Soil Nutrient Deficiency Research Articles

Isolation, Identification and Production of Encapsulated Bradyrhizobium japonicum and Study on their Viability

Rhizobium, a nitrogen-fixing bacteria is the essential feature of leguminous plants which is essential for the regeneration of nutrient-deficient soil. This study was aimed to isolate, identify, mass culture and immobilize Bradyrhizoium japonicum in encapsulated form and test their viability. Root nodules were sterilized, grinded and cultured aseptically in YEMA media containing Congo red. The obtained colon was sub-cultured to get a pure culture and different biochemical tests were conducted which proved Bradyrhizobium japonicum as the slow-growing species. The test shows a positive result of catalase production and nodulation test whereas the pH tolerance test shows more tolerance to the acidic pH. Similarly, Bradyrhizaobium japonicum can tolerate 1% and 2% NaCl concentration and it doesn’t show resistance to the penicillin disc of 10mg. The mass culture and encapsulation with sodium alginate adding sucrose as nutrient proved the simplicity for handling. Altogether 548 beads were prepared from the 100ml of the cultured broths which were viable for more than 190 days at 1%, 2% and 3% sucrose concentration but less viable at 5% and 10% sucrose concentration under room temperature.

Influence of Organic Enriched Manure and Inorganic Fertilizers on Plant Physiological Processes of Kenyan Tea Clone

Tea (Camellia sinensis L.) is one of the most popular beverages consumed in the world and Kenya is the leading exporter in Africa and only 3rd worldwide after China and India. Nutrient deficiency in soils and poor fertilization are possibly two reasons for low yields and quality of tea. The use of organic matter and mineral fertilizers has been proved to be a sound soil amendment and fertility management strategy. Therefore, this study was conducted to evaluate the possibility of using readily available organic manures in combination of inorganic fertilizers on the physiological processes of tea clones in Kenya. The study was conducted within Timbilil estate, KALRO- Tea Research Institute in Kericho County on variety clone TRFK31/8. It was laid out in a Randomized Complete Block Design (RCBD) and replicated three times. There were 14 treatments that randomly assigned in each block. Data on tea response was determined from photosynthesis rate, transpiration rate and stomatal conductance then recorded and analyzed using GenStat Version 15.1. There were significant differences between the treatments on the transpiration rate, stomatal conductance and the photosynthetic rate in both seasons for all the months recorded. The transpiration rate was highest during the wet season in the months of June, July and August while lower transpiration rates were recorded during the dry season in the months of December, January and February with 0.1 g m−2 s−1 transpiration rates recorded in several treatments in the month of February. Stomatal conductance, photosynthetic rate and transpiration rate were higher where NH4+ was introduced through the organic manure in all the seasons and therefore confirms that it is highly important to incorporate soil amendments with higher organic matter in tea production in Kenya.

Effects of straw returning combined with nitrogen fertilizer on spring maize yield and soil physicochemical properties under drip irrigation condition in Yellow River pumping irrigation area, Ningxia, China

Soil compaction and nutrient deficiency are common problems in Ningxia Yellow River pumping irrigation area, which adversely affect crop yield. A two-year (2017-2018) field experiment of straw returning combined with nitrogen fertilizer were designed. Four nitrogen application levels (pure N with 0, 150, 300 and 450 kg·hm-2) were set under the condition of full smashing of maize straw (12000 kg·hm-2) returning, with the conventional nitrogen application (pure N with 225 kg·hm-2) without straw returning as the control (CK) to investigate the effects of straw returning combined with different amounts of nitrogen fertilizer on soil physical and chemical properties and maize yield under drip irrigation condition. The results showed that, compared with no-straw returning treatment, the treatments of straw returning combined nitrogen fertilizer with 300 and 450 kg·hm-2 reduced soil bulk density (0-20 cm) by 3.3% and 5.4%, but increased soil porosity by 3.7% and 7.1%, respectively. Straw returning combined with nitrogen with 300 kg·hm-2 and 450 kg·hm-2 was the best treatment which increased soil organic matter content, available K, P, alkaline N and total N in 0-40 cm soil layer. Compared with the non-returning treatment, straw returning combined with nitrogen fertilizer 300 kg·hm-2 significantly increased soil water storage by 13.6% and 22.1%, increased maize yield by 31.1% and 46.0 % in 2017 and 2018, respectively. The analysis of yield components showed that the high maize yield was achieved mainly by increasing grain number and the100-grain weight. Curve fitting showed that the optimum amount of nitrogen fertilizer was 260 kg·hm-2. Our results provide important basis for soil fertility improvement and sustainable production.

