Effects of different tillage and straw retention practices on soil aggregates and carbon and nitrogen sequestration in soils of the northwestern China

Soil tillage and straw retention in dryland areas may affect the soil aggregates and the distribution of total organic carbon. The aims of this study were to establish how different tillage and straw retention practices affect the soil aggregates and soil organic carbon (SOC) and total nitrogen (TN) contents in the aggregate fractions based on a long-term (approximately 15 years) field experimentin the semi-arid western Loess Plateau, northwestern China. The experiment included four soil treatments, i.e., conventional tillage with straw removed (T), conventional tillage with straw incorporated (TS), no tillage with straw removed (NT) and no tillage with straw retention (NTS), which were arranged in a complete randomized block design. The wet-sieving method was used to separate four size fractions of aggregates, namely, large macroaggregates (LA, >2000 μm), small macroaggregates (SA, 250-2000 μm), microaggregates (MA, 53-250 μm), and silt and clay (SC, <53 μm). Compared to the conventional tillage practices (including T and TS treatments), the percentages of the macroaggregate fractions (LA and SA) under the conservation tillage practices (including NT and NTS treatments) were increased by 41.2%-56.6%, with the NTS treatment having the greatest effect. For soil layers of 0-5, 5-10 and 10-30 cm, values of the mean weight diameter (MWD) under the TS and NTS treatments were 10.68%, 13.83% and 17.65%, respectively. They were 18.45%, 19.15% and 14.12% higher than those under the T treatment, respectively. The maximum contents of the aggregate-associated SOC and TN were detected in the SA fraction, with the greatest effect being observed for the NTS treatment. The SOC and TN contents were significantly higher under the NTS and TS treatments than under the T treatment. Also, the increases in SOC and TN levels were much higher in the straw-retention plots than in the straw-removed plots. The macroaggregates (including LA and SA fractions) were the major pools for SOC and TN, regardless of tillage practices, storing 3.25-6.81 g C/kg soil and 0.34-0.62 g N/kg soil. Based on the above results, we recommend the NTS treatment as the best option to boost soil aggregates and to reinforce carbon and nitrogen sequestration in soils in the semi-arid western Loess Plateau of northwestern China.     

Crop yields and soil organic carbon dynamics in a long-term fertilization experiment in an extremely arid region of northern Xinjiang,China

A long-term fertilization experiment was set up in northern Xinjiang, China to evaluate the dynamics of crop production and soil organic carbon(SOC) from 1990 to 2012 with seven fertilization treatments. The seven treatments included an unfertilized control(CK) and six different combinations of phosphorus(P), potassium(K), nitrogen(N), straw(S) and animal manure(M). The balanced fertilization treatments had significantly(P0.05) higher average yields than the unbalanced ones. The treatment with 2/3 N from potassium sulfate(NPK) and 1/3 N from farmyard manure(NPKM) had a higher average yield than the other treatments. The average yields(over the 23 years) in the treatments of NPK, and urea, calcium superphosphate(NP) did not differ significantly(P0.05) but were higher than that in the treatment with urea and potassium sulfate(NK; P0.05). The results also show that the highest increases in SOC(P0.05) occurred in NPKM with a potential increase of 1.2 t C/(hm~2·a). The increase in SOC was only 0.31, 0.30 and 0.12 t C/(hm~2·a) for NPKS(9/10 N from NPK and 1/10 N from straw), NPK and NP, respectively; and the SOC in the NP, NK and CK treatments were approaching equilibrium and so did not rise or fall significantly over the 23-year experiment. A complete NPK plus manure fertilization program is recommended for this extremely arid region to maximize both yields and carbon sequestration.     

