Growth and uptake of Cd and Zn by Leucaena leucocephala in reclaimed soils as affected by NaCl salinity

Heavy metal accumulation in reclaimed soils is increasing rapidly in developing countries where the use of saline waters for irrigation is a common practice, even though salinity-heavy metal interactions are not fully understood. An example for this development is the Bangar area of Egypt where the application of contaminated amendments during the last 30 years has increased the Cd and Zn concentrations in topsoils from 0.08 to 0.76 mg · kg^—1 and from 17 to 73 mg · kg^—1 respectively. This work aimed at evaluating the uptake of Cd and Zn by Leucaena leucocephala, a leguminous tree cropped for fodder and green manure, as affected by the addition of 10 mM NaCl to irrigation water. During a 6 month field experiment, salinized and control plots were compared with respect to soil solution composition and root development as well as the uptake of Cd and Zn and their translocation to the leaves. NaCl treatment raised the concentration of organic carbon, Cd and Zn in soil solution and enhanced the uptake of Cd and Zn significantly. Salinized plants showed shorter roots, reduced retention of Cd and Zn in roots and stems and considerable translocation of both elements to the leaves. This work demonstrates that NaCl salinity affects not only the bioavailability of soil Cd and Zn but also modifies plant functions related to their acquisition and translocation to the leaves. The results provide evidence that the risk of transfer of heavy metals to the food chain and their leachability to the ground water may be greater under saline conditions than generally assumed.     

Performance of Sorghum Grown on a Salt Affected Soil Manured with Dhaincha Plant Residues Using a 15N Isotopic Dilution Technique

A field experiment was conducted on a salt-affected soil to determine the effect of application of three types of Dhaincha (Sesbania aculeata Pers.) residues (R, roots; L, shoots; L+R, shoots plus roots) on the performance of sorghum (Sorghum bicolor L.) using the indirect ¹⁵N isotopic dilution technique. Results indicated that sesbania residues (L and L+R), used as green manures, significantly increased grain yield, dry matter production, N uptake, and water use efficiency of sorghum. Percentages of nitrogen (N) derived from residues (%Ndfr) in sorghum ranged from 6.4% to 28%. The N recoveries in sorghum were 52%, 19.6% and 19.7% of the total amount contained in sesbania roots, shoots and roots plus shoots, respectively. The beneficial effects of sesbania residues are attributed not only to the additional N availability to the plants, but also to effects on the enhancement of soil N uptake, particularly in the L+R treatment. The findings suggest that the use of Sesbania aculeata residues, as a green manure, can provide a substantial portion of total N in sorghum. In addition, the use of sesbania green manure in salt-affected soils, as a bio-reclaiming material, can be a promising approach for enhancing plant growth on a sustainable basis.     

Effects of Irrigation Water Quality and Nitrogen Rate on the Recovery of 15N Fertilizer by Sorghum in Field Study

The effects of ¹⁵N-labeled ammonium nitrate on yield, uptake of nitrogen (N) by sorghum (Sorghum sudanense, Piper), and on N remaining in the soil were studied in a field experiment with different N rates (0, 50, and 100 kg N ha^?1) and with two irrigation water qualities, well water (WW) and treated wastewater (TWW). Treated wastewater irrigation increased dry matter and N yield compared to WW. At equal N rates, recovery of ¹⁵N-labeled fertilizer by plants increased with TWW irrigation compared to WW (36% versus 23%). Neither fertilizer rate nor water quality had an effect on the ¹⁵N-labeled fertilizer remaining in the 0- to 60-cm layer of soil. On average 41% in the TWW treatment (49–33%) and 38% in WW treatment was mostly present in the surface 20-cm layer. Losses of ¹⁵N-labeled fertilizer were unaffected by irrigation water quality (35%) and increased with N application rate in TWW (4% versus 31%).     

