Could biochar amendment be a tool to improve soil availability and plant uptake of phosphorus? A meta-analysis of published experiments

Abstract

As one of the most important nutrients for plant growth, phosphorus was often poorly available in soil. While biochar addition induced improvement of soil structure, nutrient and water retention as well as microbial activity had been well known, and the effect of biochar soil amendment (BSA) on soil phosphorus availability and plant P uptake had been not yet quantitatively assessed. In a review study, data were retrieved from 354 peer-reviewed research articles on soil available P content and P uptake under BSA published by February 2019. Then a database was established of 516 data pairs from 86 studies with and without BSA in agricultural soils. Subsequently, the effect size of biochar application was quantified relative to no application and assessed in terms of biochar conditions, soil conditions, as well as experiment conditions. In grand mean, there was a significant and great effect of BSA on soil available P and plant P uptake by 65% and 55%, respectively. The effects were generally significant under manure biochar, biochar pyrolyzed under 300 °C, soil pH <5 and fine-textured soil, and soils that are very low in available P. Being significantly correlated to soil P availability (R²=0.29), plant P uptake was mostly enhanced with vegetable crops of high biomass yield. Overall, biochar amendment at a dosage up to 10 t ha^-1 could be a tool to enhance soil availability and plant uptake of phosphorus, particularly in acid, heavy textured P-poor soils.

Keywords: Agricultural soil; Biochar; Meta-analysis; Phosphorus; Plant uptake; Soil amendment; Soil availability.

Fig. 1

Change in soil available P (left) and plant P uptake (right) under biochar amendment depending on experiment type and experiment duration

Fig. 2

Change in soil available P (left) and plant P uptake (right) under biochar amendment depending on feedstock type of biochar, biochar pyrolysis temperature and application rate

Fig. 3

Change in available P (left) and plant uptake (right) under biochar amendment depending on initial soil P, soil pH, and soil texture

Fig. 4

Change in available soil P (left) and plant P uptake (right) under biochar amendment depending on plant/crop types

Fig. 5

Change in plant P uptake related to changes in soil P level under biochar amendment in acid (▲, pH ≤ 6.5) and neutral/alkaline soils (◇, pH >6.5). The long dashed line and the short dashed line represents a significant correlation respectively for acid soils with pH ≤ 6.5 and for neutral/alkaline soils with pH >6.5

Fig. 6

Change in crop yield as a function of changes in P uptake under biochar amendment

Fig. 7

Change in plant P availability in amended soils as a function of biochar application rate when amended within 10 t ha⁻¹ (R²=0.05 p<0.001)

Fig. 8

Change in soil P availability as a weak function of pH change in soil pH under biochar amendment (R²=0.03, p<0.001)