Toposequential Variation in Soil Fertility and Rice Productivity of Rainfed Lowland Paddy Fields in Mini-Watershed (Nong)in Northeast Thailand

Abstract

Mini-watersheds called Nongin Thai are geographical components of rainfed lowland rice culture in Northeast Thailand, and constitute distinct units in understanding environmental constraints for low and unstable rainfed rice production there. The toposequential variation of soil fertility and its relation to rice productivity within mini-watersheds, was examined by phytometry of sampled soils and field measurements of rice growth and yield. The phytometry experiment with irrigated potted rice using soils sampled from various rice fields within each mini-watershed, revealed that soil fertility as evaluated by rice dry matter production showed a 5 times difference among the fields at most. The difference in the soil fertility was ascribed primarily to that in nitrogen (N) supply capacity, which itself had a strong correlation with soil organic carbon (SOC) content. Accordingly, the biomass production of pot-grown rice was proportional to SOC. content, which suggested the usefulness of SOC as an index for soil fertility evaluation. The effect of clay on the soil fertility was much less than that of SOC. The actual rice yield in each field also showed quite large field-to-field variation, most of which was explained by the SOC content, rice growth duration and fertilizer application rate even though water availability also affected the yield. The yield positively correlated with growth duration and hence with earlier transplanting. Both SOC and clay contents of fields showed steep gradients with ascending field elevation within mini-watersheds, resulting in a marked toposequential distribution of rice yield. The toposequential distributions of SOC and clay contents imply that rice culture after deforestation accelerated soil erosion from upper to lower fields. The large toposequential gradient in soil fertility requires different resource and crop management for each toposequential position, in order to improve rice productivity of the mini-watershed as a whole.     

保护性耕作对旱作夏玉米光合和水分利用效率日变化的影响

[目的]探讨保护性耕作对旱作夏玉米(Zea mays L.)光合和水分利用效率日变化的影响,为该地区完善和推广该技术提供理论依据。[方法]以传统翻耕无覆盖(CT)为对照,研究西北旱作地区免耕不覆盖(NT)和免耕秸秆还田(NTS)处理对夏玉米抽雄-吐丝期叶片光合特性和水分利用效率(WUE)日变化的影响。[结果]夏玉米光合速率(Pn)日变化呈"单峰"型曲线,日均Pn为NTSCTNT。气孔导度(Gs)早上出现高峰,中午和下午降至低水平小幅波动,日均为NTSNTCT。WUE变化趋势与Pn相似,表现出明显的正相关性(R2=0.701*),玉米叶片WUE日均值NTSCTNT,NTS处理效果显著,说明免耕秸秆还田处理提高玉米WUE作用较好。胞间CO2浓度(Ci)与Pn变化表现出负相关性,蒸腾速率(Tr)日变化也为"单峰"型曲线,与Pn表现出明显的正相关性(R2=0.895**),日均Tr值为NTSCTNT。[结论]免耕秸秆还田措施下玉米Pn、Gs、WUE均高于传统翻耕。因此在西北旱作夏玉米田实施免耕秸秆还田既有利于作物对有限降水的高效利用,也可促进农田系统生产力可持续提高,是较为适宜的一项耕作措施。     

自然降雨条件下化学钾肥配施有机肥对烟草生长及产量的影响

【目的】探明在自然降雨条件下化学钾肥配施有机肥对烟草云烟87生长发育、产量及经济效益的影响,为贵州省黔东南州烟草种植区烟草钾肥的合理施用提供科学依据。【方法】采用田间小区试验,设置4种施钾水平,分别为0水平(K_0:0 kg/hm^2)、1水平(K_1:120 kg/hm^2)、2水平(K_2:240 kg/hm^2)和3水平(K_3:360 kg/hm^2),4个施肥处理,同时每个处理配施有机肥(菜枯,M)2 250 kg/hm^2,调查各处理烟草在生育期内烟株主要的农艺性状、病害发生情况、烘烤后烟叶的经济性状和烟叶产量。【结果】在成熟期,K_3处理烟株各项农艺性状除节间距外均显著优于K_0处理(p<0.05),与K_0处理相比,K_3处理烟株的株高、最大叶面积、叶片数、茎围、节间距和根体积依次分别增加了27.64%、35.16%、56.38%、35.36%、17.06%和63.03%,与K_2处理相比,K_3处理相应指标增加了2.55%、4.83%、2.21%、29.27%、16.43%、22.64%。与K_0处理相比,K_3处理烟株的赤星病、花叶病和黑胫病的发病率分别降低了51.69%、41.16%和45.35%,病情指数分别降低了44.27%、28.87%和41.56%,K_2处理相应病情发病率分别降低了28.63%、22.30%、35.61%;病指数分别降低了34.68%、10.18%、31.40%。随着施钾增加烟叶产量呈增加趋势,K_3处理烟叶的产量和产值比K_0处理分别提高了26.60%和36.03%,上等烟和中上等烟比例分别提高5.82%和2.26%,K_3处理产值显著高于K_0、K_1、K_2处理。【结论】与其他施肥处理相比,K_3处理烟株大田长势好,农艺性状好,抗病能力强,可提高产量和经济效益。     

