Soil phosphorus dynamics in a long-term field experiment at Askov

Inorganic and organic soil P (P_i, P_o) fractions were followed monthly for 15 months in a 100-year-old, fertilization and crop-rotation experiment with the Rubaek-Sibbesen, macroporous resin method, the Olsen method, and the Hedley fractionation method. Resin P, and Olsen P had similar levels and variation patterns. They increased in spring after fertilization, decreased during summer and autumn, and increased again in winter after repeated slurry applications. Resin P_o decreased in spring and peaked in summer. The variation in time of the Hedley P_i and P_o fractions was relatively smaller and was neither related to season nor to fertilization. Unmanured soil contained much less total P than NPK and slurry-treated soils, but the differences in total P_i were greater than those in total P_o. Neither total P_i nor total P_o concentrations differed between NPK and slurry treatments, indicating that P_o in animal manure is quickly mineralized. All P_i and P_o fractions were smaller in unmanured than in fertilized treatments. These differences were relatively largest for resin P_i and resin P_o, i.e., the most labile fractions, and decreased for the medium and less labile P_i and P_o fractions. The reactions by resin P_i, Olsen P, and resin P_o to seasons and treatments indicate that these fractions are estimates of the most labile pools of P_i and P_o in soil, which make them relevant for shortterm studies. The medium and less labile P_i and P_o fractions of the Hedley fractionation method seem more relevant for long-term studies.     

有机复混磷肥对石灰性土壤无机磷形态组成及其变化的影响

实验室培养条件下,研究了有机复混磷肥对石灰性土壤无机磷组成变化的影响。结果表明: 1）单独施用有机物料对提高土壤速效磷含量的影响不大,但施用磷肥,无论是磷酸一铵化肥还是有机复混磷肥,均显著提高了土壤速效磷含量;施用有机复混磷肥提高土壤速效磷的幅度（67.5mg/kg～80.4mg/kg）高于施用磷酸一铵化肥处理（62.3mg/kg）;有机复混磷肥中有机物料的含量高低对土壤速效磷含量的影响不大。2）单独施用有机物料具有提高土壤Ca2-P含量的作用,且明显提高了Ca8-P含量,但对Al-P、Fe-P、O-P、Ca10-P含量影响不大;施用无机磷肥和有机复混磷肥,显著提高了土壤Ca2-P、Ca8-P、Al-P含量,而对Fe-P、O-P、Ca10-P含量的影响很小;与磷酸一铵化学磷肥处理相比,施用有机复混磷肥对Ca2-P含量影响较小,但明显提高了Ca8-P含量,Fe-P含量也表现增加的趋势,而Al-P含量明显降低,O-P和Ca10-P含量的变化则没有明显规律;有机复混磷肥中有机物料的比例高低对土壤无机磷组成变化的影响没有表现出明显的规律性。3）施用磷肥引起速效态Ca2-P和缓效态Ca8-P的变化最大,其它形态无机磷的变化相对较小。与磷酸一铵化肥处理相比,有机复混磷肥处理Ca8-P的变异提高幅度增加,而Al-P的变异提高幅度减小,其它指标库容的变异幅度与之相近。4）施磷处理土壤速效磷含量与土壤Ca2-P、Ca8-P含量呈线性正相关,相关系数分别达到0.9888、0.9867,而Al-P、 Fe-P、O-P、Ca10-P与土壤速效磷相关性不显著,磷肥施入土壤后,土壤无机磷库中Ca2-P、Ca8-P的变化对土壤速效磷含量的贡献最大。     

