PHOSPHORUS SOURCE EFFECTS ON DRYLAND WINTER WHEAT IN CROP- FALLOW ROTATIONS IN EASTERN WASHINGTON

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1 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 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

2 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 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 Rlston 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).

3 5 Lind, cv. 'Bruehl' 7 Dry mtter yield t nthesis (l Dry mtter with fluid Dry mtter with dry Rlston, cv. 'Eltn' 7 Dry mtter yield t nthesis (l Dry mtter with fluid Dry mtter with dry 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 Trends indicted y lines re significnt t p <.5.

4 Lind, cv. 'Bruehl' 7 Dry mtter yield t nthesis (l Dry mtter with fluid Dry mtter with dry Rlston, cv. 'Buermeister' 7 Dry mtter yield t nthesis (l Dry mtter with fluid Dry mtter with dry 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 Trends indicted y lines re significnt t p <.5.

5 5 Lind cv. 'Bruehl' Dry mtter yield t nthesis (l Dry mtter with fluid Dry mtter with dry Rlston cv. 'Buermeister' Dry mtter yield t nthesis (l Dry mtter with fluid Dry mtter with dry 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 Trends indicted y lines re significnt t p <.1.

6 Tissue P (%) 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 in L. Murphy (ed) Proceedings of the Fluid Fertilizer Forum, Scottsdle, Arizon, Ferury 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 '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: