共查询到19条相似文献，搜索用时 109 毫秒
1.
果园生草对~(15)N利用及土壤累积的影响 总被引：1，自引：0，他引：1
以2 a生红富士/平邑甜茶为试材,采用15N同位素示踪技术,研究了种植3种牧草(白三叶、鼠茅草和黑麦草)对苹果植株生长,氮素利用、损失及其在0~60 cm土层残留情况的影响。结果表明:与单作苹果相比,生草栽培后苹果植株总鲜重、新梢粗度、新梢长度及根冠比皆成增加的趋势;苹果植株根长、根长密度及根表面积均以种植白三叶处理最大,其次为种植鼠茅草,最低的为单作苹果;不同处理间氮素利用率差异显著,种植白三叶后苹果植株氮素利用率最高,种植鼠茅草次之,单作苹果最低;生草栽培后15N残留主要集中在0~20 cm土层,且其15N残留量显著高于单作苹果。而在20~40 cm及40~60 cm土层15N残留量则以单作苹果最高,种植黑麦草次之,最低的为种植白三叶;生草栽培后氮素损失率为单作苹果种植黑麦草种植鼠茅草种植白三叶。表明种植白三叶、鼠茅草及黑麦草在促进苹果植株氮素利用的同时,也一定程度上减弱了土壤氮素的损失。 相似文献
2.
化学调控和施磷对玉米/花生间作磷吸收利用和间作优势的影响 总被引：6，自引：0，他引：6
为了研究化学调控和磷肥对玉米/花生间作体系磷营养的调控效应,于2012—2013年在河南科技大学农场进行田间试验,试验设单作玉米、单作花生、玉米/花生间作和玉米/花生间作+化学调控4种种植方式,分别施磷[180 kg(P2O5)·hm–2]和不施磷共8个处理,研究了间作玉米和间作花生不同器官磷含量、磷积累分配的特点,分析了化学调控和施磷对间作体系磷间作优势的影响。结果表明:间作显著提高了玉米籽粒磷含量、茎和籽粒磷积累量,促进了磷向籽粒分配;明显降低了花生各器官磷含量、磷积累量,不利于磷向果仁分配;与单作玉米和单作花生相比,间作提高了玉米/花生间作体系磷吸收量,磷吸收间作优势为15.99~19.54 kg(P)·hm–2。在玉米小口期喷施化学调控剂提高了间作玉米籽粒磷含量,降低了茎、叶和籽粒的磷积累量,提高了磷向籽粒分配比例;提高了间作花生果仁磷含量和茎、叶和果仁磷积累量,促进了磷向果仁分配。化学调控间作玉米施磷肥显著增加了间作玉米和花生各器官的磷含量以及磷积累量,提高了磷向玉米籽粒和花生果仁分配比例,促进了间作体系对磷的吸收;磷吸收间作优势为19.50~22.00 kg(P)·hm–2,比不施磷提高16.51%~57.51%,达到显著差异水平。这表明玉米/花生间作具有明显磷间作优势,化学调控间作玉米再施磷有利于间作体系磷吸收量增加,显著提高磷间作优势。因此,生产上可以采用化学调控同时施磷肥来进一步提高磷间作优势。 相似文献
3.
通过2年盆栽试验，探讨不同磷水平下玉米–大豆间作根际土壤无机磷组分、土壤有效磷含量及作物磷吸收的差异，明确土壤无机磷组分、土壤有效磷与作物磷吸收之间的相互关系。试验设置玉米单作、大豆单作、玉米–大豆间作3种种植方式以及3个P2O5施用水平(0、50、100 mg/kg，分别记作P0、P50、P100)，共9个处理。结果表明：与单作相比，2018年和2019年在P0、P50和P100水平下，间作显著提高玉米和大豆的籽粒产量，并显著提高玉米和大豆植株的磷素吸收量。与常规施磷水平(P100)下的单作处理相比，玉米–大豆间作在磷肥减少50%(P50)的条件下，并未降低玉米和大豆的磷吸收量与籽粒产量。3个磷水平下，间作提高了玉米和大豆根际土壤有效磷含量，而降低了根际土壤总无机磷以及Fe-P、Al-P、Ca-P、O-P的含量；同时适当增施磷肥显著提高了玉米和大豆根际土壤总无机磷及各无机磷组分的含量。本试验条件下，间作促进土壤中Fe-P、Al-P、Ca-P和O-P的活化(尤其是Fe-P)，是低磷胁迫下间作土壤有效磷含量与作物磷吸收量增加的重要原因。玉米–大豆间作具有节约磷肥、维持作物产量及根际土壤有... 相似文献
4.
