Ground Cover Supplement : GC Supplement - Profit from crop nutrition 2013
8 southern region nitrogen CritiCal to phosphorus response phosphorus and nitrogen are pro connected in southern region soi ANeCDOTAl eVIDeNCe FROM across southern Australia suggests early dry matter responses to applied phosphorus often do not translate into grain yield. Victorian Department of environment and Primary Industries researcher Dr Roger Armstrong has spent the past few years trying to work out why. “We’ve found that nitrogen management is crucial to getting the most from phosphorus fertiliser,” Dr Armstrong says. “We found grain yield responses to nitrogen alone but no grain yield responses to phosphorus alone unless nitrogen was also applied.” Dr Armstrong says many growers failed to get an adequate yield response to nitrogen fertiliser during the Millennium Drought, but with the return of more favourable seasons, responses to nitrogen were becoming increasingly prevalent. “I think it’s time for southern growers to reassess their nitrogen applications, particularly in light of its importance in getting the best yield returns from applied phosphorus.” The exact nature of the relationship between nitrogen and phosphorus on grain yields in southern region cropping systems will be examined further in a PhD research project being partly funded as part of the second phase of the More Profit from Crop Nutrition program. FIxed phOsphOrus In other research, university of Adelaide researcher Dr Therese McBeath found that wheat crops generally use only between three and 30 per cent of applied phosphorus. “We found that crops tend to use the applied phosphorus to access other soil phosphorus pools and that much of the applied phosphorus is tied up or ‘fixed’ and not immediately available to crops, at least in the short to medium term,” Dr McBeath says. Dr McBeath used a radioactive labelling method (P33) to track the extent to which this fixed phosphorus made a contribution to crop nutrition. “We found that in some soils a small but important proportion of soil phosphorus taken up by wheat was derived Recent research in South Australia has shown stubble to contain about one to five kilograms per hectare of inorganic plant-available phosphorus. from these fixed phosphorus pools.” The research team also found that some crops were better than others at using fixed phosphorus. “Canola was better able to access fixed phosphorus than wheat and the recently developed DGT-P test was better at estimating the availability of the fixed phosphorus pools than the Colwell-P test.” Starter phosphorus, particularly during dry starts to the season, was critical for the crop to establish a root system that could effectively explore the soil for plant-available phosphorus pools. “It’s important that starter phosphorus is applied so the crop can easily access it – preferably by banding it with the seed – because phosphorus is particularly important during early growth stages of crops,” Dr McBeath says. □ GRDC Research Codes DAV00095, DAV00125 More information: Dr Roger Armstrong, Victorian DEPI, 03 5362 2111, firstname.lastname@example.org stubble PhosPhorus In other research done as part of the More Profit from Crop Nutrition project, University of Adelaide PhD student Sarah Noack examined the contribution of phosphorus in crop residues to subsequent crops. Crop stubbles sampled in the summers of 2010-11 and 2011-12 contained amounts of phosphorus equivalent to one to five kilograms of phosphorus per hectare. The surprising find was that most of the stubble phosphorus was in an inorganic rather than organic form and therefore immediately available to crops (as well as soil microorganisms). The type, size, placement and overall stubble load, as well as rainfall and soil moisture, influenced the timing and amount of phosphorus released from stubbles to soil. Within 80 days of application to the soil, a significant amount of stubble phosphorus was released and taken up by the subsequent wheat crop for all treatments. The proportion of wheat phosphorus derived from stubble ranged from nine to 16 per cent across the three residue-management treatments. The remaining wheat phosphorus came from fertiliser (19 to 23 per cent) and soil (63 to 72 per cent) sources. On average, 50 per cent of the added stubble phosphorus in the conventional tillage treatments was detected in plant, microbial and resin phosphorus pools compared with 20 per cent for the two surface stubble treatments. This was most likely due to the lower moisture content of surface stubble in no-till systems resulting in less microbial activity and hence lower rates of stubble phosphorus release.
GC Supplement - Farm business management 2013
GC Supplement - Frost