Long-term effects of gravel―sand mulch on soil organic carbon and nitrogen in the Loess Plateau of northwestern China

Gravel–sand mulch has been used for centuries to conserve water in the Loess Plateau of northwestern China. In this study, we assessed the influence of long-term(1996–2012) gravel–sand mulching of cultivated soils on total organic carbon(TOC), light fraction organic carbon(LFOC), microbial biomass carbon(MBC), total organic nitrogen(TON), particulate organic carbon(POC), mineral-associated organic carbon(MOC), permanganate-oxidizable carbon(KMn O4-C), and non-KMn O4-C at 0–60 cm depths. Mulching durations were 7, 11 and 16 years, with a non-mulched control. Compared to the control, there was no significant and consistently positive effect of the mulch on TOC, POC, MOC, KMn O4-C and non-KMn O4-C before 11 years of mulching, and these organic C fractions generally decreased significantly by 16 years. LFOC, TON and MBC to at a 0–20 cm depth increased with increasing mulching duration until 11 years, and then these fractions decreased significantly between 11 and 16 years, reaching values comparable to or lower than those in the control. KMn O4-C was most strongly correlated with the labile soil C fractions. Our findings suggest that although gravel–sand mulch may conserve soil moisture, it may also lead to long-term decreases in labile soil organic C fractions and total organic N in the study area. The addition of manure or composted manure would be a good choice to reverse the soil deterioration that occurs after 11 years by increasing the inputs of organic matter.     

长期定位施肥对旱作农田土壤有机碳及其组分的影响

基于田间定位试验,研究了长期施肥对旱作冬小麦农田土壤有机碳及其组分的影响,试验包括4个处理:不施肥(CK)、氮磷配施(NP)、化肥与有机肥配施(NPM)以及长期休闲地(BL)。结果表明:长期持续施肥30年后,在0~30 cm土层,NPM处理土壤有机碳、微生物量碳、潜在矿化碳以及碳库管理指数分别较CK提高了42.2%、55.9%、40.9%和40.0%(P0.05),NP处理土壤有机碳和微生物量碳与CK差异不显著,潜在矿化碳和碳库管理指数分别提高了29.1%和20.0%(P0.05),施肥对两种活性有机碳含量的影响在15~30 cm土层表现更加显著;与种植作物相比,长期休闲显著降低了土壤潜在矿化碳含量,BL处理较CK降低了20.5%(P0.05)。相关性分析表明,土壤有机碳、潜在矿化碳、微生物量碳以及碳库管理指数两两之间存在着显著的相关性,且有机碳组分含量与土壤有机碳含量在处理间变化具有一致性(除NP处理外),两种活性有机碳相对含量在各处理间差异均不显著。总的来说,长期持续施入有机肥能够有效地增加旱作农田土壤有机碳同时增加其活性组分,有助于培肥地力和土壤固碳。     

Effects of long-term cultivation practices and nitrogen fertilization rates on carbon stock in a calcareous soil on the Chinese Loess Plateau

Soil organic carbon(SOC) and soil inorganic carbon(SIC) are important C pools in the Loess Plateau of Northwest China, however, variations of SOC and SIC stocks under different cultivation practices and nitrogen(N) fertilization rates are not clear in this area. A long-term field experiment started in June 2003 was conducted to investigate the SOC and SIC stocks in a calcareous soil of the Chinese Loess Plateau under four cultivation practices, i.e., fallow(FA), conventional cultivation(CC), straw mulch(SM), and plastic film-mulched ridge and straw-mulched furrow(RF), in combination with three N fertilization rates, i.e., 0(N0), 120(N120), and 240(N240) kg N/hm~2. Results indicate that the crop straw addition treatments(SM and RF) increased the contents of soil microbial biomass C(SMBC) and SOC, and the SOC stock increased by 10.1%–13.3% at the upper 20 cm soil depth in comparison to the 8-year fallow(FA) treatment. Meanwhile, SIC stock significantly increased by 19% at the entire tested soil depth range(0–100 cm) under all crop cultivation practices in comparison to that of soil exposed to the long-term fallow treatment, particularly at the upper 60 cm soil depth. Furthermore, moderate N fertilizer application(120 kg N/hm~2) increased SOC stock at the upper 40 cm soil depth, whereas SIC stock decreased as the N fertilization rate increased. We conclude that the combined application of crop organic residues and moderate N fertilization rate could facilitate the sequestrations of SOC and SIC in the calcareous soil.     

