Effect of Long-Term Fertilization on Soil Productivity and Nitrate Accumulation in Gansu Oasis

A long-term （1982-2001） field experiment was conducted in a calcareous soil under wheat （Triticum aestivum L.）-wheat （Triticum aestivum L.）-maize （Zea mays L.） rotation system at Zhangye, Gansu Province, China to determine the effects of long-term fertilization on crop yield, nutrients interactions, content and accumulation of nitrate-N in soil profiles. Twenty- four plots in a split-plot factorial with a combination of eight treatments （from nitrogen （N）, phosphorus （P）, potassium （K） and farmyard manure （M） applications） and 3 replications were selected. Main treatments were M and without M, and the sub-treatments were no-fertilizer （CK）, N, NP and NPK. When P and K fertilizers were part of treatments, their ratio to N was 1N：0.22P：0.42K. All M, P and K fertilizers were applied as the basal dressing. The grain yield was harvested each experimental period and straw yield for the period from 1988 to 1997. After crop harvest in 2000, the soil was sampled from the 0-20, 20-60, 60-100, 100-140 and 140-180 cm depths to determine NO3^--N content. Maize yield of CK in 2000 was only 28.2% of that in 1984, and wheat in 2001 was 25.7% of that observed in 1982. Average impact of fertilizers on grain yield decreased in the order of N 〉 M 〉 P 〉 K. Yield response to N and P fertilizers increased with progress of the experiment. The impact of K fertilizer showed no increase in grain yield during the initial 6 years （1982-1987）, moderate increase in the next 5 years （1988-1992）, and considerable increase in the last 9 years （1993-2001）. The straw yield trend was similar to grain yield. Accumulation and distribution of NO3^--N in soil was significantly affected by annual fertilizations. Mineral fertilizers （NP and NPK） led to NO3^- -N accumulation in most subsoil layers, with major impact in the 20-140 cm depth. The combination of mineral fertilizers and farmyard manure （MNP and MNPK） reduced soil NO3^--N accumulation in comparison to mineral fertilizers, It can be argued that long-term fertilization significantly enhanced grain and straw yield in this rotation scheme. The findings of this research suggest that it is important to balance application of mineral fertilizers and farmyard manure in order to protect soil and underground water from potential NO3^--N pollution while sustaining high productivity in the oasis agro-ecosystem.

Impact of Long-Term Fertilization on Cropland Soil Fauna Community at Loess Soil, Shannxi, China

The relationship between long-term fertilization and cropland network for soil fertility and fertilizers in Loess soil of Shannxi soil fauna was studied at the station＇s experiment research Provincefrom Jul. 2001 to Oct. 2002. Six types of long-term fertilizer were carried out for this study including non-fertilizer （CK）, abandonment （ABAND）, nitrogenous and phosphors and potassium fertilizers combined （NPK）, straw and NPK （SNPK）, organic material and NPK （MNPK） and 1.5 times MNPK （1.5MNPK）. 72 soil samples were collected and 5 495 species of cropland soil fauna obtained by handsorting and Cobb methods at 4 times, belonging to 6 Phyla, 11 Classes, 22 Orders, 2 Superfamilies, 61 Families and 35 Genera. The result showed that different fertilizer had significantly impacted on the cropland soil fauna （F = 2.24, P〈0.007）. The number of the cropland soil fauna was related to the soil physicochemical properties caused by long-term fertilization. The result by principal component analysis, focusing on the number of 15 key soil fauna species group＇s diversity, evenness of community and the total soil fauna individuals indicated that the effects of SNPK, NPK, MNPK and 1.5MNPK were significantly different from that of the cropland soil fauna, in which, SNPK and NPK had the positive effect on cropland soil fauna, and MNPK and 1.5 MNPK had the negative affect, others could not be explained. By principal component I, the synthetic effect of different fertilization on the total soil fauna individuals and the group was most significant, and the effect was little on evenness and diversity. By value of eigenvectors, the maximum one was 9.6248, and the minimum one was - 1.0904, that means the 6 types of fertilization did not affect evenly the cropland soil fauna.

