Seasonal and Annual Variations of CO_2 Fluxes in Rain-Fed Winter Wheat Agro-Ecosystem of Loess Plateau, China

To accurately evaluate the carbon sequestration potential and better elucidate the relationship between the carbon cycle and regional climate change, using eddy covariance system, we conducted a long-term measurement of CO 2 fluxes in the rain-fed winter wheat field of the Chinese Loess Plateau. The results showed that the annual net ecosystem CO 2 exchange （NEE） was （-71.6±5.7） and （-65.3±5.3） g C m-2 y-1 for 2008-2009 and 2009-2010 crop years, respectively, suggesting that the agro-ecosystem was a carbon sink （117.4-126.2 g C m-2 yr-1）. However, after considering the harvested grain, the agro- ecosystem turned into a moderate carbon source. The variations in NEE and ecosystem respiration （R eco ） were sensitive to changes in soil water content （SWC）. When SWC ranged form 0.15 to 0.21 m3 m-3, we found a highly significant relationship between NEE and photosynthetically active radiation （PAR）, and a highly significant relationship between R eco and soil temperature （T s ）. However, the highly significant relationships were not observed when SWC was outside the range of 0.15-0.21 m3 m-3. Further, in spring, the R eco instantly responded to a rapid increase in SWC after effective rainfall events, which could induce 2 to 4-fold increase in daily R eco , whereas the R eco was also inhibited by heavy summer rainfall when soils were saturated. Accumulated R eco in summer fallow period decreased carbon fixed in growing season by 16- 25%, indicating that the period imposed negative impacts on annual carbon sequestration.

Effects of Farmyard Manure and Inorganic Fertilizer Application on Soil Physico-Chemical Properties and Nutrient Balance in Rain-Fed Lowland Rice Ecosystem

A field experiment was conducted to assess the effects of combined application of farm yard manure (FYM) and inorganic NP fertilizers on soil physico-chemical properties and nutrient balance in a rain-fed lowland rice production system in Fogera plain, northwestern Ethiopia. The study was carried out during the main cropping seasons of 2010 and 2011. Twenty-seven treatments comprising a factorial combination of three rates of FYM (0, 7.5, and 15 t·ha-1), three rates of nitrogen (0, 60, 120 kg·N·ha-1) and three rates of phosphorus (0, 50 and 100 kg·P2O5·ha-1) were tested. The experiments were laid out as a randomized complete block design with three replications. Bulk density, organic matter content, and available water holding capacity, total N, and available P of the soil were measured just after harvesting the rice crop. Results showed that application of 15 t·FYM·ha-1 significantly increased soil organic matter and available water holding capacity but decreased the soil bulk density, creating a good soil condition for enhanced growth of the rice crop. Application of 15 tFYM·ha-1 increased the level of soil total nitrogen from 0.203% to 0.349%. Combined application of 15 t·ha-1·FYM and 100 kg·P2O5·ha-1 increased the available phosphorous from 11.9 ppm to 38.1 ppm. Positive balances of soil N and P resulted from combined application of FYM and inorganic N and P sources. Application of 15·t ha-1·FYM and 120 kg·N·ha-1resulted in 214.8 kg·ha-1·N positive balance while application of 15 t·ha-1·FYM and 100 kg·P2O5·ha-1 resulted in a positive balance of 69.3 kg·P2O5·ha-1 available P. From the results of this experiment, it could be concluded that combined application of FYM and inorganic N and P fertilizers improved the chemical and physical properties, which may lead to enhanced and sustainable production of rice in the study area.