Changes in aggregate-associated organic carbon and nitrogen after 27 years of fertilization in a dryland alfalfa grassland on the Loess Plateau of China

Changes in the distribution of soil aggregate sizes and concentrations of aggregate-associated organic carbon(OC) and nitrogen(N) in response to the fertilization of grasslands are not well understood. Understanding these changes is essential to the sustainable development of artificial grasslands. For understanding these changes, we collected soil samples at 0–20 and 20–40 cm depths from a semi-arid artificial alfalfa grassland after 27 years of applications of phosphorus(P) and nitrogen+phosphorus+manure(NPM) fertilizers on the Loess Plateau of China. The distribution of aggregate sizes and the concentrations and stocks of OC and N in total soils were determined. The results showed that NPM treatment significantly increased the proportions of 2.0 mm and 2.0–0.25 mm size fractions, the mean geometric diameter(MGD) and the mean weight diameter(MWD) in the 0–20 cm layer. Phosphorous fertilizer significantly increased the proportion of 2.0 mm size fractions, the MGD and the MWD in the 0–20 cm layer. Long-term application of fertilization(P and NPM) resulted in the accumulation of OC and N in soil aggregates. The largest changes in aggregate-associated OC and N in the 0–20 cm layer were found at the NPM treatment, whereas the largest changes in the 20–40 cm layer were found at the P treatment. The results suggest that long-term fertilization in the grassland leads to the accumulation of OC and N in the coarse size fractions and the redistribution of OC and N from fine size fractions to coarse size fractions.     

长期施肥对绿洲农田土壤有机碳和无机碳的影响

以中国科学院阜康荒漠生态站的绿洲农田养分循环长期定位试验（始于1990年）为研究平台,研究了无施肥处理（CK）、单施化肥处理（NPK）、有机/无机配施处理（NPKM）和秸秆还田处理（NPKS）下,土壤无机碳(SIC)和有机碳(SOC)在剖面和各施肥年限的含量变化特征及其影响。结果表明：施肥、剖面层次和施肥年限对SOC与SIC含量变化影响显著(P<0.01)。在各施肥处理中,与CK相比,NPK、NPKM和NPKS的SOC与SIC含量明显增加(P<0.05）,并且有机/无机肥配施模式下的SIC含量显著高于单施化肥模式;在剖面层次间,SIC含量从0～20 cm 的9.12 g/kg 增加到40～60 cm 的9.94 g/kg,而SOC变化趋势与之相反。表明合理施肥能够增加土壤表层有机碳含量,有机/无机配施会使耕层以下土壤无机碳增加。     

Hierarchical responses of soil organic and inorganic carbon dynamics to soil acidification in a dryland agroecosystem,China

Soil acidification is a major global issue of sustainable development for ecosystems. The increasing soil acidity induced by excessive nitrogen(N) fertilization in farmlands has profoundly impacted the soil carbon dynamics. However, the way in which changes in soil p H regulating the soil carbon dynamics in a deep soil profile is still not well elucidated. In this study, through a 12-year field N fertilization experiment with three N fertilizer treatments(0, 120, and 240 kg N/(hm~2·a)) in a dryland agroecosystem of China, we explored the soil p H changes over a soil profile up to a depth of 200 cm and determined the responses of soil organic carbon(SOC) and soil inorganic carbon(SIC) to the changed soil p H. Using a generalized additive model, we identified the soil depth intervals with the most powerful statistical relationships between changes in soil p H and soil carbon dynamics. Hierarchical responses of SOC and SIC dynamics to soil acidification were found. The results indicate that the changes in soil p H explained the SOC dynamics well by using a non-linear relationship at the soil depth of 0–80 cm(P=0.006), whereas the changes in soil p H were significantly linearly correlated with SIC dynamics at the 100–180 cm soil depth(P=0.015). After a long-term N fertilization in the experimental field, the soil p H value decreased in all three N fertilizer treatments. Furthermore, the declines in soil p H in the deep soil layer(100–200 cm) were significantly greater(P=0.035) than those in the upper soil layer(0–80 cm). These results indicate that soil acidification in the upper soil layer can transfer excess protons to the deep soil layer, and subsequently, the structural heterogeneous responses of SOC and SIC to soil acidification were identified because of different buffer capacities for the SOC and SIC. To better estimate the effects of soil acidification on soil carbon dynamics, we suggest that future investigations for soil acidification should be extended to a deeper soil depth, e.g., 200 cm.     

