Available Nitrogen in Paddy Soils Depth: Influence on Rice Root Morphology and Plant Nutrition

Abstract

Nitrogen (N) is a key nutrient for rice (Oryza sativa L.) and its availability in soil profile can influence the plant root morphology and total nutrient uptake. This study evaluated if N from deeper soil layers would increase rice root growth, N uptake and influence plant nutritional status. Flooded rice was grown in undisturbed soil samples from three locations with 15 N-labeled ammonium sulfate application at different depths (0, 10, 20, 30, and 45 cm). At rice heading, chlorophyll content and photosynthesis rate were measured at flag leaves and rice biomass production, root morphology, and total N and 15 N uptake were evaluated. Higher biomass and N uptake were observed with N application at near soil surface layers. The majority of rice N uptake was derived from soil, which was more evident when N fertilizer was injected at 45 cm deep (on average 74%). The highest root growth was observed at the near surface layers with constant decrease in depth, up to 60 cm. Roots from deeper layers exhibited smaller diameter, as they were mainly highly branched roots. The N application at 30 and 45 cm depths provided N later in the season, resulting in plants with lower total biomass but with higher N content in aboveground biomass, with higher chlorophyll content, photosynthesis rate, and carboxylation efficiency by Rubisco. The N available below 20 cm contributes to plant nutrition and root growth, hence soils with available N in depth likely cause plants to function more optimally in photosynthates supply.

Straw Incorporation Coupled with Deep Placement of Nitrogen Fertilizer Improved Grain Yield and Nitrogen Use Efficiency in Direct-Seeded Rice

“…Many researchers reported that deep placement of N fertilizer significantly enhanced the NUE and grain yield as compared with surface broadcasting (Miah et al 2016;Gaihre et al 2018;Yao et al 2018b). Deep placement of N fertilizer could substantially reduce the NH 4 + -N concentration in surface water but improve the soil NH 4 + -N contents (Ke et al 2018;Drescher et al 2020). Wang et al (2019) reported that reduced chemical fertilizer combined with straw retention could produce comparable grain yield to conventional rice production systems with surface broadcasting dose of NPK fertilizers.…”

Nitrogen Regulates the Grain Yield, Antioxidant Attributes, and Nitrogen Metabolism in Fragrant Rice Grown Under Lead-Contaminated Soil

“…Previous study showed that deep placement urea at 7-10 cm decreased the loss of urea compared with the broadcast urea method (Siddique et al 2020). and root growth of rice (Drescher et al 2020). Deep placement of N is generally an effective way to improve the ultilization of N fertilizer.…”

Variations of Bacterial and Diazotrophic Community Assemblies throughout the Soil Profile in Distinct Paddy Soil Types and Their Contributions to Soil Functionality

“…Rice plant prefers NH 4 + -N to NO 3 − -N as an N source ( 1 ). For Hapli type soil, the greater supply of NH 4 + -N in the subsoils might contribute to root growth and plant nutrition through an enhanced photosynthesis rate ( 55 ). The lower NH 4 + -N storage in Fe-accumuli soil might be attributable to the reduced N input provided by diazotrophs and high N loss mediated by denitrification.…”