Are decomposition and N release from organic mulches determined mainly by their chemical composition?

The influence of chemical composition on the decomposition and N release rates from samples of 11 organic mulches enclosed in nylon mesh bags was assessed under field conditions at the University of California, Riverside. Time was adjusted by temperature and the cumulative temperature-adjusted days (tad) were used to model the pattern of the decay and N release. The chemical composition of the mulches significantly affected their decay. In descending order of significance, the concentration of the polar extractable carbon fraction (C_P) and the acid insoluble fraction (C_AI) were significantly correlated with decomposition during the year of study. Correlation was positive with C_P and N and negative with C_AI (mostly lignin). The C_P was selected as the best predictor for mulch decomposition during the early and intermediate phases of this process (36 and 195 tad), but C_AI was selected as the best variable for predicting the fraction of the initial mulch mass remaining at the end of the study (397 tad). N was immobilized, as indicated by temporary increases in N masses in mulches above initial conditions, in shredded redwood, pine trimmings and in two of three compost mulches. Immobilization was most pronounced during the first 36 tad of the study, with a maximum rate that varied from 6 to 11.5% above the initial N concentrations. At the end of the study N releases ranged from 97% of initial N (grass clippings) to only 8% (one of the composts.) The C_P was selected as the best predictor for N remaining in the four sampling dates (397 tad) and explained from 52 to 68% of the variation in N release as a percentage of initial N content.     

Water and temperature dynamics in a clay soil under winter wheat: influence on straw decomposition and N immobilization

Summary Winter wheat grown on a clay soil was subjected to one of four treatments. The control was not irrigated; the drought treatment had screens to divert rainwater; the irrigation and irrigation/fertilization treatments were irrigated using a drip-tube system with liquid fertilizer (200 kg N ha^-1 year^-1) applied daily in the irrigation/fertilization treatment according to predicted plant uptake. All other treatments also received 200 kg N, but as a single application of bag fertilizer. Soil temperature was monitored. Soil moisture was measured using gravimetric samplings and a capacitance method. Litter bags with barley straw were buried at 10 cm depth in the spring and sampled repeatedly during the growing season. Decomposition rates were calculated assuming exponential decay and that water-soluble components were immediately decomposed or leached from the litter bags. Rates were highly dependent on soil moisture, and the constants ranged from 0.11% day^-1 in the drought treatment to 0.55% day^-1 in the irrigation/fertilization treatment. A simulation model with driving variables based on Q ₁₀ temperature dependence and a log/linear relationship between soil water tension and activity was fitted to the data. The control and drought treatments showed high climate-corrected decomposition constants. The high values were attributed to low and erratic mass loss due to drought, and to low precision in the conversions from water content to tension in the dry range. The irrigated treatments showed good fits, and there was little or no difference in decomposition rates between the two irrigated treatments. The N dynamics of the straw differed considerably between treatments, and the ranking of plots in terms of net immobilization in the straw was control>irrigation/fertilization>irrigation>drought.     

Differential effects of soil properties on leaf nitrogen release

 Identifying the determinants of the N dynamics of plant prunings or litter is important for the efficient management of agroecosystems in order to improve their productivity. The plant materials in these ecosystems are managed as soil surface mulches or are incorporated into the soil. Numerous studies have been conducted to investigate which plant chemical parameter best governs N release. In these studies, different plant materials have been incorporated into a soil with a set of known characteristics. The objective of the present study was to examine the effects of different soil properties on N release from plant leaves, when they were incorporated into soils under non-leaching conditions. A laboratory incubation experiment (for 8 weeks) was carried out with dried and ground leaves of six leguminous plants and wild sunflower, which were mixed with three soils (alfisol; ultisol, udult; ultisol, humult). Leaf cellulose was the major chemical parameter that determined leaf N release in the alfisol and ultisol, udult. In the ultisol, humult, the C/N ratio and hemicellulose concentration were better related to N release. Cellulose was not a good indicator of N release in the ultisol, humult, possibly due to a low soil pH which did not favour the activity of the cellulose-degrading enzymes of microbes active in decomposition. Soil pH determined the specific C source that was used to generate energy for microbial action and N mineralization/immobilization. It also had an effect on the nitrification of the mineralized N. The levels of labile soil C fractions governed the mode or nature of N release (i.e. mineralization or immobilization). The levels of labile leaf C fractions incorporated into the soils governed the extent of N release. The soil N concentration in the decomposable organic matter pool, as compared to the leaf N concentration, determined whether leaf N limited its own release. It is recommended from this study that, in grouping different leaf materials as sources of N, the properties of soils into which they are incorporated should also be considered, in addition to leaf quality in terms of its chemical composition. In future studies, the relationships identified under laboratory conditions in this experiment should be verified under field conditions. Received: 3 December 1997     