Effect of Leucaena leucocephala (Lam) de Wit. as a green manure on nitrogen uptake and yield of rice

Summary Field studies were conducted over two seasons to examine the effect of Leucaena leucocephala as a green manure on the N uptake and yield of rice grown under lowland conditions. The treatments were 0, 4, 8, and 12t Leucaena ha^-1 with 0,44, and 88 kg N ha^-1 as urea in a factorial combination. N uptake was evaluated at maximum tillering, panicle initiation, and harvest. The incorporation of Leucaena increased N uptake throughout the vegetative period in both seasons, irrespective of the mineral-N level. At all levels of N, the grain yield increased significantly following the incorporation of Leucaena, and in both seasons the Leucaena treatment of 8 t ha^-1 was almost as effective as the highest mineral-N application.     

Dynamics of nodulation,nitrogen fixation,nitrogen use and biomass yield over time in pot-grown Leucaena leucocephala (Lam.) de Wit

The dynamics of nodulation, N₂-fixation and N use in Leucaena leucocephala cv. K28 over time was investigated in a screenhouse at 4, 8, 12 and 16 months after planting (MAP) using the ¹⁵N-labelling method. Leucaena had a consistently increasing pattern of nodulation, dry biomass and nitrogen yield. A sharp rise in nodulation was observed between 12 and 16 MAP, whereas for biomass, N accumulation and N₂-fixation, and N₂-fixation, an upward surge occurred between 4 and 12 months. Nodulation, N accumulation, N₂-fixation and biomass yield all peaked at 16 MAP. Along with the steady increase in N₂-fixation throughout the 16-month growth period, the % N derived from the atmosphere rose from 17.9% to 61.5%, 70.1% and 74%, equivalent to 191, 1623, 2395 and 3385 mg N₂ fixed plant^-1 at 4, 8, 12 and 16 MAP, respectively. Nitrogen assimilation from soil and fertilizer decreased inversely to the increase in symbiotic nitrogen fixation with time.     

Growth and Nitrogen Fixation in Dhaincha/Sorghum and Dhaincha/Sunflower Intercropping Systems Using 15Nitrogen and 13Carbon Natural Abundance Techniques

A field experiment on dhaincha, sunflower, and sorghum plants grown in monocropping and intercropping systems was conducted to evaluate growth and nitrogen (N₂) fixation using ¹³carbon (C) and ¹⁵N natural abundance techniques. Intercropping of sesbania/sorghum showed a greater efficiency than monocropping in producing dry matter during the entire growth period, whereas the efficiency of producing dry matter in the sesbania/sunflower intercropping was similar to that in the monocropping system. Moreover, sorghum plants (C4) were more competitive than sesbania (C3) for soil N uptake, whereas sesbania seemed to be more competitive than its associated sunflower (C3). Nitrogen uptake in the mixed stand of sesbania/sorghum was improved as a result of the increase in soil N uptake by the component sorghum and the greater root nodule activity of component sesbania without affecting the amount of N₂ fixed. The Δ ¹³C in plant materials was affected by plant species and the cropping system.     

Nitrogen contribution by leucaena (Leucaena leucocephala) prunings to maize in an alley cropping system

Summary The N uptake of maize was assessed on an Alfisol in a sole crop and in an alley cropping system in southwestern Nigeria. Although the application of prunings increased the maize N content in both sole and alley-cropped maize, the N contributed to the maize by the prunings was low, ranging between 4.4 and 23.8 kg ha^–1. This was equivalent to 3.2% and 9.407% of the N released during decomposition of the prunings. Application of the prunings increased the grain yields of the sole maize by 38% and the maize yield in the alley-cropped plots by 104%, compared with yields in the corresponding plots where prunings were not applied. The results indicate that part of the N from the prunings was retained in the soil organic-N pool. Maize N, dry weights and grain yields were lowest in the alley-cropped plots where prunings were removed, probably because of competition between the maize and the hedgerow trees.     

