Comparative effect of human urine and ammonium nitrate application on maize (Zea mays L.) grown under various salt (NaCl) concentrations

The present study investigates the effect of urine and ammonium nitrate on maize (Zea mays L.) vegetative growth, leaf nutrient concentration, soil electrical conductivity, and exchangeable‐cations contents under various concentrations of NaCl in a soil substrate. The experiment was arranged in a completely randomized block design with eight replications under greenhouse conditions. The experimental soil substrate was made from a 1 : 1 : 1 volume‐ratio mixture of compost, quartz sand, and silty‐loam soil. Salinity was induced by adding 0, 15, and 30 mL of 1 M NaCl solution per kg of substrate to achieve an electrical conductivity (EC) of 1.3 (S0), 4.6 (S1), and 7.6 (S2) dS m^–1. Nitrogen sources were urine and ammonium nitrate applied at 180 and 360 mg N (kg soil substrate)^–1. Basal P and K were added as mono potassium phosphate in amounts equivalent to 39 mg P and 47 mg K (kg substrate)^–1, respectively. In the S0 treatment, a 3‐fold increase in EC was measured after urine application compared to an insignificant change in ammonium nitrate–fertilized substrates 62 d after sowing. Under saline conditions, application of 360 mg N (kg soil)^–1 as urine significantly decreased soil pH and maize shoot dry weight. At the highest salt and N dose (S2, N360) 50% of urine‐fertilized plants died. Regardless of salinity there was no significant difference between the two fertilizers for investigated growth factors when N was supplied at 180 mg (kg soil)^–1. Leaf N and Ca contents were higher after urine application than in ammonium nitrate–fertilized plants. At an application rate of 180 mg N (kg soil)^–1, urine was a suitable fertilizer for maize under saline conditions. Higher urine‐N dosages and/or soil salinity exceeding 7.6 dS m^–1 may have a deleterious effect on maize growth.     

Effects of mineral and biofertilizers on barley growth on compacted soil

Abstract

Biofertilizers are an alternative to mineral fertilizers for increasing soil productivity and plant growth in sustainable agriculture. The objective of this study was to evaluate possible effects of three mineral fertilizers and four plant growth promoting rhizobacteria (PGPR) strains as biofertilizer on soil properties and seedling growth of barley (Hordeum vulgare) at three different soil bulk densities, and in three harvest periods. The application treatments included the control (without bacteria inoculation and mineral fertilizers), mineral fertilizers (N, NP and P) and plant growth promoting rhizobacteria species (Bacillus licheniformis RC04, Paenibacillus polymyxa RC05, Pseudomonas putida RC06, and Bacillus OSU-142) in sterilized soil. The PGPR, fungi, seedling growth, soil pH, organic matter content, available P and mineral nitrogen were determined in soil compacted artificially to three bulk density levels (1.1, 1.25 and 1.40 Mg m^?3) at 15, 30, and 45 days of plant harvest. The results showed that all the inoculated bacteria contributed to the amount of mineral nitrogen. Seed inoculation significantly increased the count of bacteria and fungi. Data suggest that seed inoculation of barley with PGPR strains tested increased root weight by 9–12.2%, and shoot weight by 29.7–43.3% compared with control. The N, NP and P application, however, increased root weight up to 18.2, 25.0 and 7.4% and shoot weight by 31.6, 43.4 and 26.4%, respectively. Our data show that PGPR stimulate barley growth and could be used as an alternative to chemical fertilizer. Soil compaction hampers the beneficial plant growth promoting properties of PGPR and should be avoided.     

