Response of the pigeonpea-Rhizobium symbiosis to salinity stress: variation among Rhizobium strains in symbiotic ability

Summary There were significant differences among pigeonpea [Cajanus cajan (L.) Millsp] Rhizobium sp. strains (IC 3506, IC 3484, IC 3195, and IC 3087) in their ability to nodulate and fix N₂ under saline conditions. Pigeonpea plants inoculated with IC 3087 and IC 3506 were less affected in growth by salinity levels of 6 and 8 dS m^-1 than plants inoculated with the other strains. For IC 3506, IC 3484, and IC 3195, there was a decrease in the number of nodules with increasing salinity, while the average nodule dry weight and the specific nitrogenase activity remained unaffected. However, in IC 3087, the number of nodules increased slightly with increasing salinity. Leaf-P concentrations increased with salinity in the inoculated plants irrespective of the Rhizobium sp. strain, and leaf-N concentrations decreased with increasing salinity in IC 3484 and IC 3195 only. Shoot-Na and-Cl levels were further increased in these salt-sensitive strains only at 8 dS m^-1. Therefore there may be scope for selecting pigeonpea Rhizobium sp. symbioses better adapted to saline conditions. The Rhizobium sp. strains best able to form effective symbioses at high salinity levels are not necessarily derived from saline soils.Submitted as JA No. 919 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

The effect of soil liming on shoot development, root growth, and cluster root activity of white lupin

 The effects of a limed soil upon root and shoot growth of white lupin (Lupinus albus L.) were investigated using soil tubes and pots. After 75 days in the soil tubes, the combined taproot and lateral root dry weight in limed soil (2.5% CaO w/w) was significantly less than in neutral pH soil (by 57%). However, the dry weight and numbers of cluster roots remained comparable between the treatments, demonstrating for the first time that the cluster roots respond differently to the rest of the root system. Cluster roots accounted for 17% of the total root biomass in neutral soil, increasing significantly to over 30% in limed soil. When grown for 43 days in pots containing soil with different additions of lime (0.5–2.5% CaO w/w), soil citrate concentrations were higher than in the neutral pH soil treatment in all except the 2.5% lime treatment, in which they were lower. In both experiments, shoot dry weights were lower in the presence of the limed soil compared with those in the neutral pH soil. Although a reduction in shoot dry weight was not apparent at 21 days in the limed-soil tubes, the initiation of fewer mainstem leaf primordia indicated a slower shoot development than occurred in the neutral soil. Plants grown in the limed-soil tubes showed leaf yellowing and some chlorosis within 9 days. At the final harvest, the shoot phosphorus and manganese concentrations were significantly lower in plants grown in limed soil compared with those in the neutral pH soil, whereas the concentration of calcium was higher. Received: 11 October 1999     

Soluble organic nitrogen in agricultural soils

 The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha^–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding. Received: 10 June 1999     

Retention of dissolved organic matter by illitic soils and clay fractions: Influence of mineral phase properties

The dependency of the retention of dissolved organic carbon (DOC) on mineral phase properties in soils remains uncertain especially at neutral pH. To specifically elucidate the role of mineral surfaces and pedogenic oxides for DOC retention at pH 7, we sorbed DOC to bulk soil (illitic surface soils of a toposequence) and corresponding clay fraction (< 2 μm) samples after the removal of organic matter and after removal of organic matter and pedogenic oxides. The DOC retention was related to the content of dithionite‐extractable iron, specific surface area (SSA, BET‐N₂ method) and cation exchange capacity (pH 7). The reversibility of DOC sorption was determined by a desorption experiment. All samples sorbed 20–40 % of the DOC added. The DOC sorption of the clay fractions explained the total sorption of the bulk soils. None of the mineral phase properties investigated was able to solely explain the DOC retention. A sorption of 9 to 24 μg DOC m^–2 indicated that DOC interacted only with a fraction of the mineral surface, since loadings above 500 μg m^–2 would be expected for a carbon monolayer. Under the experimental conditions used, the surface of the silicate clay minerals seemed to be more important for the DOC sorption than the surface of the iron oxides. The desorption experiment removed 11 to 31 % of the DOC sorbed. Most of the DOC was strongly sorbed.     

