Aims Cracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research investigated how soil macropores through a simulated plough pan affects root growth of contrasting deep and shallow rooting rice genotypes. Methods Deep rooting Black Gora and shallow rooting IR64 rice varieties were grown in packed cores of unsaturated soil in a controlled greenhouse. Simulated biopores and cracks (macropores) were inserted through the plough pan to form treatments with no macropores, biopores, cracks, and combined cracks and biopores. Different root parameters such as root length density (RLD), root volume, root diameter, number of root tips and branches were measured. The number of roots was calculated manually, including the number of roots growing through macropores in the plough pan layer. Results Plough pans with macropores had 25–32% more roots than with no macropores. RLD was 55% greater in the plough pan layer if cracks were present compared to biopores. Conversely, RLD was 26% less in subsoil if the plough pan had cracks compared to biopores. Different root parameters were greatly influenced by the presence of macropores in the plough pan, and deep-rooted Black Gora produced 81% greater RLD, 30% more root numbers and 103% more branching than the shallow rooted rice genotype IR64 within the plough pan layer. Conclusions Macropores greatly improve rice root growth through plough pans for a deep rooting but not a shallow rooting rice variety. Whereas cracks produce a greater number of roots in the plough pan, biopores result in greater root branching and root numbers deeper in subsoil.
<p>Rice is often grown as multiple crops in one year, with reduced tillage upland cropping following flooded cropping gaining prominence due to water use, soil degradation and labour demands.&#160; This study explored whether a deep rather than shallow rooting rice cultivar grown in a flooded cropping cycle, benefited deeper root growth of follow-on rice in an upland, reduced tillage cropping cycle. In a greenhouse study, a simulated flooded paddy was planted with deep (Black Gora) and shallow (IR64) root cultivars and a plant-free control.&#160; Artificial plough pans were made in between the topsoil and subsoil to form different treatments with no plough pan (0.35 MPa), soft plough pan (1.03 MPa) and hard plough pan (1.70 MPa). After harvest of this &#8216;first season&#8217; rice, the soil was drained and undisturbed to simulate zero-tillage upland, with a photoperiod insensitive variety (BRRI Dhan 28) planted. Root length, root surface area, root volume, root diameter, number of root tips and branches were measured.&#160; The number of roots penetrating the plough pan was measured from camera images and X-ray CT. The overall root length density (RLD), root surface area, number of root tips and branching of BRRI Dhan 28 did not vary between plough pan and no plough pan treatments.&#160; Compared to the shallow rooting rice genotype,&#160; the deep rooting rice genotype as a &#8216;first season&#8217; crop promoted 19 % greater RLD, 34 % greater surface area and 29 % more branching of BRRI Dhan 28 in the subsoil. In the topsoil, however, BRRI Dhan 28 had 28 % greater RLD, 35 % greater surface area and 43 % more branching for the shallow rather deep rooting genotype planted in the &#8216;first season&#8217;.&#160; The results suggest that rice cultivar selection for a paddy cycle affects root growth of a follow-on rice crop grown under no-till, with benefits to subsoil access from deep rooting cultivars and topsoil proliferation for shallow rooting cultivars.</p>
<p>Time results in large changes to soil infiltration characteristics due to weather, mechanical stability and the action of biology. &#160;Even as the water status changes in a wetting soil, swelling may alter infiltration characteristics. Our laboratory has developed several novel approaches to measure how soil water infiltration characteristics vary over time and are influenced by biological processes or weathering stresses.&#160; The measurements are often combined with an assessment of mechanical properties and pore structure so that underlying processes driving soil structure dynamics can be disentangled. An overview and a discussion of the benefits and challenges of the approaches will be provided.</p><p>A small-scale infiltrometer (sub-mm size) was adapted to allow for measurements of water infiltration and repellency at aggregate or rhizosphere scale.&#160; It has been applied in numerous studies exploring the impacts of biological exudates, plant roots and weathering.&#160; More recent research has compared results from this infiltrometer with X-Ray CT imaging to determine the impacts of soil pore structure on infiltration characteristics.&#160; A challenge with a small-scale infiltrometer is experimental error caused by tip contact with the soil and the shape of the wetting front.&#160; This has been demonstrated from repeated tests on repacked sands and sieved soils.</p><p>If soil aggregates, spatial variability or hot spots like the rhizosphere are not of interest, conventional infiltration measurements with flow across the entire surface of a soil core offer less laboratory experimental error. &#160;We used this approach to explore the dynamics of soil wetting and swelling as affected by a range of biological exudates.&#160; Repacked soil discs were wetted by a sintered disc attached to a weighed water reservoir, with swelling measured dynamically in horizontal and vertical directions using infra-red sensors.&#160; Whereas polygalacturonic acid (PGA) had no affect on sorptivity, increasing concentrations of lecithin and actigum decreased sorptivity, likely due to different mechanisms of surface tension and viscosity respectively.&#160; Total swelling was positively correlated with water sorptivity for both lecithin and actigum, suggesting that an expanding pore structure in the unconfined soil discs may enhance water uptake rates.&#160; Biological exudates therefore have dual impacts on decreasing wetting and swelling rates, which will affect soil structural stability.</p><p>Current research is exploring soil structural stability impacts on soil hydrological properties over time.&#160; This includes field studies exploring the impacts of soil amendments and management practices, and laboratory studies with controlled structural changes from wetting/drying and mechanical stresses.&#160; In this work, changes in water infiltration due to stresses are explained from pore structure analysis with X-Ray CT imaging and mechanical stability tests.</p>
An experiment was carried out at the research field of the Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU).There were four nutrient treatments i.e., E1= NPKS recommended dose; E2= NPKS + Zn 5 Kg ha -1; E3= NPKS + Zn (5 Kg ha -1 ) + B (3 Kg ha -1 ) E4= NPKS + Zn (5 Kg ha -1 ) + B (3 Kg ha -1 ) + Mo (2 Kg ha -1 ) and three spacing S1= 20 x 10 cm 2 ; S2 = 20 x 15 cm 2 and S3 = 20 x 20 cm 2 .Micronutrient and spacing combined had a distinct positive response in crop growth attributes and chlorophyll content of rice. The tallest plant height (147.0 cm) and root length (13.50 cm) highest panicle length (22.56 cm) was attained in the treatment E2S3 but the maximum tillers per hill (14.95) and effective panicle per hill (14.17) were recorded in treatment E2S2. Physiological parameter i.e., LAI, CGR, RGR, NAR, total chlorophyll content of rice also responded significantly and the appropriate combination was E4S2treatment. Based on vegetative growth, physiological parameters and yield attributes the treatment combination E4S2 showed the best performance. Keywords-Growth, chlorophyll, yield attributes and nutrients. I. II.MATERIALS AND METHODS An experiment was conducted at the research field of the Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur. Soil of this experimental site was a silty clay loam under the Salna series of Shallow Red Brown Terrace.The experimental design was split plot having three replications. Experimental variables were consisted different combination of three micronutrients
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