肯尼亚玉米生产现状与产量限制因子分析

玉米作为肯尼亚的主要粮食作物,其种植和生产对于减少饥饿、保障国家粮食安全具有非常重要的意义。本文从玉米的种植、分布、多年(1961—2014年)产量变化等方面对肯尼亚玉米的生产和现状进行了介绍,结合当地的自然环境因素和农业生产管理水平,分析了肯尼亚玉米生产的限制因素,指出水、肥、种子质量是玉米产量提高的主要限制因子。通过对田间不同施肥处理玉米产量与水、肥投入的分析,提出采用集水-排灌技术,对玉米季降水进行调控和再分配;增加化肥投入量,尤其是增加磷肥施用,保证玉米生长所需;秸秆还田改善土壤结构等技术,最终实现玉米增产的目标。为在肯尼亚推广不同水、肥管理和耕作技术,开展玉米旱作高产种植提供理论支撑。     

渭北旱塬“赤霞珠”葡萄浆果膨大期光合特性研究

【目的】分析山地和平地赤霞珠葡萄(Vitis viniferaL.cv Cabernet Sauvignon)的光合作用特性,为形成持续发展的葡萄与葡萄酒生产体系提供依据。【方法】采用LI-6400便携式光合测定仪,分析了陕西省耀州区山地和平地两个葡萄园中赤霞珠葡萄浆果膨大期叶片的净光合速率、蒸腾速率、胞间CO2浓度和气孔导度等生理生态指标。【结果】山地和平地赤霞珠葡萄的净光合速率日变化相似,均表现出双峰曲线,首峰出现在上午10:00,次峰小于首峰,出现在下午15:00以后;山地和平地赤霞珠葡萄叶片的净光合速率、蒸腾速率、胞间CO2浓度和叶绿素含量差异显著,水分利用效率和气孔导度差异不显著,在光响应曲线内的最大净光合速率和表观量子效率分别为14.40μmol/(m2.s),0.036和12.58μmol/(m2.s),0.035,在CO2响应曲线内的最大净光合速率和羧化效率分别为23.99μmol/(m2.s),0.061和18.43μmol/(m2.s),0.059,模拟曲线的R2值都大于0.94;不同海拔条件下净光合速率与PAR、蒸腾速率和气孔导度呈极显著正相关,与胞间CO2浓度呈显著负相关。【结论】山地条件下葡萄具有高光效和高产的光合特性。     

Yield of rice under water and soil salinity risks in farmers’ fields in northeast Thailand

This study focused on the variability of rice yield under water and soil salinity risks in farmers’ fields in northeast Thailand. A rice plot was monitored in 24, 16 and 11 farmers’ fields during the rice seasons 2005, 2006 and 2007, respectively. The results emphasized that few plots were continuously submerged during the 2005 season, when rainfall was low. Drought significantly affected the rice yield, yield components and the internal efficiency (IE) of the absorbed nutrients, while slight soil salinity had the only significant effect of increasing the IE of potassium (IEK). In the very rainy 2006 and 2007 seasons, most fields were continuously submerged, and in contrast to 2005, the slight soil salinity that was recorded had significant effects not only on IEK, but also on rice yield, spikelet sterility and 1000-grain weight. The yield decrease due to drought was about 87% and that due to salinity was 20%. When neither salinity nor water were limiting, the soil nutrient supply was high enough to achieve about 80% of the maximum yield reported in the literature for the rice cultivar in this area. As both drought and salinity risks are hardly avoided by the current farmers’ management they should be taken into account in the way technical recommendations to farmers are formulated.     

Investing in water for food, ecosystems, and livelihoods: An overview of the comprehensive assessment of water management in agriculture

The authors of the recently completed Comprehensive Assessment of Water Management in Agriculture (CA) concluded that there are sufficient water resources to produce food for a growing population but that trends in consumption, production and environmental patterns, if continued, will lead to water crises in many parts of the world. Only if we act to improve water use will we meet the acute fresh water challenge. Recent spikes in food prices, partially caused by the increasing demand for agricultural products in non-food uses, underline the urgent need to invest in agricultural production, of which water management is a crucial part. The world experienced similar pressure on per capita food supplies and food prices in the 1960s and 1970s, but the challenges now are different than those we experienced 50 years ago. The world's population is substantially larger, there are many more people living in poverty, and the costs of many agricultural inputs are much higher. The current situation and the long-term outlook require a fresh look at approaches that combine different elements such as the importance of access to water for the poor, providing multiple ecosystem services, rainwater management, adapting irrigation to new needs, enhancing water productivity, and promoting the use of low-quality water in agriculture. This special issue highlights the analysis behind a number of policy options identified by the CA, a five-year multi-disciplinary research program involving 700 scientists. This introductory article sets the background and context of this special issue, introduces the key recommendations from the CA and summarizes the papers in this issue.     