Effect of successive cuttings on uptake and partitioning of 15N among plant parts of Leucaena leucocephala

Summary We studied the effect of three successive cuttings on N uptake and fixation and N distribution in Leucaena leucocephala. Two isolines, uninoculated or inoculated with three different Rhizobium strains, were grown for 36 weeks and cut every 12 weeks. The soil was labelled with 50 ppm KNO₃ enriched with 10 atom % ¹⁵N excess soon after the first cutting. Except for the atom % ¹⁵N excess in branches of K28 at the second cutting, both the L. leucocephala isolines showed similar patterns of total N, fixed N₂, and N from fertilizer distribution in different parts of the plant at each cutting. The Rhizobium strain did not influence the partitioning of ¹⁵N among the different plant parts. Significant differences in ¹⁵N enrichment occurred in different parts. Live nodules of both isolines showed the lowest atom % ¹⁵N excess values (0.087), followed by leaves (0.492), branches (0.552), stems (0.591), and roots (0.857). The roots contained about 60% of the total plant N and about 70% of the total N derived from fertilizer over the successive cuttings. The total N₂ fixed in the roots was about 60% of that fixed in the whole plant, while the shoots contained only 20% of the fixed N₂. We conclude that N reserves in roots and nodules constitute another N source that must be taken into account when estimating fixed N₂ or the N balance after pruning or cutting plants. ¹⁵N enrichment declined up to about fivefold in the reference and the N₂-fixing plants over 24 weeks following the ¹⁵N application. The proportion and the amounts of N derived from fertilizer decreased, while the amount derived from N₂ fixation increased with time although its proportion remained constant.     

Influence of Unflooded Mulching Cultivation on Nitrogen Uptake and Utilization of Fertilizer Nitrogen by Rice

Abstract

Through unflooded mulching in field plots and ¹⁵nitrogen microplot tracer experiments, nitrogen (N) uptake of rice and N utilization have been studied compared with normal irrigation cultivation. The results showed that N uptake of unflooded rice and N derived from fertilizer (NDFF) of root, stem, and grain under mulching cultivation were lower than that under cultivation without mulching. However, the NDFF of rice under unflooded cultivation was higher than that under normal irrigation cultivation. The N utilization has been greatly enhanced under unflooded cultivation without mulching and unflooded plastic film cultivation with mulching as compared with normal irrigation. At the same time, there was no significant difference on the N uptake of unflooded rice among different ways of mulching cultivations. During the growth period of rice, no prominent differences were found in the soil residue, recovery, and N losses of fertilizer except the N uptake of rice between unflooded mulching and normal irrigation. The yield of rice under film mulching and straw mulching cultivation was higher than that of cultivation without mulching in the condition of unflooded cultivation, whereas the yield of rice under irrigation cultivation was higher than that under unflooded cultivation.     

局部涂抹纳米碳与尿素溶液对桃树梢叶生长及氮素吸收、分配的影响

以7年生的鲁星油桃为试材,采用15 N同位素示踪技术进行田间涂抹试验,研究不同浓度纳米碳与相同浓度尿素溶液(0μg/mL+0.2%,50μg/mL+0.2%,100μg/mL+0.2%,200μg/mL+0.2%,分别以CK、NC50、NC100、NC200表示)涂抹部分叶片对桃树局部梢叶生长、氮素吸收及分配的影响,以期为桃树栽培过程中施用碳纳米提供新的思路和有益的参考。结果表明:与对照相比,施用纳米碳后桃树涂抹叶片单叶面积明显增加,叶绿素含量显著提高,NC200处理下叶片的净光合速率、蒸腾速率和气孔导度比对照提高了15.8%,30.0%,12.4%;纳米碳的施用提高了桃树新梢的干物质积累量,NC100、NC200处理比对照增加了10.5%和12.9%,提高了新梢各部位的全氮含量;高浓度的纳米碳(NC200处理)提高了新生器官对氮素的吸收征调能力(Ndff值);随纳米碳浓度的增大氮素的利用效率显著提高,NC50、NC100、NC200处理的氮素利用率比对照提高了13.6%,29.5%,40.0%;此外,新生嫩叶部分以NC200处理的氮素分配率最高,达19.55%,NC50、NC100、NC200处理氮素分配率比对照提高了4.5%,16.2%,17.1%,差异显著。以上结果表明,纳米碳能够促进新梢叶片对氮素的吸收利用,有效提高叶绿素含量、光合作用效率及新梢局部氮素利用率,影响氮素在梢叶各部位间的分配,促进氮素向生长中心(新生嫩叶)的转移。     

