Effect of phosphate fertilization on crop yield and soil phosphorus status

To evaluate the effect of three phosphorus (P) fertilization regimes (no P, P input equivalent to P off‐take by crops, P input higher than P off‐take) on crop yield, P uptake, and soil P availability, seven field experiments (six in crop rotations, one under permanent grassland) were conducted in Switzerland during nine years (six trials) or 27 years (one trial). Soil total P (Pt), inorganic P (Pi), organic P (Po), and the amount of isotopically exchangeable soil P were measured in the 0–20 cm and 30–50 cm layers of the arable soils and in the 0–10 cm layer of the permanent grassland soil. Omitting P fertilization resulted in significant yield decreases only in one field crop trial as the amount of P isotopically exchangeable within one minute (E_1min) reached values lower than 5 mg P (kg soil)^–1. In the absence of P fertilization Pi decreased on average from 470 to 410 mg P (kg soil)^–1 in the upper horizon of 6 sites while Po decreased only at two sites (from 510 to 466 mg P (kg soil)^–1 on average). In all the treatments of the trials started in 1989 the E_1min values of the upper horizon decreased on average from 15.6 to 7.4 mg P (kg soil)^–1 between 1989 and 1998. These decreases were also observed when P inputs were higher than crops needs, showing that in these soils the highest P inputs were not sufficient to maintain the high initial available P levels. Finally for the six arable trials the values of the isotopic exchange kinetics parameters (R/r₁, n, C_P) and P exchangeable within 1 minute (E_1min) at the end of the experiment could be estimated from the values measured at the beginning of trial and the cumulated P balance.     

How does the Hedley sequential phosphorus fractionation reflect impacts of land use and management on soil phosphorus: A review

The Hedley sequential‐phosphorus (P)‐fractionation method has been used in many countries to study the effects of land‐use and management systems on soil P. Many data sets have been obtained but collectively never have been considered or to goal topic reviewed. Therefore, the objectives of this review were to compile and systematically evaluate these data. The data generated over many years were grouped into temperate, and subtropical and tropical soils of different land use and duration of soil‐management studies. In natural ecosystems, vegetation types and composition and percent of vegetation covers substantially affected all P fractions with pronounced impacts on the labile and moderately labile P. In short‐term studies (≤ 10 y), changes in the labile and moderately labile inorganic P (P_i) fractions were detected when more P (e.g., by factor 5) was applied than commonly recommended for agricultural crops. However, without P application the changes in all P fractions were subtle in temperate soils, but declines were significant in labile and moderately labile P in subtropical and tropical soils. In both temperate and tropical climates, medium (10–25 y) and long‐term (>25 y) cultivation without P application depleted all P fractions, whereas most of P fractions increased with continuous P application, regardless of the amount and source of P. Synthesis of data resulted in multiple‐regression functions which described differences in labile and moderately labile P fractions as function of differences in amount of P application and duration of the experiments. Moreover, the correlation analysis also showed strong association among most of the P fractions. Current limitations in data interpretation of Hedley fractionation can be overcome by the application of ³¹P nuclear–magnetic resonance (NMR) and X‐ray absorption near‐edge fine‐structure (XANES) spectroscopy.     

Comparisons of soil test phosphorus by Olsen,Bray P1, Mehlich I and Mehlich III methods

Abstract

A study was undertaken to evaluate the agreement among different university laboratories performing the Olsen, Bray P1, and Mehlich I tests for P on a diverse group of noncalcareous agricultural soils and to develop relationships among the Olsen, Bray P1, Mehlich I, and Mehlich III soil tests. For each test, the results from the individual laboratories were highly correlated (r² ≥ 0.90) and in almost all instances the slopes of the equations describing the relationships among laboratories approached one, The results indicate that the Olsen, Bray P1 and Mehlich I soil tests may be performed with a high degree of precision when standard soil test procedures are followed.

