Comparisons of energy balance and evapotranspiration between flooded and aerobic rice fields in the Philippines

The seasonal and annual variability of sensible heat flux (H), latent heat flux (LE), evapotranspiration (ET), crop coefficient (K_c) and crop water productivity (WP_ET) were investigated under two different rice environments, flooded and aerobic soil conditions, using the eddy covariance (EC) technique during 2008-2009 cropping periods. Since we had only one EC system for monitoring two rice environments, we had to move the system from one location to the other every week. In total, we had to gap-fill an average of 50-60% of the missing weekly data as well as those values rejected by the quality control tests in each rice field in all four cropping seasons. Although the EC method provides a direct measurement of LE, which is the energy used for ET, we needed to correct the values of H and LE to close the energy balance using the Bowen ratio closure method before we used LE to estimate ET. On average, the energy balance closure before correction was 0.72 ± 0.06 and it increased to 0.99 ± 0.01 after correction. The G in both flooded and aerobic fields was very low. Likewise, the energy involved in miscellaneous processes such as photosynthesis, respiration and heat storage in the rice canopy was not taken into consideration.Average for four cropping seasons, flooded rice fields had 19% more LE than aerobic fields whereas aerobic rice fields had 45% more H than flooded fields. This resulted in a lower Bowen ratio in flooded fields (0.14 ± 0.03) than in aerobic fields (0.24 ± 0.01). For our study sites, evapotranspiration was primarily controlled by net radiation. The aerobic rice fields had lower growing season ET rates (3.81 ± 0.21 mm d⁻¹) than the flooded rice fields (4.29 ± 0.23 mm d⁻¹), most probably due to the absence of ponded water and lower leaf area index of aerobic rice. Likewise, the crop coefficient, K_c, of aerobic rice was significantly lower than that of flooded rice. For aerobic rice, K_c values were 0.95 ± 0.01 for the vegetative stage, 1.00 ± 0.01 for the reproductive stage, 0.97 ± 0.04 for the ripening stage and 0.88 ± 0.03 for the fallow period, whereas, for flooded rice, K_c values were 1.04 ± 0.04 for the vegetative stage, 1.11 ± 0.05 for the reproductive stage, 1.04 ± 0.05 for the ripening stage and 0.93 ± 0.06 for the fallow period. The average annual ET was 1301 mm for aerobic rice and 1440 mm for flooded rice. This corresponds to about 11% lower total evapotranspiration in aerobic fields than in flooded fields. However, the crop water productivity (WP_ET) of aerobic rice (0.42 ± 0.03 g grain kg⁻¹ water) was significantly lower than that of flooded rice (1.26 ± 0.26 g grain kg⁻¹ water) because the grain yields of aerobic rice were very low since they were subjected to water stress.The results of this investigation showed significant differences in energy balance and evapotranspiration between flooded and aerobic rice ecosystems. Aerobic rice is one of the promising water-saving technologies being developed to lower the water requirements of the rice crop to address the issues of water scarcity. This information should be taken into consideration in evaluating alternative water-saving technologies for environmentally sustainable rice production systems.     

“万元田”建设现状及发展对策——以浙江省衢江区为例

“万元田”是指每667m^2的耕地上年种植产值达1万元以上。总结了浙江省衢州市衢江区“万元田”的6种主要种植模式,以及实现“万元田”价值的营销策略。同时,分析了“万元田”的主要特点及制约因素,提出了建设“万元田”的发展对策。     