泥石流频发区人工新银合欢林群落特征

采用植物群落学研究方法,对干热河谷泥石流频发区人工新银合欢林进行研究。结果表明：该人工林群落植物种类比较简单,科属组成极为分散,区系成分单调;科级地理成分热带性质较强（41.91%）,属级地理成分也以热带性质为主（45.16%）;群落物种组成以由中、小型叶面积、单叶、非全缘、纸质和革质的地面芽植物为主;垂直结构单调,虽可分为乔木层、灌木层、草本层,但乔灌层均以新银合欢占优势,草本层盖度低。群落处于不稳定的状态,应在人为干预的手段下进行分化和演替。     

Effect of Potassium Fertilizers on Cotton Yield and Nitrogen Uptake Efficiency in an Aridisol

A field experiment was carried out to study the effect of different rates of potassium (K) fertilizer [0, 50, 100, and 150 potassium oxide (K₂O) ha^–1] in the presence of increased supply of nitrogen (N) (120, 180, and 240 kg N ha^–1) on cotton (Gossypium hirsutum L.) yield and the N and K use efficiencies using the ¹⁵N isotopic dilution technique. Potassium fertilizer increased cotton yield, which was significant and more pronounced with the application of N in the high level (N3). The greatest cotton yield (6442 kg ha^–1) was obtained in N2K3 treatment with an increase of 14% over the control. In addition, K fertilizer significantly increased N uptake efficiency in the N2 and N3 treatments. The greatest N uptake efficiency (98%) was in N2K3 treatment. The greatest K uptake efficiency (42%) was occurred in N3K1 treatment. In conclusion, the use of K fertilizer could be useful when growing cotton in soils of moderate to high N content to improve N uptake efficiency and consequently increase cotton yield.     

Evaluation of the 15Nitrogen Isotope Dilution Technique for Estimating Crop Nitrogen Uptake from Organic Residues

Abstract

A field experiment was conducted to test the new approach for estimating crop nitrogen (N) uptake from organic inputs. The soil was prelabeled with ¹⁵N by applying ¹⁵N fertilizer to sunflower crop (Helianthus annuus L. var. Viki). The ¹⁴N plots, which received unlabelled fertilizer, were also set up. At harvest, ¹⁵N labeled residues were added to the unlabeled soils at a rate of 73 kg N ha^?1 (direct technique) and unlabeled residues were added to the ¹⁵N‐labeled soils at the same rate (indirect technique). Control plots without residues were also established. All plots were sown with the wheat (Triticum aestivum L. var merchouch)–fababean (Vicia faba L.)–wheat (Triticum aestivum L. var merchouch) cropping sequence.

In the cropping sequence, the first, second and third crop derived respectively 12.01, 2.4, and 1.93 kg N ha^?1 from crop residues estimated by the direct method and 14.77, 3.3, and 1.85 kg N ha^?1 estimated by the indirect method. The results showed no significant difference between the two techniques, which suggests that the new soil prelabeling technique compares well with the direct technique.     

土壤供保氮能力决定稻田氮肥增产效果和利用率

黑龙江五常和江苏常熟分属我国东北和华东单季稻区优质粳米的代表性产地,但五常维持水稻高产所需氮肥投入量通常远低于常熟而其增产效果优于常熟。由于两地水热条件、作物品种、农田管理和土壤类型均不同,究竟是何原因导致这种区域差异尚不清楚。为探究土壤因素的影响,在两地稻田分别取黑土型水稻土(BS)和乌栅土(WS),设不施氮(CK)、低氮和高氮(N 150和300 kg·hm^-2标记尿素)处理,开展盆栽试验,比较水稻产量、氮肥利用及总损失的土壤差异,并结合室内淹水矿化培养试验,研究两种水稻土氮素矿化特征。结果发现：在相同气候和水稻品种及管理条件下进行的盆栽试验中,各处理水稻产量、氮肥增产效果及地上氮素吸收累积量BS均优于WS,差值法氮肥利用率BS较WS高出20.0～28.7个百分点,然而¹⁵N示踪法氮肥利用率BS却仅较WS高5.56～8.01个百分点。尽管施氮后水稻吸收土壤氮均增加,但BS土壤来源氮增量较WS高95.0%～215%。根据CK和相应施氮处理水稻地上部土壤来源氮差值可计算土壤氮素表观激发量在BS为173～354 mg·pot^-1     

