耕作方式对苜蓿(Medicago sativa)地土壤团粒的影响

以甘肃干旱区连作5年和轮作1年的苜蓿(Medicago sativa)地土壤为研究对象,对不同耕作方式下土壤团粒结构、容重、含水量指标进行研究。结果表明:在轮作和连作模式下,随着土壤深度的增加,0.25mm土壤团粒质量在干筛和湿筛处理下均降低,0.25mm团粒累积质量越大,分形维数越小。在浸水条件下,粒径为0.5~0.25mm的土壤团聚体含量最高,其它粒径团聚体含量依粒径的增大而降低。轮作土壤含水量呈现先增加后降低、最后再增加的变化过程;0~60cm土层水分含量最高(13.881%),60~80cm土层含水量下降到较低值(10.343%),80~100cm土层水分迅速恢复(13.811%)。连作和轮作土壤容重随土壤深度均呈现依次增大变化,连作最大值为1.425%比最小值高出17.6%,轮作最大值1.432%比最小值高出18.7%。     

生草覆盖和植物篱措施对红壤坡地土壤侵蚀调控效应研究

以安溪官桥为研究区,在已有研究工作的基础上采取野外调查与人工降雨野外模拟试验相结合的方法,研究了植被对山坡地土壤侵蚀的调控机理．研究表明,翻耕地在生草覆盖的条件下,产流量与径流系数均减少70％左右,平均入渗率提高3倍多．说明生草覆盖条件下大量的降雨以入渗的形式流入土壤中,且径流含沙量与产流产沙量均显著低于生草覆盖前,其中平均含沙量减少87．5％,产沙量减少97％．根据对野外试验小区的多年观察,说明植物篱具有缓解坡度、提高土壤抗冲性等明显的保水保土效益．因此,采取适当措施减少产流量以及提高降雨向土壤水分的转化率,均可有效减少坡地土壤流失量．     

Soil water depletion depth by planted vegetation on the Loess Plateau

Evapotranspiration of much planted vegetation exceeds precipitation, and this can deplete soil water and cause a deep dry layer in the soil profile, which is a serious obstacle to sustainable land use on the Loess Plateau, China. This study aimed to determine water depletion depth of planted grassland, shrub, and forest in a semiarid area on the Loess Plateau. Soil moisture of five vegetation types was measured to >20 m in depth. The vegetation types were crop, natural grasse, seven-year-old planted alfalfa (Medicago sativa L.), 23-year-old planted caragana (Caragana microphylla Lam.) shrub, and 23-year-old planted pine (Pinus tabulaeformis L) forest land. Through comparing moisture of planted alfalfa grass, caragana shrub, and pine forest to crop and natural grassland, the depth and amount of soil water consumed by grassland, caragana brush and pine forest was determined. The depth of soil water depleted by alfalfa, caragana brush, and pine forest reached 15.5, 22.4 and 21.5 m, respectively. Supported by National Basic Research Program of China (Grant No. 2007CB407204) and National Natural Science Foundation of China (Grant No. 40471082)     

施肥及刈割对干旱地区紫花苜蓿产量和品质的影响

在黄土高原中部干旱区采用随机区组试验,研究3个施氮水平(0、51.75、103.5 kg·hm^-2)和3个磷水平(0、126、252 kg·hm^-2)下不同刈割次数(3、4次)对“甘农3号”紫花苜蓿种植当年和第2年产量、株高、再生速度及品质的影响,并对紫花苜蓿生长两年中各指标进行比较.结果表明:干旱地区“甘农3号”紫花苜蓿在具备灌溉条件下,种植当年施肥可显著提高产量、株高和再生速度,且4次刈割下显著高于3次刈割;施肥也能增加紫花苜蓿粗蛋白含量,降低中性洗涤纤维和酸性洗涤纤维含量,4次刈割下品质更好;高氮低磷处理(N 103.5 kg·hm^-2+P₂O₅ 126 kg·hm^-2)下效果最好,单施氮肥较单施磷肥效果好.同时,第2年紫花苜蓿产量显著高于第1年,第1年增幅较第2年明显,说明在试验地区,“甘农3号”紫花苜蓿种植当年施肥更有效,第2年施肥仍有益;在灌溉和配施N103.5 kg·hm^-2+P₂O₅ 126 kg·hm^-2条件下,种植当年即可实现4次刈割.     

黄土高原坡耕地苜蓿产量及水土流失地形分异模拟——以延安燕沟流域为例

退耕还林还草是目前黄土高原整治生态环境和控制水土流失的主体政策。为使生态退耕政策得到有效落实,本文基于WIN-YIELD软件,以延安燕沟流域为例,利用2006年延安站的逐日气象数据和燕沟流域地貌、土壤及土地利用等资料,模拟分析了不同地形高程、坡度和坡向条件下坡耕地种植苜蓿的秸秆干物质产量、水土流失量及其地形分异特征。结果表明:在黄土高原,地形坡度是影响苜蓿秸秆干物质产量和泥沙流失的重要因素,苜蓿秸秆产量模拟值随地形坡度的增大而减小,泥沙流失的模拟值随地形坡度的增大而增大;地形高程1000 m以下的地域种植苜蓿其产量明显高于1000 m以上的地域,坡耕地苜蓿产生径流和泥沙随地形高程的变化不显著;地形坡向对苜蓿秸秆产量和水土流失量的影响不大。     