通过三室隔网分室盆栽模拟试验,研究了分室不同磷(P)源[无机磷(磷酸二氢钾)和有机磷(大豆卵磷脂),P添加量均为50 mg·kg-1]添加和根室接种不同丛枝菌根真菌(AMF)[Glomus mosseae(GM)、Glomus etunicatum(GE)]对间作玉米种植红壤无机磷形态的影响。结果表明:无论接种与否,间作处理使根室土壤有效磷含量显著降低,说明间作能够促进玉米植株对土壤有效磷的吸收,且有效磷的耗竭从根际土壤开始。除OP50-单作玉米处理的Org-P外,接种AMF均一定程度增加了各形态无机磷含量。此外,根室土壤有效磷的主要组分为Ca2-P、Al-P和Org-P,其中Org-P与土壤有效磷有着极显著的负相关关系。 相似文献
5.
果园带状生草对果园面源污染的控制效果 总被引：5，自引：0，他引：5
利用径流小区法观测琯溪蜜柚园套种不同宽度草带果园土壤流失量、径流量,并研究其对氮、磷面源污染的控制效果及不同施肥水平下适宜草带的调控效果.结果表明:(1)不同处理中,全园生草控制果园面源污染效果最好,径流、土壤、总氮、总磷年流失量分别为422.7 m3/hm2,26.0 t/km2,0.793 kg/hm2,78.8g/hm2;2.0m草和1.5m草带处理效果居中;1.0m草带处理最差,分别为927.0 m3/hm2,57.4t/km2,2.050 kg/hm2,279.3 g/hm2.(2)各处理都可极显著或显著降低径流量、土壤流失量、径流总磷、可溶性磷浓度和流失量,且控制磷流失效果相同,而1.0m草带处理时径流可溶性磷浓度和流失量与其他3个处理差异达极显著或显著水平.(3)人工生草(全园、带状生草)处理都可极显著降低径流总氮、铵态氮、可溶性氮浓度和流失量.(4)1.5m和1.0m草带处理径流硝态氮浓度显著高于全园生草和自然生草处理,而全园生草、2.0m和1.5m草带处理都可极显著降低径流硝态氮流失量.(5)不同施肥水平下,全园生草高肥、草带高肥、中肥、低肥处理径流总氮流失量分别为对照的16.46％,49.09％,41.60％,41.11％;磷总流失量分别为对照38.58％,41.73％,33.86％,35.43％;土壤流失量分别为对照18.29％,47.78％,53.97％,67.78％;径流量分别为对照25.14％,47.98％,48.53％,58.93％;草带高肥处理径流总氮、硝态氮浓度明显或显著高于低肥处理,超过了果园种植1.5m草带时百喜草的控制氮流失能力. 相似文献
6.
间作作物菌根菌丝对红壤磷形态的影响 总被引：1，自引：0，他引：1
丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)在植物与土壤系统中扮演着重要的角色,能促进寄主植物对养分尤其是磷(P)的吸收。间作在提高土壤P素利用及增产增收等方面具有重要作用。本研究通过三室隔网分室盆栽模拟试验,在玉米/大豆间作种植体系下,对菌丝室进行不同形态P处理[不施P(P0)、施用无机磷(IOP50)、施用有机磷(OP50)],同时在根室进行不同AMF处理[不接种(NM)、接种Funneliformis mosseae(FM)],研究了不同外源形态P添加和AMF处理下,菌根作物对菌丝室红壤中不同形态P吸收利用的影响。结果表明:与单作-FM-IOP50处理相比,间作-FM-IOP50处理下的玉米P吸收量显著增加150.2%,大豆P吸收量增加24.5%;除大豆单作-P0处理外,接种FM均明显降低菌丝室土壤有效磷含量。除大豆单作-FM处理外,施用IOP50使土壤有效磷含量在单作条件下最高,而在间作条件下则最低。对红壤P形态的分级结果表明,接种AMF均一定程度增加了Ca_2-P、Al-P、Org-P、O-Al-P、Ca_(10)-P的含量,而间作则显著提高了作物对土壤Ca_2-P、Fe-P的吸收;相比其他处理,土壤Ca_2-P、Org-P、O-Al-P含量在间作-FM-IOP50组合处理下较高(P0.05)。相关分析显示,Ca_2-P与玉米植株P吸收量呈显著负相关,而O-Al-P与大豆植株P吸收量呈显著负相关。总之,接种FM、磷肥施用与间作均在一定程度上促进了宿主作物对P的吸收累积。其中间作-FM-IOP50组合是促进间作玉米生长、P素吸收及Ca_2-P、Org-P、O-Al-P增加的最佳组合,通过促进无机磷的活化而改善作物对P素的吸收利用,有效削减土壤P素的残留,若将其应用于滇池流域,可望减少P素的流失。 相似文献
7.