Leaf chlorophyll readings as an indicator of nitrogen status and yield of spinach (Spinacia oleracea L.) grown in soils amended with Luecaena leucocephala prunings

A field study was conducted to evaluate the nitrogen status and yield of spinach grown in soils amended with prunings of Leucaena leucocephala, (applied at a rate of 3, 5, 7 or 11 t ha^?1). A ‘no fertilizer’ 0 nitrogen (N) and 150 kg N ha^?1 (recommended) were the control treatments. SPAD readings were recorded for the top six leaves. Nitrogen sufficiency indices were used to indicate the N status of plants. Application of L. leucocephala prunings increased spinach yields (8.98–13.86 t DM ha^?1) relative to the 0N treatment (1.35 t DM ha^?1) and yields increased with increasing rate of pruning application. SPAD readings showed a linear increase with the increase in applied prunings. There was preferential distribution of N to upper leaves. The relationship between shoot N concentration and SPAD readings was linear and strongest for the top three leaves (r² = 0.84–0.92). The results indicate the potential of chlorophyll meter readings in assessing N status of leafy vegetables grown on soils amended with different levels of legume tree prunings.     

Nitrogen fixation in soybeans as influenced by cultivar and Rhizobium strain differences

Summary The effect of soybean variety and Rhizobium strain, as well as the level of nitrogen fertilizer, were tested in a field experiment in Greece. Three nodulating varieties were used and one non-nodulating variety as control, with two Rhizobium strains, one commercially available and one isolated from the soil of the experimental site. Nitrogen fertilizer labeled with ¹⁵N enabled the nitrogen derived from the atmosphere (Ndfa), from the soil (Ndfs), and from the fertilizer (Ndff) to be estimated. Statistical analyses showed that the combined variety-strain effect was responsible for most of the variation observed in all parameters, either measured directly or calculated, while the nitrogen level had no effect. The locally isolated strain generally performed equally as well as the commercial one. With the highest yielding variety in particular, the nitrogen-fixing efficiency of soybean nodules, expressed as plant total nitrogen in excess of that in the non-nodulated control in relation to nodule dry weight, was even superior. Taking into account the low fertilizer recovery by plants, it is suggested that adapted cultivars properly inoculated can fix most of the nitrogen they need for high yields. This is of great economic importance for crops with high nitrogen-fixing efficiency, like the soybeans used in this work, which can fix more than 200 kg N/ha, as ¹⁵N dilution and nitrogen difference evaluations have confirmed. The local cultivars in this connection were superior to the United States cultivar, while the difference between cultivars in symbiotic performance were not due to the ability to nodulate, but rather to a much higher nodule-specific efficiency. The commercially available strain was found to produce generally more nodules and the locally isolated strain produced less but larger and more efficient nodules. Finally, the grains from the nodulated plants contained significantly smaller quantities of Fe, Ni, Cu, Zn, and especially Mo compared with non-nodulated plants, as determined by X-ray fluorescence techniques.     

Substitution Effect of Pig Manure for Nitrogen Fertilizer on Nitrogen-Use Efficiency

Pot experiments using a ¹⁵N isotope technique were conducted to quantify the substitution effect of pig manure (PM) for chemical fertilizer (CF) nitrogen (N) on N-use efficiency. Treatments include a control, 100% CF N, 100% PM N, and portions of PM N (25?75%) substitution for CF N. With an increase portion of PM, N in wheat and maize plants derived from the CF (%Ndff) significantly (P < 0.05) decreased from 76.6 to 35.1% and 79.8 to 40.9%, whereas N derived from PM (%Ndfm) increased from 13.1 to 57.0% and 5.4 to 47.1%. Plant availability of PM N was equivalent to 33% and 28% of CF N for wheat and maize, and 10?17% and 12?20% of PM N were recovered by wheat and maize plants, respectively. The PM N could substitute for 33% CF N. Combinations of PM with CF did not improve N efficiency compared with equivalent rate of CF alone.     