Changes in cropland topsoil organic carbon with different fertilizations under long-term agro-ecosystem experiments across China's Mainland

Topsoil soil organic carbon(SOC) data were collected from long-term Chinese agro-ecosystem experiments presented in 76 reports with measurements over 1977 and 2006.The data set comprised 481 observations(135 rice paddies and 346 dry croplands) of SOC under different fertilization schemes at 70 experimental sites(28 rice paddies and 42 dry croplands).The data set covered 16 dominant soil types found in croplands across 23 provinces of China's Mainland.The fertilization schemes were grouped into six categories:N(inorganic nitrogen fertilizer only),NP(compound inorganic nitrogen and phosphorus fertilizers),NPK(compound inorganic nitrogen,phosphorus and potassium fertilizers),O(organic fertilizers only),OF(combined inorganic/organic fertilization) and Others(other unbalanced fertilizations such as P only,K only,P plus K and N plus K).Relative change in SOC content was analyzed,and rice paddies and dry croplands soils were compared.There was an overall temporal increase in topsoil SOC content,and relative annual change(RAC,g kg-1 yr-1) ranged -0.14-0.60(0.13 on average) for dry cropland soils and -0.12-0.70(0.19 on average) for rice paddies.SOC content increase was higher in rice paddies than in dry croplands.SOC increased across experimental sites,but was higher under organic fertilization and combined organic/inorganic fertilizations than chemical fertilizations.SOC increase was higher under balanced chemical fertilizations with compound N,P and K fertilizers than unbalanced fertilizations such as N only,N plus P,and N plus K.The effects of specific rational fertilizations on SOC increase persisted for 15 years in dry croplands and 20 years in rice paddies,although RAC values decreased generally as the experiment duration increased.Therefore,the extension of rational fertilization in China's croplands may offer a technical option to enhance C sequestration potential and to sustain long-term crop productivity.

Detection, Mapping and Assessment Change in Urban and Croplands Area in Al-Hassa Oasis, Eastern Region in Saudi Arabia Using Remote Sensing and Geographic Information System

Croplands are decreasing due to the expansion of urban areas into rural communities and to some extent due to sand accumulations. Increases in population numbers, new development, in addition to the accumulation of sand and soil salinity are the major driving force leading to abandonment and shrinking of cropland. The aim of this study was to investigate and assess to what extent agricultural lands are affected by urban development in the Al Hassa oasis, Eastern region in Saudi Arabia by employing Landsat time series data of years 1988, 2000 and 2017 as the main source of information. A set of ground truth, control points (GCPs) was also used besides population census data. Unsupervised classifications approach, Normalized Difference Vegetation Index (NDVI) and change detection methods were used here. Urban area during 2000-2017 exhibits much higher increase compared to 1988-2000, while the arable lands declined to −3.4% in 1988-2000 and increased to 22% during 2000-2017. The data analysis results provided new accurate numerical information supported by a graphical representation in regard to the decrease and increase in urban and agricultural lands. Therefore the findings of this study should be considered by decision maker for improving and development the agriculture activities in rural and urban communities.

基于递归特征消除−随机森林模型的江浙沪农田土壤肥力属性制图

以江苏省、浙江省、上海市农田为研究区,选用气候、地形、植被、土壤属性等自然环境协变量,及农业机械总动力、每公顷农用化肥施用量、农业总产值、农村用电量等农业活动变量,利用递归特征消除方法(RFE)对环境协变量进行筛选,基于筛选后的最优变量组合建立随机森林(RF)模型,进行表层土壤pH、有机碳、全氮、全磷、全钾、铵态氮、硝态氮、有效磷、速效钾、交换性钙、交换性镁11种主要土壤肥力属性的空间分布预测,并采用100次重复的十折交叉验证法进行验证。结果表明:①11个模型筛选出的环境协变量类型主要集中在气候、地形与植被变量,表征人类农业活动的变量在有机碳、全磷、全钾、铵态氮和有效磷预测中体现重要作用。②11个模型的决定系数(R^(2))在0.27~0.53,pH、速效钾、交换性镁和交换性钙的预测模型决定系数(R^(2))均在0.45以上。本研究表明人类活动变量对于土壤肥力预测具有重要意义,而递归特征消除−随机森林模型(RFE-RF)可以用于农田主要土壤肥力属性制图,为农业生产提供准确的土壤肥力属性空间分布信息。

