.2% of applied ¹⁵N. The total ¹⁵N recovery (¹⁵N uptake by crops and residual in 0–100 cm soil layer) in the MNPK and NPK soils (84.5% and 86.6%, respectively) were both significantly higher than that in the No-F soil (59%) after two growing seasons. The ¹⁵N uptake by wheat in two growing seasons was higher in the MNPK soil than in NPK soil. Therefore, we conclude that a high proportion of the residual ¹⁵N was lost during the summer fallow under different land management in dryland farming, and that long-term combined application of manure with inorganic fertilizer could increase the fertilizer N uptake and decrease N loss.     

添加生物炭对酸性红壤中玉米生长和氮素利用率的影响

Biochar added to soil can improve crop growth through both direct and indirect effects, particularly in acidic, highly weathered soils in subtropical and tropical regions. However, the mechanisms of biochar improving crop growth are not well understood. The objectives of this study were i） to determine the crop responses to biochar addition and ii） to understand the effect of biochar addition on N use efficiency. Seven acidic red soils varying in texture, p H, and soil nutrient were taken from southern China and subjected to four treatments： zero biochar and fertilizer as a control（CK）, 10 g kg-1biochar（BC）, NPK fertilizers（NPK）, and 10 g kg-1biochar plus NPK fertilizers（BC＋NPK）.15N-labeled fertilizer was used as a tracer to assess N use efficiency. After a 46-d pot experiment,biochar addition increased soil p H and available P, and decreased soil exchangable Al3＋, but did not impact soil availabe N and cation exchange capacity（P 〉 0.05）. The N use efficiency and N retained in the soil were not significantly affected by biochar application except for the soil with the lowest available P（3.81 mg kg-1） and highest exchanageable Al3＋（4.54 cmol kg-1）. Greater maize biomass was observed in all soils amended with biochar compared to soils without biochar（BC vs. CK, BC＋NPK vs. NPK）. This agronomic effect was negatively related to the concentration of soil exchangeable Al3＋（P 〈 0.1）. The results of this study implied that the liming effect of biochar improved plant growth through alleviating Al toxicity and P deficiency, especially in poor acidic red soils.     

长江中游双季稻田不同轮作方式对土壤质量的影响

研究长江中游地区不同种植模式和秸秆还田管理下农田土壤养分、有机碳及其酶活性的变化,评估农业管理措施对土壤质量的影响,可为长江中游双季稻区农业资源高效利用及可持续发展提供理论依据。2012—2017年进行不同轮、连作长期定位试验,设置冬季休耕—双季稻,冬种紫云英—、油菜—、大蒜—和轮作(马铃薯、大蒜、油菜和紫云英年际轮作)—双季稻5个处理,在冬季作物秸秆和水稻秸秆双重还田条件下,通过运用多元方差分析、相关性分析和主成分分析等统计方法,结合南方双季稻田土壤的适宜性,筛选出最小数据集(minimum data set,MDS)中土壤质量指标并测定,最后采用模糊数学方法对双季稻区的土壤质量进行定量评价。结果表明,在长江中游双季稻区,经过6年的冬季种植合适作物并秸秆双重还田,相比冬季休闲处理,除冬季种植大蒜处理外,其他冬种处理均能有效提高稻田土壤质量10.73%～12.91%,不同冬种方式下双季稻田的土壤质量高低依次为不同冬种轮作(0.726)冬季种植油菜(0.723)冬季种植紫云英(0.712)冬季休闲(0.643)冬季种植大蒜(0.638)。由此可见,适宜的轮作方式及秸秆双重还田能显著提高双季稻土壤质量,这为南方稻田健康可持续发展提供了理论支撑。     

不同施氮量对水稻氮素吸收与分配的影响

运用15N示踪法研究了不同施氮量对两个品种水稻（4007和武运粳15）干物质积累量与其对15N吸收及分配的影响。结果表明,当施氮量超过N 150 kg/hm2时, 两个品种水稻子粒产量均不再显著增加。4007在4个施氮量下(N 100,150,200和 250 kg/hm2)分别比无氮区增产22.3%,36.9%,43.2%和38.1%;武运粳15分别增产10.6%,18.8%,27.1%和21.5%。同一施氮量下,4007子粒中15N累积量显著高于武运粳15,但茎叶和根中没有差异。增加施氮量降低了15N在水稻子粒中的分配比例,但提高了茎叶中15N的分配比例。15N在根中的分配比例不受施氮量和品种的影响。研究结果还表明,同一施氮量下,4007对肥料氮的总体利用率要比武运粳15高3～6个百分点。     

Stable carbon isotope ratios of water-extractable organic carbon affected by application of rice straw and rice straw compost during a long-term rice experiment in Yamagata,Japan

