Co-composts of sewage sludge, farm manure and rock phosphate can substitute phosphorus fertilizers in rice-wheat cropping system.

In the present study, various co-composts of sewage sludge (SS), farm manure (FM) and rock phosphate (RP) were prepared and their influence on phosphorus (P) uptake, soil P restoration and growth of rice crop and residual effect on wheat crop were investigated. The treatments comprised of T1 (control, no amendment), T2 (452 kg Nitrophos ha-1, T3 (724 kg SS50:FM50 ha-1), T4 (594 kg SS100:FM0 ha-1), T5 (728 kg SS25:FM25:RP50 ha-1), T6 (726 kg SS5O:FM25:RP25 ha-1), T7 (508 kg SS75:FM0:RP25 ha-1), and T8 (546 kg SS50:FM0:RP50 ha-1). The post-experimental soil samples were analyzed for pH, EC, OM, Olsen's P. The plant samples (grains and straw of both crops) were analyzed for concentrations of P, and heavy metals. The P adsorption by post-wheat composts-amended soil was tested through Langmuir, and Freundlich adsorption isotherms. The investigated parameters (biomass, grain and straw yield, plant height and P concentrations in plant parts) were significantly increased in all composts as compared to the control treatment. The P uptake by the plants was higher in compost treatments as compared to the control and NP that shows long-term residual effect of applied composts. The maximum grain yield (1.63 Mg ha-1) was obtained in T5 followed by T6 (1.52 Mg ha-1). The P concentration in rice grains were recorded in the trend as T8 (2.55%) > T6 (2.24%) > T4 (1.92%) = T3 (1.88%) > T7 (1.62%). It is evident that the combined application of FM (25%) and RP (50%) enhanced the effect of SS (25%) in terms of P bioavailability and yield parameters and can be effectively used as P fertilizer.

Efficiency of various sewage sludges and their biochars in improving selected soil properties and growth of wheat (Triticum aestivum).

Due to increasing demand of P fertilizers and gradual decrease in P resources, recyclable P is the focus of researchers in recent years. Sewage sludge (SS) is a municipal waste that contains appreciable amounts of P and probably other nutrients. In present study, the effects of various SS and their biochars (450 °C for 2 h) were investigated on soil properties and P uptake in wheat (Triticum aestivum) with and without P fertilizer. The biomass of plants and grain yield were significantly increased with application of SS and their biochars as compared to the control treatment either without or with P application. Moreover, there was significant interaction between treatments and P application for the concentration of K, and P in shoots and roots of wheat. Shoot P concentration was not significantly affected with SS than biochars whereas root P concentration was higher in SS treatments than respective biochars. Higher increase in Olsen's P concentration was observed in populated area sludge applied-soil as compared to disposal sludge and their biochars. Overall, it is observed that SS application increased the wheat yield and P concentrations in plants than control depending upon SS types whereas biochar application decreased the P concentration in roots. Grain yield and P concentration in shoots were not significantly affected for the treatment with P fertilizers than without P. Sewage sludge and their biochars might be a potential source of P but further research is needed to recommend the use of modified SS-biochars as source of available P for crops.

Effects of co-composting of farm manure and biochar on plant growth and carbon mineralization in an alkaline soil.

In the present study, the effects of co-composts of biochar (BC) and farm manure (FM) on the growth of wheat (Triticum aestivum L.) and carbon mineralization in an alkaline soil were investigated. The co-composts of FM and BC were prepared at various ratios (FM100:BC0, FM75:BC25, FM50:BC50, FM25:BC75, FM0:BC100) using aboveground piles and were used in two separate experiments conducted simultaneously. In the plant growth trial, prepared co-composts were applied at a rate of 2% w/w and wheat was grown at two fertilizer levels (half and full) until maturity. In the incubation experiment, same treatments were used and carbon mineralization was studied over a period of 79 days. The priming effect and net CO2 efflux were calculated using CO2 release data. Analysis of postincubation soil showed no significant effect of treatments on the pH of soil. However, electrical conductivity and organic matter were significantly influenced by all treatments. The increasing BC ratio in the compost reduced the carbon mineralization in soil in a dose-additive manner. Increase in BC proportion in composts (FM50:BC50, FM25:BC75, FM0:BC100) stabilized the native carbon of the soil and caused negative priming effect (-1.9, -5.6, and -8.48%, respectively). Regarding plant growth, the results showed an enhancement in the grain yield with the application of compost than control. Total nitrogen (N), phosphorus, and potassium (K) contents of the soil were also increased by the application of compost than control (un-amended soil). Significantly higher N and K concentrations in wheat plants were also examined when soil was treated with compost than control. The use of compost with half fertilizer was better in increasing grain yield, especially with higher BC proportion in the compost than FM.

Biochar enhances the cadmium tolerance in spinach (Spinacia oleracea) through modification of Cd uptake and physiological and biochemical attributes.

Cadmium (Cd) has no known role in plant biology and is toxic to plants and animals. The Cd mainly accumulated in agricultural soils through anthropogenic activities, such as sewage water irrigation and phosphorus fertilization. Biochar (BC) has been proposed as an amendment to reduce metal toxicity in plants. The objective of this study was to evaluate the role of BC (cotton stick at a rate of 0, 3, and 5 %) on Cd uptake and the photosynthetic, physiological, and biochemical responses of spinach (Spinacia oleracea) grown in Cd-spiked soil (0, 25, 50, 75, and 100 mg Cd kg-1 soil). The results showed that Cd toxicity decreased growth, photosynthetic pigments, gas exchange characteristics, and amino acid and protein contents in 52-day-old spinach seedlings. The Cd treatments increased the concentrations of Cd, sugar, ascorbic acid, and malondialdehyde (MDA) in plants. The application of BC ameliorated the harmful effects of Cd in spinach plants. Under Cd stress, BC application increased the growth, photosynthesis, and protein contents and decreased Cd concentrations and MDA contents in plants. The maximum BC-mediated increase in dry biomass was about 25 % with 5 % BC application in control plants. It is concluded that BC could ameliorate Cd toxic effects in spinach through changing the physiological and biochemical attributes under Cd stress.