绿洲灌区密植对氮肥减量玉米产量的补偿潜力

【目的】针对绿洲灌区玉米生产氮肥用量过高的问题,探究通过密植补偿氮肥减量对玉米产量负效应的可行性。【方法】2019—2021年,以施氮水平为主区,设地方习惯施氮(N_(2),360 kg·hm^(-2))、减量25%施氮(N_(1),270 kg·hm^(-2))两个水平;以种植密度为副区,设传统(M_(1),7.8万株/hm^(2))、中(M_(2),10.4万株/hm^(2),增密33%)、高(M3,12.9万株/hm^(2),增密66%)3个密度水平,进行裂区试验,重点研究氮肥减量条件下增密对玉米产量及其构成因素的影响。【结果】(1)氮肥减量导致玉米籽粒产量、生物产量分别降低4.0%、4.9%。减氮条件下,中密度可以产生籽粒产量补偿效应,N_(1)M_(2)较对照N_(2)M_(1)提高4.1%;高密度处理N_(1)M3生物产量补偿效应最大,较对照提高14.2%。(2)通过回归分析模拟得到:减氮条件下,当种植密度提高至8.4万株/hm^(2)可以与对照N_(2)M_(1)籽粒产量持平,并在10.6万株/hm^(2)时获得最大产量13537kg·hm^(-2),较对照提高4.9%。(3)氮肥减量引起穗数、穗粒数和千粒重分别降低5.0%、3.3%和3.4%;中、高密度分别较传统密度提高穗数27.9%、49.7%,降低穗粒数3.8%、8.4%,降低千粒重5.2%、8.9%。中密度较传统密度对收获指数无显著影响,而高密度使收获指数降低14.2%。N_(1)M_(2)较对照N_(2)M_(1)通过穗数增加补偿了减氮引起穗数、穗粒数及千粒重的下降,从而实现丰产。(4)氮肥减量降低拔节期至抽雄吐丝期的玉米生长率7.2%—8.4%;中、高密度较传统密度提高苗期至大喇叭口期玉米生长率27.3%、60.3%。(5)氮肥减量条件下,N_(1)M_(2)较对照提高叶、茎和鞘干物质转运量达9.6%、13.6%和3.7%,提高叶和茎对籽粒产量的贡献率5.3%和9.0%。【结论】通过合理密植可以补偿减氮引起的玉米产量下降,在施氮量270 kg·hm^(-2)的基础上增密至10.4万株/hm^(2),能够最大化产量补偿效应,是绿洲灌区玉米节氮稳产丰产的可行措施。

我国羊养殖量及其粪尿资源化利用潜力分析

为了解我国各地区羊粪尿产量及其资源化利用潜力,本研究依据统计年鉴数据和粪尿产排污系数,估算了2021年我国各省份羊粪尿产生量、羊粪尿肥料化和能源化利用潜力,进一步测算了羊粪尿养分农田耕地负荷。结果表明,2021年全国羊粪尿总产生量达2.91亿t,其中总氮(TN)、总磷(TP)、总钾(TK)含量分别为91.08万、19.28万t和73.89万t,可有效替代氮肥(以尿素计)255.31万t、磷肥(以P_(2)O_(5)计)108.45万t、钾肥(以K_(2)O计)191.82万t,可产沼气165.95亿m^(3),具有较高的肥料化与能源化利用潜力。青海和西藏两省份农田耕地负荷居全国第一和第二,消纳羊粪尿时,应充分考虑耕地、农牧交错带、林地和草地等多种土地类型。