Water use efficiencies of maize cultivars grown under rain-fed conditions

Enhancing water use efficiencies of rain-fed maize is a requirement for sustainable maize production, particularly in areas prone to low/drought and erratic rainfall patterns. This study was conducted to assess the relationship between total biomass/grain yield and water use efficiencies of three maize cultivars (Golden Crystal, Mamaba and Obatanpa) grown under rain-fed conditions in a coastal savannah agro-ecological environment of Ghana. Results of the study showed that a unified linear model, WUETDM = 0.03TDM with R2 = 0.765 and P ≤ 0.001, described adequately the relation between wa-ter use efficiency and total biomass (dry matter), which is applicable for the three maize cultivars for both the major and minor cropping seasons. A linear model could only, however, describe adequately well the relation between WUEGY and GY for the major (WUEGY = 0.001GY – 0.67;R2 = 0.996;P ≤ 0.001) and minor (WUEGY = 0.002GY + 0.289;R2 = 0.992;P ≤ 0.001) cropping seasons for all the maize cultivars. The linear models developed for the maize cultivars, re-lating WUEGY to GY, are specific to each of the crop growing seasons, indicating that seasonal rainfall impacts significantly on harvest index of the maize cultivars but differently in each of the crop growing seasons as a results of dif-ferences in seasonal rainfall. However, the models could be used to estimate water use efficiencies of each of the three maize cultivars given the appropriate TDM and GY as inputs for the environment under which the study was conducted.

Resilience, reliability and risk analyses of maize, sorghum and sunflower in rain-fed systems using a soil moisture modeling approach

This paper is aimed at examining the applicability of methods for resilience, reliability and risk analyses of rain-fed agricultural systems from modeled continuous soil moisture availability in rain-fed crop lands. The methodology involves integration of soil and climatic data in a simple soil moisture accounting model to assess soil moisture availability, and a risk used as indicator of sustainability of rain-fed agricultural systems. It is also attempted to demonstrate the role of soil moisture modeling in risk analysis and agricultural water management in a semi-arid region in Limpopo Basin where rain-fed agriculture is practiced. For this purpose, a daily-time step soil moisture accounting model is employed to simulate daily soil moisture, evaporation, surface runoff, and deep percolation using 40 years (1961-2000) of agroclimatic data, and cropping cycle data of maize, sorghum and sunflower. Using a sustainability criterion on crop water requirement and soil moisture availability, we determined resilience, risk and reliability as a quantitative measure of sustainability of rain-fed agriculture of these three crops. These soil moisture simulations and the sustainability criteria revealed further confirmation of the relative sensitivity to drought of these crops. Generally it is found that the risk of failure is relatively low for sorghum and relatively high for maize and sunflower in the two sites with some differences of severity of failure owing to the slightly different agroclimatic settings.

Carbon Budget Dynamics over a Rain-Fed Maize Agricultural Ecosystem in Northeast China and Its Regulation

Based on the eddy-covariance observation data over rain-fed maize agricultural ecosystem during 2005-2011, the dynamics of net ecosystem CO2 exchange (NEE) and its control mechanism were analyzed in the present study. We found that the average carbon budget of non-growing season, growing season and annual were 153.16 - 202.03 g C/m2, −689.36 - −488.17 g C/m2, and −316.96 - −487.33 g C/m2, respectively. Maize carbon content of grain yield was −226.6 - −339.94 g C/m2, accounting for 55.4% of carbon budget in the growing season. From sowing to seven-leaf stage, the carbon budget of this ecosystem was characterized by carbon release, with the rate of 0.028 ±0.0056 mg CO2 m−2⋅s−1. From seven-leaf to mature stage, the carbon budget was characterized by carbon absorption, with the rate of −0.256 ±0.0693 mg CO2 m−2⋅s−1. The key meteorological factors affecting annual carbon budget included daily average temperature (R = −0.81, P = 0.03) and saturated vapor pressure deficit (R = −0.64, P = 0.12). At the same photosynthetically active radiation (PAR) level, CO2 assimilation rate was linearly correlated with leaf area index (P 【0.05), and the slopes increased with PAR, indicating the increase in net ecosystem CO2 exchange in growing season was unlikely to be resulted from the extension of growing season. On the contrary, the carbon sink of rain-fed maize ecosystem in growing season might be decreased by extending the growing season ahead of the sowing date.

