N analyser

Leaf samples were analyzed for macro and micro at Bemlab (Pty) Ltd. (Somerset West, Cape Town, South Africa), a commercial laboratory. Leaves were washed with Teepol solution, rinsed with de-ionised water, and dried at 70 °C overnight in an oven. The dried leaves were then milled and ashed at 480 °C, and shaken up in a 50:50 HCl (50%) solution for extraction through filter paper [52 ,53 ]. The potassium (K), phosphorus (P), Ca, Mg, sodium (Na), manganese (Mn), iron (Fe), copper (Cu), zinc (Z), and boron (B) contents of the extracts were analyzed using the Ash method. The total nitrogen (N) content of the leaves was determined through total combustion in a Leco N-analyser. The amounts of N, P, K, Ca, and Mg were converted from percentage (%) to mg/kg. 10,000 was used as the conversion factor.

Bulbs of randomly selected plants from each treatment were analysed for macro-element and micro-element contents using an inductively coupled mass spectrometry (ICP-MS) and a LECO-nitrogen analyser with appropriate standards (Bemlab (PTY) Ltd., Somerset West, South Africa). Each treatment had three replicates. Briefly, the bulbs were cleaned in a Teepol solution, rinsed with deionised water, and dried in an oven at 70 °C overnight. Thereafter, the dried bulbs were pulverised, ashed at 480 °C, and agitated in a 50:50 HCl (50%) solution for extraction through filter paper [29 ], and then used to determine the potassium (K), phosphorus (P), calcium (Ca), magnesium (Mg), sodium (Na), manganese (Mn), iron (Fe), copper (Cu), zinc (Z), and boron (B) content of the extracts. Total combustion in a Leco N-analyser was used to assess the bulbs’ total nitrogen (N) contents. N, P, K, Ca, and Mg values were converted from percentages to mg/kg using a conversion factor of 10,000 [30 ].