Changes in soil organic carbon and nitrogen after 26 years of farmland management on the Loess Plateau of China

Soil carbon(C) and nitrogen(N) play a crucial role in determining the soil and environmental quality. In this study, we investigated the effects of 26 years(from 1984 to 2010) of farmland management on soil organic carbon(SOC) and soil N in abandoned, wheat(Triticum aestivum L.) non-fertilized, wheat fertilized(mineral fertilizer and organic manure) and alfalfa(Medicago Sativa L.) non-fertilized treatments in a semi-arid region of the Loess Plateau, China. Our results showed that SOC and soil total N contents in the 0–20 cm soil layer increased by 4.29(24.4%) and 1.39 Mg/hm2(100%), respectively, after the conversion of farmland to alfalfa land. Compared to the wheat non-fertilized treatment, SOC and soil total N contents in the 0–20 cm soil layer increased by 4.64(26.4%) and 1.18 Mg/hm2(85.5%), respectively, in the wheat fertilized treatment. In addition, we found that the extents of changes in SOC, soil total N and mineral N depended on soil depth were greater in the upper soil layer(0–30 cm) than in the deeper soil layer(30–100 cm) in the alfalfa land or fertilizer-applied wheat land. Fertilizer applied to winter wheat could increase the accumulation rates of SOC and soil total N. SOC concentration had a significant positive correlation with soil total N concentration. Therefore, this study suggested that farmland management, e.g. the conversion of farmland to alfalfa forage land and fertilizer application, could promote the sequestrations of C and N in soils in semi-arid regions.     

长期秸秆和地膜覆盖对旱作冬小麦农田土壤碳组分的影响

地表覆盖秸秆和地膜是我国西北旱作农田土壤固碳的重要田间管理措施,但其对土壤碳组分的长期影响尚不明确。基于田间定位试验,设生育期高量秸秆覆盖(9 000 kg·hm^-2,HSM)、生育期低量秸秆覆盖(4 500 kg·hm^-2,LSM)、夏闲期秸秆覆盖(9 000 kg·hm^-2,FSM)、生育期地膜覆盖(PM)和无覆盖对照(CK)共5个处理,研究了秸秆覆盖和地膜覆盖12 a和13 a后旱作冬小麦农田土壤总有机碳(SOC)、颗粒有机碳(POC)、潜在矿化碳(PCM)和微生物量碳(MBC)含量的变化规律。2 a平均结果表明：与CK相比,HSM和LSM处理均显著提高了0～10 cm土层各碳组分含量以及10～20 cm土层SOC、POC、MBC含量,同时还显著提高了0～20 cm土层POC和MBC占SOC的比例;而FSM和PM处理对各土层土壤碳组分含量及其占SOC的比例均无显著影响。土壤碳组分含量相互之间均存在极显著正相关关系。综上可知,长期生育期秸秆覆盖能有效提高旱作冬小麦农田耕层土壤有机碳及其组分含量,且提高覆盖量有助于促进...     