不同作物秸秆在旱地和水田中的腐解特性及养分释放规律

以水稻、小麦、玉米秸秆和油菜、蚕豆青秆为研究对象,采用尼龙网袋法,研究了不同秸秆翻埋入旱地和水田后的腐解特性及养分释放规律,以期为紫色丘陵区农业秸秆循环利用和秸秆还田技术提供理论依据。结果表明:秸秆翻埋还田后,5种供试秸秆腐解速率均表现为前期(0~60 d)快、后期(60~360 d)慢。经过360 d的腐解,旱地秸秆累积腐解率为52.88%~75.80%,表现为油菜水稻玉米小麦蚕豆趋势,且蚕豆青秆累积腐解率显著低于其余秸秆;水田中秸秆累积腐解率为45.01%~62.12%,表现为水稻玉米小麦油菜蚕豆趋势。5种秸秆在旱地和水田中养分释放率均表现为钾磷氮碳,在试验终点,旱地中秸秆碳、氮、磷和钾释放率分别为65.50%~87.37%、54.64%~69.72%、89.65%~98.96%和79.92%~96.63%,且油菜秸秆养分释放率高于其他4种秸秆;水田中秸秆碳、氮、磷、钾释放率变幅分别为49.95%~69.57%、32.89%~77.11%、90.70%~96.80%、77.45%~90.47%。总体表现为秸秆在旱地土壤中的累积腐解率和养分释放率均大于水田,旱地油菜和水稻秸秆较易腐解,水田水稻和玉米秸秆较易腐解释;秸秆中钾素释放速率较高。     

The impact of harvester ants on decomposition, N mineralization, litter quality, and the availability of N to plants in the Mojave Desert

In arid areas of North America, nests of the seed-harvesting ant Pogonomyrmex rugosus tend to be elevated in mineral nitrogen and other soil nutrients relative to other microhabitats. We investigated the roles of decomposition, N mineralization, and plant nutrient uptake in maintaining high standing stocks of nutrients in P. rugosus ant nests. Decomposition rates of standard cellulose substrates placed on the surface of ant nests and other desert microhabitats suggest that conditions found in ant nests and bare areas are conducive to higher rates of decomposition than conditions under shrubs. In laboratory incubations of moist soil, net N mineralization rates were significantly higher in soil from ant nests than from bare areas and under two of three plant species. Net N mineralization rates measured in situ were much lower than those measured in laboratory incubations, but ant nest soil still exhibited higher rates at one of two sites. Litter collected from ant mounds, composed chiefly of seed chaff, was similar in N content to litter collected from underneath the dominant plant species, but had a significantly higher mean δ¹⁵N. Using this distinctive isotope signature as a tracer, we found no evidence that large perennial shrubs tap ant nests as a source of N. An invasive, annual grass species was significantly enriched in ¹⁵N, had higher leaf %N, and produced more seeds when growing on the mound than when growing several meters away; however P. rugosus nest surfaces are typically free of such annuals. We conclude that both high rates of nutrient cycling relative to other Mojave Desert microhabitats and low N utilization by the surrounding vegetation contribute to high standing stocks of mineral N in P. rugosus nests.     

Nitrogen transfer between decomposing leaves of different N status

Nitrogen movement among microsites is thought to be an important control on patterns of ecosystem-level N cycling. In particular, N transfer between decomposing leaves may explain why litter mixtures sometimes decompose differently than would be predicted from the decomposition dynamics of each species separately. We evaluated how N moves between leaves of differing N status in leaf-pair microcosms. We collected litter from six species of trees from French Guiana (three with high N concentration, three with low) and ¹⁵N-labeled the microbial communities growing on each species. We then established microcosms with one labeled and one unlabeled leaf in a fully factorial design (each species with every species, ¹⁵N on each species) and measured ¹⁵N transfer over 28 days. There was substantial transfer of the ¹⁵N label in all cases, averaging between 15% and 30% of the ¹⁵N originally on the labeled leaf. Net N transfer from high-N to low-N leaves resulted from greater gross ¹⁵N transfer from high-N to low-N leaves than in reverse. Gross ¹⁵N transfer was controlled entirely by the N status of the source leaf, rather than by the difference in N-status of the leaves or by the characteristics of the sink leaf. For example, as much ¹⁵N was transferred from a high-N leaf to another high-N leaf as to a low-N leaf. These results support the assumption from N mineralization theories that microbes at a specific site have first access to that N and therefore control how much N is available to move to other microsites in the soil system. The strength of the gradient between microsites may then control the rate at which available N moves, but not how much N is available to move. If N transfer among different litter species is important for synergistic effects on decomposition of litter mixtures it would not be driven by the N gradient as is often hypothesized, but by the characteristics of the source leaf.     