Of the three most commonly performed tests in the U.S. (Olsen, Bray P1, and Mehlich I), the Olsen and Mehlich I tests were the most highly correlated (r² = 0.87) although the Mehlich I test removed approximately one and one half times more P than did the Olsen test. Bray P1 and Olsen and Mehlich I P were less highly correlated (r² ≤ 0.72) and the relationships between these variables were influenced by the texture of the soils. The quantity of P removed by the Bray P1 test was on the order of two and three times greater than that removed by the Olsen and Mehlich I tests, respectively. The Bray P1 and Mehlich III soil tests were highly correlated (r² = 0.97) and similar quantities of P were extracted from the soil by the two tests.     

耕作侵蚀及其对土壤肥力和作物产量的影响研究进展

在坡耕地景观内,由于农耕工具和重力作用而引起的耕作位移使土壤发生向下坡运动或向上坡运动(依赖于耕作方向),导致净余土壤量向下坡传输、堆积,重新分配,从而形成耕作侵蚀。试验研究表明耕作侵蚀是坡耕地的主要侵蚀形式之一,耕作侵蚀发生最严重的区域是坡度较大、坡体短的坡耕地。该文就耕作侵蚀的概念、发生机理、典型的耕作侵蚀模型的发展,以及耕作侵蚀对土壤肥力和作物产量影响的研究现状作了简要论述,特别总结了针对中国的地貌和耕作工具特征而进行的耕作侵蚀的研究成果。指出在一定的景观范围内,耕作侵蚀是十分严重的,甚至其严重程度已经超过了水蚀。但是相对于水蚀而言,耕作侵蚀研究还很少,因此加强耕作侵蚀的研究是十分必要的。只有这样才能正确评价农耕地侵蚀状况,准确制定土壤保持措施和采用减少耕作侵蚀力的耕作工具,从而有效地控制土壤侵蚀。     

长期不同施肥对红壤性水稻土磷素及水稻磷营养的影响

【目的】合理的土壤磷素管理对作物生产和环境保护具有重要意义。南方双季稻田土壤磷素特征及磷素吸收信息相对缺乏,本文利用江西省稻田土壤质量演变定位监测试验为平台,系统分析长期不同施肥措施下土壤全磷、磷活化系数及水稻磷素吸收量的变化特征和全磷与磷盈亏的响应关系等,为指导磷肥合理施用提供重要科学依据。【方法】从1984年开始在江西省南昌市进行长期定位试验,设置8个处理,分别为不施肥对照(CK),PK、NP、NK、NPK、70%化肥氮+30%有机肥氮(70F+30M)、50%化肥氮+50%有机肥氮(50F+50M)、30%化肥氮+70%有机肥氮(30F+70M)。早稻施用纯N、P2O5和K2O量分别为150、60和150 kg/hm^2,晚稻分别为180、60和150 kg/hm^2。早、晚稻施用的氮、磷、钾化肥均分别为尿素、过磷酸钙和氯化钾,有机肥分别为紫云英(N、P2O5、K2O含量分别为0.30%、0.08%、0.23%)和腐熟猪粪(N、P2O5、K2O含量分别为0.45%、0.19%、0.60%)。除30F+70M处理,其余处理均为等氮磷钾设计。于1984-2012年每年早、晚稻收获期采集秸秆和稻谷计产,并于晚稻收获后,测定土壤全磷和有效磷含量。分析土壤全磷、磷活化系数(PAC)及早、晚稻磷素吸收量随种植年限的变化规律,研究土壤全磷含量与磷累积盈亏的响应关系。【结果】经29年连续试验,NK处理土壤全磷含量以每年4.6 mg/kg的速度下降,而含磷化肥处理土壤全磷含量升高速率为3.3~19.4 mg/(kg·a)。有机无机配施处理(70F+30M、50F+50M和30F+70M)升高速率平均为16.1 mg/(kg·a),是施NPK肥处理的4.89倍。施磷土壤全磷含量平均增至1.07 g/kg (2010-2012平均值),较初始值提高了1.18倍。不施磷肥处理土壤磷活化系数(PCA)由试验初始的4.24%下降至2.5%左右,施磷肥处理则均显著升高,其中有机无机配施处理平均升高至8.51%,平均年升高速率是施NPK处理的2.89倍。早、晚稻磷素吸收量,施磷肥(PK、NP和NPK)和化肥配施有机肥处理(70F+30M、50F+50M和30F+70M)均显著高于CK,提高幅度分别为29.9%~124%和28.6%~103%,均衡施肥(NPK、70F+30M、50F+50M和30F+70M)磷素吸收量显著高于不均衡施肥(PK和NP)处理,前者平均分别较后两者提高了38.7%和32.9%。早、晚稻产量与磷素吸收量呈极显著线性正相关关系,每吸收磷(P) 1 kg,早稻和晚稻产量分别可提高115和106 kg/hm^2。不施肥(CK)条件下,土壤全磷变化与累积磷盈亏间无显著相关关系,施NK肥处理土壤中每亏缺磷100 kg/hm^2,土壤全磷含量降低6.0 mg/kg,施化学磷肥的3个处理,土壤中每盈余磷100 kg/hm^2,平均提高9.3 mg/kg,而3个有机–无机配施处理,土壤中每盈余磷100 kg/hm^2,平均增加63.3 mg/kg,是无机磷肥的6.78倍。【结论】无论是单施化学磷肥,还是有机无机配施均有效提高土壤全磷含量及磷活化系数,且在等磷量投入条件下,有机无机配施较单施化肥的效果更优。建议减少中国南部红壤性稻田土壤的总磷输入量和提高有机肥施用比例,以改善粮食生产和保护环境。     