不同比例有机肥替代化肥对玉米生长及水分利用效率的影响

为了探索黄土高原半干旱区全膜双垄沟播玉米适宜的有机氮替代无机氮水平,于2018—2019年通过大田试验研究了单施化肥(F100M0)、有机肥50%替代(F50M50)、有机肥37.5%替代(F62.5M37.5)、有机肥25%替代(F75M25)以及有机肥12.5%替代(F87.5M12.5)化肥和不施肥(CK)对玉米耗水特性、籽粒产量及水分利用效率的影响。结果表明：两个丰水年,玉米耗水差异主要表现在播种期50~110 cm土层和成熟期10~30 cm土层;与对照相比,F62.5M37.5和F87.5M12.5处理的籽粒产量和生物产量分别较对照增加100.6%、122.0%和132.7%、156.8%,水分利用效率和降水利用效率分别增加了73.1%、165.1%和93.6%、179.8%,水分利用效率和降水利用效率增加的原因主要是F62.5M37.5和F87.5M12.5处理协调了籽粒产量与耗水量之间的关系,使玉米水分利用效率和降水利用效率较对照分别增加。所有处理中,F87.5M12.5处理表现出与单施化肥相当的经济效益。因此,在200 kg·hm^-2施氮水平下,适度降低有机肥替代比例能提高玉米的水分利用效率和经济效益,本研究推荐有机肥替代化肥的水平为12.5%~37.5%。     

长期施肥对土肥力及作物产量的影响

对陕西关中典型土壤———土进行了连续25 a的定位施肥试验。通过对25年来不同施肥小区土壤肥力差异的分析研究表明:多年连续施肥,可以明显提高土壤中有机质、全氮、全磷、碱解氮、速效磷含量以及作物产量,即单施化肥或有机—无机肥料配合施用,都可以增强土壤养分容量及其供应强度,有利于培肥土壤,提高作物产量,其中又以有机—无机肥料配合施用的效果更好。     

耕作方式对旱地麦田土壤团聚体及其碳氮组分分布的影响

为明确蓄水保墒耕作方式下旱地麦田土壤团聚体稳定性、有机碳及碳组分和全氮及氮组分在不同粒径团聚体组分中的分布特征,深入了解不同耕作方式下土壤碳氮固持机制,以连续3 a(2017—2020年)实施不同耕作方式(免耕、深松、深翻)后冬小麦收获期0～20 cm土壤为研究对象,采用湿筛法测算土壤团聚体的构成与稳定性(R_0.25,>0.25 mm团聚体含量;MWD,平均重量直径;GMD,几何平均直径),并测定各粒径团聚体有机碳(SOC)和碳组分(重组有机碳,HFOC;轻组有机碳,LFOC;易氧化有机碳,EOC;可溶性有机碳,DOC;颗粒有机碳,POC)含量、全氮(TN)和氮组分(硝态氮,NO^-₃-N;铵态氮,NH⁺₄-N;可溶性有机氮,SON)含量,分析了碳氮组分的相关关系。结果显示：(1)免耕和深松处理>2 mm团聚体土壤比例较深翻处理分别提高8.8%和22.1%,免耕有利于增加<0.053 mm粉黏粒比例,较深松和深翻处理分别提高46.4%和27.7%。深松处理较深翻...     

有机肥对酿酒葡萄土壤微生物、酶活性及产量的影响

为明确施用不同有机肥对土壤有机质、酶活性和微生物以及酿酒葡萄产量的影响,采用田间小区设计,以5 a生赤霞珠酿酒葡萄为试验材料,研究不同有机肥对土层0～20、20～40 cm和40～60 cm中土壤有机质、酶活性和微生物的影响。以不施用有机肥为对照(CK),设置沼渣(BR)、羊粪有机肥(SMOF)、牛粪有机肥(CMOF)、猪粪有机肥(PMOF)、牛粪+沼渣有机肥(CMOF+BR)5个处理进行大田试验。结果表明:不同有机肥施用后与CK相比,土壤有机质增加6.79%～44.97%,土壤微生物碳增加19.78%～91.53%,微生物氮增加2.22倍～3.93倍,碱性磷酸酶增加57.78%～512.55%,过氧化氢酶增加53.45%～240.48%,增产15.12%～46.89%。不同土层施用牛粪有机肥相对于其它有机肥处理土壤有机质含量增长8.49%～33.29%;土壤中微生物碳、氮的含量分别增加5.30%～42.46%和6.12%～49.65%;碱性磷酸酶增大8.01%～184.63%,过氧化氢酶增加5.14%～84.27%,脲酶提高25.58%～410.70%,蔗糖酶升高6.00%～107.65%;微生物总数增多5.99%～56.56%。施用牛粪有机肥相比较其它有机肥增产7.08%～27.60%。说明在宁夏地区施用有机肥可有效提高土壤有机质的含量,增加微生物的数量,增加土壤酶活性,促进酿酒葡萄的生长发育,提高产量,其中以牛粪效果最为显著。     