Analysis and Forecasting of the Impact of Climatic Parameters on the Yield of Rain-Fed Rice Cultivation in the Office Riz Mopti in Mali

During the period spanning the 1970s and1980s, countries in the West African Sahel experienced severe drought. Its impact on agriculture and ecosystems has highlighted the importance of monitoring the Sahelian rainy season. In Sahelian countries such as Mali, rainfall is the major determinant of crop production. Unfortunately, rainfall is highly variable in time and space. Therefore, this study is conducted to analyze and forecast the impact of climatic parameters on the rain-fed rice yield cultivation in the Office Riz Mopti region. The data were collected from satellite imagery, archived meteorology data, yield and rice characteristics. The study employed Hanning filter to highlight interannual fluctuation, a test of Pettitt and the standardized precipitation index (SPI) to analyze the rainfall variability. Climate change scenarios under the RCP 8.5 scenario (HadGEM-2 ES) and agroclimatic (Cropwat) model are carried out to simulate the future climate and its impact on rice yields. The results of satellite image classifications of 1986 and 2016 show an increase of rice fields with a noticeable decrease of bare soil. The analysis of the SPI reveals that over the 30 years considered, 56.67% of the rainy seasons were dry (1986-2006) and 43.33% were wet (2007-2015). The modelling approach is applied over 1986-2006 and 2007-2015 periods—considered as typical dry and rainy years—and applied over the future, with forecasts of climate change scenarios in 2034. The results show a decrease in potential yield during dry and slightly wet years. The yields of rain-fed rice will be generally low between 2016 and 2027. Deficits are observed over the entire study area, in comparison with the potential yield. Thus, this situation could expose the population to food insecurity.

A Multi-Site Case Study on Social Vulnerability to Climate Change of Select Rain-fed Farming Communities in the Philippines

This study examines social vulnerability by exploring the socio-economic factors, infrastructures, and social networks that can determine how prone and how prepared the rain-fed farming communities are to the adverse impacts of climate change. Increased variability in climatic conditions due to climate change seriously affects the productivity of rain-fed farms. The rain-fed farming communities in the Philippines are located in poor and environmentally fragile rural areas. Their vulnerability is greatly affected by restricted entitlement and access to social and economic capitals. This study is framed on qualitative approach to provide a rich and in-depth understanding on the elements of vulnerability based on the capacities and the practical affairs of life in rain-fed communities. The three subject communities from two agricultural provinces are examined to understand how the context and interactions of people can explicate sociological themes on the social dimension of climate change. The usefulness of multi-site study in probing the unique ways of how people understand and respond to certain environmental issue is part of reflections about the methodology.

Evolution of soil and water conservation in rain-fed areas of China

Rain-fed(dryland)farming is an ancient agricultural production system in China.It occurs widely across almost the whole country,especially in the Northwest and North China.The semi-arid Loess Plateau is the most important region of rain-fed farming in China,but unfortunately,soil erosion on the Loess Plateau area is the highest in China,and indeed amongst the highest in the world.This highlights the necessity for developing practices that can reduce soil and water erosion,improve soil water use efficiency,improve crop productivity,and reduce rural poverty in the region.Many techniques of soil and water conservation are being used in rain-fed areas of China,including such systems as mulch,ridge and furrow systems.The Appendix describes a unique system of soil and water conservation,called Shatian.Modern research on conservation tillage(No Till),although essential for reducing erosion,increasing crop productivity,and ameliorating poverty,is just beginning in China.Modern conservation tillage research started in the1990s’with support from Australia and other countries.The procedures,however,were modified to be in accord with local conditions and prevailing farmer experiences.With 10 years of experimentation,results show that the most successful conservation practice on the Western Loess Plateau is no till with stubble retention.This technique helps to conserve soil water,increases soil organic carbon,improves soil structure and water infiltration,reduces soil and water erosion,and improves crop productivity and sustainability of rain-fed farming systems.However,its adoption rate remains low due to barriers such as traditional attitude,insufficient rural extension,and so forth.