Do plants respond and recover from a combination of drought and heatwave in the same manner under adequate and deprived soil nutrient conditions?

Extreme climatic conditions with extended drought periods and heatwaves are predicted to increase in frequency and severity in many regions of the world. Aside from this, other abiotic stress factors such as nutrient deficiency could pose a serious problem to plants when combined with other stressors resulting in more complex underpinning mechanisms. In the present study, we evaluated the response of Brassica napus to single and combined impacts of drought and heatwave (HW) under adequate or deprived (N-A and N-D) soil nutrient conditions. In addition, to get better insights in the plant response to combined stress, a post-stress period, pointing out a degree of the recovery after the cessation of stress, was also included. The results showed a different manner of single drought and heatwave action. The adverse effect of drought on leaf gas exchange was lagged on the growth and became more apparent only after recovery period with no obvious difference between different nutrient levels. Contrary, the growth response of nutrient-deprived plants to single HW was weak and in most cases, insignificant. Heatwave applied simultaneously with drought highly exacerbated the adverse effect of drought both under N-A and N-D conditions. Combined drought and heatwave stress resulted in the sharper decline of Asat and it was attributed to both stomatal and non-stomatal limitations. Interestingly, plants underwent combined drought and HW treatment under N-D conditions showed better aboveground growth recovery, compared to those grown under N-A conditions, while displayed far more diminished photochemistry of photosystem II and badly disturbed the C/N balance. This discrepancy came from the fact that soil nutrient deficiency, by itself, evoked strong stress under control climate conditions resulting in a dramatically slower aboveground growth of nutrient-deprived plant. In turn, although combined drought and HW stress had similar effect on the aboveground growth either under N-A or N-D conditions, the recovery of later one was better. These results highlight the necessity to look at plants’ performance under unfavorable environmental conditions beyond the actual event, since it can be depended not only on the duration of exposure but also on the legacy effect after treatment.

Nutrient Cycling in Organic Field Crops in Canada and the United States

Organic farmers have identified soil fertility and weed management as the two highest research priority areas. No review exists of research on soil nutrient management in organic field crop systems. We conducted a comprehensive review to identify the principles and factors governing nutrient management, knowledge gaps, and future research needs in organic grain and other field crop systems in Canada and the United States. We compared results from research conducted in different climates, soils, and crop rotational sequences. Results indicate that (i) dual‐use cover/green manure crops and/or animal manure are the most common sources of plant available N and other nutrients in organic field crop systems; (ii) soil nutrient deficiencies can develop through sole reliance on cover/green manure crops; (iii) dependence on animal manure can lead to N and P excesses; (iv) conventional soil testing procedures may not accurately predict crop nutrient needs; (v) greater knowledge of microbial processes governing nutrient cycling is needed; and (vi) better understanding of the impact of weeds on soil fertility may create weed and nutrient management synergies. Knowledge gaps include a lack in understanding of how the soil and plant biomes influence nutrient‐use efficiency and how crop diversity and rotations impact soil fertility, sustainability, and resilience in organic field crop systems. Likewise, interactions between weeds, crops, soil fertility, and weed management strategies are poorly understood.Core Ideas Soil, climate, fertility sources, and land use impact organic nutrient management strategies. Cover/green manure crops and animal manures are used to maintain soil fertility on organic farms. Conventional soil testing may not be ideally suited to organic systems. Tracking soil nutrient temporal changes can improve comprehensive nutrient management plans. More research of how weeds and soil microbial community structure/function impact nutrient cycling and crop production is needed.