栽培模式及施肥对玉米和大豆根际土壤磷素有效性的影响 总被引：2，自引：1，他引：2
栽培模式及施肥管理对作物吸收利用土壤磷素的影响较大,本研究为探明玉米/大豆套作系统作物根系交互作用下根际土壤无机磷组分动态变化特征,利用盆栽试验测定了玉米/大豆套作(M/S)、玉米单作(MM)和大豆单作(SS)3种栽培模式以及不施肥(CK)、施氮钾肥(NK)和施氮磷钾肥(NPK)3种施肥处理下玉米和大豆地上部生物量及吸磷量和根际与非根际土壤速效磷、无机磷组分含量,以期为优化玉米/大豆套作系统磷素管理提供理论依据。研究结果表明同一施肥水平下,套作玉米的籽粒产量显著高于单作玉米;施磷显著提高了单作玉米籽粒产量,而对套作玉米籽粒产量影响不大。无论施肥与否,套作大豆秸秆及籽粒产量均高于单作大豆。所有施肥处理均表现为套作模式下单株作物地上部磷积累量显著高于单作模式。玉米成熟期,CK、NK处理下套作玉米根际土壤速效磷含量分别比单作玉米高54.2%和71.8%;大豆始花期,NPK处理下套作大豆根际土壤速效磷含量比单作大豆高19.8%。大豆成熟期,NK、NPK处理下套作大豆根际土壤速效磷含量分别比单作大豆高23.8%和108.0%。无论是单作还是套作模式,玉米根际土壤Al-P含量在3个施肥处理下均低于非根际土壤。CK和NK处理下单作玉米根际土壤Al-P含量分别是套作玉米的1.19倍和1.22倍;NPK处理下单作玉米根际土壤Fe-P含量是套作玉米的1.21倍。在CK、NK和NPK施肥处理下,单作大豆根际土Al-P含量分别是套作大豆1.12倍、1.30倍和1.25倍,单作大豆非根际土Al-P含量分别是套作大豆的1.22倍、1.30倍和1.06倍。CK、NK处理下单作大豆根际土壤Fe-P含量分别是套作大豆的1.47倍和1.12倍。研究得出结论,低磷条件下,与单作相比,玉米/大豆套作更有利于作物对土壤Al-P、Fe-P的活化吸收。 相似文献
8.
通过盆栽模拟试验,探讨不同施磷量对玉米 -大豆间作作物生长及磷吸收的影响,并分析根际红壤中各无机磷形态的变化。结果表明:与单作相比,玉米 -大豆间作显著提高了作物地上部生物量及磷素吸收量,并具有明显的产量优势。与常规施磷水平(P100)下的单作相比,玉米 -大豆间作条件下,磷肥减施 1/2(P50)并未降低作物籽粒产量与玉米的磷吸收量。间作种植显著降低了玉米、大豆根际红壤总无机磷含量,并且无机磷减少量主要以O-P、Fe-P和 Ca-P为主。玉米、大豆根际土壤Fe-P、Al-P、Ca-P与 O-P占土壤总无机磷含量的比例主要受磷水平的调控,而种植模式对玉米和大豆根际土壤中各无机磷形态的比例(除 Fe-P外)均没有影响。在本试验条件下,玉米 -大豆间作通过根系交互作用主要促进土壤中 Fe-P、Ca-P和 O-P的活化来增加玉米与大豆的磷吸收,并具有节约磷肥、维持作物产量和磷吸收的潜力。 相似文献
9.