雨养农业区黄芩轻简化膜间直播种植技术规程

为进一步推进甘肃省雨养农业区黄芩种植机械化、精量化和轻简化生产,结合多年的试验示范和生产实践,从范围、规范性引用文件、术语和定义、生产环境、栽培技术、田间管理、采收与产地加工等方面总结出了雨养农业区黄芩轻简化膜间直播种植技术规程。

灌溉和雨养条件下不同品种小麦的农艺性状与产量关系研究

论文以百农207、周麦18、洛旱7号3个品种小麦为试验材料,对其在灌溉和雨养两种条件下的产量三因素和其他农艺性状与产量的关系进行研究.结果表明:在灌溉条件下,百农207的经济产量最高,洛旱7号和周麦18次之;在雨养条件下,百农207产量最高,周麦18和洛旱7号次之.产量及其构成因素对雨养胁迫的敏感程度存在着极显著的差异.在产量构成因素与经济产量的相关关系和通径关系中,穗粒数对经济产量的贡献最大;在雨养胁迫环境条件下,3个品种小麦的株高冬前分蘖、最高分蘖、成穗率、生物产量、经济产量和秸秆系数比灌溉条件下均有一定程度的下降,且这些性状的减少均达到了极显著水平.3个品种小麦的收获指数在两种环境条件下的增减均未达到显著水平.综合以上结果可知,百农207对水分条件的敏感程度最低,产量最为突出.

雨养农业区冬小麦品种灌浆期抗旱耐逆性评价技术规程

为进一步推进抗旱耐逆小麦品种的快速筛选及其推广应用,提高耐旱育种效率,通过半干旱雨养农业区田间生产条件下灌浆期小麦气孔性状多年多点的测定,明确小麦灌浆期抗旱耐逆性判定规则,联合主成分分析和隶属函数值方法,从适用范围、规范性引用文件、术语和定义、技术原理、基本要求、田间管理、气孔性状调查分析、评价指标的计算及评价等级等方面总结出雨养农业区冬小麦品种灌浆期抗旱耐逆性综合评价技术规程。

提升雨养夏玉米-冬小麦两熟体系生产力和土壤硝态氮累积的最优耕作模式

【目的】研究耕作模式对旱地雨养夏玉米–冬小麦(以下简称玉–麦)两熟体系生产力的影响,并对深松、翻耕在轮耕模式中的作用进行评价。【方法】定位试验于2015—2021年在中国农业科学院洛阳旱农试验基地进行。设置夏免耕秋免耕(SNAN)、夏深松秋免耕(SSAN)、夏免耕秋3年免耕1年翻耕(SNA3N1P)、夏深松秋3年免耕1年翻耕(SSA3N1P)和传统夏秋季均翻耕(CT)5种耕作模式,调查了玉米、小麦的产量和水分利用效率,2020年测定了玉米收获期0—40 cm土层土壤容重、养分含量和酶活性,以及2019—2020年度小麦收获期0—380 cm土层的硝态氮累积量。【结果】1)与CT处理相比,SNAN、SSAN、SNA3N1P和SSA3N1P处理的玉米、小麦和周年产量分别显著提高了28.4%~33.5%、23.7%~25.0%和27.1%~30.3%,水分利用效率分别显著提高了19.6%~39.2%、20.2%~29.3%和29.5%~34.5%,0—5 cm和20—40 cm土层土壤容重显著降低,0—5 cm土层的有机质含量以及0—40 cm多数土层的全氮、有效磷、速效钾含量和脲酶、蔗糖酶活性均显著提高;0—80 cm土层硝态氮累积量显著提高了44.3%~104.8%,120—380 cm土层硝态氮累积量显著降低了22.1%~34.1%。2)与夏免耕(SN)处理相比,夏深松(SS)处理对玉米和小麦产量没有显著影响,但显著降低了玉米水分利用效率,提高了10—20 cm土层有机质含量、0—20 cm土层全氮含量、0—5 cm和10—20 cm土层有效磷含量、10—20 cm土层速效钾含量、5—40 cm土层脲酶活性、0—40 cm土层蔗糖酶活性,也提高了20—40 cm土层容重和0—380 cm土层硝态氮累积量。3)与秋免耕(AN)处理相比,秋3年免耕1年翻耕(A3N1P)处理降低了0—5 cm土层的土壤养分含量,增加了5—20 cm各土层有机质含量、5—40 cm各土层速效钾含量、0—40 cm各土层脲酶和蔗糖酶活性;SN处理下的小麦水分利用效率6年均值显著提高了7.1%,SS处理下0—380 cm土层的硝态氮累积量显著降低了12.4%。4)虽然SSA3N1P处理的产量和水分利用效率与其他轮耕模式无显著差异,但其改善土壤性状和提高根层(0—80 cm)、降低深层(120—380 cm)土壤硝态氮累积量的效果最优。【结论】夏深松相比夏免耕、秋季3年免耕1年翻耕相比秋免耕均可改善土壤性状。夏深松秋3年免耕1年翻耕的改土、增产增效和优化土壤硝态氮分布的效果总体最优,是适宜雨养玉–麦两熟体系的耕作模式。