Uptake and translocation of nitrogen in patumma (Curcuma alismatifolia) by leaves or root

An adequate supply of nitrogen (N) is important for patumma growth and flower quality. This study aimed to compare the uptake and translocation of N by foliar and root application. Fertilization with ¹⁵ nitrate (NO₃)-N via roots or leaves was carried out at four stages, at the 1st to 4th fully expanded leaf (FEL) stages, and the plants were sampled at each successive stage. The uptake and translocation of ¹⁵N from foliar or root applications showed relatively similar patterns at all stages. Although the N fertilizer utilization rate by roots was higher than that via leaves, the foliar application stimulated reproductive growth by earlier flowering. The N supplied at the 1st FEL and the 2nd FEL was utilized mainly in leaves, whereas supplying N at the 3rd and 4th FEL promoted flower quality. Fertilizer application method and stage of application influence the utilization rate and translocation of N to the sink organs.     

Determination of Application Effects of Sewage Sludge on Growth,Soil Properties,and N Uptake in Komatsuna by using the Indirect 15N Isotope Method

Abstract: By using the indirect ¹⁵nitrogen (N) method, the application effects of sewage sludge (SS) on growth indices, yield, and nutrient uptake in Komatsuna (Brassica campestris var. perviridis) grown in a low fertility soil were investigated and compared with those of chemical fertilizer (CF) and no‐fertilizer (NF) treatments. The N‐use efficiencies of CF and SS were 19.7% and 12.1%, respectively, of the applied N. Therefore, the relative efficiency of the sewage sludge to chemical fertilizer was 61.5%. In comparison to NF and CF, the application of SS apparently increased the soil microbial activity, which was evaluated by measuring hydrolysis of fluorescein diacetate. After cultivation, the electrical conductivity (EC) of CF soil (0.175 dS m^?1) was significantly higher than those of NF (0.067 dS m^?1) and SS soils (0.057 dS m^?1). The concentrations of phosphorus (P), calcium (Ca), and magnesium (Mg) in SS leaves were significantly higher than those in CF leaves; however, the concentration of potassium (K) was significantly lower in SS than in CF.     

Growth and Nitrogen Fixation in Soybean as Affected by Phosphorus Fertilizer and Sheep Manure using 15N Isotopic Dilution

A field experiment was conducted to study the effect of adding different phosphorus (P) fertilizer levels [0, 40, and 80 kg phosphorus pentoxide (P₂O₅) ha^?1 (abbreviated as P0, P1, and P2, respectively)] and rates of sheep manure (M) [0, 20, and 40 ton ha^?1 (abbreviated as M0, M1, and M2, respectively)] on growth and nitrogen (N₂) fixation of soybean (Glycine max L.). Sorghum bicolor L. was employed as a reference crop to evaluate N₂ fixation using the ¹⁵N-isotpic dilution technique. Results showed that addition of P fertilizer or sheep manure had positive effects on dry-matter production, N accumulation, and seed yield. Such effects were more pronounced when adding sheep manure and P together than adding separately. Solely P fertilizer had a small impact on N₂ fixation. A tangible increase in the amounts of N₂ fixed due to manure addition occurred. The efficient use of N fertilizer (%NUE) increased significantly as the result of adding a high level of P fertilizer. However, a drastic decrease in %NUE was observed when sheep manure was added solely or in combination with P fertilizer. From productivity and ecological standpoints, P2M1 and P2M2 surpassed the other treatments in showing greater grain yield and greater N₂ fixation. However, considering the high cost of sheep manure, P2M1 was the optimal treatment for improving growth and N₂ fixation in soybean plants with minimal manure consumption. In conclusion, the integrated use of manure and P fertilizer could be considered a useful agricultural practice for improving the performance of soybean plants grown in an Aridisol. Their beneficial effects were mainly attributed to the enhancement of N₂ fixation through root growth and soil property improvements besides being a source of P and other nutrients that are essential for N₂-fixation process.