Benefits of Biochars and NPK Fertilizers for Soil Quality and Growth of Cowpea (Vigna unguiculata L. Walp.) in an Acid Arenosol

Fertilization is required for optimum plant growth, particularly in unfertile soils, while optimizing nutrient use efficiency is an alternative to reduce inorganic fertilizer needs and reduce environmental problems caused by nutrient leaching. This study investigated soil properties and cowpea yield responses to biochars (BCs) made from different feedstocks, baby corn peel biochar (BC1), branches of mango tree biochar (BC2), and rice husk biochar (BC3), applied in combination with nitrogen-phosphorus-potassium (NPK) fertilizers. The experiment was conducted in a greenhouse, using an acid sandy soil (Arenosol) that was submitted for 70 d to the following eight treatments:i) control; ii) full dose of NPK (a commercial compound fertilizer (12-24-12 of N-P₂O₅-K₂O) + urea (46% N)); iii) BC1 + half dose of NPK; iv) BC1 + full dose of NPK; v) BC2 + half dose of NPK; vi) BC2 + full dose of NPK; vii) BC3 + half dose of NPK; and viii) BC3 + full dose of NPK. All biochars were applied at a rate of 0.9% (weight/weight), and each type of biochar was combined with half and full doses of NPK fertilizers. Soil pH increased significantly (P < 0.05) in treatments with BC1 and BC2, while cation exchange capacity (CEC) and available P were higher in the treatments with BC1; BC1 and BC2 also induced higher activity of enzymes related to the P cycle and higher cowpea yield. Similar soil properties and cowpea yield parameters were obtained with the full and half doses of NPK fertilizers for each type of biochar used. In conclusion, biochars in the combination with NPK fertilizers improved soil chemistry and enzymatic activities, allowing reduced fertilizer application and food production costs in the acid soil studied.     

The use of biologically based phosphorus fractions to evaluate soil P availability in reduced P‐input paddy soils

Chemical soil phosphorus (P) extraction has been widely used to characterize and understand changes in soil P fractions; however, it does not adequately capture rhizosphere processes. In this study, we used the biologically based phosphorus (BBP ) grading method to evaluate the availability and influencing factors of soil P under four P fertilizer regimes in a typical rice–wheat cropping rotation paddy field. Soil P was assessed after seven rice‐growth seasons at multiple growth stages: the seedling, the booting and the harvest stage. Soil CaCl₂‐P, citrate‐P and HC l‐P (inorganic P, Pi) as well as enzyme‐P (organic P, Po) were not significantly different between soil treated with P fertilizer during the wheat season only (PW ) and during the rice season only (PR ) compared with soil treated during both the rice and the wheat seasons (PR +W) at all three rice‐growth stages. No P fertilizer application during either season (Pzero) significantly reduced the concentration of soil citrate‐P and HC l‐P at the rice‐seedling and harvest stages. Significant correlations were observed between the HC l extraction and Olsen‐P (R ² = 0.823, P  <  0.001), followed by enzyme‐P (R ² = 0.712, P  <  0.001), citrate‐P (R ² = 0.591, P  <  0.001) and CaCl₂‐P (R ² = 0.133, P  <  0.05). Further redundancy analysis (RDA ) suggested that soil alkaline phosphatase (S‐ALP ) activity played a role in soil P speciation changes and was significantly correlated with enzyme‐P, citrate‐P and HC l‐P. These results may improve our ability to characterize and understand changes in soil P status while minimizing the overapplication of P fertilizer.     

不同退耕还林模式对土壤生物学性质的影响效果评价

在测定土壤微生物、土壤酶活性基础上,应用主成分因子分析法建立了不同退耕还林模式下的土壤生物学性质评价体系。结果表明,土壤放线菌、真菌数量与转化酶、脲酶、纤维素酶、过氧化氢酶活性之间的相关性达到了极显著或显著水平优势微生物中的微球菌与转化酶,芽孢杆菌与纤维素酶,木霉和游动放线菌与过氧化氢酶,酵母菌与脲酶呈显著正相关关系放线菌、真菌及其微生物优势类群多样性指标在评价土壤生物学肥力质量时具有十分重要的作用4种土壤酶活性是土壤生物学肥力质量评价的重要指标而细菌、酵母等生物量较小的微生物对土壤生态肥力评价的贡献较小。用土壤综合肥力指标值(IFI)进一步评价各样地的土壤生物学肥力质量的顺序依次为:苦竹林表层>桦木林表层>农耕地表层>农耕地亚表层>农耕地深层>桦木和苦竹林亚表层>桦木林深层>苦竹林深层。苦竹对退耕地的生态改善效果,如水土保持、水源涵养和土壤生态肥力的增加等方面要优于桦木。     