东北雨养条件下加工型马铃薯新品种产量与品质表现

为探究东北雨养条件下加工型马铃薯产量与品质表现,阐明不同品种不同环境下性状差异和氮钾肥吸收规律,为推广应用加工型马铃薯新品种、实现品种升级提供理论依据。以东农314和东农322为试验材料,并以大西洋为对照品种,通过两年田间试验,设置常肥、高钾、高钾高氮3个氮钾配比,分析不同降雨量及不同施肥条件对加工型马铃薯产量性状与部分品质性状的影响。结果表明,产量和品质综合表现最佳为东农314。两个加工型新品种在单株产量和单株薯数上表现优于对照品种大西洋;在块茎形成期雨量适宜年度下单株薯数、商品薯率和各项品质表现较好,在块茎膨大期降雨充足年度下单株产量和单薯重较高。不同品种对氮钾肥调控反应不同,东农314在施用150kg·hm^(-2)钾肥的高钾处理下多数产量性状和品质性状表现较好;东农322在常肥处理下施用氮肥109.5kg·hm^(-2)、钾肥112.5kg·hm^(-2)时单薯重、商品薯率、淀粉和粗蛋白含量表现更佳。

四川水浇地和旱地空间转变下的土壤资源结构特征

为进一步揭示四川农区耕地土壤资源的过去和现状,以四川省雨养旱地和水浇地2种主要耕地类型为研究对象,探讨1985—2020年2种耕地类型的面积、空间分布和土壤资源组成的演变特征,评价土壤资源供给农业生产的多样性演变规律。结果表明:(1)1985—2020年四川省雨养旱地面积整体呈现减少趋势,水浇地面积整体呈现增加趋势。(2)川东、川中丘陵区雨养旱地面积表现为减少趋势,而攀西地区表现为增加趋势。(3)成都平原区水浇地减少,而川东、川中丘陵区表现为增加趋势。(4)雨养旱地减少的区域和水浇地增加的区域具有明显的重叠性,其发生区域的土壤资源主要从属于初育土纲、铁铝土纲和人为土纲。(5)随着雨养旱地空间分布的改变,耕地中紫色土、黄壤和水稻土占比呈现显著减少趋势。上述结果明确了四川农区耕地转移导致区域土壤资源供给农业生产的结构发生改变,也暗示了大尺度上的农田水肥管理应强化考虑水分供给能力和土壤类型变化。

云南省农业生长季热量资源的时空特征

云南省是中国典型的湿润型雨养农业区,农业发展受热量资源变化影响显著。然而,当前对湿润型雨养农业区热量资源的研究较为缺乏,尤其是对区域内不同海拔梯度下各界限温度的积温研究仍有待深入。本研究基于云南省27个气象站近50年逐日气象数据,采用气候倾向率、小波分析以及Mann-Kendall检验等研究方法,分析了云南省不同海拔地区生长季≥0℃、≥10℃及≥20℃积温的时空特征,并探讨了各积温的周期演变特征与气候变化的响应。结果表明:(1)近50年,云南省不同海拔地区的各类积温均表现出稳定增加的趋势,峰值都出现在近5年,谷值出现在20世纪70年代中期。(2)除滇中城市群区域内呈现出显著性增温现象之外,不同海拔地区的各类积温呈现出高海拔地区增温趋势高于低海拔地区的特征。(3)在海拔因素、城市热岛效应和气候变暖的协同影响下,云南省气温增长多发生在≥10℃的天数上,≥20℃积温在不同海拔地区的空间分布差异性极大,增温趋势显著大于0℃积温和10℃积温。(4)不同海拔地区各类积温都存在15~25 a和40~50 a两个变化周期,且各类积温基本在20世纪90年代出现突变点,即各类积温在近20 a的增温趋势得到显著性增强。研究结果可为云南省农业气象分析提供相对客观的农业热量资源依据,并为雨养农业区现代化农业结构的调整提供参考。

