Jianchu Shi

Characterizing root nitrogen uptake of wheat to simulate soil nitrogen dynamics

Background and aimsMichaelis-Menten (MM) kinetics and a physical–mathematical (PM) model are the popular approaches to describe root N uptake (RNU). This study aimed to examine RNU and compare the two model approaches.MethodsA hydroponic experiment (Exp.1) investigated the effects of root length, root N mass, transpiration, plant age and solution N concentration on RNU of wheat (Triticum aestivum L. cv. Jingdong 8). The two models were applied to simulate the RNU and soil N dynamics in a soil–wheat system (Exp.2), and the results were compared to the measured data.ResultsUnder the hydroponic conditions, RNU was better correlated with root N mass and transpiration than root length. The influences of solution N concentration on RNU rate per root length (MM1) and RNU rate per root N mass (MM2) were described well with MM kinetics. The kinetic parameters for MM1 changed with plant age but the parameters for MM2 were not age dependant. The description of RNU with the PM model was also independent of plant age, and was more reliable when the RNU factor decreased as a power function with the solution N concentration (PM2) than an assumed constant (PM1). In Exp.2, the root mean squared errors between the simulated and measured soil solution N concentration and the relative errors between the simulated and measured N uptake mass for MM kinetics were much larger than those for the PM model.ConclusionsBoth the MM and PM models successfully described RNU under the hydroponic conditions, but the PM model (especially PM2) was more reliable than the MM model in the soil–wheat system.

Spatial and Temporal Characteristics of Soil Moisture at Field Scale in an Arid Region of Northwest China

The knowledge of soil moisture spatial and temporal variability improves the understanding of the scale issue for hydrological and climatic studies. In the paper, daily soil moisture samplings at 144 locations were collected in the spring wheat region, and the classical statistics, geostatistics and time stability analysis were used together to discuss the temporal and spatial variability of soil moisture. The results showed that the dynamics variety of soil moisture decreased continually from surface soil to deep soil. And a linear descending relationship between the mean value and the coefficient of variation (i.e. CV) became evident. Basing on the geostatistics method, the spatial structure of soil moisture at wet condition was much stronger than that at dry condition. Time stability analysis showed there was a high time stability of soil moisture for different soil depths in the spring wheat region. So the appropriately selected five sampling points could provide accurate predictions of the field mean with low variability and small bias.

Characterizing roots and water uptake in a ground cover rice production system

Background and aims Water-saving ground cover rice production systems (GCRPS) are gaining popularity in many parts of the world. We aimed to describe the characteristics of root growth, morphology, distribution, and water uptake for a GCRPS. Methods A traditional paddy rice production system (TPRPS) was compared with GCRPS in greenhouse and field experiments. In the greenhouse, GCRPS where root zone average soil water content was kept near saturation (GCRPSsat), field capacity (GCRPSfwc) and 80% field capacity (GCRPS80%), were evaluated. In a two-year field experiment, GCRPSsat and GCRPS80% were applied. Results Similar results were found in greenhouse and field experiments. Before mid-tillering the upper soil temperature was higher for GCRPS, leading to enhanced root dry weight, length, surface area, specific root length, and smaller diameter of roots but lower water uptake rate per root length compared to TPRPS. In subsequent growth stages, the reduced soil water content under GCRPS caused that the preponderance of root growth under GCRPSsat disappeared in comparison to TPRPS. Under other GCRPS treatments (GCRPSfwc and GCRPS80%), significant limitation on root growth, bigger root diameter and higher water uptake rate per root length were found. Conclusions Discrepancies in soil water and temperature between TPRPS and GCRPS caused adjustments to root growth, morphology, distribution and function. Even though drought stress was inevitable after mid-tillering under GCRPS, especially GCRPS80%, similar or even enhanced root water uptake capacity in comparison to TPRPS might promote allocation of photosynthetic products to shoots and increase water productivity.