氮磷配施对苹果幼苗生长、土壤无机磷形态和磷素利用的影响 总被引：1，自引：0，他引：1
以矮化苹果砧木M9T337幼苗为试材,设置4个氮水平(N 0,150,300,450 mg/kg,分别以N0、N1、N2、N3表示)和2个磷水平(P_2O_5 100,200 mg/kg,分别以P1、P2表示),研究了氮磷配施对苹果砧木幼苗生长、土壤无机磷形态转化和磷素吸收利用的影响,以期为果园磷肥高效利用提供参考依据。结果表明,不同氮磷配施显著影响M9T337幼苗生物量及根系形态,以N2P2处理效果最佳,其次为N1P2处理。植株磷素积累量及磷肥利用率分别在N2P2、N2P1处理下达到最大值,同一磷水平下适量增氮可促进幼苗对磷素的吸收,有效提高植株磷肥利用率。高氮处理(N3P1、N3P2)显著抑制幼苗对土壤磷素的吸收,不利于砧木幼苗的生长。土壤有效磷(Olsen—P)含量主要受施磷量的影响,在N2P2处理下达到最大,为27.86 mg/kg;土壤碱性磷酸酶活性则在N2P1处理下最大,为2.12 mg/(g·d)。与单施磷肥相比,氮磷配施增加土壤中可供植物吸收利用的Ca_8—P、Al—P所占土壤磷库的比例,降低植物难以吸收利用的Ca_(10)—P比例,Ca_2—P的比例也有所降低;随施氮量的增加,Ca_8—P、Al—P呈现先增加后减小的趋势,均在N2P2处理下达到最大值,Ca_(10)—P随施氮量的增加呈现逐渐降低的趋势,而Fe—P、O—P含量在不同施氮量下则无明显变化趋势。合理的氮磷配施可通过改变土壤无机磷库组成,提高土壤磷素有效性,促进砧木幼苗的生长和对土壤磷素的吸收。 相似文献
10.
生草栽培对柑橘园土壤水分与有效养分及果实产量、品质的影响 总被引：42，自引：1，他引：42
试验研究生草栽培对柑橘园土壤水分和有效养分含量及果实产量品质的影响结果表明,生草栽培7～11月份干旱时期可提高果园土壤含水率;生草栽培初期降低果园土壤有效氮、磷、钙、镁、锰、铜和锌等矿质养分含量,但生草栽培2年后土壤有效氮、钾、铁和锌等矿质养分含量高于清耕对照。生草栽培可提高果实产量和果实可溶性固形物含量,降低果实柠檬酸含量,且种植百喜草比白三叶效果更明显 相似文献
11.
《Communications in Soil Science and Plant Analysis》2012,43(15-16):2398-2410
Understanding differences in the phytoavailability of various phosphorus (P) sources should improve matching P additions to plant needs and minimize excessive buildup of bioavailable P, which can degrade aquatic systems. We evaluated relative P phytoavailability (RPP) of different P sources in glasshouse and field studies. Bahiagrass (Paspalum notatum Fluggae), ryegrass (Lolium perenne L.), and a second bahiagrass crop were grown in succession in a P‐deficient soil amended with four sources of P (triple superphosphate (TSP), Boca Raton and Pompano; biosolids, and poultry manure), each applied at two rates in the glasshouse study and to an established bahiagrass pasture in the field. The RPP values estimated from plant P uptake of each organic source of P relative to TSP in the glasshouse were similar for the three croppings and similar to the estimates derived from the field study, but varied for the different P sources. Values ranged from 30% for poultry manure to 85% for Boca Raton biosolids. Boca Raton biosolid P was as readily available as P in TSP and would be classified as a high RPP (>75% RPP) source, but Pompano biosolids and manure would be classified as moderate RPP materials (25–75% RPP). The RPP values observed in manure and Pompano biosolid treatments are consistent with 50% “effectiveness” suggested for biosolid P in U.S. Environmental Protection Agency (USEPA) guidelines, whereas P bioavailability of Boca Raton biosolids is similar to mineral fertilizer. 相似文献
12.
《Communications in Soil Science and Plant Analysis》2012,43(6):1056-1071
Most fertilizer phosphorus (P) rate recommendations for the north-central United States are based on combination of a critical soil-test P value and a mass-balance calculation of fertilizer P required to maintain critical soil-test P. Accurate estimates of grain P removal are an essential component of P mass-balance calculation. Current north-central extension service guidelines recommend that estimates of corn and soybean grain P removal should be calculated using constant grain P concentrations. We reviewed research from the north-central region to determine the extent to which variation in grain P concentration accounts for differences in crop P removal and to determine whether predictions of grain P concentration can be improved through consideration of soil-test P, crop yield, and fertilizer P application. We found that soil-test P, grain yield, and fertilizer P are predictor variables that may significantly improve estimates of grain P concentration for corn and soybeans. 相似文献
13.