不同肥料对淅川库区耕地土壤氨挥发影响研究

农业肥料挥发的氨是南水北调中线水源地丹江口水库大气和水体氮的重要来源,威胁着库区水质安全。目的为探究不同肥料对库区耕地土壤氨挥发的影响,方法以淅川库区典型耕地土壤为研究对象,采用密闭式静态箱法,于2020年夏季和秋季开展不同肥料作用下土壤氨挥发的原位田间监测,分析不同肥料对土壤氨挥发速率和累积挥发量的影响,并探讨其季节性差异。结果结果表明:(1)肥料施用显著增加了土壤氨挥发速率。尿素处理的土壤氨挥发速率最大,在施肥后第4—6 d达到峰值,且波动时间最长;复合肥料处理的土壤氨挥发速率次之,峰值出现在施肥后第6—9 d;有机肥处理的土壤氨挥发速率最低,接近于土壤本底水平。(2)不同肥料作用下,土壤氨累积挥发量存在显著差异。尿素处理的累积挥发量最大,为不施肥处理的10倍,复合肥和有机肥处理的分别为不施肥处理的3倍和1倍,表明施用有机肥对氨挥发影响最小。(3)氨挥发速率存在明显的季节性差异,夏季挥发速率普遍高于秋季的。相同施肥量条件下,秋季施肥的土壤氨挥发恢复到本底水平所需时间是夏季的2倍,但净累积挥发量无明显差异(0.04~2.41 kg·hm^(−2))。尽管季节性因素影响挥发速率,但总挥发量趋于一致。秋季施肥后,日均氨挥发速率和总挥发量均较夏季的低,但对土壤和大气影响更持久。结论调整肥料施用结构,增加有机肥的使用,并减少尿素的使用,可以有效减少因肥料施用而产生的土壤氨挥发。

珠三角赤红壤常年菜地土壤肥力质量评价

赤红壤是广东省地带性土壤,研究位于该地带性土壤的菜地肥力变化特征,以客观评价耕作施肥管理的科学性,助力耕地质量保护与提升。在广东省珠三角地区广州市、江门市、肇庆市、惠州市惠阳区选取了89个蔬菜常年种植菜地,测定了耕层(0~20 cm)土壤理化指标,利用第二次全国土壤普查养分分级标准和内梅罗综合指数法分析评价土壤肥力状况。珠三角赤红壤常年菜地土壤质地以壤土、砂质壤土、粉壤土为主,分别占比46.1%、23.6%和19.1%;pH 5.83,呈微酸性;有机质含量23.83 g·kg-1,为中等水平;阳离子交换量8.67 cmol(+)·kg-1,为中等偏下水平;全氮(N)、全磷(P)、全钾(K)含量分别为1.19、1.47、12.53 g·kg-1,其中全氮和全磷含量均属中等水平,全钾含量为中等偏下水平;有效态养分中碱解氮、有效磷、速效钾含量分别为135.24、120.24、222.48 mg·kg-1,属于丰富(碱解氮和速效钾)和极丰富水平(有效磷)。内梅罗综合指数法评价结果显示,珠三角赤红壤常年菜地土壤综合肥力指数为1.69,属良好等级。相比第二次全国土壤普查广东省赤红壤普查结果,土壤全钾含量不同程度降低,pH值、有机质、全氮、碱解氮含量均不同程度提高,增幅分别为16.6%、23.5%、38.4%和62.5%;阳离子交换量、全磷、有效磷和速效钾含量大幅增加,增幅分别达1.29、6.00、65.80和3.07倍,其中土壤有效磷累积较为普遍。全氮和全磷的年均累积量分别为8.46、32.31 mg·kg-1,碱解氮、有效磷和速效钾年均累积量分别为1.20、3.04、4.30 mg·kg-1。总体上,经过近40年耕种,珠三角赤红壤常年菜地肥力水平不同程度改善,土壤pH由酸性改善为微酸性,阳离子交换性能、有机质、全氮含量提升1个等级,碱解氮和有效钾含量提升2个等级,全磷和有效磷含量分别提升3和5个等级。各肥力指标总体上由原来的极度缺乏至中等偏下状态改善为目前的中等偏下至极丰富水平,总体肥力状况良好。在实施蔬菜有机无机肥配施技术基础上,合理施用氮、钾肥,降低磷肥投入量,可以进一步提升珠三角赤红壤区菜地地力水平,维持土壤资源的可持续利用。

Soil Properties and Characteristics of Soil Aggregate in Marginal Farmlands of Oasis in the Middle of Hexi Corridor Region, Northwest China

