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Fluid Journal : Fluid Journal 2008-2009
Al-based minerals form. Beginning in fall 2004 we conducted a series of P fertility studies in a chemical fallow-winter wheat production system in the low rainfall zone of eastern Washington. Various rates of fluid P fertilizer were applied in a deep band directly beneath the seed row at planting. Responses to P were obtained in each of three years and with soil test P levels at or above critical values (Figure 1). These responses to P suggest more routine P use may be warranted in the low rainfall zones. High rates of fertilizer P appeared to reduce yield compared to intermediate rates in one year (Figure 1). Residual effects of P applications were not measured but are expected. Based on the results of this earlier research, we conducted experiments to evaluate dryland winter wheat response to fluid and dry P fertilizer in the low and high rainfall zones of eastern Washington. The intent was to compare wheat responses to dry and fluid P in more common crop-tillage fallow and annual cropping systems. Fluids shine Responses to fluid P at summer fallow locations were obtained when soil test levels were near or above historical critical values based on bicarbonate extraction (Table 1). This suggests that current soil- test-based fertilizer recommendations may be outdated and critical levels do not accurately predict a response to P in these situations. Alternatively, the bicarbonate extract may not be accurately estimating plant-available P in these recently acidified soils. Acetate-extractable P was below critical levels for 5 of 6 site years. Grain yield responses to dry P were lower than responses to fluid P at three of the 6 site-years. These were similar to results from Australian research, showing better responses to fluid P than to dry P. Interestingly, responses to fluid P rate were quadratic in 3 of the 4 site-years (Figures 2 and 3). At the highest rate of P, anthesis whole-plant dry matter and final grain yields were reduced slightly at 40 lbs/A of P2O5 compared to the low or intermediate rate. Moisture is the main limiting factor in summer fallow cropping systems at these locations. Higher rates of P apparently Figure 1. Effect of P rate on soft white winter wheat yield in low rainfall zone of eastern Washington. Soil test values in parts per million (ppm) are listed for the sodium acetate (acetate: Morgan) and sodium bicarbonate (bicarb.: Olsen) extract methods. Phosphorus rate (lb P2O5/acre) 0 20 40 60 80 100 Grain yield (bu/acre) 0 10 20 30 40 50 60 2005 4.2 acetate; 18.2 bicarb 2006 3.7 acetate; 13.5 bicarb 2007 5.6 acetate; 21 bicarb +9.7 bu/acre @ 20 lb P2O5 applied 1 bu/acre for each 6.7 lb P2O5 applied 1 bu/acre for each 5.2 lb P2O5 applied Phosphorus rate (lb P2O5/acre) 0 10 20 30 40 50 Dry matter yield at anthesis (lb/acre) 0 1000 2000 3000 4000 5000 6000 7000 Grain yield at maturity (bu/acre) 40 45 50 55 60 65 70 Dry matter with fluid 11-37-0 Dry matter with dry 11-52-0 Grain yield with fluid 11-37-0 Grain yield with dry 11-52-0 Ralston, cv. 'Eltan' Phosphorus rate (lb P2O5/acre) 0 10 20 30 40 50 Dry matter yield at anthesis (lb/acre) 0 1000 2000 3000 4000 5000 Grain yield at maturity (bu/acre) 40 45 50 55 60 65 70 Dry matter with fluid 11-37-0 Dry matter with dry 11-52-0 Grain yield with fluid 11-37-0 Grain yield with dry 11-52-0 Lind, cv. 'Bruehl' Figure 2. Effect of P rate and form on dry matter and grain yields of winter wheat at Lind (top) and Ralston (bottom) in 2005-06.
Fluid Journal 2005-2007