The potential for soil phosphorus tests to predict phosphorus losses in overland flow

Soil phosphorus tests offer a potentially powerful tool for land managers trying to predict the areas which will contribute diffuse losses of phosphorus (P) to surface water bodies through the overland flow vector – but do they work? We address this question at a range of scales, from patch (< 1 m²), through plot (several m²) to small watershed (several hectares). Our hypothesis is that as we increase the scale, and therefore the complexity of the system, soil P tests will predict P concentrations and losses associated with overland flow less well, and that this is partly due to a shift from dissolved P losses to P losses associated with eroded soil material. At the patch scale soil P tests were used to predict the P concentration and load from 24 European soils exposed to simulated rainfall under controlled conditions in the laboratory. Results showed that soil P tests were generally good predictors of reactive P <0.45 μm, but did less well at predicting total P > 0.45 μm. By combining the soil P test with measured sediment concentrations predictions of total P concentrations improved. Outdoor rainfall simulation experiments on bare soil plots (10 m²) revealed the overwhelming influence of particle bound P losses compared with P losses in the water phase. Soil P tests, which relate primarily to the dissolved P fractions in soil, were not able to predict total P losses, but were related to reactive P < 0.45 μm losses. At the watershed scale soil P tests were able to predict reactive P < 0.45 μm losses, but with considerable uncertainty. We conclude that soil P tests, in combination with sediment concentration provide a useful means of assessing the mobilization of P in overland flow, but should not be expected to provide watershed scale predictions of the movement of P into overland flow.     

Assessing soil P fractions changes with long-term phosphorus fertilization related to crop yield of soybean and maize

Long-term P Fertiliser application increases soil phosphorus (P) labile fractions, which can be associated with crop P uptake and grain yield and are useful to improve fertilizer recommendations. Research aims were to evaluate in long-term experiments with different P Fertiliser application in a Mollisol and a Vertisol: (a) the changes of soil P fractions and (b) the relationship between soil P fractions with long-term P Fertiliser application, with accumulated apparent P budget, grain P, total P uptake, soybean (Glycine max L.Merr.) and maize (Zea mays L.) grain yield. Soil P fractions were measured after 1 and 9 year since the beginning of the long-term experiments. Experiments included an initial Fertiliser application rate of 200 kg P ha⁻¹ and annual P Fertiliser application rate of 36 kg P ha⁻¹. Bray1-P, total, organic, and inorganic P in fine (<53 μm) and coarse (>53 μm) (CF) soil fractions, and in NaHCO₃ extract were measured. Initial P Fertiliser application increased inorganic and total P fractions. However, Bray1-P, total P in NaHCO₃ extract and in the CF were the fractions that most increased with continuous long-term P Fertiliser application in both sites. In the Mollisol, maize grain yield was unrelated to long-term P Fertiliser application. In the Vertisol, total P in NaHCO₃ extract, and total and organic P in the CF were more closely related to soybean grain yield than Bray1-P. We proposed soil P indices of labile inorganic and organic P that showed close relationships with soybean grain yield and may be useful to improve the diagnosis of P soil fertility.     