Temporal responses of soil biological characteristics to organic inputs and mineral fertilizers under wheat cultivation in inceptisol

A 2-year field experiment was conducted in wheat ecosystem to assess the key soil biological characteristics in inceptisols of northeastern region of India. Nine treatments using organic inputs (farmyard manure and vermicompost) and mineral fertilizers were applied by modulating the doses of organics and mineral N fertilizer. Soil enzymes (urease, phosphatase, dehydrogenase, fluorescein diacetate (FDA) and arylsulphatase), microbial biomass carbon (MBC), bacteria and fungi populations were measured before seed sowing (GS₁), at flowering stage (GS₂) and after harvest (GS₃) of wheat, whereas total organic carbon (TOC) was studied at GS₃. GS₂ recorded significantly higher soil enzyme activities, except FDA, which increased considerably at GS₃. Enzyme activities, available N and TOC significantly (p ≤ 0.05) enhanced with application of organic inputs even with reduced (50%) mineral N. Except urease and phosphatase, other enzymes did not respond significantly to mineral fertilization. Vermicompost application increased mean enzyme activities, MBC, microbial growth and TOC fractions (particulate organic carbon, humic acid and fulvic acid carbon) than farmyard manure. Significant (p ≤ 0.05) positive correlations (r = 0.61–0.87) were obtained between TOC and its fractions with studied soil enzymes. Thus, in conclusion, 5 t ha^–1 organics incorporation (especially vermicompost) in wheat fertility programme can uphold soil biological health, reduce (50%) N application and would be a sustainable option for wheat grown in inceptisols of northeastern region of India.     

Influence of Pseudomonas syringae R25 and P. putida R105 on the growth and N2 fixation (acetylene reduction activity) of pea (Pisum sativum L.) and field bean (Phaseolus vulgaris L.)

The effects of inoculating field peas (Pisum sativum L.) with Rhizobium leguminosarum and field beans (Phaseolus vulgaris L.) with R. phaseoli, alone or in combination with Pseudomonas syringae R25 and/or P. putida R105, were assessed under gnotobiotic conditions in growth pouches and in potted soil in a growth chamber. Inoculation of peas with P. syringae R25 or P. putida R105 alone had no effect on plant growth in pouches. In soil, however, the isolate R25 inhibited nitrogenase activity (as assessed by acetylene reduction assay) of nodules formed by indigenous rhizobia; strain R105 stimulated pea seedling emergence and nodulation. P. syringae R25 inhibited the growth of beans in either plant-growth system. P. putida R105, however, had no effects on beans in pouches, but reduced plant root biomass and nodulation by indigenous rhizobia in soil. Coinoculation of pea seeds with R. leguminosarum and either of the pseudomonads significantly (P<0.01) increased shoot, root, and total plant weight in growth pouches, but had no effect in soil. Co-inoculation of field beans with R. phaseoli and P. putida R105 had no effects on plant biomass in growth pouches or in soil, but the number of nodules and the acetylene reduction activity was significantly (P<0.01) increased in the soil. In contrast, co-inoculation of beans with rhizobia and P. syringae R25 had severe, deleterious effects on seedling mergence, plant biomass, and nodulation in soil and growth pouches. Isolate R25 was responsible for the deleterious effects observed. Although plant growth-promoting rhizobacteria may interact synergistically with root-nodulating rhizobia, the PGPR selected for one crop should be assessed for potential hazardous effects on other crops before being used as inoculants.     