Defining Fertilization Strategies for Sorghum (Sorghum bicolor (L.) Moench) Production Under Sudano-Sahelian Conditions: Options for Late Basal Fertilizer Application

Soil nutrient deficiency and rainfall variability impair the production of sorghum (Sorghum bicolor (L). Moench) in Sudano-Sahelian zone. The aim is to study the environmental factors that can determine the effect of fertilizer application on sorghum grain yield and to formulate tailored fertilization strategies according to sorghum varieties (hybrid and open pollinated improved varieties) and environmental context. Field experiments were conducted during the 2015 and 2016 growing seasons in Nioro du Rip and in Sinthiou Malème (Senegal). In a randomized complete block design arranged in a split-plot with four replications, three factors were tested: sorghum genotype (G: Fadda, Faourou, Soumalemba and Soumba with different cycle lengths), environment (E: irrigation and rainfed, different soil types and fertility levels), and fertilization management (M: five different combinations of application dose and application time) including T1 = no fertilizer applied; T2 (recommended practice, 100%) = 150 kg/ha of NPK (15-15-15) at emergence + 50 Kg/ha of urea (46%) at tillering + 50 kg/ha of urea at stem extension; T3 = 50% T2; T4 (100% delay) = 150 kg/ha of NPK +50 kg/ha of urea at stem extension +50 kg/ha of urea at heading ; T5 = 50% T4. Results showed that: (i) in most environments, stressed plants under late application treatments (T4 and T5) recovered biomass once the fertilizer was applied (ii); grain yield with T5 was higher than with T4 under well-watered conditions (sufficient and well distributed rainfall and eventual complementary irrigations) ; (iii) Fadda, a hybrid, responded differently to fertilization than the other varieties only for biomass production, (iv) late fertilizer application treatment (T4) gave higher grain yield than the recommended practice (T2) in the environment with low yield potential, and (v) long cycle duration genotypes benefited better from late fertilization compared to short cycle duration genotypes. This study showed that under Sudano-Sahelian conditions late fertilization of sorghum can be beneficial to grain yield if the rainy season has a slow start, depending on sorghum genotypes (i.e., cycle length), and on the initial N content of the soil.

The effects of soil phosphorus and zinc availability on plant responses to mycorrhizal fungi: a physiological and molecular assessment

The positive effects of arbuscular mycorrhizal fungi (AMF) have been demonstrated for plant biomass, and zinc (Zn) and phosphorus (P) uptake, under soil nutrient deficiency. Additionally, a number of Zn and P transporter genes are affected by mycorrhizal colonisation or implicated in the mycorrhizal pathway of uptake. However, a comprehensive study of plant physiology and gene expression simultaneously, remains to be undertaken. Medicago truncatula was grown at different soil P and Zn availabilities, with or without inoculation of Rhizophagus irregularis. Measures of biomass, shoot elemental concentrations, mycorrhizal colonisation, and expression of Zn transporter (ZIP) and phosphate transporter (PT) genes in the roots, were taken. Mycorrhizal plants had a greater tolerance of both P and Zn soil deficiency; there was also evidence of AMF protecting plants against excessive Zn accumulation at high soil Zn. The expression of all PT genes was interactive with both P availability and mycorrhizal colonisation. MtZIP5 expression was induced both by AMF and soil Zn deficiency, while MtZIP2 was down-regulated in mycorrhizal plants, and up-regulated with increasing soil Zn concentration. These findings provide the first comprehensive physiological and molecular picture of plant-mycorrhizal fungal symbiosis with regard to soil P and Zn availability. Mycorrhizal fungi conferred tolerance to soil Zn and P deficiency and this could be linked to the induction of the ZIP transporter gene MtZIP5, and the PT gene MtPT4.