The composition and stability of soil aggregate are closely related to soil quality, soil erosion, and agricultural sustainability. In this study, 49 soil samples at the 0-10 cm surface layer were collected from four soil types （i.e., Ari-Sandic Primosols, Calci-Orthic Aridosols, Siltigi-Otrthic Anthrosols, and Ustic Cambosols） in the marginal farmland in the oasis of the middle Hexi Corridor region and was used to determine the characteristics of soil aggregates. The composition of dry- and wet- sieved aggregates and the physical and chemical properties （including soil particle distribution, soil organic carbon （SOC）, calcium carbonate （CaCO3）, and oxides of Fe^3＋ and Al^3＋） of the selected soils were analyzed. The results show that soil particle size distribution is dominated by fine sand fraction in most of soils except Ustic Cambosols. Soil organic carbon concentration is 5.88 ± 2.52 g kg^-1 on average, ranging from 4.75 g kg^-1 in Ari-Sandic Primosols to 10.51 g kg^-1 in Ustic Cambosols. The soils have high calcium carbonate （CaCO3） concentration, ranging from 84.7 to 164.8 g kg^-1, which is increased with soil fine particle and organic carbon content. The percentage of 〉0.25 mm dry aggregates ranges from 65.2% in Ari-Sandic Primosols to 94.6% in Ustic Cambosols, and large dry blocky aggregates （〉5 mm） is dominant in all soils. The mean weight diameter of dry aggregates （DMWD） ranges from 3.2 mm to 5.5 mm. The percentage of 〉0.25 mm water-stable aggregate is from 23.8% to 45.4%. The percentage of aggregate destruction （PAD） is from 52.4% to 66.8%, which shows a weak aggregate stability. Ari-Sandic Primosols has the highest PAD. The distribution and characteristics of soil aggregates are in favor of controlling soil wind erosion. However, the stability of aggregate of all soils is weak and soils are prone to disperse and harden after irrigation. The mass of macro-aggregates and DMWD are positively significantly correlated with the contents of soil clay and silt, soil organic carbon （SOC）, CaCO3, and oxides of Fe^3＋ and Al^3＋. Soil fine silt and clay, SOC and CaCO3 are important agents of aggregation in this region, and the effect of SOC and CaCO3 on aggregate stability is more significant than that of soil silt and clay. Converting cropland to alfalfa forage land can increase SOC concentration, and in turn, enhance the formation of aggregates and stability. For the marginal farmlands in this fragile ecological area, converting cropland to alfalfa grassland or performing crop-grass rotation is an effective and basic strategy to improve soil structure and quality, to mitigate soil wind erosion, and to enhance oasis agricultural sustainability.

近40年江苏农田土壤pH时空变化特征及驱动因素

【目的】从县域尺度探究江苏农田土壤pH的时空变化特征及其驱动因素,为农田土壤酸化的预测、阻控以及土壤质量的提升提供科学依据。【方法】基于第二次全国土壤普查(1980年)、全国测土配方施肥(2006-2012年)以及江苏省土壤农化性状普查(2018年)数据,分析不同时期江苏农田土壤pH的时空变化特征,并利用回归分析探究影响农田土壤pH变化的主要驱动因素。【结果】2018年江苏全省农田土壤pH范围为5.61~8.31,平均7.02,其中,东部沿海和北部各市农田土壤pH较高,以中性和碱性为主;南部各市农田土壤pH较低,以酸性为主。近40年,江苏农田土壤pH平均下降0.57个单位,其中1980-2006、2006-2012和2012-2018年,年均降幅分别为0.016、0.008、0.007个pH单位。1980-2006年,江苏农田土壤pH快速下降,Ⅰ级(pH>7.5)样本点占比由60.6%降至38.0%,Ⅲ级(pH 5.5~6.5)样本点占比由8.5%增加至28.2%。2006-2018年,农田土壤pH下降趋势得到有效抑制,各级样本点占比趋于稳定。农田土壤pH变化主要与土壤初始有机碳密度、作物秸秆碳还田量和化肥施用量密切相关,其中,土壤初始有机碳密度贡献近40年江苏农田土壤pH变化的48.7%,分别高于作物秸秆碳还田量和化肥施用量的26.9%和24.4%。【结论】江苏农田土壤pH总体呈现“南酸北碱”和“东部沿海高于内陆”的空间分布特征,主要与土壤性质、土壤类型和土地利用方式有关。40年间农田土壤pH的下降并非匀速,1980-2006年的快速下降是由于大量化肥的施用,而2006-2018年的缓慢下降则是由于秸秆还田量的增加。