Satisfying future water demands for agriculture

The global demand for water in agriculture will increase over time with increasing population, rising incomes, and changes in dietary preferences. Increasing demands for water by industrial and urban users, and water for the environment will intensify competition. At the same time, water scarcity is increasing in several important agricultural areas.We explore several pathways for ensuring that sufficient food is produced in the future, while also protecting the environment and reducing poverty. We examine four sets of scenarios that vary in their focus on investments in rainfed agriculture and irrigation, and the role of international trade in adjusting for national disparities in water endowments. Rainfed agriculture holds considerable potential but requires adequate mechanisms to reduce inherent risks. Irrigation expansion is warranted in places where water infrastructure is underinvested such as sub-Saharan Africa. In South Asia the scope for improving irrigation performance and water productivity is high. International trade can help alleviate water problems in water-scarce areas, subject to economic and political considerations. We examine also a regionally optimized scenario that combines investments in rainfed and irrigated agriculture with strategic trade decisions. Compared to ‘business as usual’, this scenario reduces the amount of additional water required to meet food demands by 2050 by 80%. Some of that water could be made available for the environment and other sectors. We conclude that there are sufficient land and water resources available to satisfy global food demands during the next 50 years, but only if water is managed more effectively in agriculture.     

Spatial and temporal trends of water productivity in the lower Mekong River Basin

We estimate the physical and economic water productivities of rice and upland crops grown in the Lower Mekong River Basin and we examine their spatial and temporal trends. We discuss the constraints to low productivity, suggest measures for improvement and show the future productivity requirements for food security for increased population. Both the physical and economic water productivities of rice are higher in Vietnam, moderate in Laos, and lower in Thailand and Cambodia. In contrast, the physical water productivities of upland crops such as sugarcane and maize are highest in Thailand. The economic water productivity of upland crops is higher in Laos followed by Vietnam, Cambodia and Thailand, and is much higher than that of rice. However, the economic productivity of all crops is dominated by the productivity of rice, particularly lowland rainfed rice, which is the dominant crop in the Lower Basin. The intra-regional variation (among the provinces within a country) of productivity is not substantial. There is an increasing trend of both physical and economic water productivity in all four riparian countries; however, the increase is more prominent in Laos and Vietnam. The economic productivity of upland crops is much higher than that of rice and therefore cultivation of more upland crops can significantly increase farm-level incomes, with positive impacts on reducing poverty. Increasing upland crops areas is unlikely to have any impact on the food security of the basin. The current rate of increase of both production and productivity of rice is considerably greater than the rate required to feed the expected extra population by 2050, suggesting that food security is not threatened by the population increase. There appears to be considerable scope to increase productivity and maintain the export potential of the basin.     

不同耕作措施对雨养冬小麦碳足迹的影响

为了解不同耕作管理措施对我国北方旱作农田作物生产生命周期内生产资料及生产过程碳排放足迹的影响,在山西省临汾市尧都区连续15年保护性耕作长期定位试验基地,利用静态箱-气相色谱法连续两年测定了不同秸秆管理和耕作措施(秸秆不还田旋耕、秸秆还田旋耕、秸秆覆盖免耕)下,旱作冬小麦田N_2O周年排放通量,并对不同耕作管理措施的生产资料和生产过程中的碳排放进行全面分析与计算,以估算不同耕作措施的碳足迹。结果表明:1)秸秆覆盖免耕和秸秆不还田旋耕条件下旱作冬小麦田N_2O年度累积排放量较秸秆还田旋耕分别平均减少19.2%和18.9%;2)旱作冬小麦在秸秆覆盖免耕条件下产量最高;3)旱作农田碳足迹中氮肥生产、农田N_2O直接排放和柴油消耗排放占到总排放足迹的90%以上;4)秸秆覆盖免耕较其他耕作方式的碳足迹低,两年试验期间,较秸秆还田旋耕处理碳足迹分别低11.0%和6.9%,较秸秆不还田旋耕处理碳足迹分别低7.9%和8.3%。5)在半干旱地区,秸秆覆盖免耕处理单位产量碳足迹最低,是本研究中低碳低排的推荐措施。本研究结果可为旱作农田以低碳减排为目标的可持续发展提供科学依据。