Growth effects in tropical nickel‐agromining ‘metal crops' in response to nutrient dosing

Abstract

Agromining is an emerging technology that utilizes selected ‘metal crops' (= hyperaccumulator plants) to extract valuable target metals from unconventional resources for profit from mineralised soils. Growth characteristics, shoot metal concentrations, and agrominable locations are important considerations in economic agromining. Globally, the greatest potential for nickel (Ni) agromining exists in the tropics. However, the agronomic systems of tropical ‘metal crops' have not been previously tested. Furthermore, it is currently unknown whether nutrient dosing of prospective tropical agromining Ni ‘metal crops’ could possibly cause a shoot Ni‐dilution effect which may ultimately limit economically viable Ni yields. We undertook a pioneering study on Ni uptake and growth responses to nutrient dosing in two promising tropical ‘metal crops' (Phyllanthus rufuschaneyi and Rinorea cf. bengalensis). The experiment consisted of a large randomised block growth trial in large pots over 12 months in Sabah (Malaysia). At 3‐month intervals, the plants were exposed to soluble treatments that altered available concentrations of nitrogen (N), phosphorus (P), and potassium (K). We found strong positive growth responses to N and P additions in P. rufuschaneyi, whereas K additions had negative growth effects. In R. cf. bengalensis, all treatments had positive growth effects. The increases in biomass in response to nutrient dosing did not significantly reduce shoot Ni concentrations in both species, with the exception of N addition in P. rufuschaneyi. This study reveals that Ni uptake and growth responses to nutrient dosing are species‐dependent, primarily influenced by the ecophysiology of the species. Inorganic fertilization could possibly be an important component of the management of local ‘metal crops' to be used in viable commercial agromining in the tropics, but this needs to be tested in the field with different formulations of N, P, and K.

The potential of Blepharidium guatemalense for nickel agromining in Mexico and Central America

“…Blepharidium guatemalense responded strongly to synthetic fertilization with a three-fold increase in foliar Ni concentrations. This surprising result contrasts with most previous research which reports a negligible effect in shoot Ni concentrations in Ni hyperaccumulators after mineral fertilization (Shallari et al, 2001;Kidd and Monterroso, 2005;Bani et al, 2015a;Nkrumah et al, 2019a). However, this increase on the shoot Ni concentrations has been reported in B. coddii with a two-fold increase as a response to N additions (B. H. .…”

“…There is usually an increase in shoot biomass of Ni hyperaccumulators in response to synthetic fertilization growing in ultramafic substrates (e.g. P. rufuschaneyi (Nkrumah et al, 2019a), and Odontarrhena spp. (Bani et al, 2015a;Álvarez-López et al, 2016)).…”

“…bengalensis, have been tested in pots and in the field to evaluate their response to synthetic fertilization, pH adjustment and organic amendments addition, among other treatments (Nkrumah et al, 2019b(Nkrumah et al, , 2019c(Nkrumah et al, , 2019d. A maximum Ni yield of 250 kg Ni ha -1 has been estimated for a large-scale agromining operation using P. rufuschaneyi under field conditions in Sabah (Nkrumah et al, 2019a).…”

Cobalt hyperaccumulation in Rinorea cf. bengalensis (Violaceae) from Sabah: accumulation potential and tissue and cellular-level distribution of cobalt

“…Phytomining has been intensively explored principally for Ni, mainly because there are known suitable species (O. chalcidica, P. rufuschaneyi and R. cf. bengalensis) and substrates that can be used to achieve economically viable nickel yields from hyperaccumulator 'metal crops' (Bani et al 2015;Li et al 2003;Nkrumah et al 2019b). Cobalt phytomining is potentially more profitable than Ni because of its higher value despite being volatile (in the last 5 years, Ni remained around $15 kg -1 while Co oscillated between $30-90 kg -1 ).…”

Bacterial community diversity in the rhizosphere of nickel hyperaccumulator plant species from Borneo Island (Malaysia)

“…Within this flora, hyperaccumulator plants have the ability to concentrate metals in their aerial parts, whatever the concentration found in the soil (Baker, 1981). There are about 700 taxa of plants that are known to hyperaccumulate one or more metals, and around 90% of these accumulate Ni (van der Ent et al, 2013;Pollard et al, 2014;Galey et al, 2017;Reeves et al, 2017;van der Ent et al, 2017;Kidd et al, 2018;Nkrumah et al, 2019). In the case of Ni hyperaccumulator plants, the threshold of Ni accumulation is at least 1000 mg Ni kg −1 of dry weight in aerial parts (0.1% of plant biomass; .…”