Contributions from different microbial processes to N2O emission from soil under different moisture regimes

Nitrous oxide emissions from a sandy-loam textured soil wetted to matric potentials of either-1.0 or-0.1 kPa were determined in laboratory experiments in which the soil was incubated in air (control), air plus 10 Pa C₂H₂ (to inhibit nitrification), 100 kPa O₂ (to suppress denitrification), 10 kPa C₂H₂ (to inhibit N₂O reduction to N₂ in denitrification) or following autoclaving. The total N₂O production, consumption and net N₂O emission from the soils together with the contributions to N₂O emission from different processes of N₂O production were estimated. The rate of N₂O production was significantly greater in the wetter soil (282 pmol N₂O g^-1 soil h^-1) than in the drier soil (192 pmol N₂O g^-1 soil h^-1), but because N₂O consumption by denitrifiers was also greater in the wetter soil, the net N₂O emissions from the wetter and the drier soils did not differ significantly. Non-biological sources made no significant contribution to N₂O emission under either moisture regime and biological processes other than denitrification and nitrification made only a small contribution (1% of the total N₂O production) in the wetter soil. Denitrifying nitrifiers were the predominant source of N₂O emitted from the drier soil and other (non-nitrifying) denitrifiers were the predominant source of N₂O emitted from the wetter soil.     

氮素形态对油菜秸秆腐解及养分释放规律的影响

采用尼龙网袋研究法,研究了不同形态氮素对油菜秸秆腐解及养分释放规律的影响,以期为农业秸秆循环利用和改善秸秆还田效果提供理论依据。试验设置4个处理：不添加氮素（CK）、添加尿素（PU）、添加尿素硝酸铵（UAN）和添加石灰氮（CaCN₂）,周期120 d。结果表明,油菜秸秆腐解表现为前期快（0~30 d）、后期慢（30~120 d）的特征。120 d时,油菜秸秆累积腐解率为46.08%~52.34%,碳、氮、磷和钾的释放率分别为44.25%~51.52%、51.19%~54.87%、52.82%~58.45%和96.61%~97.46%。添加氮素可以显著促进油菜秸秆腐解。120 d时,添加氮素处理较CK处理油菜秸秆的累积腐解率提高10.80%~13.59%。不同形态氮素对秸秆的腐解特征和碳氮磷钾释放速率的效应不同。其中,PU处理秸秆腐解过程分两个阶段,快速腐解（0~30 d）和缓慢腐解（30~120 d）;30 d时油菜秸秆的腐解率达40.39%,30 d后腐解速率逐渐趋于稳定,120 d时腐解率达51.06%。UAN处理腐解过程分3个阶段,快速腐解（0~30 d）、腐解减缓（30~60 d）和缓慢腐解（30~120 d）;30 d时腐解率达40.67%,30~60 d腐解率上升7.54%,120 d时腐解率为51.63%。CaCN₂处理的秸秆腐解过程分两个阶段,快速腐解（0~30 d）和缓慢腐解（30~120 d）;其促进腐解作用主要表现在60 d后,60 d时油菜秸秆腐解率达44.37%,120 d时腐解率为52.34%。与不施氮处理相比,120 d时UAN处理秸秆累积腐解率提高12.04%,碳、氮和磷累积释放率分别提高9.33%、7.19%和6.97%。各处理对秸秆钾的释放率影响不显著。综合来看,以UAN促进油菜秸秆腐解的效果较为显著。     

