PHOSPHORUS SOURCE EFFECTS ON DRYLAND WINTER WHEAT IN CROP- FALLOW ROTATIONS IN EASTERN WASHINGTON Richrd Koenig, Deprtment of Crop nd Soil Sciences Aron Esser, Lincoln/Adms County Extension Wshington Stte University, Pullmn ABSTRACT Whet growers in estern Wshington re in elow-mintennce phosphorus (P) progrm where P removl exceeds P ppliction. Susurfce nding nd griculturl-induced soil ph decline my e responsile for the high fertilizer P use efficiency. Experiments conducted in 24-27 showed responses to P t rtes higher thn typiclly pplied. The present 3-yer study ws initited to compre drylnd whet responses to rnge of fluid P (mmonium polyphosphte;, 1, 2 nd 4 l P 2 nd one dry P (MAP; 2 l P 2 fertilizer rte. Sites were locted in low rinfll (<12-inch), summer fllow cropping res. Dry mtter yield nd tissue P concentrtion were mesured t nthesis nd grin yield t mturity. Qudrtic grin yield responses to fluid P were oserved in four of the six site-yers. High rtes of fluid P reduced yield, possily due to P stimultion of vegettive growth nd susequent depletion of stored soil moisture. Grin yields with dry P fertilizer were similr to or lower thn with fluid P t three of six site-yers. Tissue nlysis t nthesis indicted P vilility ws lower with dry MAP thn with fluid APP. Results indicte good potentil for drylnd whet to respond to fluid P in the low rinfll, crop-fllow nd chemicl fllow res of estern Wshington. Intermedite rtes of fluid P should e pplied to optimize yields. INTRODUCTION Whet growers in estern Wshington re in elow-mintennce P fertility progrm. In low (<12-inch nnul) precipittion, winter whet-fllow environments, few growers use P fertilizer due to low yield potentil nd need to minimize input costs. Yet, mny growers report stle or incresing soil test P concentrtions. The mjority of growers in estern Wshington plce P in nd eneth the surfce with nitrogen, or directly with the seed. Clerly, this plcement method is leding to high P use efficiency. However, the sustinility of this P mngement progrm is questionle. We re interested in explining the pprent contrdiction etween elowmintennce P pplictions nd the pprent increse in soil test P concentrtions. One explntion my e relted to chnging soil ph. In lkline soil, inorgnic P is ssocited minly with C-sed minerls. In cidic soil, inorgnic P is ssocited minly with Fe/Al-sed minerls. In the pst 25 yers soil ph hs declined throughout estern Wshington nd northern Idho due to the use of mmonium-sed fertilizers. It is likely tht this recent ph decline hs or will result in shift in inorgnic P forms from clcium to Fe/Al-sed minerls. During the trnsition from neutrl/lkline to cidic soil ph, solule nd plnt ville forms of P my temporrily increse s clcium-sed minerls dissolve nd Fe/Al-sed minerls form. Beginning in fll 24 we conducted series of P fertility studies in chemicl fllowwinter whet production system in the low rinfll zone of estern Wshington. Vrious rtes of fluid P fertilizer were pplied in deep nd directly eneth the seed row t plnting. Reponses to P were otined in ech of three yers nd with soil test P levels t or ove criticl vlues. These responses to P suggest more routine P use my e wrrnted in the low rinfll zones. Bsed on the results of this erlier reserch we conducted experiments to evlute drylnd winter
whet responses to fluid nd dry P fertilizer in low (<12-inch) rinfll zone of estern Wshington Stte. The intent ws to compre whet responses to dry nd fluid P in more common crop-tillge fllow systems. MATERIALS AND METHODS Studies were conducted t two loctions in the low rinfll zone of estern Wshington in 25-6, 26-7, nd 27-8. Initil soil test P ws mesured t ech site (Tle 1). The sites fetured winter whet grown in trditionl, 2-yer crop-tillge fllow rottion. Ech study included four rtes of fluid mmonium polyphosphte P (, 1, 2 nd 4 l P 2 plced in deep nd with nitrogen (32--) nd one rte of dry MAP (2 l P 2. Phosphorus ws plced 2 weeks efore seeding. Seeding rtes were 4 l/cre with 12-inch spcing. Soft white or hrd red winter whet ws sown s indicted in the figures. Ech tretment ws replicted four times in rndomized complete lock experiment design. Individul plot dimensions were 7-8 feet wide y 5 feet long. Aove-ground dry mtter production ws mesured y hrvesting six liner feet of plnt row from ech tretment t nthesis. Beginning in 27, tissue ws nlyzed for totl P. Grin yield ws mesured y hrvesting n re five feet (4 rows) in width y pproximtely 4 feet in length from the center of ech plot with smll plot comine. Tle 1. Study loction nd verge initil soil test P ( to 1-foot depth). Soil test P y method (mg/kg soil) Loction Yer Acette P Bicronte P Lind 25-6 7.3 12.1 26-7 3.9 11. 27-8 3.3 14.3 Rlston 25-6 5.8 17.8 26-7 5.5 22.5 27-8 5.4 27. Adequte soil test vlues = 8 mg/kg for cette nd 16 mg/kg for icronte (Koenig, 25). RESULTS AND DISCUSSION Responses to fluid P were otined when soil test levels were ner or ove historicl criticl vlues (Figures 1-3; Tle 1). This suggests current soil test-sed fertilizer recommendtions my e outdted nd criticl levels do not ccurtely predict response to P. Grin yield responses to dry P were lower thn to fluid P t 3 of the 6 site-yers. This is similr to results from Austrli showing etter responses to fluid P thn to dry P (Hollowy et l., 24). Tissue P concentrtion ws sttisticlly higher for fluid P thn for dry P t 2 of 4 siteyers for which tissue P ws mesured. This suggests tht dry P ws less ville thn fluid P nd supports tissue nd grin yield responses to P source (Figures 2-3). Interestingly, grin responses to fluid P rte were qudrtic in 4 of the 6 site-yers (Figures 1 nd 2). At the highest rte of P, nthesis whole-plnt dry mtter (3 site-yers) nd finl grin yields (4 site-yers) were reduced slightly over the intermedite P rte. Moisture is min limiting fctor in the summer fllow cropping systems t these loctions. Higher rtes of P pprently stimulted excessive vegettive growth tht depleted stored soil moisture nd reduced lte-seson vegettive nd grin yields. This is similr to the hying off response oserved in whet grown in low moisture, crop-fllow rottions in Austrli (Vn Herwrden et l., 1998).