利用航空成像光谱数据研究土壤供氮量及变量施肥对冬小麦长势影响

以推扫式成像光谱仪PHI(Pushbroom Hyperspectral Imager)获取的冬小麦拔节期、灌浆初期及乳熟期的航空影像数据为基础，提取反映冬小麦长势的光谱特征值，结合地面调查数据，分析了研究区冬小麦的长势情况；对不同时相光谱特征值与土壤基础供氮量、土壤总供氮量以及变量施肥量进行统计分析，分析结果显示：土壤基础供氮量、土壤总供氮量的空间分布差异对冬小麦长势有明显的影响，其中，土壤基础供氮量是影响冬小麦长势的重要因素，它对冬小麦的长势影响贯穿冬小麦的整个生育期；此外，该文还通过变量施肥前后作物     

基于自然光照反射光谱的温室黄瓜叶片含氮量预测

利用便携式光谱辐射仪测量了自然光照条件下温室黄瓜叶片的光谱反射率,并计算了反射率光谱的一次微分光谱。反射率光谱以及一次微分光谱与叶片含氮量的相关分析表明,温室内光谱特性与叶片含氮量相关性最大的敏感波段分别是505～664 nm和685～722 nm。当利用原始光谱进行分析时,通过变量筛选得到了4个敏感波长,分别是568、596、640和664 nm。偏最小二乘回归分析(PLSR)以及归一化颜色指数(NDCI)分析都表明,建模时的相关系数R_C>0.800,模型验证时的相关系数R_V>0.700。对微分光谱进行的相关分析结果表明,利用单一敏感波长520 nm就可获得理想模型,建模时的相关系数为0.880,模型验证时的相关系数为0.787。对比原始光谱的PLSR模型与一阶微分光谱的一元线性回归模型可以得知,原始光谱以及一阶微分光谱都可用于温室内叶片含氮量的预测,而且一阶微分光谱在一些特殊的波长处具有更高的预测能力,这些模型将成为开发便携式作物长势诊断仪器的技术基础。     

冬小麦施用控释氮肥增产效应研究初报

冬小麦施用 2种控释N肥田间小区试验研究结果表明 ,不同灌水量、等N量下冬小麦施用乐喜施控释N肥 (F2 )和众品控释N肥 (F3 )均比施用普通尿素 (F1)显著提高产量 ,产量结构明显改善 ,N素利用效率分别提高 3%～ 5 % (W1)和 2 %～ 6 % (W2 ) ,经济效益F3 处理增收 10 82元 /hm2 ,而F2 处理平均减收 6 32 7元 /hm2 ,收获期耕层土壤所保持的N量较多。     

不同秸秆还田模式与氮肥施用量对土壤N2O排放的影响

以山东省桓台县为试验地点,分析在高产条件下,不同秸秆还田模式和氮肥施用量对农田N2O排放的影响.试验结果表明,氮肥施用量与秸秆还田模式都是影响土壤N2O排放的重要因素;小麦秸秆还田可以大大降低土壤N2O的排放,施用有机粪肥是影响N2O排放的另一重要因素.     

氮、磷的农业非点源污染防治方法

非点源污染最主要的影响就是使水体富营养化、水质变差,从而影响到生产、生活、社会与经济的发展,其中氮、磷的农业非点源污染又是最主要的。经过30多年的研究,非点源污染研究逐渐从初期的定性化研究转向定量化,由统计、调查与机理研究转向实用治理研究。就众多的防治方法来看,大体可以分为两大类,即“源”(Source)防治和“汇”(Sink)防治。     

小麦氮素营养与籽粒灌浆期氮素转移的研究进展

对小麦氮素营养与籽粒灌浆期氮素转移研究进展进行了综述。过去进行的大量研究结果表明,小麦籽粒最终累积的氮素有相当一部分来自于灌浆期间营养器官中氮素的再转移,来自营养器官氮(内源氮)与土壤中新吸收氮(外源氮)的比例基本上是1:2。因此,花后营养器官氮素营养水平是决定小麦籽粒产量、籽粒中氮素累积量和蛋白质含量的一个重要因素。灌浆期间营养器官氮素向籽粒发生转移的同时,常常伴随着叶片光合性能的下降和叶片的衰老。不同基因型品种在灌浆期的氮素转移程度不同,表现为随品种演替,旗叶、茎秆和叶鞘中氮素的输出率增加,而转移氮对籽粒氮的贡献率却下降。氮收获指数(NHI)可以描述植物向籽粒分配氮的能力,是衡量作物对氮利用效率的指标。氮收获指数存在显著的基因型差异,虽然现代小麦品种吸氮量高于古老品种,但氮收获指数在现代和古老小麦品种间的差异因不同研究者而异,有的认为现代品种高于古老品种,但也有人认为与年代无关;小麦氮收获指数一般在0.55～0.80之间,很少超过0.8。过去对小麦籽粒灌浆期间的氮素转移虽然进行了大量研究工作,取得了许多重要进展,但仍有许多问题需要进一步深入研究,如根冠关系和灌浆过程中氮素转移的相互关系,田间个体和群体调控及不同高产栽培模式下灌浆过程中氮素转移的