Long-Term Crop Rotation Effects on Organic Carbon,Nitrogen, and Phosphorus in Haplustoll Soil Fractions

Soil organic matter (SOM) or carbon (SOC) consists of a number of fractions (which can be separated by granulometric wet sieving) having different properties among them. Information on fraction nutrient distribution and long-term crop rotations is lacking for semiarid environments. The objective of this research was to study the agronomic effects on soil OC, N, and P fractions. The humified OC was the largest and least variable fraction of the SOC. Soil under continuous mixed pasture had higher OC contents than under annually tilled treatments. Similarly, soil total nitrogen under the cropped treatments decreased from 1.7 g N kg-¹ in noncultivated soils (reference plots) to 1.0, 0.7 an 0.7 g N kg-¹ under mixed pasture, pasture-crop, and wheat-crop respectively, in the fine soil fraction. The reference plots also showed significantly lower levels of organic phosphorus (P o ) in comparison to the other treatment (from 67.1 w g P o g-¹ to greater than 100 w g P o g-¹ in the fine fraction of the treatments and years). The noncultivated soil showed larger values of P o and inorganic P in the large-size granulometric fraction (0.1-2 mm) than in the soil fine fraction (0-01 mm). However, the rotation treatments had greater concentrations of P in the fine fraction. The P o from the coarse fraction appears to be the most labile and sensitive fraction to tillage and environmental conditions, and may be closely related to P availability.     

有机-无机肥配施对黄土高原半干旱区农田土壤N2O排放的影响

为探明不同施肥方式对旱作麦田土壤N₂O排放的影响,以不施肥(CK)为对照,设置单施有机肥(M)、单施无机肥(N)、有机-无机肥配施(MN)3种施肥方式,采用静态箱-气相色谱法对春小麦地土壤N₂O排放通量进行测定,并对其影响因子(NO^-₃-N、NH⁺₄-N、土壤温度、土壤含水量)和春小麦产量进行同期测定。结果表明：春小麦地在整个生育期内表现为N₂O排放源,各处理均在施肥后出现N₂O排放峰。不同处理土壤N₂O累积排放量表现为N>MN>M>CK,N₂O净损失量(以氮计算)为1.175 8～1.428 kg·hm^-2,占当季施氮量的1.12%～1.36%,有机-无机肥配施降低了氮肥中氮素以气态形式的损失量。MN、N、M处理春小麦产量分别较CK处理增加了45.1%、31.0%、18.8%,各处理土壤NO^-_3<...     

长期施肥对渭北旱塬麦田土壤线虫群落特征的影响

为探究长期定位施肥对黄土高原渭北旱塬麦田土壤线虫群落的影响,以长武国家黄土高原农业生态试验站的长期定位试验（1984—2018年）为平台,调查裸地（L）以及不施肥（CK）、施氮磷肥（NP）、单施有机肥（M）、氮磷肥配施有机肥（MNP）的小麦田土壤线虫群落数量、组成结构和生态功能指数,并分析其与土壤理化性质的关系。结果表明：（1）小麦田土壤线虫数量显著高于裸地,而CK、M和MNP处理使小麦田中土壤线虫数量比NP处理提高了31.63%~56.20%;（2）施肥减缓了长期种植小麦导致的食细菌线虫（特别是头叶属）相对丰度的下降,单施有机肥的处理（M）植食性线虫相对丰度显著降低,同时,相比于CK,施用有机肥的M和MNP处理杂食/捕食线虫相对丰度分别增加了18.4%和8.24%,表明有机肥对杂食/捕食线虫的促进作用;（3）长期施肥处理土壤线虫Shannon多样性指数（H）和指示土壤健康状况的瓦斯乐卡指数（WI）分别为1.80~2.19和0.36~0.68,相较于裸地（H=2.36;WI=1.57）有所下降,但M和MNP处理的线虫成熟度指数（MI）和结构指数（SI）均高于其他处理（L、CK和NP处理）,表明施用有机肥有助于土壤食物网维持复杂的结构和成熟稳定的状态;（4）不同施肥措施下土壤全氮、有机碳、微生物生物量碳和氮以及可溶性碳的变化是影响土壤线虫数量和群落特征的重要环境因素。     