施钾对甜叶菊糖苷跃变期生理指标和产量品质的影响

为提高河西绿洲灌区甜叶菊产量和品质,提升该区甜叶菊市场竞争力。以谱星6号为试验材料,比较了不同施钾水平(K2O 0、60、90、120、150 kg/hm^(2))对甜叶菊糖苷跃变期生理指标以及产量品质的影响。结果表明,不同施钾处理下,甜叶菊整个糖苷跃变期叶片各生理指标含量达到峰值的时间有所不同,叶片SOD活力、含钾量均在现蕾前5 d达到最高,可溶性蛋白、SPAD值、含氮磷量、总苷含量以及叶片干物质量在现蕾初期达到最高,POD活力、可溶性糖含量在现蕾后5 d达到最高,以上各指标均以施用K2O 120 kg/hm^(2)处理表现最佳。其中总苷含量最高,达128.4 g/kg,较不施钾肥增加14.19%;产量也最高,达7007.64 kg/hm^(2),较不施钾肥增加57.24%;净收益达5.26万元/hm^(2),比不施钾多3.40万元/hm^(2)。通过甜叶菊叶片理化指标与产量品质的相关性分析,以上各生理指标与产量品质均呈现显著或者极显著的正相关关系。在当地甜叶菊生产中施用K2O 120 kg/hm^(2),且在现蕾初期采摘叶片可获得较好收益。

绿洲灌区水肥耦合对连作饲用型高粱‘近甜1号’生长的调控效应

以荒漠绿洲沙荒地饲用型‘近甜1号’(BJ0601)高粱(Sorghum bicolor)头茬种植的最佳水肥需求(灌溉量7800 t·hm^(−2);施肥量600 kg·hm^(−2))和栽培模式(株距×行距:23 cm×40 cm)为依据,以头茬和轮作为对照,对连作3年的‘BJ0601’生长适应性(生长发育、茎秆鲜重、种子产量和质量等)、茎秆糖含量及土壤地力(有机碳、矿质养分)变化等进行分析。结果表明:与头茬相比,‘BJ0601’轮作茎秆鲜重无显著差异(P>0.05),但种子产量(925.1 kg·hm^(−2))显著低于头茬(2029.5 kg·hm^(−2))(P<0.05)连作3年后‘BJ0601’生长适应性受到明显抑制;与头茬相比,‘BJ0601’连作3年后出苗数、成苗率及株高分别降低了11.5%、11.4%和43.7%,茎秆鲜重(57.8 t·hm^(−2))和种子产量(677.2 kg·hm^(−2))分别降低了26.4%和71.5%;各处理茎秆可溶性糖含量无显著差异。‘BJ0601’连作3年后土壤地力显著下降。与头茬和轮作相比,连作3年后‘BJ0601’根区10-20 cm土层有机碳含量降低了34.4%和36.7%,碱解氮、速效磷和速效钾含量降低了71.9%和43.9%、85.7%和38.8%、30.9%和16.9%(其他耕作层养分变化同10-20 cm土层)。然而,在高水肥耦合(灌溉量9000 t·hm^(−2);施肥量825 kg·hm^(−2))下,‘BJ0601’连作3年茎秆鲜重(74.9 t·hm^(−2))和种子产量(962.6 kg·hm^(−2))与最佳水肥下连作3年相比分别提高了29.6%和66.3%,且茎秆鲜重和茎秆可溶性糖含量与头茬和轮作相比无显著差异。连作显著影响‘BJ0601’的生长适应性及土壤地力状况,但高水肥耦合和轮作能够减轻连作对‘BJ0601’生长的抑制作用,减缓土壤地力衰退。在荒漠绿洲区须对‘BJ0601’的灌溉施肥方式、耕作措施和栽培管理等进行综合改善,以减缓连作障碍对‘BJ0601’生长及土壤肥力造成的不利影响,才能保证‘BJ0601’高生产力和水肥资源的高效利用。