小麦和苜蓿根系分泌物中饱和烃馏分

为深入研究根系分泌物对根际土中有机物贡献的特点,用柱色层族组成分离方法, 对小麦和苜蓿根际土及二者交界地中提出的可溶有机物采用了GC/MS分析测定。从样品的非极性馏分中分析检测出正构烷烃、类异戊二烯烷烃及酯类3个系列的生物标志化合物,并对小麦地、苜蓿地及二者的交界地中的正构烷烃的奇偶优势比（OEP）、∑C₂₂^-/∑C₂₃⁺比值和姥植比（Pr/Ph）进行了分析比较。小麦和苜蓿的GC/MS的主峰均为nC₃₁,正构烷烃奇偶优势比OEP值大小顺序为苜蓿地>交界地>小麦地,且三者数值均>1.4。正构烷烃∑C₂₂^-/∑C₂₃⁺比值大小顺序为小麦地>交界地>苜蓿地。姥植比（Pr/Ph）的比较结果为苜蓿地>交界地>小麦地。这表明小麦和苜蓿根系分泌物进入土壤后演化程度不一样,小麦地有机质演化程度高于苜蓿地。     

混合盐碱胁迫对紫花苜蓿苗期氮磷吸收及生理特性的影响

以“甘农3号”紫花苜蓿为试验材料,采用营养液沙培试验,用两种中性盐(NaCl和Na₂SO₄)及两种碱性盐(NaHCO₃和Na₂CO₃), 配成5种混合盐A(NaCl:Na₂SO₄=1:1)、B(NaCl:NaHCO₃=1:1)、C(NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃=1:1:1:1)、D(Na₂SO₄:Na₂CO₃=1:1)、E(NaHCO₃:Na₂CO₃=1:1),设4个盐浓度(25、50、100、150 mmol·L^-1)模拟盐胁迫,研究混合盐碱胁迫对紫花苜蓿苗期氮、磷吸收及生理特性的影响。结果表明:随着盐浓度增加,苜蓿根瘤固氮酶活性和植株全氮含量下降,全磷含量无明显变化,而脯氨酸(Pro)、丙二醛(MDA)、可溶性糖含量和超氧化物歧化酶(SOD)活性均升高,同一盐浓度水平下各处理间其含量的升高顺序为E>D>C>B>A,在高胁迫强度下(150 mmol·L^-1) 除全磷含量外,各项指标增减均达显著水平。混合盐碱胁迫能够对紫花苜蓿根瘤固氮酶组分结构造成不可逆的破坏,使苜蓿自身固氮能力的下降,最终导致植株全氮含量下降。随着盐浓度的上升,植株可以通过提高其体内脯氨酸和可溶性糖的含量来维持细胞水势,减少细胞渗透胁迫对植物的伤害。     

Response of artificial grassland carbon stock to management in mountain region of Southern Ningxia,China

Grassland is a major carbon sink in the terrestrial ecosystem. The dynamics of grassland carbon stock profoundly influence the global carbon cycle. In the published literatures so far, however, there are limited studies on the long-term dynamics and influential factors of grassland carbon stock, including soil organic carbon. In this study, spatial-temporal substitution method was applied to explore the characteristics of Medicago sativa L.(alfalfa) grassland biomass carbon and soil organic carbon density(SOCD) in a loess hilly region with different growing years and management patterns. The results demonstrated that alfalfa was the mono-dominant community during the cutting period(viz. 0–10 year). Community succession began after the abandonment of alfalfa grassland and then the important value of alfalfa in the community declined. The artificial alfalfa community abandoned for 30 years was replaced by the S. bungeana community. Accordingly, the biomass carbon density of the clipped alfalfa showed a significant increase over the time during 0–10 year. During 0–30 year, the SOCD from 0–100 cm of the soil layer of all 5 management patterns increased over time with a range between 5.300 ± 0.981 kg/m2 and 12.578 ± 0.863 kg/m2. The sloping croplands had the lowest SOCD at 5.300 ± 0.981 kg/m2 which was quite different from the abandoned grasslands growing for 30 years which exhibited the highest SOCD with 12.578 ± 0.863 kg/m2. The ecosystem carbon density of the grassland clipped for 2 years increased 0.1 kg/m2 compared with the sloping cropland, while that of the grassland clipped for 10 years substantially increased to 10.30 ± 1.26 kg/m2. Moreover, the ecosystem carbon density for abandoned grassland became 12.62 ± 0.50 kg/m2 at 30 years. The carbon density of the grassland undisturbed for 10 years was similar to that of the sloping cropland and the grassland clipped for 2 years. Different management patterns imposed great different effects on the accumulation of biomass carbon on artificial grasslands, whereas the ecosystem carbon density of the grassland showed a slight increase from the clipping to abandonment of grassland in general.     

半干旱区紫花苜蓿地上干物质量增长动态

根据甘肃半干旱地区紫花苜蓿试验资料,用Logistic方程描述干物质增长规律,建立模型,分析其干物质变化特性,得出甘肃半干旱区紫花苜蓿生长特点。