Nano pyrite driven root foraging increases production of the heavy feeders, viz., cauliflower, cabbage and tomato in nutrient deficient soil with no fertiliser application

Plant draws nutrition from soil and air, while former contributes minerals and water, the later provides carbon dioxide. Similar to early man, who wandered around, hunting for resources, roots ‘forage’ underneath into the soil for nutrients. Root foraging is a function of nutrient availability. Here, for the first time, we show, root foraging which is quantified by the root architecture, can be modulated by a brief nano pyrite (FeS2) intervention. A 3 h root treatment of plant saplings with a 100 μg ml−1 suspension of nano FeS2, followed by transplantation onto a fallow land with no fertiliser application, influences root architecture and yield of cabbage, cauliflower, and tomato. These ‘heavy feeder’ vegetables drawing significant nutrients from the soil, are grown and consumed globally. This root treatment strategy, if applied for ‘heavy feeders’, can contribute towards sustainable vegetable farming with reduced fertiliser input; thus helping the marginal farmers across the world.

New Biofortification Tool: Wheat TaCNR5 Enhances Zinc and Manganese Tolerance and Increases Zinc and Manganese Accumulation in Rice Grains

Heavy metal contaminants and nutrient deficiencies in soil negatively affect crop growth and human health. The plant cadmium resistance (PCR) protein transports heavy metals. The abundance of PCR is correlated with that of cell number regulator (CNR) protein, and the two proteins have similar conserved domains. Hence, CNR might also participate in heavy metal transport. We isolated and analyzed TaCNR5 from wheat (Triticum aestivum). The expression level of TaCNR5 in the shoots of wheat increased under cadmium (Cd), zinc (Zn), or manganese (Mn) treatments. Transgenic plants expressing TaCNR5 showed enhanced tolerance to Zn and Mn. Overexpression of TaCNR5 in Arabidopsis increased Cd, Zn, and Mn translocation from roots to shoots. The concentrations of Zn and Mn in rice grains were increased in transgenic plants expressing TaCNR5. These roles of TaCNR5 in the translocation and distribution of heavy metals mean that it has potential as a genetic biofortification tool to fortify cereal grains with micronutrients.

Agroforestry and Biodiversity

Declining biodiversity (BD) is aecting food security, agricultural sustainability,and environmental quality. Agroforestry (AF) is recognized as a possible partial solution forBD conservation and improvement. This manuscript uses published peer-reviewed manuscripts,reviews, meta-analysis, and federal and state agency documents to evaluate relationships betweenAF and BD and how AF can be used to conserve BD. The review revealed that floral, faunal, and soilmicrobial diversity were significantly greater in AF as compared to monocropping, adjacent croplands, and within crop alleys and some forests. Among the soil organisms, arbuscular mycorrhizaefungi (AMF), bacteria, and enzyme activities were significantly greater in AF than crop and livestockpractices. Agroforestry also creates spatially concentrated high-density BD near trees due to favorablesoil-plant-water-microclimate conditions. The greater BD was attributed to heterogeneous vegetation,organic carbon, microclimate, soil conditions, and spatial distribution of trees. Dierences in BDbetween AF and other management types diminished with time. Evenly distributed leaves, litter,roots, dead/live biological material, and microclimate improve soil and microclimate in adjacentcrop and pasture areas as the system matures. Results of the study prove that integration of AFcan improve BD in agricultural lands. Selection of site suitable tree/shrub/grass-crop combinationscan be used to help address soil nutrient deficiencies or environmental conditions. Future studieswith standardized management protocols may be needed for all regions to further strengthen thesefindings and to develop AF establishment criteria for BD conservation and agricultural sustainability.

Soil nutrient adequacy for optimal cassava growth, implications on cyanogenic glucoside production: A case of konzo-affected Mtwara region, Tanzania.