磷肥中腐植酸添加比例对玉米产量、磷素吸收及土壤速效磷含量的影响

【目的】 腐植酸可提高磷肥的肥效,对于其在磷肥中适宜添加量的研究可为我国磷肥的增效减量提供依据。【方法】 将腐植酸增效剂按1%、5%、10%和20%的比例添加到磷酸一铵中,制成四种腐植酸磷肥试验产品（HP1、HP2、HP3和HP4）,利用土柱栽培试验研究在等磷量（施P2O5量0.1g/kg干土）投入及等肥料重量（施磷肥实物量0.16g/kg干土,即施P2O5量分别减少1%、5%、10%、20%）投入情况下,腐植酸磷肥对玉米产量、磷素吸收利用及土壤速效磷含量的影响。【结果】 1）在等磷量施用情况下,与普通磷肥（P）相比,四种腐植酸磷肥处理玉米籽粒产量增加4.5%～13.6%,且腐植酸添加量越大产量越高,均显著高于普通磷肥处理;在等肥料重量施用下,随着腐植酸磷肥施入P2O5量的减少,玉米籽粒产量逐渐降低,当P2O5施用量减少20%时籽粒产量与普通磷肥处理相比仍未显著降低。2）腐植酸磷肥处理在等磷量施用下较普通磷肥处理可显著提高玉米籽粒磷吸收量和地上部吸磷总量,分别增加6.0%～15.4%和6.3%～14.0%,但秸秆磷吸收量无显著变化;当腐植酸磷肥施入P2O5量减少20%时籽粒磷吸收量和地上部磷吸收总量会显著低于普通磷肥处理。3）与普通磷肥处理相比,在等磷量施用下,腐植酸磷肥的表观利用率提高5.9～13.1个百分点,农学利用率、偏生产力分别提高26.5%～79.1%、4.5%～13.5%,且均达到显著水平。4）施入腐植酸后主要影响050cm土层的土壤速效磷含量,其中1530cm土层速效磷含量增加最为显著,与普通磷肥处理相比增加18.1%～36.6%。【结论】 腐植酸增效剂在1%～20%的添加比例范围内对磷肥均具有较好的增效作用,可提高玉米产量、磷素吸收量及磷肥利用效率,并可提高土壤中的速效磷含量,且腐植酸添加量越大效果越好;利用腐植酸的增效作用来减少磷肥施用量是可行的,在当前磷肥施用量的基础上可减少磷肥用量20%左右而保证玉米不减产。     

生物碳对土壤磷素和棉花养分吸收的影响

通过两年温室盆栽试验,研究了不同磷肥用量下生物碳对土壤磷素含量、 棉花生长和养分吸收的影响。试验以棉花秸秆为原料制备生物碳,制成三种热解温度（450℃、 600℃和750℃）的生物碳,分别以BC450、 BC600和BC750表示,同时以空白土壤为对照（CK）; 磷肥（P2O5）用量设3个水平0、 0.25、 0.5 g/kg（分别以P0、 P1、 P2表示）。研究结果表明,施用生物碳可显著提高土壤磷素含量及其有效性,随着生物碳热解温度的升高,土壤水溶性磷、 速效磷及全磷含量均显著增加,且对三种磷素含量的影响表现为水溶性磷 全磷 速效磷。施用生物碳处理两年棉花的干物质重均显著高于对照,但不同热解生物碳处理对两年棉花干物质重的影响各异。施用生物碳可显著增加棉花养分吸收量,总体表现为750℃ 600℃ 450℃。因此,施用生物碳可显著提高土壤磷素含量,促进棉花生长和养分吸收; 热解温度是影响生物碳质量的重要因素,生物碳的热解温度越高（450~750℃）,其促进作用越好。     