作物生长模型的应用研究进展

作物生长模型不仅能够进行单点尺度上作物生长发育的动态模拟,而且能够从系统角度评价作物生长状态与环境要素的关系。本文通过梳理当前作物生长模型应用的诸多研究成果,剖析模型在气候变化对农业生产影响研究、作物生长模型区域应用中的关键问题,总结了当前以作物生长模型为核心的农业决策支持系统开发的研究情况,意在促进作物生长模型在生态、农业、区域气候资源和气候变化等研究中更广泛地应用。结果表明,作物生长模型在国内外的研究与应用广泛而深入,在气候变化背景下,应用作物生长模型进行历史时期气候条件和农业气象灾害对作物生产状况和产量的影响研究已相当广泛且相对成熟。利用全球气候模式（GCM）或区域气候模式（RCM）构建未来气候变化情景,再与作物生长模型耦合已发展成为评估未来气候变化对农业生产影响的重要手段。通过集成与整合多作物生长模型、多气候模式集合模拟、优化气候模拟数据订正方法可有效降低气候变化对农业生产影响评估的不确定性。遥感数据同化技术能够将站点模型运用到区域尺度上评价不同环境因子对农业生产的影响,拓宽了作物生长模型的应用尺度范围并有效提高作物产量估算的精度。以作物生长模型为核心的农业决策支持系统的研究与应用越来越多元化,是辅助农业生产管理和决策的重要工具。然而,由于作物生态系统的复杂性,作物生长模型模拟结果仍存在很大的不确定性,今后对作物生长机理及过程间耦合机制的探索还需加强,以便进一步完善和改进模型,促进作物生长模型更广泛地应用。     

农作物秸秆利用技术现状及发展对策

农作物秸秆作为一种重要的可再生生物质资源,它的合理开发利用越来越受到人们的关注。介绍了秸秆综合利用的现状,包括还田技术、能源化技术、饲料化技术和工业应用技术等。这些技术虽然均能够在一定程度上将秸秆资源化利用,但在实际应用中仍存在一些不足。因此,进一步开发秸秆综合利用新技术,实现秸秆利用的资源化、高效化和产业化是发展的必然趋势。     

The use of a water budget model and yield maps to characterize water availability in a landscape

Crop yield maps may contain substantial corollary information regarding the distribution of yield related soil properties across a landscape. One of these properties is water holding capacity (WHC). Since WHC is an important parameter for crop models and is also critical for crop yield, our objective was to determine if WHC could be estimated by matching simulated yield with yield map data. We collected soil cores for water retention measurements and recorded plant phenological stages from 60 plots on four transects over two growing seasons (1997 and 1998). Soil cores were also sampled on 40 other locations set out on a grid pattern. We utilized a simple water budget model that uses the relative transpiration ratio to calculate relative yield from available water in the soil profile. Rainfall, potential evapotranspiration and soil water holding capacity are input. An optimization program varies the WHC to produce a grain yield similar to the one from the yield map at a particular location. This analysis was carried out over several scales by averaging yields over 55 m×71 m, 27 m×35 m, and 11 m×14 m areas. Yield data from 2 years were used. Yields from the transects in both years were significantly related to measured WHC in the surface 0–10 cm of soil. The calculated stress indices from the water budget model and estimated available WHC calculated for the 1997 data were similar to those calculated for the 1998 data where data were aggregated in 27 by 35 m or larger blocks. The contour map of estimated WHC was similar to the map of measured WHC for some features though there were also some differences. Use of multiple years of yield data are required to give stable results for estimated water holding capacities.. This information could be used in a farm management plan by allowing a producer to classify a field into areas that are buffered against drought and areas more susceptible to drought.     

济宁地区1970～2012年热量资源变化特征及其对作物生长的影响

利用济宁地区11个县站1970~2012年逐日气象观测资料,运用最小二乘法进行线性倾向估计,分析济宁地区主要热量资源的时间、空间变化趋势及其对作物生长的影响。结果表明:济宁近43年作物生长季年平均气温整体呈阶段性上升趋势,增温速率为0.30℃/10a;≥0℃活动积温为5 222.1℃·d,增加速率为86.7℃·d/10a;≥10℃的积温为4 777.2℃·d,增温速率为77.4℃·d/10a;0℃负积温绝对值为99.1℃·d,增温速率为14.1℃·d/10a。≥0℃、≥10℃持续的日数增加4.5天和3.2天,稳定通过≥0℃、≥10℃初日提前了3天和2天,≥0℃、≥10℃的终日分别晚2天和1天。作物生长季内有效积温的增加,使冬小麦—夏玉米的生产系统受到显著影响,其中冬前生长积温增加导致传统播期的冬小麦冬前旺长,因此冬小麦须推迟播期以适应气候变暖带来的不利影响;对于夏玉米来说,由于热量的增加和冬小麦播期的推后,改变了原有套种模式,可以推迟至小麦收获后进行夏直播。     