土地利用从水稻种植至蔬菜种植的转换对土壤中磷素赋存形态的影响

Excess phosphorus (P) from agricultural soils contributes to eutrophication in water bodies. Samples (n=60) were taken from sites where rice paddies have been converted to vegetable fields for 0, < 10, 10-20, and > 20 years and analyzed for five inorganic P (P_i) fractions, three organic P (P_o) fractions, and several soil parameters to investigate how land use conversion affects P_i and P_o fractions in a peri-urban area of China with soils characteristic of many agricultural areas of Asia. Significant increases of 33, 281, 293, and 438 mg kg^-1 were found for soluble and loosely bound P_i (SL-P_i), aluminum-bound P_i (Al-P_i), calcium-bound P_i (Ca-P_i), and iron-bound P_i (Fe-P_i), respectively, after conversion from rice paddies to vegetable fields. Most of the increase in P_i was in the form of Fe-P_i, which increased from 8% of total P (TP) on paddy soil to 31% on the soil with > 20-year vegetable cultivation, followed by Al-P_i, which increased from 2% to 19% of TP. For Po fractions, there was no significant change in P concentrations. The conversion of land use from paddy fields to high intensity vegetable fields was causing significant changes in soil P fractions. Management practices were causing a buildup of soil P, primarily in the Fe-P_i fraction, followed by Ca-P_i and Al-P_i fractions. If current trends continue, a 30%-70% increase in TP could be expected in the next 20 years. Farmers in the area should reduce P application and use to maximize P uptake.     

不同用量有机肥对陇东旱塬黑垆土磷素形态转化及有效性的影响

以覆盖黑垆土土壤为材料,研究了不同用量有机肥对土壤磷素有效性及不同形态无机磷含量的影响。结果表明:在陇东旱塬黑垆土上施肥能够增加全磷、有效磷含量,有机肥增加效果更明显,且随有机肥施用量的增加而增加。无磷肥输入的氮肥处理区,活性较强的Ca_2-P、Ca_8-P、A1-P和Fe-P含量都有所降低,而较稳定态的O-P和Ca_(10)-P含量则有所提高。与CK相比,有机肥处理随有机肥用量的增加,Ca_2-P、Ca_(10)-P、A1-P含量表现为增加,而Ca_8-P、Fe-P、O-P则相反。同时Ca_2-P与有机质、有效磷显著正相关,与p H值显著负相关。因此,在本试验条件下,从有效态的Ca_2-P和难溶性的Ca_(10)-P含量变化来看,在施等量氮的基础上配施农家肥60 000 kg·hm~(-2)更有利于活化土壤磷和减缓磷吸附,从而提高磷素的有效性。     

外源磷对土壤无机磷的影响及有效性

通过对我国具有代表性的几个典型土类15年长期定位试验的CK和NPK处理以及原始土壤中无机磷组分的分析，研究施磷肥对土壤无机磷形态的影响及有效性。结果表明，原始土壤中闭蓄态磷和Ca10-P占无机磷比例大，土壤磷有效性低；在不施外源磷条件下连续耕作，各个土类的无机磷总量均逐年减少，其中主要是Ca2-P、Al-P和Fe—P明显降低；长期施用磷肥提高了土壤无机磷总量（TIP）和各组分的含量，其中以Ca2-P、Al-P和Fe—P提高比例显著，而0-P和Ca10-P提高的比例少。说明累积在土壤中的肥料磷多以有效性较高的形态存在。     

有机酸对不同磷源施入石灰性潮土后无机磷形态转化的影响

采用室内培养和化学分析的方法研究了几种有机酸对石灰性潮土无机磷形态转化的影响。结果表明,1)石灰性潮土中磷素主要以有效性很低的磷酸盐(Ca10-P等)形式存在,而有效性较高的磷酸盐(Ca8-P等)含量较少,Ca2-P就更少。2)不同磷源施入土壤后,无机磷总量相应增加。磷酸二氢钾与磷酸二钙主要向Ca8-P、Al-P等有效性相对较差的磷素形态转化,磷酸八钙、氟磷灰石、磷酸铁、磷酸铝等有效性较差的磷源,在较短的时期内主要以自身的形态存在。3)施加各种有机酸可以不同程度地降低土壤中Fe-P、Al-P和Ca10-P含量,增加Ca2-P、Ca8-P和O-P含量,总的趋势是促进土壤中植物难以利用的无机磷形态向植物可以利用的形态转化。这种促进能力因有机酸种类和性质的不同而不同,其作用大小顺序为草酸柠檬酸酒石酸。     

长期不同施肥下潮土磷素演变特征及其对磷盈亏的响应

以"国家潮土土壤肥力与肥料效益长期监测站"的定位试验为平台,选取试验中的5个处理,即1)NK(不施磷肥);2)NPK(施氮磷钾化肥);3)MNPK(NPK化肥+有机肥);4)1.SMNPK(MNPK处理施肥量的1.5倍);5)SNPK(NPK化肥+秸秆还田),分析不同施肥下土壤全磷(TP)和有效磷(Olsen-P)的演...     