陇东旱塬区复种马铃薯田蛴螬及金针虫防治药剂筛选试验

陇东旱塬区种植冬油菜和冬小麦后,土地闲置期可复种马铃薯,但蛴螬、金针虫等地下害虫对马铃薯为害严重,科学合理防治蛴螬、金针虫对保证马铃薯产量非常重要。为筛选出陇东旱塬区复种马铃薯田防治蛴螬、金针虫危害的低毒高效的适宜药剂,以马铃薯品种陇薯7号为指示品种,蛴螬、金针虫为防治对象,选用3种高效低毒杀虫剂对各药剂的拌种或喷沟处理进行田间防效试验,调查各处理蛴螬、金针虫虫口基数,出苗期的出苗率、受害率、安全性和成熟期的受害率、安全性。结果表明,35%噻虫嗪种衣剂、60%帮巧时种衣剂防效均达85%以上,且拌种处理和喷沟处理无显著差异。60%帮巧时悬浮种衣剂拌种和喷沟防效均好,分别为88.44%、90.36%;折合产量高,分别为16407.41、17066.14 kg/hm^(2),较空白对照分别增产16.71%、21.40%,较常规药剂对照分别增产12.07%、16.57%;保产效果好,分别为95.39%、96.20%。见于此,60%帮巧时悬浮种衣剂可作为陇东旱塬区复种马铃薯田蛴螬、金针虫防治的候选杀虫剂;并建议用48.00 mL的药量稀释10倍液后拌种薯100 kg,将525.00 mL的药量稀释250倍液,按225 L/hm2喷沟。

半干旱雨养区小麦叶片光合生理生态特征及其对环境的响应

分析了黄土高原半干旱雨养农业区田间春小麦叶片光合生理生态特征及其对环境因子的响应。结果表明,天气晴朗时,净光合速率日变化呈典型的双峰曲线,有“午休”现象,上午明显高于下午,且不同生育期峰值出现的迟早不同。蒸腾速率日变化呈不明显的双峰型,其出现最大值的时间晚于净光合速率出现最大值的时间。在生长季节,叶片净光合速率、蒸腾速率和气孔导度均受到多个环境因子的共同影响。不同时期,起主导作用的环境因子不同,且同一个因子对几个生理指标的影响程度和强度都有差异,其中,光合有效辐射是对蒸腾速率影响最强烈的环境因子,湿度对光合作用的影响大于温度。受环境因子制约最为显著的生理指标是叶片的蒸腾速率和气孔导度。

降雨对旱作春玉米农田土壤呼吸动态的影响

土壤呼吸是调控全球碳平衡和气候变化的关键过程之一,降雨作为重要的扰动因子,在不同区域和不同环境条件下,对土壤呼吸具有复杂的影响。研究降雨对农田土壤呼吸及其分量的影响,对准确预测未来气候变化下陆地生态系统碳平衡具有重要意义。对黄土高原东部典型春玉米农田生态系统生长季内3次降雨前后土壤呼吸及其分量进行了原位连续观测,结果表明:在土壤湿润的条件下,降雨对春玉米农田土壤呼吸及其分量具有明显的抑制作用,在土壤湿度大于27%后土壤呼吸及其分量随土壤湿度上升呈明显下降,且对温度的敏感性降低。土壤呼吸及其分量在降雨前后的变化受土壤温度和土壤湿度的共同影响。降雨量、降雨历时和雨前土壤含水量决定了土壤呼吸及其分量对降雨响应的程度和时长。土壤呼吸及其分量对土壤温度的敏感性各不相同,微生物呼吸对温度的敏感性最高,Q10为5.14;其次是土壤呼吸,Q10为3.86;根呼吸的温度敏感性相对最低,Q10为3.24。由于土壤呼吸分量对温度和湿度的敏感性不同,降雨后根呼吸的比例有所升高。