Soils in areas affected by konzo (a cassava cyanide intoxication paralytic disorder) are predominantly infertile and probably unable to supply cultivated cassava with the nutrients it needs to achieve optimal growth. Soil nutrient supply in these areas could also be influencing cyanogenic glucoside production in cassava, however there is hardly any knowledge on this. An assessment of soil nutrient levels on crop fields in konzo-affected areas was therefore carried out to determine their adequacy for optimal cassava growth. Konzo-affected Mtwara region of Tanzania, was used as a case study. Whether soil nutrient supply influences cyanogenic glucoside production in cassava cultivated in konzo-affected areas and how it could be doing this, was additionally investigated. To investigate this, correlations between total hydrogen cyanide (HCN) levels (a measure of cyanogenic glucoside content) in cassava roots and various soil nutrient levels on crops fields were carried out. This was followed by an investigation of relationships between cases of cassava cyanide intoxication and soil nutrient levels on crop fields from which the consumed toxic cassava roots had been harvested. Cases of cassava cyanide intoxication were used as a proxy for high cyanogenic glucoside levels in cassava roots. Logistic regression analysis was used in the latter investigation. Other important non-nutrient soil chemical characteristics, like pH and soil organic carbon, were also included in all analysis performed. The results revealed that most soil nutrients known to have reducing effects on cassava cyanogenic glucosides, like potassium (mean = 0.09 cmol/kg, SD = 0.05 cmol/kg), magnesium (mean = 0.26 cmol/kg, SD = 0.14 cmol/kg) and zinc (mean = 1.34 mg/kg, SD = 0.26 mg/kg) were deficient on several crop fields. The results also showed that cyanogenic glucosides in cassava roots could be increased with the increased supply of sulphur in soils in bitter cassava varieties (rs = 0.593, p = 0.032), and with the increased supply of P in soils in all cassava varieties (rs = 0.486, p = 0.026). The risk of cassava cyanide intoxication occurring (and thus high cyanogenic glucoside levels in cassava) was found to be likely increased by cultivating cassava on soils with high pH (X2 = 8.124, p = 0.004) and high iron (X2 = 5.740, p = 0.017). The study managed to establish that cassava grows under conditions of severe nutrient stress and that soil nutrient supply influences cyanogenic glucoside production in cassava cultivated in konzo-affected areas of Mtwara region. Despite the multiple soil nutrient deficiencies on crop fields, low soil fertility was however not the only probable cause of increased cyanogenic glucosides in cassava, as high soil nutrient levels were also found to be potential contributors.

A multifaceted rhizobacterium Paenibacillus lentimorbus alleviates nutrient deficiency-induced stress in Cicer arietinum L.

Nutrient deficiency in soil is one of the limiting factors responsible for stunted growth and poor flowering/fruiting of crops which result in decline in overall agricultural productivity. However, one important strategy to overcome the problem of nutrient deficiency and to avoid use of chemical fertilizers is the use of plant growth promoting rhizobacteria (PGPR). Paenibacillus lentimorbus NRRL B-30488 (hereafter B-30488), an efficient PGPR has been reported to have various plant growth promoting traits that help crops to mitigate various environmental stresses. Therefore, the present work was designed to examine the application of B-30488 on chickpea growth under nutrient stress condition. Plants inoculated with B-30488 showed positive modulation in physio-biochemical behaviour and mineral nutrient uptake for better growth and development. Alteration in gene expression and metabolic profile under nutrient stress condition in chickpea also supported the stress amelioration capability of B-30488. Principal component analysis statistically proved that improved growth performance of chickpea plants under nutrient stress was mainly due to B-30488 induced modulation of metabolic pathways. To the best of our knowledge, this is the first study for analysis of growth promotion and stress alleviation in chickpea plants subjected to nutrient stress in presence of PGPR B-30488.

