Biochar application rate affects biological nitrogen fixation in red clover conditional on potassium availability

Abstract

Increased biological nitrogen fixation (BNF) by legumes has been reported following biochar application to soils, but the mechanisms behind this phenomenon remain poorly elucidated.We investigated the effects of different biochar application rates on BNF in red clover (Trifolium pratense L.) Red clover was grown in mono or mixed cultures with red fescue grass (Festuca rubra L.) and plantain (Plantago lanceolata L.) at a range of different biochar application rates (0, 10, 50 and 120 t ha -1 ). In a separate experiment, nutrient effects of biochar on BNF were investigated using nitrogen, phosphorous and potassium (N, P, K) and micronutrient fertilisation using the same plant species.Biochar addition increased BNF and biochar applied at a rate of 10 t ha -1 led to the highest rate of BNF. Total biomass also showed the greatest increase at this application rate. An application rate of 120 t ha -1 significantly decreased biomass production in both single and mixed cultures when compared to the control, with the greatest reduction occurring in red clover. Furthermore, BNF was significantly higher in pots in which red clover was grown in mixed cultures compared to monocultures. In the absence of biochar, K fertilization caused a significant increase in BNF. For N, P, and micronutrient fertilization, BNF did not significantly differ between treatments with and without biochar addition.We conclude that different biochar applications rates lead to different effects in terms of BNF and biomass production. However, due to the high variety of biochar properties, different application rates should be investigated on a case specific basis to determine the optimum biochar application strategies.4

Effect of biochar amendment on yield and photosynthesis of peanut on two types of soils

“…Recent studies suggest that K fertilization effect of biochar is critical for promoting growth, biological N fixation and competitive ability of legume species (Mia et al 2014;Oram et al 2014). In our study, the high K concentration in the peanut shell biochar may also contribute to the production response of peanuts, especially on redoxi-hydrosol which displays a very strong K deficiency.…”

Biochar and biochar-compost as soil amendments: Effects on peanut yield, soil properties and greenhouse gas emissions in tropical North Queensland, Australia

“…Because biochar contains ash and so adds nutrients such as K, Ca and Mg to the soil solution, increasing the pH of the soil and providing readily available nutrients for plant growth (Glaser et al, 2002). Recent studies suggest that a K fertilization effect associated with biochar is critical for promoting growth, biological N fixation and the competitive ability of legume species (Mia et al, 2014;Oram et al, 2014;Xu et al, 2015). In this study, high K concentrations in the Com and COMBI treatments may also have contributed to the peanut yield response associated with the organic amendments, where a significant increase in soil available K was observed.…”

Enhanced biological N2 fixation and yield of faba bean (Vicia faba L.) in an acid soil following biochar addition: dissection of causal mechanisms

“…A more recent glasshouse study by Guerna et al (2015) demonstrated that biological N 2 fixation increases following biochar amendment, resulting from increased plant P uptake which was associated with a 360 % increase in mycorrhizal colonisation. In contrast, Mia et al (2014) suggested that improved biological N 2 fixation in red clover (Trifolium pratense L.) following biochar amendment resulted from improved K nutrition in a moderately acid soil. The authors suggest this benefit could be short term only due to the relatively high availability of K from the biochars used.…”