不同还田方式下拉巴豆秸秆腐解及养分释放特征

为明确拉巴豆秸秆的腐解和养分释放规律,采用网袋法模拟研究拉巴豆在覆盖还田、土埋还田和水淹还田方式下的腐解动态。结果表明:不同还田方式下,拉巴豆茎秆在0~20 d腐解速率较快,之后腐解缓慢;在100d时,覆盖还田、土埋还田和水淹还田方式下累计腐解率分别达42.4%、74.3%、66.9%。经过100 d的腐解,覆盖还田方式下碳、氮、磷、钾的累计腐解率分别为28.8%、14.3%、47.7%、86.2%;土埋还田方式下碳、氮、磷、钾的累计腐解率分别为68.0%、62.3%、85.2%、94.8%;水淹还田方式下碳、氮、磷、钾的累计腐解率分别为63.0%、55.0%、82.0%、91.1%,拉巴豆茎秆养分的释放速率表现为钾磷碳氮。3种还田方式下茎秆累计腐解率及碳、氮、磷、钾等养分的累计释放率均表现为土埋还田水淹还田覆盖还田。     

不同覆盖材料土壤生态效应与玉米增产效应研究

田间试验研究不同覆盖材料土壤生态效应与玉米增产效应结果表明,小麦秸秆、地膜、高粱秆片和纸板覆盖均有显著保水作用及明显水分表聚现象,即0～10cm表层土壤含水量明显高于下层土壤,地膜覆盖兼有显著增温效应,而小麦秸秆、高粱秆片和纸板覆盖土壤温度却明显低于对照。除纸板外其他覆盖材料均不同程度增加0～2 0cm土层土壤细菌、真菌和放线菌数量,且以秸秆覆盖增幅最大。各覆盖处理均显著增加玉米株高、茎粗和叶面积指数,不同程度提高玉米生育前期倒1、2、3叶净光合速率。小麦秸秆、地膜、高粱秆片、纸板覆盖处理分别比对照增产19.4 %、17.2 %、16 .1%和13.3% ,其增产原因主要是由于穗长和穗粒数的增加所致     

Constant and diurnally-varying temperature regimes lead to different temperature sensitivities of soil organic carbon decomposition

In a 122-day incubation experiment with two soil types under four temperature treatments, we examined whether the temperature sensitivity of soil organic carbon (SOC) decomposition differed between constant and diurnally-varying soil temperature regimes. We calculated the Q₁₀ values after accounting for changes in substrate availability and quality among treatments over time. The Q₁₀ values under constant temperature regime were consistently and significantly higher than those under diurnally-varying temperature regime, particularly in the later stages of decomposition (by up to 30%). This result indicated that different temperature regime was one of the important factors causing the current controversy about the temperature sensitivity of SOC decomposition in published reports.     

Tree pruning mulch increases soil C and N in a shaded coffee agroecosystem in Hawaii

Agroforestry can increase the sequestration of carbon (C) in soils of tropical agroecosystems through increased litter and tree pruning inputs. Decomposition of these inputs is a key process in the formation of soil organic matter and in nutrient cycling. Our objectives were to study decay of tree pruning mulch and effects on soil C and N in a shaded coffee agroecosystem in Hawaii. Chipped tree pruning residues (mulch) were added to coffee plots shaded with the Leucaena hybrid KX2 over three years. We measured mulch decomposition and nitrogen loss over one year and changes in soil carbon and nitrogen (N) over two years. Mass loss of mulch was 80% over one year and followed first-order decay dynamics. There was significant loss from all major biochemical components. Net N loss from the mulch was positive throughout the entire period. The C:N and lignin:N ratios of the mulch declined significantly over the decomposition period. Mulch additions significantly increased soil C and N in the top 20 cm by 10.8 and 2.12 Mg ha⁻¹, respectively. In the no-mulch treatment, there was no significant change in soil C or N concentration, but a decline in soil bulk density led to a significant decline in total soil C. Leucaena mulch can provide an important source of organic C and N to coffee agroecosystems and can help sequester C lost as plant biomass during shade tree management.     

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.     

