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Low soil phosphorus (P) availability is a limiting factor for crop production. Application of livestock manure as organic fertilizer can increase soil P availability, but may cause soil contamination with antibiotics such as sulfadiazine (SD), thus adversely affecting plant growth and nutrient uptake. The effects of P (0 and 50 mg kg−1) and SD (0, 1, 10, and 100 mg kg−1) levels on plant growth, root development, and nitrogen (N) and P uptake of maize and soybean were examined in a pot experiment using a loess soil as the test soil. High levels of SD considerably inhibited plant growth of both crops. Both P fertilization and SD negatively affected root development of both crops, especially at higher SD levels. For both crops, the average root diameter and the proportion of thick roots increased with increasing soil SD level. When soil SD level was ≤10 mg kg−1, the effects of P fertilization and SD on plant N and P concentrations, and N:P, N- and P-utilization efficiency were not significant in most cases. The effects of SD on plant N and P nutrition could not be of a great concern when soil SD level was ≤10 mg kg−1. Overall, soil SD pollution could reduce plant biomass and inhibit root development of soybean and maize, with a stronger effect on root development than on plant biomass at a high soil SD level (≥10 mg kg−1). In agricultural production, attention should be paid to soil SD pollution via manure application. [ABSTRACT FROM AUTHOR]

Application of coal fly ash (CFA) as a soil amendment has produced great agronomic benefits. However, there are potential risks of using CFA for soil amelioration, due to the abundance of some elements, both essential and non-essential in plants, which can cause phytotoxicity and it even may cause health problems for humans through the food chain. A pot experiment was conducted to investigate the effects of various CFA application rates (5%, 10%, 20%, 40%, and 80%) on plant growth, accumulation of essential nutrient elements and potentially toxic trace elements in erect milkvetch grown on a loess soil. The results showed that plant growth was significantly enhanced by the 5%, 10%, and 20% CFA treatments, while a CFA application rate ≥ 40% did not benefit plant growth, or even considerably inhibited plant growth. Plant phosphorus nutrition was improved by CFA application, but concentrations of potassium, copper, and zinc in plants declined when CFA was applied. Concentrations of molybdenum, boron, and selenium in plants generally increased with CFA application rate. A 5% CFA application rate is appropriate for the loess soil, a higher rate will cause phytotoxicity in erect milkvetch. CFA is a promising source of nutrients such as phosphorus, rational application of CFA to soil can enhance plant growth and improve plant phosphorus nutrition. [ABSTRACT FROM AUTHOR]

Background and Aims Soil phosphorus (P) deficiency and salinity are constraints to crop productivity in arid and semiarid regions. Salinity may weaken the effect of P fertilization on plant growth. We investigated the interactive effects of soil P availability and salinity on plant growth, P nutrition and salt tolerance of two alfalfa (Medicago sativa) cultivars. Methods A pot experiment was carried out to grow two cultivars of alfalfa in a loess soil under a combination of different rates of added P (0, 40, 80 and 160 mg P kg−1 soil as monopotassium phosphate) and sodium chloride (0, 0.4, 0.8 and 1.6 g NaCl kg−1 soil). Plant biomass, concentrations of P ([P]), sodium ([Na]) and potassium ([K]) were determined, and rhizosheath carboxylates were analysed. Key Results There were significant interactions between soil P availability and salinity on some, but not all, of the parameters investigated, and interactions depended on cultivar. Plant growth and P uptake were enhanced by P fertilization, but inhibited by increased levels of salinity. Increasing the salinity resulted in decreased plant P-uptake efficiency and [K]/[Na]. Only soil P availability had a significant effect on the amount of tartrate in the rhizosheath of both cultivars. Conclusions Increased salinity aggravated P deficiency. Appropriate application of P fertilizers improved the salt tolerance of alfalfa and increased its productivity in saline soils. [ABSTRACT FROM AUTHOR]

Aims: Carboxylate release by roots has been considered a strategy for mobilisation and acquisition of phosphorus (P). However, recently, it was argued that carboxylate release may be a way to discharge surplus carbon produced under conditions that limit plant growth. Plant P status may not be the main factor driving carboxylate release by roots. Instead, plant nitrogen (N) status and/or N:P ratio of the soil or plant may play a more important role in enhancing carboxylate release. Methods: A greenhouse pot experiment was performed to grow alfalfa in a P-deficient soil, supplied with two rates of P (0 and 20 mg kg−1) in combination with four forms of nitrogen (N) at five rates (0, 25, 50, 75, and 100 mg kg−1), to explore the effects of P rate, N form, N rate, and their interactions on plant growth, P and N status, and carboxylate release, and to determine the factors driving carboxylate release. Results: Nitrogen addition weakened the positive effect of P addition on plant growth, and increased plant N and P concentrations; P addition increased plant P concentration, but weakened the effect of N addition on plant N concentration. The amount of tartrate increased dramatically with increasing N rate, which decreased shoot growth, depending on N form. At high P supply, tartrate exudation correlated negatively with shoot biomass. Conclusions: Nitrogen addition to P-deficient alfalfa decreased shoot growth and enhanced the release of tartrate, likely to discharge surplus carbon; and the effects varied with N form. [ABSTRACT FROM AUTHOR]