5 Lind, cv. 'Bruehl' 7 Dry mtter yield t nthesis (l 4 3 2 1 Dry mtter with fluid 11-37- Dry mtter with dry 11-52- 5 4 1 2 3 4 5 7 Rlston, cv. 'Eltn' 7 Dry mtter yield t nthesis (l 5 4 3 2 1 Dry mtter with fluid 11-37- Dry mtter with dry 11-52- 5 4 1 2 3 4 5 Figure 1. The effect of phosphorus rte nd form on dry mtter nd grin yields of winter whet t Lind (top) nd Rlston (ottom) in 25-6. Trends indicted y lines re significnt t p <.5.
Lind, cv. 'Bruehl' 7 Dry mtter yield t nthesis (l 5 4 3 2 1 Dry mtter with fluid 11-37- Dry mtter with dry 11-52- 5 4 1 2 3 4 5 7 Rlston, cv. 'Buermeister' 7 Dry mtter yield t nthesis (l 5 4 3 2 1 Dry mtter with fluid 11-37- Dry mtter with dry 11-52- 5 4 1 2 3 4 5 Figure 2. The effect of phosphorus rte nd form on dry mtter nd grin yields of winter whet t Lind (top) nd Rlston (ottom) in 26-7. Trends indicted y lines re significnt t p <.5.
5 Lind cv. 'Bruehl' Dry mtter yield t nthesis (l 4 3 2 1 Dry mtter with fluid 11-37- Dry mtter with dry 11-52- 5 4 35 3 1 2 3 4 5 7 Rlston cv. 'Buermeister' Dry mtter yield t nthesis (l 5 4 3 2 1 Dry mtter with fluid 11-37- Dry mtter with dry 11-52- 5 4 35 3 1 2 3 4 5 Figure 3. The effect of phosphorus rte nd form on dry mtter nd grin yields of winter whet t Lind (top) nd Rlston (ottom) in 27-8. Trends indicted y lines re significnt t p <.1.
Tissue P (%).2.15.1 Fluid P Dry MAP P Control ns.5. Lind 7 Rlston 7 Lind 8 Rlston 8 Loction-Yer Figure 4. Effects of P rte nd form on tissue P concentrtion t nthesis t Lind nd Rlston loctions in 27 nd 28. Phosphorus rtes were 2 l P 2 /cre. Within site-yer, rs cpped with the sme letter re not significntly different (α =.5); ns = no significnt difference mong tretments for given site-yer. CONCLUSIONS Results indicte good potentil for drylnd whet to respond to fluid P in the low rinfll, cropfllow res of estern Wshington. Intermedite rtes of fluid P should e pplied to optimize yields nd prevent grin yield reductions in this moisture limited environment. Phosphorus vilility from dry MAP is pprently not s gret s from fluid APP in this environment. REFERENCES Hollowy, R.E., B.M. Frischke nd D.M. Brce. 24. Residul effects of MAP nd APP on clcreous soils. Pp 119-124 in L. Murphy (ed) Proceedings of the Fluid Fertilizer Forum, Scottsdle, Arizon, Ferury 22-24. Koenig, R. 25. Estern Wshington Nutrient Mngement Guide: Drylnd winter whet. EB1987, Wshington Stte University Extension, 5p. Vn Herwrden, A.F., G.D. Frquhr, J.F. Angus, R.A. Richrds, nd G.N. Howe. 1998. 'Hying-off', the negtive grin yield response of drylnd whet to nitrogen fertiliser. I. Biomss, grin yield, nd wter use. Austrlin Journl of Agriculturl Reserch 49:167-181.