Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Fluid Journal 2008-2009
Dr. Richard Koenig and Mr. Aaron Esser !"#$%&' !"#$%&'()*+,-&'(*"(./0(1'+%2(10,.%'%30,(1*+-2&.%*- !"#$%! !"##$%&&' ()#*$+,$-)*$./$01123$455 Wheat growers in eastern Washington are in a below- maintenance P fertility program. In low (<12-inch annual) precipitation, winter wheat-fallow environments, many growers do not use P fertilizer due to low yield potential and need to minimize input costs. Growers who do use P place it in a band beneath the soil surface with nitrogen (N) or directly with the seed at rates below crop removal. Band placement method is leading to high P use efficiency (PUE). However, the sustainability of this P management program is questionable given the negative input/output balance. We are interested in explaining the apparent contradiction between below-maintenance P applications and the apparent increase in soil test P concentrations reported by many growers. One explanation may be related to changing soil pH. In alkaline soil, inorganic P is associated mainly with Ca-based minerals. In acidic soil, inorganic P is associated mainly with Fe/ Al-based minerals. In the past 25 years soil pH has declined throughout eastern Washington and northern Idaho due to the use of ammonium-based fertilizers. It is likely that this recent pH decline has or will result in a shift in inorganic P forms from calcium to Fe/Al-based minerals. During the transition from neutral/alkaline to acidic soil pH, soluble and plant-available forms of P may temporarily increase as calcium- based minerals dissolve and Fe/ !"#$%&'()*+,-.%'/$01'2-3'45'2-3",5%'/$50.-'/1.,0'6-$,"& !"#$%&#'()*(+,&"','-..*'/.&")&(,%'0.1'*12%,)*'34",&'&.'1"#/.)*'&.' !"#$%&%#'%()*%+,-./0#'10++%2/,3.10++,-%0/*04%,1%*04(*/'%504)#'6(,'7 Summary: Quadratic responses to fluid phosphorus (P) were observed in four of six site years. High rates of fluid P reduced dry matter and grain yield, possibly due to P stimulation of vegetative growth and subsequent depletion of stored soil moisture. Grain yields with dry P fertilizer were similar to or lower than with fluid P. Results indicate a good potential for dryland wheat to respond to fluid P in the low- rainfall, crop-fallow areas of eastern Washington. Intermediate rates of fluid P should be applied to optimize plant growth and prevent yield reductions. Table 1. Study of location and average initial soil test P (0 to 1-foot depth). Soil test P by method (mg/kg soil)* Location Year Acetate P Bicarbonate P Lind 2005-2006 7.3 12.1 2006-2007 3.9 11.0 Ralston 2005-2006 5.8 17.8 2006-2007 5.5 22.5 *Adequate soil test values are 8 mg/kg (ppm) for the acetate (Morgan) method and 16 mg/kg for the bicarbonate (Olsen) method.
Fluid Journal 2005-2007