黄土丘陵沟壑区典型林地土壤微生物、酶活性和养分特征

通过对陕西吴起县黄土沟壑区退耕还林地不同林分(沙棘、刺槐、油松、小叶杨)根际与非根际土壤养分、酶活性和微生物特征进行研究,比较4种典型林分及退耕草地“根际效应”及根际对养分的截留效应,评价根际效应对土壤特性产生不同改良效果,为黄土沟壑区退耕地人工林科学选择造林树种提供理论支持。研究表明:1根际与非根际土壤中有机质含量、有效磷含量、碱解氮含量和速效钾含量表现出显著差异,有机质、有效磷、速效钾含量均呈现明显的根际聚集现象。2根际土壤微生物数量和土壤酶活性总体高于非根际,仅油松样地中过氧化氢酶活性和小叶杨样地中脲酶活性根际低于非根际。3根际土壤中脲酶活性与细菌和真菌数量相关性达到显著水平,过氧化氢酶活性与真菌相关性达到显著水平;有机质含量与细菌、放线菌数量和脲酶活性相关性达到显著水平;碱解氮、有效磷含量均与细菌、真菌数量和脲酶活性相关性达到显著水平。在非根际土壤中,土壤养分含量与土壤微生物、土壤酶活性的相关性明显降低。4从土壤肥力综合水平看,根际土壤肥力水平综合得分总体上大于非根际土壤,其中根际土壤中沙棘小叶杨油松刺槐草地。沙棘能大幅度提高土壤肥力,具有较好的土壤改良效果。     

Impact of Long-Term Application of Organics,Biological, and Inorganic Fertilizers on Microbial Activities in Rice-Based Cropping System

Organics, biological, and inorganic fertilizers play a crucial role for improving crop yield and soil properties. Accordingly, we assessed their impact on yield, microbial activities, and transformations of carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) in soils under a 12-year-old intensively cultivated rice (Oriza sativa L.), mustard (Brassica juncea L.), sesame (Sesamum indicum L.) system with sole inorganic (NPK); NPK + farmyard manure (NPKF); NPK + green manure (NPKG) (Sesbania sesban L.), and NPK + green manure + bio-fertilizer (NPKGB) (Azotobacter chroococcum+ pseudomonas putida) treatments in sub-tropical India. The system yield was much higher with NPKF (23%) and NPKGB (18%) than that with NPK. Organic supplementation had a favorable influence on soil microbial biomass C (C_mic), N (N_mic), and activities of extracellular enzymes. Results of principal component and multiple regression analyses showed significant influence of C_mic on system yield (R² = 91, p = 0.001) and S availability (R² = 62, p = 0.001). Similarly, mineralizable N and acid phosphatase could predict significantly soil available N (R² = 85, p = 0.001) and P (R² = 51; p = 0.001), respectively. Results thus indicated that integrated nutrient management (NPKF/G) improved system yield, nutrient accumulation, and microbial activities in soils.     

Stable Isotope (δ13C and δ15N) Signatures and Their Relationship among Soil Enzyme Activities in Indian Semi-arid Agricultural Soils

ABSTRACT

A field evaluation of the stable isotopes (δ¹³C and δ¹⁵N) and their relationship among physicochemical and enzyme activities was conducted in Indian semi-arid agricultural soils. Composite soil samples were collected based on organic management (ORG), inorganic management (IM), integrated crop management (ICM) and precision farming (PF) experimental plots from the fall of September 2017 to October 2018. δ¹⁵N was significantly higher (13.85 %) in ORG soils compared with ICM (13.28 %), IM (12.84 %) and PF (12.75 %). In contrast δ¹³C was higher (?13.25%) in PF soils than IM (?13.6 %), ICM (?15.07 %) and ORG (?15.23 %). Soils from ORG had significantly higher levels of total N, total C, total S, organic carbon, available N, extractable P, Soil organic carbon stock, exchangeable K and enzyme activities compared to IM, ICM and PF. Urease, β – glucosidase, acid phosphatase, alkaline phosphatase, invertase, cellulase and dehydrogenase activities significantly increased the δ¹⁵N and reduced δ¹³C in agricultural soils. Our results suggested that organic management had improved the δ¹⁵N, plant available nutrients and soil enzyme activities. Stable δ¹³C and δ¹⁵N isotopes are good indicators of monitor the soil health, carbon, and nitrogen biogeochemical cycles in Indian semi-arid agricultural soils.     