膜下滴灌玉米番茄间作农田土壤水分分布特征模拟

间作种植和覆膜滴灌是实现高产和节水的重要技术,已被广泛应用,而掌握覆膜滴灌条件下间作种植农田土壤水分分布特征对于提高水分利用效率以及增产增收都具有重要意义。该文通过2a田间试验设置高(T1)、中(T2)、低(T3)3个灌水定额处理,并通过HYDRUS2D模型模拟了间作滴灌农田不同位置土壤水分的差异性、水平水量交换以及土壤水分二维分布特征。结果表明:基于HYDRUS2D构建的间作种植滴灌农田土壤水分模型精度较高,平均相对误差为5.72%～8.14%,决定系数在0.85～0.90,均方根误差在0.017～0.023 cm~3/cm~3。对于3个灌水处理皆表现为0～40 cm土层含水率出现差异,且在0～20 cm土层含水率差异显著,2014年番茄侧和玉米侧土壤含水率在3个灌水处理下的平均土壤含水率分别较裸地高20.17%和17.83%,2015年为16.02%和12.99%。间作滴灌农田土壤水平水量交换强烈,生育期水流主要由作物侧流入裸地侧,其中对于3个灌水处理在番茄侧0～40 cm土层净流入裸地的平均水量是玉米侧的1.3倍,约为60mm/a,并且0～40cm土层由作物侧流入裸地的水量是40～100cm土层的2.5倍。二维土壤水分分布显示,滴灌湿润体与作物根系分布匹配性较好,灌水后1d湿润饱和区主要集中在0～30cm土层,其中T1、T2、T3处理的饱和区面积分别为559.14,288.61和109.78 cm~2。灌水2 d后,低灌水处理(T3)存在较明显的水分亏缺,缺水区面积是充分灌溉(T1)的30倍。研究结果可为间作滴灌农田制定灌溉制度提供参考。     

不同保水剂对土壤水分和氮素保持的比较研究

保水剂应用对土壤水肥利用效率具有重要影响。本文采用土柱模拟试验方法,以不施保水剂处理为对照,比较3种保水剂——聚丙烯酸盐类保水剂(A)、有机–无机复合保水剂(B)、腐植酸型多功能保水剂(C)对土壤水分和两种氮肥(尿素、硝酸铵)的保持效应,筛选保水剂与氮肥的合理施用配合。8次土壤淋溶结果表明:3种保水剂对土壤水分和两种氮肥都有保持作用,但差异明显。在保水方面,A、B保水剂土壤水分保持效果较好且保水效果相近,C保水剂相对较差;随浇水次数增加,3种保水剂的保水效果均有所降低。在保肥方面,C保水剂对两种氮素的保持效果显著优于对照,且对硝酸铵保持效果优于对尿素的保持效果;A保水剂对尿素的保持效果明显,但对硝酸铵的保持效果很小,淋溶8次后,甚至对氮素淋溶有促进作用;B保水剂对尿素的保持效果8次淋溶后与C保水剂相近,对硝酸铵的保持效果介于其他两种保水剂之间。此外,保水剂对土壤脲酶活性有一定影响,其变化与氮素转化有关;施用尿素的土壤中,保水剂对土壤脲酶活性的影响为B保水剂C保水剂A保水剂,而施用硝酸铵的土壤中为A保水剂B保水剂C保水剂。     

不同植被覆盖条件下土壤水分蒸发的比较

 为探讨不同植被对当地土壤水分动态变化及其蒸发过程的影响,于2001年7—10月,对宁夏固原县4种不同植被覆盖下土壤水分蒸发做了对比研究。在观测期内,不同条件下土壤水分蒸发的强弱依次表现为,弃耕地>华北落叶松林地>铁杆蒿+长芒草地>中国沙棘林地;各种条件下,土壤水分蒸发在生长季的旺盛时期(7—8月)要显著高于生长季后期(9—10月)。土壤水分蒸发的昼夜分段测定表明,在观测期内,土壤水分的蒸发在夜间出现了“负平衡”,尤其进入9—10月以后,这一现象更为突出,说明夜间凝结水数量大于相应的蒸发量。     

环保地膜覆盖对土壤水分及玉米产量的影响

为了提高旱作农区降雨利用效率,并解决地膜覆盖造成的环境污染问题,在渭北旱塬进行了普通地膜、生物降解膜和液态膜玉米集雨种植栽培试验。结果表明：普通地膜和生物降解膜覆盖处理在玉米不同生育阶段较对照0～60 cm土层土壤贮水量均有所提高,与液态膜及不覆盖处理（CK）相比呈显著性差异（p＜0.05）;不同材料覆盖处理的土壤水分空间变化规律相同,普通地膜和生物降解膜覆盖处理可有效提高土壤含水率,并能增强0～200 cm土层土壤含水率的稳定性;普通地膜和生物降解膜处理的玉米籽粒产量比对照（CK）分别提高了19.96%和19.67%,水分利用效率分别比对照提高32.08%和31.81%,均与对照（CK）呈显著性差异,液态膜处理的籽粒产量及水分利用效率与对照无显著性差异。可见,生物降解膜与普通地膜在土壤保水及对玉米产量的影响方面均具有显著效果,且相互间没有明显差异,生物降解膜可以替代普通地膜应用于农业生产。     