节水灌溉减施磷肥对黑土稻作产量及土壤磷利用与平衡的影响

为探寻节水灌溉减施磷肥对黑土稻作磷利用及土壤磷平衡的影响,于2020年和2021年开展大田试验,以常规淹灌+常规施磷肥(CK,45 kg/hm2)作对照,节水灌溉模式下设置5个磷肥施用梯度：0（CP0,不施磷肥）、18 kg/hm2（CP1,减磷60%）、27 kg/hm2（CP2,减磷40%）、36 kg/hm2（CP3,减磷20%）、45 kg/hm2（CP4,常规施磷）。分析节水灌溉模式下减施不同程度磷肥对稻田产量、地上部植株吸磷量和土壤剖面各土层有效磷含量的影响,并计算土壤磷素表观平衡量和磷肥利用率。结果表明：2020年水稻收获后节水灌溉减施磷肥各处理表层土壤有效磷含量均显著低于CK处理的土壤有效磷含量（P<0.05）;2021年水稻收获后CP3处理表层土壤有效磷含量显著高于CK处理（P<0.05）。CP3处理2020年和2021年的地上部植株磷素积累量显著高于常规施肥CP4处理和CK处理,分别为14.64和15.86 kg/hm2（P<0.05）。地上部植株各器官磷素积累量由大到小为籽粒、茎鞘、叶。与常规施肥相比,2 a年CP3处理均显著提高了磷肥的吸收利用效率、农学利用率,显著降低土壤磷素盈余量（P<0.05）。综合考虑,节水灌溉下减施常规磷肥用量20%为黑土区适宜的磷肥施用量,2 a均提高水稻产量和磷肥利用率,且土壤磷素盈余量低。研究可为黑土区磷肥施用提供理论依据。     

Effects of fallow or planting wheat (Triticum aestivum L.) and fertilizing P or fertilizing P and N practices on soil carbon and nitrogen in a low-organic-matter soil

Soil carbon (C) and nitrogen (N) are important for maintaining soil fertility, and they are considerably affected by soil use and management. In the present study, we conducted an 8-year ?eld experiment on loessial dryland soil (Eum-Orthic Anthrosol, Food and Agriculture Organization of the United Nations (FAO)) in the southern Loess Plateau, China. We tested four soil management regimes—i.e., winter wheat (Triticum aestivum L.) cultivation with phosphorus (P) fertilization (WP), winter wheat cultivation with N and P fertilization (WNP), natural fallow (NF) and bare fallow (BF)—to evaluate their effects on soil C and N fractions. After 8 years, compared with the WNP treatment, the total soil organic nitrogen (SON) in the WP treatment decreased by 14.6% and 36.8%, and microbial biomass nitrogen (MBN) by 35.6% and 61.1%, at 0–20 and 20–40 cm soil depths, respectively. The soil heavy fraction nitrogen (HFN) and light fraction nitrogen (LFN) in the WP treatment also decreased by 36.6% and 39.4%, respectively. Furthermore, BF treatment decreased total soil organic carbon (SOC), heavy fraction carbon (HFC), LFN and MBN at both soil depths with average reductions of 43.4%. The NF treatment decreased light fraction carbon (LFC) by 17.0% at 0–20 cm soil depth, as well as MBN by 24.8% and 71.2%, and inorganic C by 29.1% and 23.8%, at 0–20 and 20–40 cm soil depths, respectively. There was no significant difference of microbial biomass C concentration among the WP, NF and BF treatments. These results confirmed that a lack of N fertilization decreased SON, BF reduced both SOC and SON, and NF decreased soil inorganic C. Therefore, the managements of a recommended rate of N fertilizer application and shortened time of bare fallow are critical for maintaining or increasing SON fraction sequestration, and natural fallow management is not a useful method for maintaining soil fertility in dryland in the Loess Plateau in China.

