Larger bioavailability of soil phosphorus for irrigated rice compared with rainfed rice in Madagascar: results from a soil and plant survey

Irrigated rice is less prone generally to phosphorus (P) deficiency than rainfed rice because redox reactions release P upon soil flooding. It is not known whether that is also true in highly weathered soils of Madagascar where the combination of high soil Fe and low P input may impede significant release of P. Soils and flag leaf samples were collected in 2010 in 38 irrigated rice and 46 rainfed rice fields belonging to private farmers. A critical flag leaf P content was derived from a P‐dosed pot trial study with three soils, and the results suggested 2.4 g P/kg as the critical value. Average flag leaf P was significantly larger in irrigated than in rainfed rice (2.2 compared with 1.7 g P/kg), and flag leaf P was below the critical value in 76% of irrigated rice fields while this fraction was 100% in rainfed rice. Nitrogen and K deficiencies were less prevalent. Flag leaf P increased with increasing soil pH and soil pH explained partially differences in leaf P between irrigated and rainfed rice. Flag leaf P was unrelated to soil organic matter, but increased with oxalate‐extractable soil P (P_o). Multiple regression analysis revealed greater leaf P at equal soil P_o and equal pH in irrigated compared with rainfed rice. Grain yield estimates (1‐m² squares) increased with flag leaf P but not with leaf N and K. In a regression model, about 42 % of the yield variance was explained with soil P_o and a rice‐growing system. The survey suggests that P is the main limiting nutrient for rice, and that soil P bioavailability is larger for irrigated than for rainfed rice in weathered soils of Madagascar.     

Inter-relationships among cane yield and commercial cane sugar and their component traits in autumn plant crop of sugarcane

Seventeen diverse clones of sugarcane (Saccharum spp.) (7 early, 6 mid season and 4 late) were planted in October 1991 and 1992 in flooded (FE) and non flooded (NFE) environments for evaluation of cane yield, commercial cane sugar (CCS), internode length, internode number, stalk length, stalk thickness (circumference), stalk number, sugar recovery, and stalk weight. Cane yield showed significant positive phenotypic correlation coefficient (PCC) with stalk number in FE (P ≤ 0.05) and NFE (P ≤ 0.01). Stalk length had a significant positive PCC with stalk weight in both environments, and with internode length in FE (P ≤ 0.05). Commercial cane sugar also expressed significant positive PCC with cane yield in both environments (P ≤ 0.01), but with stalk number only in NFE (P ≤ 0.05). Genotypic correlation coefficients were generally in the same direction as PCC but higher in magnitude. In both environments, stalk number and stalk weight had relatively high positive direct effects on cane yield. However, flooding tended to enhance the direct effect of stalk weight and diminish the direct effect of stalk number on cane yield. Only cane yield and sugar recovery had high direct effects on CCS. Selection for improvement of cane yield can be based on stalk number and stalk weight in both environments. High yielding clones can be further screened for more sugar recovery to improve CCS. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flooding tolerance of spelt (Triticum spelta L.) compared to wheat (Triticum aestivum L.) – A physiological and genetic approach

In marginal, agroclimatic zones, yield is often affected by flooding, but the effect is much less for winter spelt (Triticum spelta L.) than for winter wheat (Triticum aestivum L.). This study evaluates the reaction of a wheat x spelt population (F₅ RILs of Forno x Oberkulmer) to flooding stress in the early phase of germination. Lines with greater tolerance to 48 h flooding just after imbibition showed less electrolyte leakage (r = -0.79) indicating greater membrane integrity and better survival. Five QTL explaining 40.6% of the phenotypic variance for survival to flooding were found, and localized on the chromosomes 2B, 3B,5A, and 7S. The tolerance to 48 h flooding four days after sowing was best correlated with the mean germination time (r = 0.8), indicating that the plants with a fast coleoptile growth during flooding are less susceptible to flooding. Ten QTL were found for seedling growth index after flooding explaining 35.5% of the phenotypic variance. They were localized on chromosomes 2A, 2B, 2D, 3A, 4B, 5A, 5B, 6A, and 7S. Standard varieties of spelt and wheat showed the same tolerance characteristics. The possibility to use marker assisted selection for flooding tolerance is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of aerobic conditions in the rhizosphere of rice on the dynamics and availability of phosphorus in a flooded soil – A model experiment