土壤水分状况对14C标记秸秆的腐解及腐殖质中碳素分布的影响

¹⁴C-tracer technique and closed incubation method were used to study straw ¹⁴C decomposition and distribution in different fractions of newly formed humus under different moisture regimes. Decomposition of straw ¹⁴C was faster during the initial days, and slower thereafter. Decay rate constants of straw ¹⁴C varied from 3.29 × 10^-3 d^-1 to 7.06 × 10^-3 d^-1. After 112 d incubation, the amount of straw ¹⁴C mineralized was 1.17~1.46 times greater in submerged soils than in upland soils. Of the soil residual ¹⁴C, 9.08%~15.73% was present in humic acid (HA) and 31.01%~37.62% in fulvic acid (FA). Submerged condition favored the formation of HA, and HA/FA ratio of newly formed humus (labelled) was greater in submerged soils than in upland soils. Clay minerals affected the distribution of straw ¹⁴C in different humus fractions. Proportion of ¹⁴C present in HA to ¹⁴C remaining in soil was greater in Vertisol than in Ultisol.     

Litterfall,decomposition, and nitrogen release in two age groups of trees in Casuarina equisetifolia plantations in the dry tropical Vindhyan plateau,India

Litterfall, decomposition, and N release in 5-year-old and 8-year-old plantations of Casuarina equisetifolia (Forst.) in the dry tropical region of the Vindhyan plateau were studied during 1989–1990. Maximum litterfall occurred in May. The total litterfall ranged from 7.2 to 9.9t ha^-1 year^-1 in the 5-year-old stand and from 11.3 to 12.7t ha^-1 year^-1 in the 8-year-old stand over the 2-year period. Photosynthetic branchlets contributed 87–95% to the total litter. The relative decomposition rates of litter components of the ash-free mass were highest in the rainy months (4.7 to 9.9mg g^-1 day^-1) followed by winter (2.8 to 3.6 mg g^-1 day^-1) and lowest in the summer months (1.7 to 3.0 mg g^-1 day^-1). Similar patterns were observed for N release. The annual decay constant was highest for cone litter and lowest for photosynthetic branchlets. During decomposition, the photosynthetic branchlets showed N immobilization in November and April, the twig litter in March, and the roots in January and February. N release per unit area (g m^-2) was maximum from the photosynthetic branchlets (5.3–6.3) followed by cones (4.4) > roots (3.4) > twigs (2.6–3.2). The combination of the litter C:N ratio, moisture, and temperature with the relative decomposition rate in a multiple regression analysis explained 66–84% of the variability in mass loss and 58–66% of the variability in N release.     

土壤带状湿润均匀性对膜下滴灌棉花生长及水分利用效率的影响

为探明膜下土壤带状湿润均匀性在膜下滴灌技术应用中的重要性,该文设置滴头流量1.69(W169)、3.46(W346)和6.33 L/h(W633)3种土壤湿润区处理,研究不同膜下土壤带状湿润均匀性对棉花行间土壤基质势、株高、叶面积、根系生长、籽棉产量和水分利用效率的影响。结果表明:随着土壤湿润区由窄深型(W169)向宽浅型(W633)过渡,膜下土壤带状湿润均匀性越好,行间棉花根系分布和植株生长也愈加均匀、产量及水分利用效率也越高。窄深型土壤湿润区的膜下内、边行棉花根长密度、籽棉理论总产和实际总产差值分别为386.3 m/m3、976和509.3 kg/hm2,其水分利用效率分别为7.2和14.8 kg/(mm·hm2)。宽浅型土壤湿润区的膜下内、边行棉花根长密度、籽棉理论总产和实际总产差值分别为142.01 m/m3、171和190.6 kg/hm2,其水分利用效率分别为9.2和11.0 kg/(mm·hm2)。初步证明了宽浅型土壤湿润区能在保持水分利用效率不降低的情况下,显著提高了棉花产量。表明在膜下滴灌技术设计中应关注膜下土壤带状湿润均匀性指标。该指标还是确定滴灌带间距依据。