Nitrogen fertilization impacts on water dynamics and crop performance in Bengaluru

verfasst von

Albara Mousa Issa Almawazreh

betreut von

Stephan Peth

Abstract

In recent decades, Bengaluru's urban expansion led to increased irrigated land and mineral fertilizer use, exerting pressure on scarce water resources. It is therefore important to estimate the efficiency of increased N fertilization and its corresponding effects on field water cycle under irrigated and rainfed conditions. With several studies describing N effect on water cycle as complex and dynamic, we adopted a comprehensive approach that includes intensive field sampling to estimate main soil physical and chemical parameters, calibrating a mechanistic hydraulic model and simulating soil moisture over several seasons, as well as using UAV based thermal sensing to investigate canopy temperature differences as a proxy for N deficiency and crop water stress. We employed this approach on two agricultural field experiments in Bengaluru, South India, where three crops common in the region, maize, finger millet, and lablab, were grown in rotation. Our results suggest that physical and chemical soil qualities differed between the two experimental sites due to the different management histories on those fields. Less favorable conditions of lower plant available water and higher acidity were identified on the rainfed experiment (RE) as opposed to the irrigated experiment (IE). Those differences in addition to differences in plant traits and seasonal rainfall variation modulated N effect on the crops and water cycle. The modeling study revealed noticeable influence of N fertilization on water cycle only on the RE, where higher N levels were associated with around 60 and 30 mm higher transpiration, 30 and 20 mm lower evaporation and 30 and 15 mm lower percolation per season for maize and millet, respectively. On the other hand, higher N levels led to higher water use efficiency (WUE) values in both experiments with 10–30 kg/ha/mm and 7–10 kg/ha/mm higher values compared to the low N levels for maize and finger millet, respectively. Extreme dry conditions that occurred in 2018 hindered maize plants from absorbing N and consequently minimized the differences in WUE between the different treatment levels. Positive impact of N fertilization on WUE of lablab was observed only under water-limited conditions. The thermal camera sensor results align with the modeling study, showing a more noticeable N impact on the RE with poorer soil conditions (p = 0.000245). Canopy temperatures of maize and finger millet receiving higher N were 2.1°C and 1.3°C cooler than those that received none, respectively, compared to 0.7°C and 0.6°C cooler on the IE (p = 0.118). Significant correlations were found between canopy temperatures and leaf chlorophyll content (LCC) for maize in the RE and millet in the IE. Canopy and soil temperatures correlated significantly when analyzed without considering crop species. Achieving these results required a novel thermal drift correction algorithm developed in this dissertation, reducing drift by up to 45% and lowering the drift standard deviation to less than 1°C. This ensured accurate thermal mapping for robust statistical analysis.

Organisationseinheit(en)

AG Bodenbiophysik

Typ

Dissertation

Anzahl der Seiten

121

Publikationsdatum

21.10.2024

Publikationsstatus

Veröffentlicht

Ziele für nachhaltige Entwicklung

SDG 2 – Kein Hunger

Elektronische Version(en)

https://doi.org/10.15488/18027 (Zugang: Offen)