Good P supply through the root zone can improve crop growth. Placing some P fertiliser deeper into cropping soils can help supply the needs of maturing crops. Where subsoils are low in P, deep placing P can deliver yield gains.
Looking closer at the roots
Researchers in northern NSW and southern QLD wanted to find out how chickpea roots responded to deep banded P. As well as starter P, deep P fertiliser was placed at 20 cm depth, in bands 33 cm apart. Chickpeas were sown between the bands. Images of the roots were captured using minirhizotrons during the season to measure changes in root development.
What are minirhizotrons?
A minirhizotron is a camera placed in clear tube. The tube is set into the soil, close to a growing plant. Photos are taken regularly as the roots develop. Root tracing software analyses the images, measuring root length, width, and density.
In this trial, a minirhizotron took images of root growth every 10mm down the profile to 800mm depth. Minirhizotrons allow researchers to see if deep P fertiliser produced any changes in chickpea root systems.
Secondary roots grew better
Initially, there were more roots at the surface where starter P was applied. After a few weeks, roots started exploring and using the banded fertiliser. Chickpeas with access to deep P had more roots. Their roots were longer, thicker, and colonised a bigger volume of soil. The chickpeas with better root systems had more above ground biomass.
Waterlogging and disease later in the 2016 season meant the crop failed, so we can’t relate the root system changes to yield.
Finding the right bandwidth
Research into ideal bandwidth is ongoing. P bands have been placed at different widths (side bands, 33cm and 66cm apart). The aim is to identify the ideal spacing of P bands for best crop nutrition.