中国农田施用化学氮肥的固碳潜力及其有效性评价

按照2003年氮肥施用情况和农业专家对不同作物提出的推荐施肥量,设定了"氮肥施用现状"和"按推荐量施肥"两个情景,在搜集和整理全国典型的农业长期定位实验站数据的基础上,将全国划分为4个农业区,分析了两种情景下我国农田土壤的固碳潜力;同时根据我国生产氮肥的化石能源消耗以及施用氮肥的数据,采用国内以及IPCC提供的相关参数,计算了施用化肥导致的温室气体泄漏,并提出"有效固碳潜力"的概念作为评价固碳潜力有效性和固碳措施可行性的标准.我国农田土壤在两种情景下的固碳潜力分别为21.9和30.2 Tg C·a-1;但两种情景下生产和施用化学氮肥的温室气体泄漏量分别达到了72.9和91.4 Tg C·a-1,使两种情景下有效固碳潜力分别为-51.0和-61.1 Tg C·a-1;而"按推荐量施肥"还将增加10.1 Tg C·a-1的温室气体净排放.因此,施用氮肥在我国农田土壤不具备有效固碳潜力,作为固碳措施不可行.鉴于施用化肥是我国粮食安全的基本保障,建议在保证粮食生产的前提下,提高氮肥利用率,适当减少氮肥施用量,以利于温室气体的减排.

北京市郊典型农田施肥研究与分析

通过问卷调查形式,对京郊粮田、菜田和果园3种农田施肥现状进行研究。结果表明,菜田和果园化肥施用量较高,氮、磷、钾肥均显著高于粮田。菜田和果园氮肥用量分别为1741.0和1172.8 kg/hm2,分别是粮田氮肥用量的4.5和3.0倍;磷肥用量分别为1375.1和996.4 kg/hm2,分别是粮田磷肥用量的15.5倍和11.2倍;钾肥用量分别为791.3和602.4 kg/hm2,分别是粮田钾肥用量的21.1和16.1倍。另外,3种利用方式的农田氮、磷和钾肥施用比例不同,粮田为75.4%、17.3%和7.3%;果园为42.3%、36.0%和21.7%;而菜田为44.6%、35.2%和20.3%。3种种植类型中均存在氮肥投入过量、钾肥不足的问题。

施肥处理对春季冻融期灰漠土农田温室气体排放的影响

绿洲灰漠土冻融交替明显,但缺乏该时期气体通量及动态变化方面的研究。选取NPK(氮磷钾肥)、NPKS(0.9NPK+0.1秸秆氮)、NPKM(1/3NPK+2/3羊粪氮)和NPKM+(1.5倍NPKM)处理作为研究对象,利用静态箱气相色谱法开展2013—2014年春季冻融期温室气体排放观测试验。结果显示,春季冻融期间,有机肥添加处理CO_2排放量较高,其中NPKM+和NPKM处理CO_2平均排放量分别为C 113 mg m^(-2) h^(-1)和85 mg m^(-2) h^(-1),其次为NPKS(72 mg m^(-2) h^(-1))、NPK(75 mg m^(-2) h^(-1))和CK(35 mg m^(-2) h^(-1))。同样,NPKM+和NPKM处理有相对更高的N_2O排放,春冻平均排放通量分别为N 73μg m^(-2) h^(-1)和42μg m^(-2) h^(-1),显著高于NPKS(22μg m^(-2) h^(-1))和NPK(17μg m^(-2) h^(-1))处理(p<0.05)。CH_4排放量相对较低,各处理无明显差异(p>0.05)。分析发现,N_2O在冻融期呈现先增加后急剧减少的趋势,CO_2变幅不明显。与全年总排放量相比,冻融期(27 d)N_2O的排放量占全年的9%~18%,CH_4冻融期间排放比重占全年排放量的6%~14%。所以,冻融交替期是灰漠土农田温室气体排放的相对高发时期,估算温室气体排放时应充分考虑。