Relationships between relative crop yields,soil test phosphorus levels,and fertilizer requirements for phosphorus

Abstract

More uniformity in methods of deriving fertilizer P recommendations from crop response data should improve accuracy and precision of fertilization rates. Experimental data that relate crop yields to soil test levels and describe the effect of fertilizer P on soil test levels provide the basis for determining fertilization rates for specific crop‐soil situations. A modification of the Mitscherlich equation was used in derivation of a new equation for calculating fertilizer P requirements as a function soil test levels of P. The equation was applied to response data for 4 crops.

Response curves and fertilizer requirements as calculated for corn, soybeans, alfalfa, and clover‐grass indicated that soybeans yielded relatively more than the other three crops at low soil test levels of P. Corn and alfalfa required higher soil test levels to reach 95% maximum yield and required higher rates of fertilizer P when initial test levels were low.     

不同磷水平下小麦蚕豆间作对根际有效磷及磷吸收的影响

【目的】探明不同磷水平下小麦–蚕豆间作对根际有效磷含量及作物磷吸收量的影响,提高磷肥利用率。【方法】2015—2016和2016—2017两季田间试验在云南农业大学试验基地耕作红壤上进行,供试小麦品种为云麦-52,蚕豆品种为玉溪大粒豆。设施P2O5 0 (P0)、45 (P45)和90 kg/hm^2 (P90)三个水平,和单作(M,包括小麦单作MW和蚕豆单作MF)和间作(I)两种种植模式。每季在小麦分蘖期、拔节期、抽穗期、灌浆期和成熟期,蚕豆分枝期、开花期、结荚期、籽粒膨大期、收获期采取根际土样测定有效磷含量。在小麦蚕豆收获期测定单、间作小麦、蚕豆产量,并测定作物地上部磷含量。计算土地当量比(LER)来衡量间作优势,并用磷肥农学利用率来反映磷肥的吸收效率。【结果】与单作相比,在P0、P45、P90水平下,2016年间作种植显著提高了小麦籽粒产量12.5%、21.7%和17.3%,2017年间作蚕豆产量较单作分别降低了16.8%、11.7%和8.2%。三个磷水平下,小麦–蚕豆间作具有产量优势,土地当量比(LER)为0.95~1.18。与常规施磷水平(P90)下的单作相比,小麦–蚕豆间作条件下,磷肥减施1/2 (P45)并未降低小麦和蚕豆产量。间作种植对小麦根际有效磷含量无显著影响(除2016年成熟期外),但2017年,在蚕豆分枝期、开花期、结荚期,间作则分别降低蚕豆根际有效磷含量20.8%、44.5%和18%。与P90单作相比,间作P45处理几乎不会降低小麦、蚕豆根际有效磷含量。小麦、蚕豆磷吸收量主要受磷水平的调控,种植模式对小麦和蚕豆磷的吸收量及磷肥农学利用率均没有影响。【结论】在本试验条件下,小麦–蚕豆间作提高了小麦籽粒产量,降低了蚕豆产量;间作种植主要是改变了蚕豆生育前期根际有效磷含量,但对作物的磷吸收量没有影响。小麦–蚕豆间作具有减施磷肥、维持作物产量和根际土壤有效磷的潜力。     

Effect of superphosphate applications on soil phosphorus and on crop phosphorus removal by the strawberry

Abstract

Rate of superphosphate application significantly increased the Bray #2 (easily acid soluble plus adsorbed P) and “AlPO₄”; fractions for 3 successive years. A single dolomitic limestone application increased “FePO₄”; by an average of 36% one year after application. Crop P removal by the strawberry cv. ‘Acadia’ was approximately 2–3 ppm each year and it was not possible to relate this small amount to any of the soil P fractions determined.     

