Abstract
Compared with other crops, legumes have superior ability to mobilize part of non-labile phosphorus (P) into labile/available forms. We explored the P-mobilization potential of selected grain legumes and its influence on growth, P uptake, and yield under P-deficient conditions. A pot experiment was carried out in a greenhouse with soybean (<em>Glycine max </em>L.), cowpea (<em>Vigna</em> <em>unguiculata </em>L.), green gram (<em>Vigna radiata </em>L.), and black gram (<em>Vigna mungo </em>L.) with two P fertilizer applications; without (Pdeficient) and with (P-sufficient) Department of Agriculture recommended rates of triple super phosphate. Each crop was harvested at maturity and the bulk and rhizosphere soils were collected to quantify different P fractions using Hedley’s sequential fractionation. Dry weight and P accumulation in different plant organs, <em>i.e. </em>roots, stems, leaves, and pods, were measured. Most plant organs maintained similar dry weight and tissue-P concentration irrespective of the P levels applied. All crops reduced their total plant-P uptake under P-deficient conditions. However, this did not make any change in either pod dry weight or P concentration of pods. Soybean and mung bean had a greater P accumulation compared to cowpea and black gram under both P levels. In contrast, cowpea and black gram showed improved P use efficiency (PUE) than other two legumes. Available P concentration (NaHCO3-P) in rhizosphere soil is greater than that in bulk soil in soybean and cowpea whereas the rhizosphere NaHCO3-P content in mung bean was greatly decreased compared to that of bulk soil when the crop was cultivated in P-deficient soil. The concentration of non-labile P fraction in rhizosphere of all grain legumes were significantly low compared to that of the bulk soil. Results suggest that selected grain legumes could be cultivated in P-deficient soil as they can adapt either through enhancing P uptake or increasing PUE.
Highlights
Phosphorus (P) is a key structural constituent of important molecules such as phospholipids, sugarphosphates, and ribosomal RNA and plays a central role in energy transfer and metabolic regulation while serving as an essential element for protein synthesis (Veneklaas et al, 2012; Lambers and Plaxton, 2015)
Dry weights of plant organs were significantly different for the crop type whereas P level and interaction effects were non-significant (P>0.05; Table 1)
As P bioavailability is generally greatest in the topsoil layer, topsoil foraging is known to be an efficient strategy to increase P uptake, which could attain through increased production of axial roots, greater lateral root density, and greater number of root hair and its length (Lynch and Brown, 2001; Lynch, 2019)
Summary
Phosphorus (P) is a key structural constituent of important molecules such as phospholipids, sugarphosphates, and ribosomal RNA and plays a central role in energy transfer and metabolic regulation while serving as an essential element for protein synthesis (Veneklaas et al, 2012; Lambers and Plaxton, 2015). P is one of the least available macronutrients in many terrestrial and aquatic ecosystems (Hallama et al, 2019). Application of Pfertilizers has been the most common management strategy to overcome crop-P deficiency that encounters in many cropping lands. This would not be a sustainable approach as global rock phosphate reserves, which are the major source of P fertilizers, are projected to exhaust by the end of this century. Up to 80% of applied P is fixed in the soil as insoluble forms while some amount runs off to aquatic and marine ecosystems (Lambers and Plaxton, 2015; Hallama et al, 2019). Agricultural P runoff has been identified as a primary factor in the eutrophication of lakes, rivers, and estuaries (Schoumans et al, 2014)
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