The secretion of O₂ by rice roots results in aerobic conditions in the rhizoshere compared to the bulk flooded soil. The effect of this phenomenon on the adsorption/desorption behavior and on the availability of phosphorus (P) in a flooded soil was investigated in a model experiment. An experimental set‐up was developed that imitates both O₂ release and P uptake by the rice root. The results showed that O₂ secretion significantly reduced P adsorption/retention and increased P desorption/release in the “rhizosphere” soil, compared to the anaerobic bulk soil. The P uptake by an anion exchange resin from both unfertilized and P‐amended soil was significantly increased. The results confirm that the O₂ secretion is an important mechanism to enhance P availability and P uptake of rice under flooded conditions, where the “physico‐chemical” availability of P in the anaerobic bulk soil is strongly reduced. The decrease of P availability in the P‐amended flooded bulk soil was mainly associated with the almost complete transformation of the precedingly enriched Al‐P fraction into Fe‐bound P with extremely low desorption/release characteristics during the subsequent flooding.     

季节性淹水对长江滩地69杨木材材性及其变异的影响

以安微新洲滩地上生长的６９杨为材料,研究季节性淹水对６９杨木材材性及其变异的影响。结果表明,与未淹水相比,长江滩地季节性淹水对６９杨纤维形态特征影响不大,０．０５水平下方差分析检验不显著;对木材微纤丝角,木材密度,木材干缩率和力学性质影响较大,０．０５水平下方差分析检验显著,其中,微纤丝角,基本密度,抗弯弹性模量,抗 度和气干体积缩率分别增加了１５．６％,５．９％,１５．７５,１７．２％和２８．５     

越桔耐涝品种的筛选

通过对盆栽越桔采用田间观察、生理生化指标测定等方法 ,研究了引种越桔 5个类型10个品种的耐涝能力。结果表明 ,5个类型越桔的耐涝能力 ,笃斯越桔强于高丛越桔、半高丛越桔和红豆越桔 ,矮丛越桔耐涝能力最差。但半高丛、矮丛越桔中也有一些品种表现出较强的耐涝能力。各品种按耐涝能力由强到弱排列依次为 :艾朗 >兰丰 >科丽尔 >北村 >圣云 >7917>美登 =斯卫克 >芝妮 >北空     

淮河流域中上游圩区治理分区除涝设计探讨

在淮河流域的干、支流中上游沿岸圩区 ,分区除涝方法是排涝及时、缩短下游淹没时间 ,充分发挥除涝工程效益的方法。分区降涝互不窜排 ,运行简便 ,除低农业生产成本 ,减轻农民负担 ,达到减灾免灾之目的     

淹水胁迫下银杏主要生化指标的变化

以3年生的银杏幼树为实验材料．经过淹水处理后．测定不同时间银杏叶片内主要生化指标——丙二醛（MDA）、游离脯氨酸（PRO）、可溶性糖以及超氧化物歧化酶（SOD）含量的变化．结果表明：淹水后的前9天．银杏叶片丙二醛含量无明显变化．第10天．其MDA含量显著增加．达到18．7μmol／g．比对照MDA含量（7．2μmol／g）增加1倍多；淹水后第8天．银杏叶片游离脯氨酸（PRO）含量显著增高．达到101．4μg／g．为对照的2倍多；随着淹水时间的延长．银杏叶片可溶性糖的含量逐渐增加，第9天达到32．9mg／g，随后维持在较高水平上；在淹水后前几天．SOD的活性增加较快．第5天．SOD活性达到最高值854．6U／g．第6天开始下降，到第11天时．其活性为78．8U／g．远远低于对照组．     

霍林河流域洪水径流演变规律及驱动机制研究

霍林河是松嫩平原西部地区科尔沁、向海和查干湖湿地的重要补给水源,其洪泛作用对流域洪泛区环境系统的景观维系起着决定作用。选取流域3个代表测站近50年来的年最大洪峰流量序列,分析流域洪水径流演变的规律及驱动机制,包括自然和人为干扰两方面,可以为流域防洪减灾及洪水资源化利用提供理论依据。霍林河洪水以雨洪型为主,洪水多发于降雨...