SORGHUM PRODUCTION PRACTICES IN AN INTEGRATED CROP-LIVESTOCK PRODUCTION SYSTEM IN MAKUENI COUNTY, EASTERN KENYA

Productivity of sorghum has been below potential in arid and semi-arid lands of Kenya, due to poor agronomic practices and soil nutrient deficiency. Sorghum crop is fairly drought tolerant, resistant to waterlogging, and yields are reasonably better in infertile soils compared to other crops. Proper agronomic practices would significantly increase yields as well as nutrient content in grains and crop residues used as livestock feed. The objective of this study was to investigate the existing sorghum production practices and sorghum use as food and feed sources. A survey involving 90 farmers from sorghum producing areas in Makueni County was conducted. The survey focused on the varieties and fertilizers used, trends in yields, constraints to sorghum production and the present strategies used for sorghum as animal feed. Most farmers (84.4%) used uncertified seeds from own saved sources, and the commonly grown variety was Seredo (44.5%) due to resistance to bird damage. The majority (32.1%) of farmers recorded very low yield of sorghum grain, from151 to 250 kg ha-1. Most farmers (68.9%) used farmyard manure in sorghum production, while 30.9% of the farmers did not use any fertilizer. All farmers indicated that their greatest challenge in sorghum production was inadequate rainfall. Bird damage to the crop was a chronic problem to most (73.3%) farmers. The majority (58.9%) of farmers conserved sorghum residue for feed as hay. The findings show the need to provide technical information and guidance on the production practices, such as choosing best-yielding seed varieties, proper methods of pest and disease control and proper use and conservation of sorghum residue as animal feed.

Biochar phosphorus concentration dictates mycorrhizal colonisation, plant growth and soil phosphorus cycling

We aimed to determine the relationship between biochar properties and colonisation of roots by arbuscular mycorrhizal (AM) fungi in agricultural soil. We used a range of biochars that differed in pH, water holding capacity, C, N and P concentrations to investigate interactions between biochar and AM fungi. A glasshouse experiment was conducted with subterranean clover and wheat, amended separately with 34 sources of biochar (applied at 1% w/w), to investigate potential responses in a phosphorus (P) deficient agricultural soil. Plant growth responses to biochar ranged from positive to negative and were dependent on biochar P concentration, available soil P and AM root colonisation. The higher the nutrient P concentration in biochar, the lower was AM colonisation. Growth responses of wheat and clover to the application of various biochars were mostly positive, and their growth was correlated, but biochar contributions to soil fertility varied with biochar properties. When nutrient concentrations are higher in biochars, especially for P and N, plants can gain access to nutrients via the plant roots and mycorrhizal hyphae. Thus biochar amendments can increase both plant nutrient uptake and crop production in nutrient deficient soil.

The farm income and food security implications of adopting fertilizer micro-dosing and tied-ridge technologies under semi-arid environments in central Tanzania

Adopting fertilizer input and rainwater harvesting techniques play a significant role in minimizing soil nutrient deficiency and moisture stress impact, both prime causes of low crop productivity in Sub-Saharan Africa. This study analyses the extent to which fertilizer micro-dosing (MD) and tied-ridge (TR) technologies can improve smallholder farmers’ food security and farm income. A household survey data along with on-farm trial data collected from semi-arid Tanzania is used for the analysis. The trade-off analysis for multi-dimensional impact assessment model (TOA-MD) is applied for the income and food security impact assessment. The on-farm trial shows a yield increase ranging from 10 to 300 percent for millet, and between 60 and 400 percent for sunflower. The TOA-MD analysis shows that between 52 and 79 percent of farms could be positively influenced to adopt the technologies. The increase in mean net return per farm ranges between 186 and 305 PPP USD. Adoption of the technologies would decrease the percentage of food insecure farmers between 1.8 and 7.1 percent. The study concludes that the technologies have the potential to improve yield and farm income for many farmers. However, these technologies alone would not bring significant change in terms of reducing poverty and food insecurity.