Lime was investigated as a soil amendment to decrease phosphorus (P) loss in runoff from two Delaware sandy loam soils, one high and one low in P. Soils were limed at three rates (control and target pH values of 6 and 6.8, respectively), packed into runoff boxes (2,000?cm2) and received simulated rainfall (80?mm?h?1 for 30?min). Lime showed potential to decrease P loss in runoff, but its effectiveness was soil specific and dependant on other management factors also. Lime decreased dissolved reactive P (DRP) and dissolved organic P (DOP) loss by 20?C25 and 52?C93?%, respectively, for the high-P soil and particulate P (PP) by 13?% for the low-P soil. The majority of P lost in runoff was DOP (3?C29?%) or PP (64?C96?%). Lime increased PP losses from the finer-textured soil following P application, indicating that increased P sorption can lead to increased losses if P is sorbed to more erodable particles. Initial soil P status was more important than liming in determining P loss. While amendments may decrease P losses in the short term, addressing nutrient imbalances at the field scale is clearly necessary in the long term. Losses increased significantly following inorganic P application. Although P was sorbed rapidly, with less than 2?% of added P removed in runoff, mean concentrations in excess of 700???g?l?1 DRP, 2,500???g?l?1 OP and 6,500???g?l?1 PP were recorded for both soils immediately following P application. 相似文献
14.
紫色土磷素流失的环境风险评估-土壤磷的“临界值” 总被引：10，自引：0，他引：10
采用室内培养的方法,研究了3种类型的紫色土旱地和淹水土壤磷素流失的环境阈值。结果表明:无论是淹水土壤或旱地生境,3种紫色土Olsen-P与CaCl2-P之间都存在一个"临界值",酸性、中性和钙质紫色土磷素淋失临界点的Olsen-P含量分别为67.2、85.8和113.8 mg kg-1。淹水土壤磷素环境敏感值在酸性、中性和钙质紫色土上,Olsen-P含量分别为49.2、77.9和92.1 mg kg-1。3种紫色土在淹水还原条件下土壤磷环境敏感临界值比旱地低,淹水还原条件提高了紫色土磷向水体释放的风险。淹水土壤Olsen-P含量与田表水TP、DP浓度之间存在"临界值",酸性、中性和钙质土临界值处土壤Olsen-P含量分别为(65±1.41)mg kg-1(、96.7±2.7)mg kg-1和(105.5±1.1)mg kg-1。土壤0.01 mol L-1 CaCl2-P与田表水TP、DP之间呈极显著的线性关系。可以利用这些指标对紫色土区域土壤磷环境风险进行评价,并确定区域磷肥的最佳管理策略。 相似文献
15.
为研究溶磷真菌菌群对土壤磷素有效性的影响,首先在室内对3株不同种类溶磷真菌(1株属于被孢霉属Z1,1株为青霉属Z2,1株为黑曲霉Z3)的组合效应进行了研究,确定了最佳的菌株组合Z1+Z2+Z3,试验选用Z1、Z2、Z3组成菌群作为试验菌株;然后通过盆栽油菜试验研究溶磷真菌配施难溶态磷(磷酸三钙和磷矿粉)对土壤磷素有效性的影响。结果表明:溶磷真菌处理土壤有效磷、有机质、碱性磷酸酶、蔗糖酶含量和油菜产量分别比基质处理显著增加了60.00%,20.21%,56.45%,53.81%,14.38%,溶磷真菌配施难溶态磷上述各指标都高于单施溶磷真菌处理;单施溶磷真菌对土壤最大吸磷量的影响与基质无差异,溶磷真菌配施难溶态磷可以显著降低土壤最大吸磷量,溶磷真菌+磷酸三钙和溶磷真菌+磷矿粉处理土壤最大吸磷量比溶磷真菌处理显著减少158.7,47.6 mg/kg,溶磷真菌各处理土壤吸附常数都低于对应的基质处理,溶磷真菌可以降低土壤对磷的吸附。在土壤上溶磷真菌应与难溶态磷配合施用,对提高土壤磷素有效性有积极的作用。 相似文献
16.