Effect of land use on some soil properties related to the risk of loss of soil phosphorus

Although land use clearly modifies soil properties, the intensity of the modifications depends on the management procedures and also on the soil properties themselves. To enable construction of models that describe soil nutrient losses, extensive databases corresponding to soils under different land use must be made available. Analysis of 404 samples of soils (from Galicia, NW Spain), under different types of use revealed that most of the soil properties underwent changes in the following order: forest use (least modified) ‐ grassland ‐ arable (most modified). Decreases in the contents of organic matter, extractable oxides and P‐adsorption capacity followed the same order, as did increases in the contents of available P (total, inorganic and organic), P desorbed with distilled water, and degree of P saturation. In general, in all of the soils, independently of their use, the amount of P desorbed (whether total P, molybdate reactive P or particulate P) was more closely related to the degree of P saturation than to the levels of P extracted with bicarbonate. Copyright © 2007 John Wiley & Sons, Ltd.     

Simulating the soil phosphorus dynamics of four long-term field experiments with a novel phosphorus model

Phosphorus is a nonrenewable resource, which is required for crop growth and to maintain high yields. The soil P cycle is very complex, and new model approaches can lead to a better understanding of those processes and further guide to research gaps. The objective of this study was to present a P-submodel, which has been integrated in the existing Carbon Candy Balance (CCB) model that already comprises a C and N module. The P-module is linked to the C mineralization and the associated C-pools via the C/P ratio of fresh organic material. Besides the organic P cycling, the module implies a plant-available P-pool (P_av), which is in a dynamic equilibrium with the nonavailable P-pool (P_na) that comprises the strongly sorbed and occluded P fraction. The model performance was tested and evaluated on four long-term field experiments with mineral P fertilization, farmyard manure as organic fertilizer and control plots without fertilization. The C dynamics and the P_av dynamics were modelled with overall good results. The relative RMSE for the C was below 10% for all treatments, while the relative RMSE for P_av was below 15% for most treatments. To accommodate for the rather small variety of available P-models, the presented CNP-model is designed for agricultural field sites with a relatively low data input, namely air temperature, precipitation, soil properties, yields and management practices. The CNP-model offers a low entry threshold model approach to predict the C-N and now the P dynamics of agricultural soils.     

A quantitative study of native soil phosphorus supply to plants

Abstract

Rhodes grass (Chloris gayana Kunth ) plants were grown on various soil types In order to study the relationships between the available and hardly available soil P fractions. Results indicate that when plants are grown intensively in soils for long periods without additional P fertilization, recharge rate of the available fraction of soil P becomes a limiting factor. An approach to determine the recharge rate, using data on plant uptake and changes in sodium bicarbonate extractable soil P content are suggested.     

