Seedball-Induced Changes of Root Growth and Physico-Chemical Properties in the Rhizosphere of Pearl Millet Seedlings
Charles Ikenna Nwankwo1, Ludger Herrmann1, Doris Vetterlein2, Sebastian R.G.A. Blaser2, Günter Neumann3
1University of Hohenheim, Inst. of Soil Science and Land Evaluation, Germany
Seedball technology is a cheap “seed-pelleting-technique” that combines 80g sand, 50g loam, 25ml water, 2.5g seeds and 1g NPK-mineral-fertiliser to produce about ten seed-containing-balls of 1.5 – 2.0cm diameter size to enhance pearl millet seedlings establishment. Despite its significance for seedling improvement, little is known about early root-development and nutrient-dynamics in the root-zone, influenced by root activity. Therefore, our major objective was a non-destructive monitoring of nutrient-distribution and early root-development in seedball–derived pearl millet seedlings (one seedling/tube) using a computer-tomography (CT) assisted-scanner (XT H 225; NikonR Alzenau, Germany) with a micro-focus X-ray tube and suction-cup methods. Measurements were conducted at three time intervals at 7, 14 and 21 days after planting (DAP). Three treatments comprising non-coated seeds (control), nutrient-free seedballs (SB) and NPK - seedball (SB+NPK) were used to germinate and grow seedlings in cylinder tubes (height: 25cm, diameter: 7cm) for 24 days under controlled growth-chamber conditions (temperature: 30°C, humidity: 65%, light: 12 h light, 300µmol m2/s ) in a completely randomised design of six treatment repetitions on a sandy soil (pHCaCl2: 4.5, >90% sand, P-Bray: 33.2 mg/Kg). A soil moisture content of 16% (w/w) was adjusted gravimetrically every 24th h. Suction cups (www.rhizosphere.com) were used for sampling of soil solutions from the upper 3.5cm soil layer (seedball location) and lower (7.0 cm) parts of the growth-tubes. Root dry-matter increments by 30%, and shoot biomass and shoot dry-matter by 164% and 225% in SB+NPK compared to non-coated-seed control and by 60% and 57% compared with the nutrient-free SB variant were observed. The X-ray CT-scanning images revealed more intense development at the upper layer in the SB+NPK treatments detectable within the first 14 DAP which may reflect the well-documented root-attracting properties of localised N and P supply. The P concentration in the soil solution collected from SB+NPK root-zone was significantly 954,999% and 4,049% higher than in the non-coated-seed control and the SB variant, respectively. This was associated with 10% and 48% increase of electrical conductivity (EC), respectively. EC and P determined in the sampling-solutions declined with time, reflecting root uptake and/or translocation of nutrients into deeper soil layers.
Keywords: Arid/semi-arid seedlings, local materials, pearl millet roots, rhizosphere dynamics, seedball technology, seedlings establishment,
Contact Address: Charles Ikenna Nwankwo, University of Hohenheim, Inst. of Soil Science and Land Evaluation, Emil-Wollf Strasse 27, 70599 Stuttgart, Germany, e-mail: c.nwankwouni-hohenheim.de