Cultivation of potato – use of plastic mulch and row covers on soil temperature,growth, nutrient status,and yield

Potato is one of the most important crops in the world because of its high nutritional value; however, traditional cultivation in bare soil may render low yields and poor quality. Crop production efficiency can be increased by using plastic mulching and row covers to modify root zone temperature and plant growth, in addition to reduction in pest damage and enhance production in cultivated plants. However, there is little information demonstrating the effect of row covers in combination with plastic mulch on potato. The aim of this study was to assess the change in root zone temperature and its effect on growth, leaf nutrient, and yield of potato using plastic mulch of different colors, in combination with row covers. Seed of cultivar Mondial was planted in May 2012. The study included four plastic films: black, white/black, silver/black, aluminum/black, and a control with bare soil, which were evaluated alone and in combination with row covers removed at 30 days after sowing in a split-plot design. Higher yields were obtained when no row cover (43.2 t ha^?1) and the white/black film (42.2 t ha^?1) were used. Leaf nitrogen, sulfur, and manganese concentration were higher in plants when row cover was used; in contrast, no–row cover plants were higher in Fe and Zn. Mulched plants were higher in Mn concentration than control plants. There was a quadratic relationship between mean soil temperature and total yield (R² = 0.94), and between plant biomass and total yield (R² = 0.98), between leaf area with total yield (R² = 0.98).     

连续三年添加制革厂堆肥后土壤微生物生物量研究

Brazilian industry produces huge amounts of tannery sludge as residues, which is often disposed by landfilling or land application. However, consecutive amendment of such composted industrial wastes may cause shifts in soil microbial biomass （SMB） and enzyme activity. This study aimed to evaluate SMB and enzyme activity after 3-year consecutive composted tannery sludge （CTS） amendment in tropical sandy soils. Different amounts of CTS （0.0, 2.5, 5.0, 10.0, and 20.0 t ha-1） were applied to a sandy soil. The C and N contents of SMB, basal and substrate-induced respiration, respiratory quotient （qCO2）, and enzyme activities were determined in the soil samples collected after CTS amendment for 60 d at the third year. After 3 years, significant changes were found in soil microbial properties in response to different CTS amounts applied. The organic matter and Cr contents significantly increased with increasing CTS amounts. SMB and soil respiration peaked following amendment with 10.0 and 20.0 t ha-1 of CTS, respectively, while qCO2 was not significantly affected by CTS amendment. However, soil enzyme activity decreased significantly with increasing CTS amounts. Consecutive CTS amendment for 3 years showed inconsistent and contrasting effects on SMB and enzyme activities. The decrease in soil enzyme activities was proportional to a substantial increase in soil Cr concentration, with the latter exceeding the permitted concentrations by more than twofold. Thus, our results suggest that a maximum CTS quantity of 5.0 t ha-1 can be applied annually to tropical sandy soil, without causing potential risks to SMB and enzyme activity.     

Synergetic use of biochar and synthetic nitrogen and phosphorus fertilizers to improves maize productivity and nutrient retention in loamy soil

Abstract

This study was designed to investigate the effect of biochar on maize production and nutrient retention with recommended full and half dose of nitrogen (N) and phosphorus (P) nutrition in loamy soil. In the first study, maize was grown in pots with four levels of biochar (0, 2, 4, and 6?t?ha^?1) under two levels of NP fertilizer, viz. recommended (200–150?kg?NP?ha^?1) and it’s half (100–75?kg?NP?ha^?1) dose. The prominent improvement in plant roots traits, leaf area, plant growth, morphological and yield-related parameters were observed with addition of biochar at 2 and 4?t?ha^?1; while, plant height, number of grains per cob, grains and biological yield decreased with biochar addition 6?t?ha^?1 along with full dose of NP nutrition. In subsequent field studies, two levels of biochar along with control (0, 2, 4?t?ha^?1) were investigated. The more improvement in root growth, leaf area and crop growth was observed when biochar was applied at 2?t?ha^?1 with full NP nutrition. Biochar application at 2?t?ha^?1 with full NP nutrition produced the highest grain yield (6.64?t?ha^?1); however, biochar addition (2?t?ha^?1) with half NP nutrition resulted in better grain yield than full dose of NP to enhance maize production as compared with full dose of NP without biochar. Therefore, biochar addition (2?t?ha^?1) with half-recommended dose of NP prominently improved the maize productivity in loamy soil and serve as better in replacement of full dose of NP fertilizer.     