ABSTRACT

Hot-water- and water-extractable organic matter were obtained from soil samples collected from a rice paddy 31 years after the start of a long-term rice experiment in Yamagata, Japan. Specifically, hot-water-extractable organic carbon and nitrogen (HWEOC and HWEON) were obtained by extraction at 80°C for 16 h, and water-extractable organic carbon and nitrogen (WEOC and WEON) were obtained by extraction at room temperature. The soil samples were collected from surface (0–15 cm) and subsurface (15–25 cm) layers of five plots that had been treated with inorganic fertilizers alone or with inorganic fertilizers plus organic matter, as follows: PK, NPK, NPK plus rice straw (RS), NPK plus rice straw compost (CM1), and NPK plus a high dose of rice straw compost (CM3). The soil/water ratio was 1:10 for both extraction temperatures. We found that the organic carbon and total nitrogen contents of the bulk soils were highly correlated with the extractable organic carbon and nitrogen contents regardless of extraction temperature, and the extractable organic carbon and nitrogen contents were higher in the plots that were treated with inorganic fertilizers plus organic matter than in the PK and NPK plots. The HWEOC and WEOC δ¹³C values ranged from ?28.2% to ?26.4% and were similar to the values for the applied rice straw and rice straw compost. There were no correlations between the HWEOC or WEOC δ¹³C values and the amounts of HWEOC or WEOC. The δ¹³C values of the bulk soils ranged from ?25.7% to ?23.2% and were lower for the RS and CM plots than for the PK and NPK plots. These results indicate that HWEOC and WEOC originated mainly from rice plants and the applied organic matter rather than from the indigenous soil organic matter. The significant positive correlations between the amounts of HWEOC and HWEON and the amount of available nitrogen (P < 0.001) imply that extractable organic matter can be used as an index for soil fertility in this long-term experiment. We concluded that the applied organic matter decomposed more rapidly than the indigenous soil organic matter and affected WEOC δ¹³C values and amounts.     

头季稻氮肥运筹对再生稻干物质积累、产量及氮素利用率的影响

为探讨头季稻不同肥料运筹方式对再生稻产量和氮素利用率的影响,以杂交稻组合"Ⅱ优航2号"为材料,在头季施氮量225.00kg·hm-2的基础上,研究了不同基蘖穗肥氮素配比[3种基蘖肥与穗肥配比分别为8:2(N1)、7:3(N2)、6:4(N3)]头季稻-再生季稻氮素累积量、干物质生产、产量及氮素利用率的特性。结果表明:与N1、N2相比,头季成熟期N3处理氮素累积量分别增加9.26%、3.54%,头季齐穗期～头季成熟期N3处理氮素转移量分别增加21.47%、6.76%,整个生育期N3处理干物质净积累总量分别增加5.10%、4.78%。N3处理头季产量最高,达12431kg·hm-2,极显著高于N1、N2处理;氮肥利用率达46.44%,比N1、N2处理提高14.81%、5.43%;氮肥农学利用率达20.66kg·kg-1,比N1、N2处理提高14.97%、12.34%。研究结果还表明,头季不同基蘖穗肥氮素配比对再生稻再生季的影响不显著。     

Effects of preceding compost application on the nitrogen budget in an upland soybean field converted from a rice paddy field on gray lowland soil in Akita,Japan

Abstract

The annual nitrogen (N) budget was measured in a soybean-cultivated upland field during the first year after conversion from a paddy field on gray lowland soil, which is typically found on the Sea of Japan side of northern Japan. Forage rice was cultivated on lysimeter fields for 4 consecutive years with applications of chemical fertilizer, immature compost, or mature compost (the control, immature compost, and mature compost plots, respectively), and then the fields were converted to upland fields for soybean (Glycine max [L.] Merrill cultivar Ryuho) cultivation. Input (seed, bulk N deposition, and symbiotic dinitrogen [N₂] fixation) and output (harvested grain, leached N via drainage water, and nitrous oxide emission) N flows were measured, and the field N budget was estimated from the difference between the input and output. The soybean plants in the immature and mature compost plots grew well and had higher yields (498–511 g m)^?2) compared to the control plot (410 g m)^?2). Total N accumulation in the soybean plants derived from N₂ fixation (g N m)^?2) in the mature compost plot (27.7) was higher than those in the control (18.1) and immature compost plots (19.9). Percentages of soybean N accumulation derived from N₂ fixation ranged from 53% to 74%. N derived from symbiotic N₂ fixation accounted for more than 90% of the total N input, whereas harvested grain accounted for approximately 85% of the total N output. N leaching mainly occurred during the fallow period, accounting for 13–15% of the total N output. The annual N budgets were negative (?10.0,?14.2, and ?6.4 g N m)^?2 year)^?1 for the control, immature compost, andmature compost plots, respectively). The Nloss from the immature compost plot was higher than that of the control plot, because the N output in harvested grain was higher, and the N input by N₂ fixation was similar between plots. While the N loss from the mature compost plot was lower than that of the control plot because the N output in harvested grain was higher, as was the case in the immature compost plot, the N input by N₂ fixation was also higher. Preceding compost application—whether immature or mature compost—to paddy fields increased the subsequent soybean yield during the first year after conversion. This result suggests that N loss and the following decrease in soil N availability in the field could be mitigated by increased N₂ fixation resulting from mature compost application with an appropriate application practice.