Abbreviations: HFC: heavy fraction carbon; HFN: heavy fraction nitrogen; LFC: light fraction carbon; LFN: light fraction nitrogen; MBC: microbial biomass carbon; MBN: microbial biomass nitrogen; SOC: soil organic carbon; SON: soil organic nitrogen     

Dynamics of phosphorus fractions in a savanna Alfisol under continuous cultivation

Abstract. We examined the dynamics of inorganic P (P_i) and organic P (P_o) pools of a savanna Alfisol under continuous cultivation complemented with nitrogen (N) and phosphorus (P) fertilizers with or without cow manure (D), using a modified Hedly fractionation. Continuous cultivation without P fertilizer decreased the concentration of P_i and P_o, pools including the residual P fraction compared with an unfertilized treatment with natural vegetation. Adding P fertilizers alone or in combination with D (P, NPK, D+P, D+NP and D+NPK) increased the concentration of labile P_i pools, but decreased the concentration of P_o, pools and the residual P fraction. The tendency of the residual P fraction to decrease along with P_o pools suggested that the residual P fraction was largely P_o. This is consistent with the correlation between the residual P fraction and total P_o (r=0.74^**) and the residual P fraction and organic carbon content (r=0.47^**). Analysis of the relationships between plant available P, estimated by resin-extractable P, and the more stable P_i and P_o, pools indicated that 85% of the variation in resin-P was atiributable to the hydroxide extractable P_i, (OH-P_i) and HCI-P_i which acted as sinks for fertilizer-P. The contribution of the residual P fraction to resin-P was indirect via bicarbonate-extractable P_o (HCO₃-P_o) and OH-P_o. These results also clarify why attempts to find P extraction methods which correlate well with response to P and to P uptake in the savanna have given inconsistent results.     

固体磷肥和液体磷肥对石灰性土壤不同形态无机磷及磷肥肥效影响的研究

土壤磷固定是影响石灰性磷肥肥效的主要原因。本文在田间滴灌条件下采用连续浸提的方法对液体磷肥和固体颗粒磷肥及其不同施用方法对石灰性土壤各形态无机磷含量动态变化的影响进行了研究,并比较了不同处理下加工番茄磷素营养效应。结果表明:各施肥处理0—20 cm土层Ca2-P和Ca8-P含量随施肥时间明显下降,而Ca10-P含量则显著上升,表明磷肥在石灰性土壤中不断向Ca10-P转化并被固定。液体磷肥追肥处理0—20 cm土层Ca2-P含量在各时期均显著高于其他施肥处理(P＜0.05),且液体磷肥追肥可以明显保持土壤0—20 cm土层较高的Ca8-P含量。与其他施肥处理相比,液体磷肥追施可减少石灰性土壤对磷的固定,增加0—20 cm土层Ca2-P和Ca8-P含量(P＜0.05),显著提高土壤磷的有效性。液体磷肥追施处理可显著提高加工番茄叶片含磷量和经济产量(91725 kg/hm2)。与传统过磷酸钙颗粒磷肥作基肥处理（CK1）相比,液体肥料全做追肥可使加工番茄经济产量提高26.7%,并明显提高了磷肥利用率。在滴灌条件下石灰性土壤上液体磷肥分次追施比传统的固体颗粒磷肥基施具有明显的优势,是一种非常具有应用前景的施肥方式。     