Douglas J. Soldat A. Martin Petrovic Quirine M. Ketterings 《Water, air, and soil pollution》2009,199(1-4):33-44
Phosphorus (P) loss from urban areas has been identified as a major contributor to declining surface water quality. The objective of this study was to determine the relationship between extractable soil P, depth of soil sampling, and dissolved reactive P (DP) concentration in runoff from turfgrass areas. At each site, runoff was generated on turfgrass and adjoining areas where turfgrass cover was removed. Across all six locations and the wide range of nutrient management schemes, variation of extractable soil P concentration and saturation ratios of 0–2cm samples accounted for 49–59% (r 2 = 0.49–0.59, n = 92) of variation of DP concentration in runoff from bare soil and soil with turfgrass cover. Despite a high degree of soil P stratification, changing sampling depth generally did not improve the relationship between soil test P and runoff DP concentrations. Across the narrower range of soil P levels common to lawns in New York (0–50mg kg?1 Morgan extractable soil P), none of the soil tests or P saturation levels (for 0–2cm depth) could accurately predict runoff P concentrations from soil with turfgrass cover (r 2 = 0.02 to 0.23, n = 72). For bare soil plots, restricting the analysis to the same range (<50mg kg?1 Morgan extractable P) did not alter the relationship between soil test P and runoff DP concentrations observed for the entire range (0–658mg kg?1) of soil-test P concentrations. These results suggest soil testing will not be an effective tool to predict runoff from turfgrass areas across the range of soil P levels common to New York State. 相似文献
17.
《Communications in Soil Science and Plant Analysis》2012,43(7):1053-1064
Phosphorus (P) is both a macronutrient for plants and an effective amendment to reduce lead (Pb) toxicity in soil. Thus, in Pb-polluted soil with low P availability, P will act as a nutrient as well as a Pb-immobilizing agent. However, this has not been fully investigated. A soil with 2.50 mg kg?1 Olsen P was spiked with soluble Pb and then amended with superphosphate to examine the effect of P on soil Pb availability and ryegrass (Lolium perenne L. cv. Aubisque) growth. It was found that P/Pb = 2 increased ryegrass yield by 804% and decreased root Pb concentration and soil diethylenetriaminepentaacetic acid (DTPA)–extractable Pb concentration by 25.6% and 1.0%, respectively. As P amendment increased to P/Pb = 4, both plant yield and root Pb concentration declined compared with P/Pb = 2. Results of the sequential extraction indicated that the proportion of carbonate phase Pb decreased, while that of the manganese oxide phase increased as P was added. The proportion of residual Pb was little affected by the amendment. The results suggest that in soils with low P availability and high Pb availability, availability of soil Pb and root concentration of Pb are less affected, whereas the toxicity of Pb is greatly depressed by the P amendment; P/Pb = 2 is high enough to alleviate the stresses of low P availability. 相似文献
18.
《Communications in Soil Science and Plant Analysis》2012,43(9):1071-1084
Water-extractable phosphorus (WEP) in manures can influence the risk of phosphorus (P) losses in runoff when manures are land applied. We evaluated several manure handling and extraction variables to develop an extraction procedure for WEP that will minimize pre-analysis manure-sample-handling effects on WEP measurements. We also related manure WEP determinations to runoff dissolved reactive phosphorus (DRP) concentrations found in previously conducted field simulated rainfall experiments using the same manures to evaluate WEP as a predictor of P runoff losses. Dairy and poultry manure WEP concentrations increased with manure-to-water extraction ratio and shaking time. Relative to fresh manures, drying and grinding dairy manures before analysis usually decreased WEP concentrations, while WEP in poultry manures was often increased. Pre-analysis handling effects on WEP were minimized at the 1:1000 extraction ratio with a 1-h shaking time. Relationships between manure WEP and runoff DRP concentrations were strongly influenced by season of year and WEP extraction procedure. The best prediction of DRP concentration in spring runoff experiments was with manure WEP concentration at the 1:1000 extraction ratio. With fall runoff studies, DRP concentrations were best predicted with WEP application rate rather than concentration. These seasonal differences can be explained by the greater percentage of rainfall that ran off in the fall compared to the spring. For all studies, runoff DRP concentrations were strongly related (r2 = 0.82) to the ratio of runoff to rainfall volumes, confirming that models need to take runoff hydrology into account as well as manure WEP in P-loss risk assessments. 相似文献