连续14年保护性耕作对土壤总有机碳和轻组有机碳的影响

依托于2001年布设在陇中黄土高原半干旱雨养农业区的保护性耕作定位试验,于2014年测定了5种保护性耕作(免耕+秸秆覆盖NTS、免耕NT、传统耕作+秸秆翻埋TS、传统耕作+地膜覆盖TP和免耕+地膜覆盖NTP)和传统耕作T处理下小麦-豌豆双序列轮作中表层土壤(0~5、5~10、10~30 cm)总有机碳(SOC)和轻组有机碳(LFOC)在作物生育期前后的变化。结果表明:土壤总有机碳和轻组有机碳在土壤剖面上均随着土层深度的增加而降低;相比传统耕作T,NTS和TS处理能显著提高0~30 cm土层中SOC、LFOC的含量,在作物播种前较T分别提高了19.51%、64.58%和13.36%、42.08%,在收获后分别提高了28.00%、85.37%和18.61%、77.82%,而SOC、LFOC含量NT和TP处理与T处理间差异不显著;从作物播种前至收获后,各处理下0~30 cm土层SOC含量均有减小趋势,其中NTS和TS处理变化量最小,NT和TP处理加大了作物生育期间SOC和LFOC的消耗;LFOC可以灵敏地反应出土壤有机碳的变化。因此,在该区推行以免耕、秸秆覆盖为主的保护性耕作措施更有利于碳的积累和土壤质量的改善,促进该区农业的可持续发展。     

不同氮水平下有机肥碳氮比对土壤硝态氮残留量的影响

采用盆栽试验的方法，研究N0（不施氮）、N1（施N0．067g／kg）、N2（施N0．133g／kg）、N3（施N 0．266g/kg）、N4（施N 0．400g／kg）4个不同氮水平下施入M1（C／N：31．8）、M2（C／N：42．5）、M3（C／N-66．6）不同C/N的有机肥对土壤NO3^-残留量的影响。结果表明：在N0，N1，N2水平下，3种不同C／N的有机肥对土壤NO3^-残留量的影响不显著，在N3，N4水平下，M1能够增加土壤NO3^-的残留量，M2和M3能够降低土壤NO3^-的残留量。N3M1，N4M1处理的土壤NO3^-含量分别比N3，N4处理增加了11．6％和14．4％；N3M2，N3M3处理分别比N3处理降低了15．9％和37．9％；N4M2，N4M3处理与N4处理相比差异不显著。     

河西绿洲灌漠土长期施肥效应及土壤生产力演变

张掖绿洲灌漠土连续21 a长期肥料试验结果表明:与无肥处理产量下降相对照,施肥的增产效果逐年提高,平衡施肥增产幅度显著大于单施氮肥。单施氮肥处理土壤生产力水平由第1轮作周期的89.8%降为第7轮作周期的28.5%;在不施用有机肥条件下,种植到第3轮作周期时作物开始对施钾有反应,施钾增产率为5.5%~22.7%;氮磷钾化肥长期配合施用,作物产量水平持续不减,土壤生产力平均达93.5%,表明氮磷钾化肥配合施用并不破坏土壤生产力。有机肥与氮肥配合施用,其交互作用为正效应;有机肥与磷、钾化肥配合施用交互作用为负效应。不施任何肥料时,绿洲灌漠土土壤生产力平均下降59.6%(第1~4轮作周期);到第5~7轮作周期时,土壤生产力下降幅度保持在16.7%~22.7%相对较低且稳定的水平;化肥对作物产量的贡献份额平均为50.5%;有机肥贡献份额为21.6%;土壤自然肥力贡献份额平均为19.0%。