Predicting Rice Lodging Risk from the Distribution of Available Nitrogen in Soil Using UAS Images in a Paddy Field

Area of Science:

• Agricultural Science
• Agronomy
• Remote Sensing

Background:

• Rice lodging reduces yield and quality, particularly in susceptible varieties like Koshihikari.
• Excess soil available nitrogen (SAN) above 200 mg N kg^-1 necessitates reduced basal fertilizer application.
• Commercial farmers often apply one-shot basal fertilizer, potentially leading to excessive nitrogen levels.

Purpose of the Study:

• To investigate the relationship between rice lodging and soil available nitrogen (SAN) in Koshihikari rice.
• To assess the spatial distribution of lodging severity and SAN using unmanned aircraft system (UAS) imagery.
• To provide recommendations for optimizing fertilizer application to prevent lodging.

Main Methods:

• Utilized UAS multispectral images to analyze canopy height models for lodging severity.
• Developed a SAN estimating equation using regression analysis on green and red band pixel digital numbers.
• Created a 1 m mesh soil fertility map by rasterizing estimated SAN values.

Main Results:

• A heavily lodged area in the Koshihikari paddy field coincided with higher SAN levels.
• A negative correlation was observed between rice inclination angle and estimated SAN.
• Lodging occurred even when SAN levels were within the recommended optimum range (80-200 mg N kg^-1).

Conclusions:

• One-shot basal fertilizer application for Koshihikari rice should be reduced when total absorbable nitrogen (SAN + fertilizer nitrogen) exceeds 200 mg N kg^-1.
• Spatial mapping of SAN and lodging severity using UAS is effective for precision agriculture.
• Optimizing nitrogen management is key to mitigating rice lodging and improving crop yield and quality.