Review of Rice Response to Fertilizer Rates and Time of Nitrogen Application in Ethiopia

Rice productivity in Ethiopia is estimated at 2.8 t ha-1, which is much lower than the World’s average of 4.4 t ha-1. Weeds, pests, soil nutrient deficiencies and terminal moisture stress are the major causes of low rice productivity in Ethiopia. Poor soil fertility is among the major factors limiting the rice production. Appropriate fertilizer application is an important management practice to improve soil fertility and production of rice. Availability of plant nutrients, particularly nitrogen at various plant growth stages is of crucial importance in rice production. Recommendations on different period of nitrogen fertilizer application were given for various production systems. Traditionally, Diammonium phosphate and urea (supplying nitrogen and phosphorus) were the major fertilizers used by farmers in Ethiopia, creating nutrient imbalances in soils. Therefore, to make the soil well supplied with all the plant nutrients in the readily available form and to maintain good soil health, it is necessary to use organic manures in conjunction with inorganic fertilizers to obtain optimum yields. The integrated use of NP and FYM gave higher yields than application of either NP or FYM alone for many crops production. Different experiments were conducted to tackle rice soil fertility constraints. The major focuses of the experiments include inorganic fertilizers application rates, application times and their integration with organic fertilizers. The review paper summarizes the results of the experiments conducted on rice fertilizer rates and timings of nitrogen applications.

Soil acidity and nutrient deficiency cause poor legume nodulation in the permanent pasture and mixed farming zones of south-eastern Australia

Pasture legumes must be adequately and effectively nodulated in order to reach nitrogen-fixation targets. Of 225 pasture paddocks sampled across the Central Tablelands, Central West, Monaro and Riverina regions of New South Wales, 93% had inadequate legume nodulation. Legume content was significantly higher in the mixed faming zone (>50%, Central West and Riverina) than the permanent pasture zone (26%, Central Tablelands; 28% Monaro). Available phosphorus (P) was below critical levels in 40% of paddocks sampled and sulfur (S) in 73% of paddocks; >35% of all paddocks had soil pHCa <5.0. Deficiency of P was more prevalent in the Central Tablelands (63% of paddocks), whereas S deficiency occurred more frequently in the Central West (95% of paddocks). Legume nodule scores were associated with host legume species, soil pH, available P and/or S, and cation exchange capacity, which collectively accounted for 73% of variation. For Trifolium spp., at soil pHCa >5.55, nodulation was predicted to be near adequate (score 3.95, where adequate = 4). At pHCa <5.55, higher available S resulted in a higher nodulation score (2.42) than in paddocks where S was deficient (score 0–1.97). These results suggest that improving the capacity of legumes to supply nitrogen should focus on addressing soil acidity and plant nutrition, specifically P and S.

Evaluating the effects of elevated concentrations of urea, phosphogypsum and paper mill sludge on soil chemical, microbial and exoenzyme dynamics

Urea, phosphogypsum (PG) and paper mill sludge (PMS) are commonly used to address soil nutrient deficiency. In this study, these chemicals were used at recommended agricultural dose (RAD) along with low and high concentrations to assess their effects on soil chemical and biological quality. Urea was applied at 0.5, 1.0, 1.5 g/kg soil, PG at 50, 100, 150 g/kg soil and PMS at 5, 10, 15 g/kg soil. Significant variation in soil pH, electrical conductivity and organic carbon (OC) were noticed in response to chemical concentration and treatment types. The percent OC reduction was high in PG and PMS treated soils. Percent nitrogen and phosphorous in soil increased with the concentrations of urea and PG. Invariably, lower bacterial and fungal population were observed in treated soils relative to control. Activities of amylase, cellulase, invertase, dehydrogenase and protease were inhibited at high concentration of all test chemicals with minor deviations. The study indicated that bacterial population and exoenzymes could be useful markers to evaluate soil toxicity due to hyper concentrations of urea, PG and PMS in soil.