土壤水盐运动模式研究及其在干旱区农田的应用

采用预估校正法求解土壤水分运动的h型Richards方程 ,此方法可以控制一定的迭代步数 ,但同样可达到二阶精度。同时采用具有二阶高精度的差分法求解土壤盐分运移的对流扩散方程 ,此格式可避免采用一般差分格式时出现的数值弥散问题。并将上述数学模式对干旱区绿洲棉田 ,在蒸散条件下土壤水分运动和土壤盐分向上运动积累过程进行数值模拟 ,模拟结果与测量值吻合较好 。

开垦对绿洲农田碳氮累积及其与作物产量关系的影响

以新疆策勒绿洲近百年来不同开垦年限农田为研究对象,采用空间序列换算时间序列的方法,研究绿洲农田开垦过程中土壤有机碳和全氮密度、碳氮比(C/N)及速效氮含量的垂直变化特征,并探讨了农田土壤碳氮变化与作物产量的关系。结果表明:荒漠土壤开垦后,显著增加了表层土壤(0—20 cm)有机碳和全氮密度,随开垦年限延长对深层土壤(40—200 cm)有机碳密度也有一定的影响,如在开垦30 a左右时下降了36.4%,但在100 a左右时则增加了52.0%。耕层土壤C/N随开垦年限延长而明显增加,深层土壤除100 a农田外其它均有不同程度下降;不同土层C/N与速效氮含量呈负相关关系,仅在开垦初期(0—10 a)达到显著水平。不同年限农田的玉米产量存在显著差异,且和有机碳及全氮密度(0—200 cm)均呈显著正相关;棉花除100和10 a农田产量差异较小外,在其它农田间均达显著水平,但和有机碳及全氮密度无明显相关性。由此可见,在现有投入条件下,提高土壤碳氮累积量对增加玉米产量仍有十分重要作用,但对棉花产量的影响不明显。

土壤有机质对农田管理措施的动态响应

土壤有机质在农田肥力、环境保护、农业可持续发展等方面具有重要意义。它不仅决定农作物产量 ,而且在全球碳素循环中起着重要作用。由于大气 CO2 浓度升高与全球气候变暖等一系列环境问题的加剧 ,全球碳素循环受到越来越多的关注。农田具有大气 CO2 源和库的双重潜力。历史上由于人类对农田的过度开垦和耕种 ,造成土壤有机质含量大幅度下降 ,降低了农田的作物产量潜力 ;同时导致大量的碳以 CO2 形式由陆地生态系统排放到大气圈 ,加剧了全球温室效应。大量研究结果表明 ,诸如耕作、种植制度、施肥等农田管理措施能够显著地影响土壤有机质动态 ,而免耕、提高复种指数、合理的轮作换茬、有机肥料和化肥的施用以及弃耕农田还林还草等保护性管理措施则能够提高农田土壤有机质含量 ,使农田起到大气 CO2汇的作用。综述了近年来农田管理对土壤有机质动态影响研究方面的进展。

黑河中游临泽绿洲农田土壤有机质时空变化特征

土壤有机质是表征土壤质量的一个重要指标，持续稳定的有机质含量是土壤维持生产能力的基础。土壤有机质的动态演变可以表征土地利用和管理水平。结合地理信息系统，运用地统计方法研究了黑河中游的临泽县绿洲农田20多年来土壤有机质含量的时空变化特征。结果表明：（1）1982年0～20cm耕层土壤有机质含量平均为12．78±4．38g／kg，2008年平均为13．76±4．02g／kg；从1982—2008年，有机质含量总体有所上升。（2）两个时期的土壤有机质的实验变异函数值与理论变异函数拟合均较好；克立格插值和不同时期的有机质空间分布图叠加运算表明，由于人为活动的影响，土壤有机质的结构性空间变化程度有所减弱。（3）临泽县土壤有机质含量和变化具有一定的区域性特点：南部的山前平原地区土壤有机质含量较高，呈现上升趋势；中部地势低下的区域土壤有机质相对较高，由于农田面积扩大，有机肥供应不足而下降显著；北部绿洲与戈壁交错带土壤有机质偏低。总体来看，临泽县土壤有机质含量有所上升，但局部地区的有机质发生了下降。为了防止局部区域土壤有机质下降引起土壤退化，应该采取加大有机肥投入和实施秸秆还田等措施。