基于EOS/MODIS数据的裸土多层土温遥感反演研究——以陕西省为例

以EOS/MODIS为数据源,采用地表温度(LST)遥感信息模型耦合土壤温度CERES模型反演多层裸土土温。结果表明:土壤温度的模拟值与实测值的变化趋势比较一致,不同土层反演值和地面观察值的相关性均达极显著水平;5~60 cm土层土壤温度的平均绝对误差随土层加深逐渐降低,40~60 cm土层土壤温度的平均绝对误差降至1℃以内,但80、160 cm两层的反演精度误差则相对较大,说明结合其他模型,遥感能够反演一定深度土层的土壤温度,并达到一定精度。     

杂草对作物产量损失预测的复合函数模型

本文根据杂草与作物在田间竞争所表现出的三大特征，应用幂函数与双曲线函数的复合模型（y=d^r/（a＋bd^l）来模拟杂草密度与作物产量间的关系，通过对7组不同来源的杂草与作物竞争资料的模拟，证明幂双曲线函数复合模型具有实际的生物学意义，能准确地描述多种杂草和多种作物间的竞争关系，预测杂草为害作物可能造成的产量损失。为杂草的经济防除和进一步建立杂草防除的生态经济阚值模型提供科学的依据。     

不同轮耕方式对渭北旱塬麦玉轮作田土壤物理性状与产量的影响

为研究不同轮作模式对渭北旱作冬小麦?春玉米一年1熟轮作田土壤物理性状和产量的影响,于2007—2014年在陕西省合阳县冬小麦?春玉米轮作田连续7年实施了保护性耕作定位试验,测定和分析了免耕/深松、深松/翻耕、翻耕/免耕、连续免耕、连续深松和连续翻耕6种轮耕模式下麦田0~60 cm土层物理性状、0~200 cm土层土壤湿度和小麦产量的变化。结果表明:1)不同轮耕模式0~40 cm土层土壤容重、孔隙度和田间持水量差异显著,其中以免耕/深松效果最显著;0~60 cm土层免耕/深松轮耕处理平均田间持水量较连续翻耕处理提高12.9%;2)轮耕对土壤团聚体特性影响明显,免耕/深松0.25 mm水稳性团聚体含量(R0.25)最高,结构体破碎率和不稳定团粒指数(ELT)最低,水稳性均重直径(WMWD)最高,水稳性和力稳性团聚体分形维数(D)均最低;3)小麦生育期间免耕/深松处理0~200 cm土层土壤蓄水量和小麦产量较连续翻耕分别增加17.7 mm和9.5%。综合可知,轮耕有利于耕层土壤物理结构改善,免耕/深松更有利于耕层土壤大团聚体形成和土壤结构稳定,利于土壤蓄水保墒和作物增产,为渭北旱塬区麦玉轮作田较适宜的轮耕模式。     

The effect of deficit irrigation on crop yield and vegetative development of Olea europaea L. (cvs. Frantoio and Leccino)

Water is the most important environmental constrain determining plant growth and fruit yield of olive tree plantations. Although olive trees are resilient to water-limited conditions of Mediterranean-type agroecosystems, crop yields may respond positively to any additional water up to a limit. A field experiment on olive trees was carried out with the aim to present guidelines for efficient management of irrigation scheduling, based on the relationship between plant water status and optimum fruit yield. These relationships were monitored during 2 years by analysing the influence of deficit irrigation strategies on vegetative development and yield parameters on mature modern-trained olive trees of cvs. Frantoio and Leccino. Treatments were: a non-irrigated control (rainfed) and three treatments that received seasonal water amount equivalent to 33, 66 and 100% of ET_C in the period August–September, from the beginning of pit hardening to early fruit veraison. Atmospheric evaporative demand and soil moisture conditions were regularly monitored. Seasonal dynamics of plant water relations varied among treatments, and responded to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. All measurements of tree water status were highly correlated with one another. Differences in yield between treatments indicated that water availability might have affected fruit weight before flowering or during the early stages of fruit growth rather than later in summer season. Results concerning crop yield revealed that irrigation of olive trees from the beginning of pit hardening could be recommended, at least in the experimental conditions of this study and in view of differences between genotypes.