Evaluating the effects of elevated concentrations of urea, phosphogypsum and paper mill sludge on soil chemical, microbial and exoenzyme dynamics

Urea, phosphogypsum (PG) and paper mill sludge (PMS) are commonly used to address soil nutrient deficiency. In this study, these chemicals were used at recommended agricultural dose (RAD) along with low and high concentrations to assess their effects on soil chemical and biological quality. Urea was applied at 0.5, 1.0, 1.5 g/kg soil, PG at 50, 100, 150 g/kg soil and PMS at 5, 10, 15 g/kg soil. Significant variation in soil pH, electrical conductivity and organic carbon (OC) were noticed in response to chemical concentration and treatment types. The percent OC reduction was high in PG and PMS treated soils. Percent nitrogen and phosphorous in soil increased with the concentrations of urea and PG. Invariably, lower bacterial and fungal population were observed in treated soils relative to control. Activities of amylase, cellulase, invertase, dehydrogenase and protease were inhibited at high concentration of all test chemicals with minor deviations. The study indicated that bacterial population and exoenzymes could be useful markers to evaluate soil toxicity due to hyper concentrations of urea, PG and PMS in soil.

Arbuscular mycorrhizal fungi ameliorate the chemical properties and enzyme activities of rhizosphere soil in reclaimed mining subsidence in northwestern China

In semi-arid region of northwestern China, underground mining subsidence often results in decreased vegetation coverage, impoverishment of soil fertility and water stress. In addition, the physical-chemical and biological properties of soil also change, resulting in more susceptible to degradation. In particular, subsidence causes disturbance of the symbioses of plant and microbe that can play a beneficial role in the establishment of vegetation communities in degraded ecosystems. The objective of this study was to evaluate the effects of revegetation with exotic arbuscular mycorrhizal fungi (AMF) inoculum on the chemical and biological properties of soil over time in mining subsidence areas. Soils were sampled at a depth up to 30 cm in the adjacent rhizosphere of Amorpha fruticose Linn. from five reclaimed vegetation communities in northwestern China. In August 2015, a field trial was set up with five historical revegetation experiments established in 2008 (7-year), 2011 (4-year), 2012 (3-year), 2013 (2-year) and 2014 (1-year), respectively. Each reclamation experiment included two treatments, i.e., revegetation with exotic AMF inoculum (AMF) and non-AMF inoculum (the control). Root mycorrhizal colonization, glomalin-related soil protein (GRSP), soil organic carbon (SOC), soil nutrients, and enzyme activities were also assessed. The results showed that mycorrhizal colonization of inoculated plants increased by 33.3%–163.0% compared to that of non-inoculated plants (P<0.05). Revegetation with exotic AMF inoculum also significantly improved total GRSR (T-GRSP) and easily extracted GRSP (EE-GRSP) concentrations compared to control, besides the T-GRSP in 1-year experiment and the EE-GRSP in 2-year experiment. A significant increase in SOC content was only observed in 7-year AMF reclaimed soils compared to non-AMF reclaimed soils. Soil total N (TN), Olsen phosphorus (P) and available potassium (K) were significantly higher in inoculated soil after 1–7 years of reclamation (except for individual cases), and increased with reclamation time (besides soil Olsen P). The exotic AMF inoculum markedly increased the average soil invertase, catalase, urease and alkaline phosphatase by 23.8%, 21.3%, 18.8% and 8.6%, respectively (P<0.05), compared with the control. Root mycorrhizal colonization was positively correlated with soil parameters (SOC, TN and soil available K) and soil enzyme activities (soil invertase, catalase, urease and alkaline phosphatase) in both AMF and non-AMF reclaimed soils (P<0.05), excluding available K in non-AMF reclaimed soils. T-GRSP (P<0.05) and EE-GRSP (P<0.05) were significantly correlated with the majority of edaphic factors, except for soil Olsen P. The positive correlation between root mycorrhizal colonization and available K was observed in AMF reclaimed soils, indicating that the AMF reclaimed soil with a high root mycorrhizal colonization could potentially accumulate available K in soils. Our findings concluded that revegetation with exotic AMF inoculum influenced soil nutrient availability and enzyme activities in the semi-arid ecosystem, suggesting that inoculating AMF can be an effective method to improve soil fertility and support restoration of vegetation communities under poor conditions like soil nutrient deficiency and drought.