施磷对吊兰修复镉污染土壤及土壤酶活性的影响

选用吊兰进行室内盆栽,研究在Cd污染土壤中,施用不同剂量磷肥对吊兰生理指标、土壤酶活性等的影响,为合理施用磷肥,提高Cd污染土壤的植物修复效果提供参考依据。结果表明:吊兰在100mg/kg的Cd污染土壤中能正常生长,施P对吊兰的叶绿素、细胞膜透性、抗氧化酶活性影响显著(p0.01),表现为低浓度促进,高浓度抑制作用。当施磷量为200mg/kg时,叶绿素含量、CAT酶活性最大,外渗电导率和MDA含量最低,POD酶活性开始上升,说明施磷能使吊兰的细胞膜受害程度最低,抗氧化作用增强。同时,施P有利于改善Cd污染土壤的酶系统,对过氧化氢酶、脲酶的活性表现为低浓度促进、高浓度抑制,对蔗糖酶的活性表现相反,对磷酸酶的活性表现抑制作用;且200mg/kg的磷处理时,过氧化氢酶、脲酶的活性最高,蔗糖酶的活性最低。4种土壤酶活性均与P浓度呈高度相关性(p0.05),相关性为脲酶过氧化氢酶蔗糖酶磷酸酶。     

Long-term effects of heavy metals from composted municipal waste on some enzyme activities in a cultivated soil

A 3-year field experiment on a calcareous Fluventic Xerochrept planted with corn (Zea mays L.) was carried out to evaluate the effects of amending the soil with high and low rates of composted municipal waste on soil enzyme activities (alkaline phosphomonoesterase, phosphodiesterase, arylsulphatase, dehydrogenase, and l-asparaginase). These enzyme activities all increased when compost was added at rates of up to 90 t ha^-1, and the phosphatases continued to show a linear increase with compost rates of up to 270 t ha^-1. The addition of mineral fertilizer increased enzyme activities in unamended soil, and masked the stimulating effect of compost on the amended soils. Heavy metals did not affect soil enzyme activities up to a compost addition of at least three times the amount specified by Italian law.     

Effects of Bt-cotton on biological properties of Vertisols in central India

Growing areas under transgenic crops have created a concern over their possible adverse impact on the soil ecosystem. This study evaluated the effect of Bt-cotton based cropping systems on soil microbial and biochemical activities and their functional relationships with active soil carbon pools in Vertisols of central India (Nagpur, Maharastra, during 2012–2013). Culturable groups of soil microflora, enzymatic activities and active pools of soil carbon were measured under different Bt-cotton based cropping systems (e.g. cotton-soybean, cotton-redgram, cotton-wheat, cotton-vegetables and cotton-fallow). Significantly higher counts of soil heterotrophs (5.7–7.9 log cfu g^?1 soil), aerobic N-fixer (3.9–5.4 log cfu g^?1 soil) and P-solubilizer (2.5?3.0 log cfu g^?1 soil) were recorded in Bt-cotton soils. Similarly, soil enzymatic activities, viz. dehydrogenase (16.6–22.67 µg TPF g^?1 h^?1), alkaline phosphatase (240–253 µg PNP g^?1 h^?1) and fluorescein di-acetate hydrolysis (14.6–18.0 µg fluorescein g^?1 h^?1), were significantly higher under Bt-cotton-soybean system than other Bt- and non-Bt-cotton based systems in all crop growth stages. The growth stage-wise order of soil microbiological activities were: boll development > harvest > vegetative stage. Significant correlations were observed between microbiological activities and active carbon pools in the rhizosphere soil. The findings indicated no adverse effect of Bt-cotton on soil biological properties.     

冰雪灾害后林窗对杉木林土壤性质的影响

During January–February 2008, a severe ice storm caused significant damages to forests in southern China, creating canopy gaps and changing soil nutrient availability and enzyme activity. To understand the relationships between gap size, changes in the soil environment and the effects that these changes have on soil processes, we investigated the effects of gap size on soil chemical and biological properties in the forest gaps in a Cunninghamia lanceolata stand in northern Guangdong Province, southern China. Ten naturally created gaps, five large(80–100 m~2) and five small(30–40 m~2), were selected in the stand of C.lanceolata. The large gaps showed a significant increase in light transmission ratio and air and soil temperatures and a decline in soil moisture, organic matter,N and P compared with the small gaps and the adjacent canopy-covered plots in the 0–10 cm soil. The differences in organic matter and nutrient levels found between the large and small gaps and the canopy-covered plots may be related to changes in environmental conditions. This indicated rapid litter decomposition and increased nutrient leaching in the large gaps. Moreover, the lowest levels of catalase, acid phosphatase and urease activities occurred in large gaps because of the decline in their soil fertility. Large forest gaps may have a region of poor fertility, reducing soil nutrient availability and enzyme activity within the C.lanceolata stand.     

