The added value of biochar when applied along with fertilizers, beyond that of the fertilizers themselves, has not been summarized. Focusing on direct comparisons between biochar additions (≤20 t ha−1) – separately considering the addition or not of inorganic fertilizers (IF) and/or organic amendments (OA) along with biochar – and two different controls (with and without the addition of IF and/or OA), we carried out a meta‐analysis to explain short‐term (1‐year) field responses in crop yield across different climates, soils, biochars and management practices worldwide. Compared with the non‐fertilized control, a 26% (CI: 15%–40%) increase in yield was observed with the use of IF only, whereas that of biochar along with IF caused a 48% (CI: 30%–70%) increase. Compared with the use of IF only, the addition of biochar along with IF caused a 15% (CI: 11%–19%) increase in yield, indicating that biochar was as effective as fertilizers in increasing crop yields when added in combination. The use of biochar alone did not increase crop yield regardless of the control considered. Whereas in the short term, liming may have partly contributed to the beneficial effect of biochar (>90% was plant‐derived) when added along with IF, a separate meta‐analysis – using those studies that reported crop yields for different years after a single biochar application – showed a 31% (CI: 17%–49%) increase in crop yield over time (≥ 3 years), which denotes the influence of biochar properties other than liming (i.e. an increase in CEC). Our results also suggest that biochar application rates > 10 t ha−1 do not contribute to greater crop yield (at least in the short term). Data limitations precluded identification of the influence of feedstock, production conditions or climatic conditions without bias. As the response of crop yield to biochar addition was less a result of climatic zones or soil type than fertilizer use (chiefly N additions), the choice of nutrient addition along with biochar should be priorities for future research and development regardless of the region.

No abstract

Cadmium (Cd) toxicity is a widespread problem in crops grown on contaminated soils, and little information is available on the role of inorganic amendments in Cd immobilization, uptake, and tolerance in crops especially under filed conditions. The effect of three amendments, monoammonium phosphate (MAP), gypsum, and elemental sulfur (S), on Cd immobilization in soil and uptake in wheat and rice plants, under rotation, were investigated under field conditions receiving raw city effluent since >20 years and contaminated with Cd. Three levels of each treatment, 0.2, 0.4, and 0.8% by weight, were applied at the start of the experiment, and wheat was sown in the field. After wheat harvesting, rice was sown in the same field without application of amendments. Both crops were harvested at physiological maturity, and data regarding grain yield, straw biomass, Cd concentrations, and uptake in grain and straw, and bioavailable Cd in soil and soil pH were recorded. Both MAP and gypsum application increased grain yield and biomass of wheat and rice, while S application did not increase the yield of both crops. MAP and gypsum amendments decreased gain and straw Cd concentrations and uptake in both crops, while S application increased Cd concentrations in these parts which were correlated with soil bioavailable Cd. We conclude that MAP and gypsum amendments could be used to decrease Cd uptake by plants receiving raw city effluents, and gypsum might be a better amendment for in situ immobilization of Cd due to its low cost and frequent availability.

No abstract

Urbanization and industrialization have resulted in contamination of soils with heavy metals and other pollutants. Nickel (Ni) is one of the toxic metals, which adversely affect plant growth by altering different physiological and metabolic processes. Mineral nutrients can reduce toxic effects of Ni on physiological and metabolic functions of plants, thus improving plant growth. The role of calcium (Ca) to alleviate Ni toxicity in rice was investigated. Rice plants were grown with Ni (20 and 40 mg kg−1) and Ca (80 and 160 mg kg−1) in different combinations and without Ni and Ca as a control. Nickel (40 mg kg−1) significantly decreased shoot (54%) and root dry weights (54%), chlorophyll content (57%), the photosynthetic rate (two‐fold), transpiration rate (34%) and stomatal conductance (39%) compared to control. Application of Ni (40 mg kg−1) increased the Ni concentration in shoots 22‐fold and in roots 11‐fold compared to control. Application of Ca (160 mg kg−1) reduced the adverse effects of Ni and the studied parameters improved to the maximum values compared to control. Calcium decreased the translocation of Ni towards the shoots that was evident from a lower translocation factor (42%) for the plants supplied with Ca compared to those grown without Ca (62%). The phytotoxicity induced by Ni on different growth and physiological parameters was alleviated by Ca as indicated by the minimum values of the phytotoxicity index for Ca fed plants (0) compared to those without Ca (2.6).