Ground Cover Supplement : GC Supplement - More profit from crop nutrition II
3 Roots and nutrition ROOT RESPONSE TO FERTILISER GUIDES NUTRITION EFFICIENCY By Nicole Baxter SCIENTISTS ARE WORKING to understand if certain crop species and varieties need to be targeted to specific soil nutrition scenarios. In particular, University of New England researchers in a GRDC-funded project have been studying how crop roots explore the soil in search of nutrients. The research team, led by associate professor Chris Guppy, was tasked with understanding how the roots of wheat, barley and chickpea varieties commonly grown in New South Wales and Queensland explore the soil for nitrogen, phosphorus, potassium and sulfur. Under evaluation were 10 wheats (BaxterA, EGA GregoryA, KennedyA, LongReach CrusaderA, LongReach DartA, LongReach SpitfireA, Sunco, SunguardA, SuntopA and Sunvale), five barleys (CommanderA, Gairdner, HindmarshA, Scope CLA and ShepherdA) and six chickpeas (KyabraA, PBA BoundaryA, PBA HatTrickA, PBA PistolA, PBA SlasherA and YorkerA). Associate Professor Guppy says while his team did not expect to see cereal or chickpea roots respond to potassium or sulfur, they did expect roots to respond to nitrogen and phosphorus. "Among the lines we tested, phosphorus appears to trigger increased root growth," he says. "The cereals didn't respond to nitrogen and this seems odd because a long history of science suggests roots respond to patches of nitrogen, with starter nitrogen a key driver." Additional trials are underway to confirm the results. ROOT PLASTICITY TO NUTRIENTS To investigate how roots respond to phosphorus, the researchers developed a phosphorus plasticity index by comparing the root length density in the phosphorus-enriched band to the root length density outside the band. Plants considered to have highly plastic roots were those with relatively more roots in the phosphorus-enriched band (Figure 1). Associate Professor Guppy says although some of the cereal varieties produced up to four times more roots in the phosphorus-enriched soil, statistically there was no significant difference between any of the lines tested. What this means for the wheat lines adapted for northern region environments is that there is only a small variation in the root plasticity trait in response to phosphorus. "We hope to repeat these experiments with southern and western-adapted wheats and also include the historical wheat variety Federation to find out how much scope there is for breeding crops with roots that can more efficiently explore the soil in search of nutrients," he says. Associate Professor Guppy found minimal root plasticity to patches of phosphorus in the six chickpeas tested, which is consistent with in-paddock observations that chickpeas have not regularly or consistently responded to bands of phosphorus. PHOSPHORUS UPTAKE Also of interest to the researchers was when cereals took up phosphorus during the growing season. Interestingly, considerable genetic variation was observed, allowing the researchers to identify how specific varieties may respond if soil phosphorus reserves are low, uniformly high, deep or stratified. "A low phosphorus supply may result from a continuous cropping history with minimal phosphorus replacement, while a high phosphorus supply may be observed on recently cleared land or if starter fertiliser rates have remained uniformly high with both surface and subsoil placement," Associate Professor Guppy says. "Stratified phosphorus may arise with regular application of starter phosphorus or in controlled-traffic farming systems, while deep phosphorus placement is a recent development following recognition of subsoil phosphorus resource depletion." Associate Professor Guppy says he would not encourage varietal selection on the basis of phosphorus responsiveness alone. However, after accounting for yield, rotation, climate and disease, there is potential to target varieties to the phosphorus supply. "BaxterA, KennedyA and HindmarshA might be worth considering when the phosphorus supply is low, while KennedyA, Sunco, SuntopA and ShepherdA could be options when the phosphorus supply is uniformly high," he says. "KennedyA, LongReach SpitfireA and Scope CLA show potential for acquiring phosphorus from phosphorus-enriched reserves located deep in the soil profile, while EGA GregoryA, SuntopA and most barley varieties may grow better if the surface supply of phosphorus is high, but subsoil reserves are low." □ G RDC Research Code UNE00020 More information: Associate Professor Chris Guppy, 02 6773 3567, firstname.lastname@example.org A variety was considered highly plastic in response to phosphorus if root growth proliferated through a phosphorus-enriched band of soil as pictured. SOURCE: ASSOCIATE PROFESSOR CHRIS GUPPY FIGURE 1 A highly plastic root. KEY POINT This research is trying to fnd out how much scope there is for breeding crops with roots that can more effciently explore the soil in search of nutrients.
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