Erosional impacts on soil properties and corn yield on Alfisols in central Ohio

Accelerated soil erosion can impact upon agronomic productivity by reducing topsoil depth (TSD), decreasing plant available water capacity and creating nutrient imbalance in soil and within plant. Research information on soil‐specific cause – effect relationship is needed to develop management strategies for restoring productivity of eroded soils. Therefore, two field experiments were established on Alfisols in central Ohio to quantify erosion‐induced changes in soil properties and assess their effects on corn growth and yield. Experiment 1 involved studying the effects of past erosion on soil properties and corn yield on field runoff plots where soil was severely eroded and comparing it with that on adjacent slightly eroded soil. In addition, soil properties and corn grain yield in runoff plots were compared on side‐slopes with that on toe‐slopes or depositional sites. Experiment 2 involved relating corn growth and yield to topsoil depth on a sloping land. With recommended rates of fertilizer application, corn grain yield did not differ among erosional phases. Fertilizer application masked the adverse effects of erosion on corn yield. Corn grain yield on depositional sites was about 50 per cent more than that on side‐slope position. Corn plants on the side‐slope positions exhibited symptoms of nutrient deficiency, and the ear leaves contained significantly lower concentrations of P and Mg and higher concentrations of Mn and K than those grown on depositional sites. Corn grain yield in experiment 2 was positively correlated with the TSD. Soil in the depositional site contained significantly more sand and silt and less clay than that on the side‐slope position. There were also differences in soil properties among erosional phases. The soil organic carbon (SOC) content was 19\7 g kg⁻¹ in slightly eroded compared with 15\1 g kg⁻¹ in severely eroded sites. Aggregate stability and the mean weight diameter (MWD) were also significantly more in slightly eroded than severely eroded soils. Adverse effects of severe erosion on soil quality were related to reduction in soil water retention, and decrease in soil concentration of N and P, and increase in those of K, Ca and Mg. Severe erosion increased leaf nutrient contents of K, Mn and Fe and decreased those of Ca and Mg. Corn grain yield was positively correlated with aggregation, silt and soil N contents. It was also negatively correlated with leaf content of Fe. Copyright © 2000 John Wiley & Sons, Ltd.     

Soil phosphorus testing for intensive vegetable cropping

Environmental concerns and rapidly decreasing phosphorus (P) resources caused a renewed interest in improving soil P tests for a more efficient P fertilization. This led to the development of better P fertilizer recommendation systems for major arable crops and grass. Nevertheless, these P fertilizer recommendation systems seem to fail for intensive vegetable crops, with often a very short growing season and limited rooting system. This leads to low P use efficiencies in the horticultural sector. In order to address this problem we set up a study to answer following questions: (1) which soil P test predicts the plant available P content for intensive vegetable crops the best and (2) can new insights, such as combining different soil P tests, improve P fertilizer recommendations for intensive vegetable crops? To this end, bulk samples of 41 soils with very different P status (based on ammonium lactate extractable P) were collected. The plant available P content of these soils was determined using six commonly used soil P tests (P‐CaCl₂, P‐water, P‐Olsen, P‐acetate, P‐lactate, and P‐oxalate) and a P fertilizer pot experiment with endive (a very P sensitive vegetable crop) was conducted. Six pots of each soil were planted with endive. Three of these pots received no P fertilization (0P) and three pots received ammonium polyphosphate equivalent to 24 kg P ha^?1 (24P). All other factors were kept constant. Relative crop yield of the 0P fertilized plants compared to the 24P fertilized plants was determined. Plotting these relative yields against the P status of the soil per soil P test allowed to fit a Mitscherlich curve through the data. Also the combination of two different soil P tests to predict the relative yield with a Mitscherlich equation was evaluated. The coefficients of variation of the soil P tests, the R² values and the relative standard errors of the parameter estimates revealed that P‐acetate and P‐water predicted the relative yield of the 0P plants the best and that combining two different soil P tests gave no extra predictive power. This finding may form the basis for the development of a new P fertilizer recommendation system for intensive vegetable crops, leading to an improved P use efficiency in horticulture. In order to develop this new system more data relating soil P test values with RY of intensive vegetable crops should be collected.     

Correlation of soil test nitrogen with potato yields

Abstract

Yield response of Idaho Russet Burbank potatoes to nitrogen fertilizer was related to soil test for inorganic N (NO₃ ^‐ and NH₄ ⁺) in a total of 27 field experiments over a 3‐year period using polynomial correlation and regression analysis. Nitrate plus ammonium nitrogen content in the surface foot of soil was found to be useful in predicting yield response of potatoes to applied nitrogen.

Correlations between yield and extractable N were considerably better when the data from each cropping system were analyzed separately than when all locations were analyzed as one group. Additional improvement was obtained by including extractable ammonium nitrogen and nitrogen in the second foot of soil respectively. The best correlation with yield was found using (NO₃ ^‐ + NH₄ ⁺)‐N in the surface foot following grain and the top two feet following non‐grain crops with R² values of 0.875 and 0.821 respectively.