Plant-available P for Maize and Cowpea in P-deficient Soils from the Nigerian Northern Guinea Savanna – Comparison of E- and L-values

Abstract

There are several indications that legumes are capable of accessing sparingly soluble phosphorus (P) in the soil through root-induced processes. We hypothesize that this plant-induced mobilization of P can be demonstrated if the plant accessible P assessed by isotopic dilution ('L-value') exceeds the corresponding values assessed in soil extracts ('E-values'). A greenhouse experiment was set up to assess if L/E ratios are affected by P supply and by crop type. The L-and E-values were determined in three P-deficient soils of the Nigerian Northern Guinea savanna (NGS), applied with various rates of TSP, for two cowpea varieties (Vigna unguiculata L., cv Dan-Ila and cv IT-82D-716) and maize (Zea mays L., cv oba super I) as a reference. Plants grown in control soils were severely P-deficient. Plant growth and shoot P uptake significantly increased with increasing P application in all three soils and for all crops, but relative yield and shoot-P responses to P application were similar between maize and cowpea. Both L-and E-values increased with increasing P application. Average L/E ratios for maize were 1.4±0.3 and were unaffected by the P application. For cowpea in contrast, L/E ratios were 3.1±0.2 (significantly larger than one) in one of the three control soils and significantly decreased to 1.3±0.1 at largest P supply. Elevated L/E ratios in cowpea were not associated with an increase in P uptake compared to the other two control soils in which no increase in L/E ratio was observed. It is concluded that cowpea is able to access non-labile P under P-deficient conditions. However, this process cannot overcome P deficiency in these soils, probably because P uptake is limited by the small P concentration in the soil solution (1-2 lg P L )1 ) and this limitation is not overcome by an increase in the accessible soil P quantity (L-value).

Phosphorus availability for three crop species as a function of soil type and fertilizer history

“…Some previous studies showed that E and L values were similar (Frossard et al 1994; Morel and Plenchette 1994;Pypers et al 2006), whereas others showed that E and L values were not identical and L values were in most cases smaller than E values sampled at the same exchange time (e.g. Buhler et al 2003).…”

“…The L value (mgkg −1 soil), the quantity of soil P available to a plant, was calculated according to Pypers et al (2006):…”

The plant availability of phosphorus from thermo-chemically treated sewage sludge ashes as studied by 33P labeling techniques

“…Indirect labeling with 32 P or 33 P has been used to investigate the plant P availability of rock phosphate (Zapata and Axmann 1995), sewage sludge (Frossard et al 1996), compost (Sinaj et al 2002) and animal manure (Oberson et al 2010). An obstacle when using indirect labeling to trace fertilizer P into plants is the contribution of unlabeled seed P to the P uptake of the plant, which must be carefully accounted for (Brookes 1982;Pypers et al 2006).…”

New perspectives for the design of sustainable bioprocesses for phosphorus recovery from waste

“…In this case, P derived from the fertiliser is assessed by comparing the SA of a fertilized plant to the SA of an unfertilized plant grown on the same soil (Fardeau et al, 1996). A difficulty using the indirect labeling is the contribution of (unlabeled) seed P to the P uptake by the plant (Nanzer et al, 2014), which can be accounted for using the method described by Pypers et al (2006). The ifference method can be used using yield, (YN YO)/FN, or nutrient uptake, (UN UO)/FN, where YN and YO are the crop yields with and without addition of nutrients, UN and UO are the nutrient uptake with and without nutrients added and FN the amount of nutrients applied, all expressed in kg ha 1.…”