黄土高原旱地小麦覆膜增产与氮肥增效分析

【目的】研究覆膜栽培条件下黄土高原旱地冬小麦产量形成规律和氮肥吸收运移特征,为旱地小麦高产高效生产提供理论依据。【方法】于2012—2016年在晋南黄土旱塬冬小麦种植区,通过农户模式(FP)、农户施肥+垄膜沟播模式(RFSF1)、监控施肥+垄膜沟播处理(RFSF2)和监控施肥+全膜覆土穴播处理(WFFHS)4种不同栽培模式,具体分析不同施肥和覆膜措施互作对黄土旱塬冬小麦产量形成、地上部氮素积累转移、土壤硝态氮残留以及土壤氮素平衡的影响。【结果】试验期间,农户模式冬小麦平均产量为3 367 kg·hm^(-2),通过监控施肥覆膜种植,平均产量可提升至4 491 kg·hm^(-2),监控施肥对籽粒产量形成的贡献率为14.8%,监控施肥和覆膜协同贡献率达24.7%—42.1%。黄土旱塬冬小麦产量形成主要取决于公顷穗数,其次是千粒重。WFFHS处理因其合理的群体构建和良好水肥条件具有最高公顷穗数、千粒重和籽粒产量,平均分别为581×104穗/hm2、44.3 g和4 785 kg·hm^(-2)。从地上部氮素转运看,冬小麦地上部吸收氮素的花后转运量与生物产量和经济产量呈极显著正相关,相关系数分别为0.959**和0.960**。农户模式小麦籽粒中3/4氮素来源于花前营养器官的转移,1/4氮素来源于花后根系土壤吸收。通过监控施肥覆膜种植可显著提高花前营养器官氮素向籽粒的转移量,其转运贡献率在81.4%—88.8%。从土壤氮素残留看,长期过量施氮已导致黄土旱塬麦田土壤硝态氮在1 m土层的累积,累积量在100 kg·hm^(-2)以上,20—60 cm土层为累积峰值。经过连续4年种植,农户模式2 m土壤硝态氮累积量达277 kg·hm^(-2),较2012年播前增加了87.7%,其中75%的硝态氮集中在0—120 cm土层,监控施肥覆膜种植处理2 m土壤硝态氮累积量较2012年播前仅增加15.7%—24.2%。试验期间土壤残留硝态氮有随降水向下淋移的趋势,表现为2016年收获期各处理在120—200 cm土层较2012年播前有10.2%—133.7%的增幅。从4年土壤氮平衡角度总体评价,土壤残留氮素具有一定后效作用,各处理氮肥表观利用率在28.8%—56.7%,氮肥表观残留率在12.1%—28.9%,氮肥表观损失率在31.2%—49.6%。监控施肥覆膜种植可减少土壤氮表观损失量和土壤残留量,增加氮表观矿化量。其中WFFHS处理更大程度上利用了历年土壤残留硝态氮和有机质的矿化氮,具有相对低的氮素表观残留率(12.1%)和氮素表观损失率(31.2%)以及相对高的氮素表观利用率(56.7%)。【结论】全膜覆土穴播监控施肥种植可更好地改善土壤水肥供应条件,更大程度利用历年土壤残留硝态氮,增加地上部氮素积累量、积累氮素向籽粒的转移贡献率,构建合理群体,最终获得显著的增产效应和较高的氮素利用效率,是黄土高原冬小麦区有效的栽培措施。

旱地小麦降水年型与氮素供应对产量的互作效应与土壤水分动态的研究

本文研究了中国黄土高原同一自然年度下的3个模拟降水,施用氮素的生产效应及至作效应,明确了在400～600mm降水范围内的产量变幅、生产潜力,及土壤水分动态变化规律。产量随着水分的增加报酬递增,水分生产效率提高,耗水系数降低。氮肥和降水有明显的相互促进作用,增加降水可促进化肥肥效,适量增加氮素可提高降水利用效率。归纳二者的关系是水多肥多增产幅度大,水少肥多导致减产,水多肥少增产幅度小,水少肥少产量最低,研究找到了水肥互作效应的定量关系,还明确了在降水充足的条件下,旱地小麦适量增施氮肥并采取部分春季追肥具有明显增产效果,这为旱地小麦春季不追肥的传统习惯提供了改进的意见。