The widespread application of antibiotics and plastic films in agriculture has led to new characteristics of soil pollution. The impacts of combined contamination of microplastics and antibiotics on plant growth and rhizosphere soil bacterial community and metabolisms are still unclear. We conducted a pot experiment to investigate the effects of polyethylene (0.2%) and norfloxacin/doxycycline (5 mg kg–1), as well as the combination of polyethylene and antibiotics, on the growth, rhizosphere soil bacterial community and metabolisms of wheat and maize seedlings. The results showed that combined contamination caused more serious damage to plant growth than individual contamination, and aggravated root oxidative stress responses. The diversity and structure of soil bacterial community were not markedly altered, but the composition of the bacterial community, soil metabolisms and metabolic pathways were altered. The co-occurrence network analysis indicated that combined contamination may inhibit the growth of wheat and maize seedings by simplifying the interrelationships between soil bacteria and metabolites, and altering the relative abundance of specific bacteria genera (e.g. Kosakonia and Sphingomonas) and soil metabolites (including sugars, organic acids and amino acids). The results help to elucidate the potential mechanisms of phytotoxicity of the combination of microplastic and antibiotics. [Display omitted] • Combined pollution reduced shoot mass by 12% compared with individual antibiotic. • The oxidative stress responses of roots were promoted by combined contamination. • Individual or combined pollution did not affect the bacterial community diversity. • Rhizosphere metabolisms were altered by individual and combined contamination. • Combined pollution simplified the relation between soil bacteria and metabolites. [ABSTRACT FROM AUTHOR]

Aims: Residues of antibiotics such as oxytetracycline (OTC) in soil can affect microbial compositions and activities, thus affecting soil P availability, and consequently plant P uptake and growth. Methods: A pot experiment was performed to grow alfalfa in a loess soil with different doses of P (0, 25, 50, and 100 mg kg−1) and OTC (0, 25, 50, and 100 mg kg−1). Plant dry mass, shoot and root P concentrations, bulk soil and rhizosheath pH, rhizosheath carboxylates, and bulk soil alkaline phosphatase activity were determined. Results: Shoot dry mass and root dry mass increased with increasing P dose, while shoot dry mass decreased with increasing OTC dose, especially at lower P doses (0 and 25 mg kg−1). Addition of OTC slightly reduced P concentrations in shoots and roots, but did not reduce plant P content consistently. Increasing OTC dose significantly reduced bulk soil alkaline phosphatase activity at 0P and strongly reduced rhizosheath tartrate amount at all P doses. Conclusions: The effects of OTC on plant growth and P uptake depended on both OTC and P doses in soil. High OTC dose had negative effects on shoot P uptake and growth, especially at lower P doses, while it had a positive effect on root growth at higher P doses. [ABSTRACT FROM AUTHOR]

Plant growth is often constrained by low availability of water and phosphorus (P) in soils in arid and semi-arid areas. Aeolian sandy soils cover >90% of the sandy area of the Mu Us Sandy Land (MUSL) in Northwest China. These soils have low water- and nutrient-retention capacity, limiting their ability to support plant growth. Pisha sandstone, a type of loose rock widely distributed in the MUSL, is regarded as an environmental hazard because it easily weathers, resulting in severe soil erosion and water loss. However, the retention capacity of the aeolian sandy soil can be significantly improved through blending with Pisha sandstone. We investigated the impacts of water supply (35% and 70% of soil water-holding capacity) and P supply (0, 5 and 20 mg P kg–1 soil) on plant growth and P and nitrogen (N) nutrition by growing lucerne (Medicago sativa L.) in MUSL aeolian sandy soil amended or not with Pisha sandstone. Soil type and P supply had greater effects than water supply on lucerne growth and on P and N nutrition. Biomass accumulation and shoot P and N concentrations were increased by amending the aeolian sandy soil with Pisha sandstone and increasing P supply. The N : P ratios in shoots indicated that plant growth was limited by P but not by N. Aeolian sandy soil amended with Pisha sandstone and supplied with P at 5 mg kg–1 enhanced lucerne growth; this practice is feasible for pasture development in the MUSL. Plant growth is often limited by low water and phosphorus (P) availability in most soils in arid and semi-arid areas. We investigated the effects of soil type, water supply and P supply on plant growth and P and nitrogen nutrition of lucerne. The results showed that soil type and P supply had greater effects than water supply, and provide a scientific basis for pasture development in arid and semi-arid areas. [ABSTRACT FROM AUTHOR]