果草套种对南方丘陵山地表层土壤微生物量碳氮及酶活性的影响

[目的]探究不同果草套种模式下0—10cm土层土壤微生物量碳、氮及酶活性的差异,为改善土壤肥力条件、促进桂林旅游城市生态循环农业经济的发展提供理论依据。[方法]在桂林潮田河流域大山口农业综合示范区内设置样地,采集表层(0—10cm)土壤样品,测定与分析不同果草套种模式下表层土壤微生物量碳、氮及酶活性的差异。[结果]0—10cm土层土壤氮磷钾、土壤微生物量碳氮和土壤酶活性大小基本表现为:阳朔金桔+牧草桂橙1号+牧草翠冠梨+牧草对照样地。其中,阳朔金桔+牧草模式对0—10cm土层土壤微生物量碳、氮含量和土壤酶活性的影响最为明显(p0.05)。相关性分析表明,土壤微生物量碳氮和3种土壤酶活性存在极显著正相关关系。[结论]果草套种模式特别是阳朔金桔+牧草模式对南方丘陵山地表层土壤肥力条件的改善作用较为明显。     

Effectiveness of Water-Saving Superabsorbent Polymer in Soil Water Conservation for Oat Based on Ecophysiological Parameters

The objective of the study was to study soil water conservation and physiological growth of oat (Avena sativa L.) using water-saving superabsorbent polymer (SAP) at 60 kg ha^?1. The effectiveness of SAP was studied under three irrigation levels (adequate, moderate, and deficient) using a new type of negative hydraulic pressure–controlled auto-irrigator. Seven weeks after sowing (WAS), the number of tillers and leaves increased significantly by 33 and 40%, respectively, under deficient irrigation due to application of SAP. The SAP had little effects on shoot dry mass (SDM) and root dry mass (RDM) under adequate and moderate irrigation but increased both parameters significantly (59 and 45%) under deficient irrigation. As a result, the water-use efficiency (WUE) increased substantially (50%) under deficient irrigation. Leaf water potential (ψ₁) under adequate irrigation exceeded that under moderate and deficient irrigation by 26.4 and 39.6%, respectively, and the application of SAP further increased it by 7.2%. The superior growth and WUE of oat treated with SAP under deficient irrigation was ascribed to maintenance of greater relative water content (RWC) in leaves as well as intercellular carbon dioxide concentration (Ci), net photosynthesis (P_N), and transpiration rate. It is suggested that the application of SAP is a suitable soil management practice for locations characterized by severe water stress.     

Effect of the introduction of the nitrogen-fixing bacteria <Emphasis Type="Italic">Pseudomonas putida</Emphasis> 23 on the nitrogen balance in soil

The inoculation of red beets with the nitrogen-fixing bacteria Pseudomonas putida 23 increased the activity of the nitrogen fixation in the rhizosphere of the plants grown on meadow soil in the central part of the Oka River floodplain. The yield of the red beets and the uptake by plants of nitrogen from the soil and from the ¹⁵N-labeled nitrogen fertilizer applied on the trial microplot increased significantly. A statistically significant additional fixation of nitrogen from the atmosphere and a positive balance of nitrogen in the soil-plant system without significant changes in the bulk content of the soil nitrogen after the plant growing were found in a greenhouse experiment with the application of P. putida. It can be supposed that the excessive nitrogen determined in this system is related to the incorporation into plants of atmospheric nitrogen fixed in the rhizosphere of the inoculated plants. The application of P. putida 23 makes it possible to decrease the rates of NPK fertilizer by two times without losses in the yield of red beets.