磷素活化剂对黑土磷形态及有效性影响的研究

试验研究了不同温度下活化剂对黑土各形态磷的影响,阐述了活化剂对Olsen-P影响的机制。结果显示,活化剂具有很好的增加土壤中有效磷的能力,在不同的温度条件下作用效果不同,施肥条件下,高温加速磷的固定。10℃时,3种活化剂活化能力为柠檬酸铵>腐植酸>活化剂H2,分别提高土壤Olsen-P的含量达40.93%、33.06%、23.20%;20℃时,活化能力为腐植酸>柠檬酸铵>活化剂H2,分别提高土壤Olsen-P含量达32.35%、24.89%、16.72%;30℃时,与CK相比Olsen-P含量没有明显增加。活化剂能促进各形态无机磷之间的转化,活化能力随温度升高而逐渐降低。SPSS分析结果证实,Al-P和Ca2-P是黑土有效磷的主要组分,与Olsen-P极相关;Ca8-P起负作用,而Fe-P作用效果不显著,但它们仍能通过影响Al-P和Ca2-P来间接影响Olsen-P。     

南亚热带森林演替过程土壤水分、有机质和交换性阳离子的变化格局

Information on the distribution patterns of soil water content （SWC）, soil organic matter （SOM）, and soil exchangeable cations （SEC） is important for managing forest ecosystems in a sustainable manner. This study investigated how SWC, SOM, and SEC were influenced in forests along a successional gradient, including a regional climax （monsoon evergreen broad-leaved forest, or MEBF）, a transitional forest （coniferous and broad-leaved mixed forest, or MF）, and a pioneer forest （coniferous Masson pine （Pinus rnassoniana） forest, or MPF） of the Dinghushan Biosphere Reserve in the subtropical region of southern China. SWC, SOM, and SEC excluding Ca^2＋ were found to increase in the soil during forest succession, being highest in the top soil layer （0 to 15 cm depth） except for Na^＋. The differences between soil layers were largest in MF. This finding also suggested that the nutrients were enriched in the topsoil when they became increasingly scarce in the soil. There were no significant differences （P = 0.05） among SWC, SOM, and SEC. A linear, positive correlation was found between SWC and SOM. The correlation between SOM and cation exchange capacity （CEC） was statistically significant, which agreed with the theory that the most important factor determining SEC is SOM. The ratio of K^＋ to Na^＋ in the topsoil was about a half of that in the plants of each forest. MF had the lowest exchangeable Ca^2＋ concentration among the three forests and Ca^2＋：K^＋ in MPF was two times higher than that in MF. Understanding the changes of SWC, SOM, and CEC during forest succession would be of great help in protecting all three forests in southern China.     

Fate of phosphorus in soil during a long‐term fertilization experiment in Finland

Accumulation and depletion of soil phosphorus (P) was studied in a long‐term (37 y) field experiment in Southern Finland. The loam soil had a high pH (7.5–7.7) due to an earlier liming. Spring barley, spring wheat, oat, and ryegrass, grown in rotation, were annually fertilized with 0, 32, or 67 kg P ha^?1 y^?1 (P₀, P₁, and P₂K) and sufficient N. The average dry matter grain yield 2,600 kg ha^?1 of the P₀ plots increased by about 500 kg ha^?1 at P₁ treatment and another 600 kg ha^?1 by P₂K. Soil samples were collected in 1978 (beginning), 1995, 2005, and 2015. According to the Chang and Jackson sequential extraction, the P₂K and P₁ treatments increased the inorganic soil P by 732 and 32 kg P ha ^?1 in 37 years, respectively, while the P₀ plots were depleted by –459 kg P ha ^?1. The P₂K treatment increased all four P fractions, extracted with NH₄Cl (easily soluble), NH₄F (Al‐P), NaOH (Fe‐P), and H₂SO₄ (Ca‐P). Continuous depletion (P₀) decreased the NH₄Cl‐P and NH₄F‐P pools, NaOH‐P and H₂SO₄‐P pools remaining stable. None of the P pools changed significantly at P₁. The remarkable gap between the measured change and the balance for the P₂K and P₁ treatments cannot be explained solely by lateral soil movement, meaning that a significant proportion of the applied P was lost either in surface runoff or transported below the investigated depth of 40 cm. Despite large P applications, the degree of P saturation reached only 20% in the P₂K topsoil, assuming a 50% reactivity of Fe and Al oxides. As derived from sorption isotherms, a high EPC₀ (i.e., equilibrium P concentration at zero net P sorption or desorption) of 1.30 mg L^?1 had been built up in the P₂K treatment, while in the P₁ treatment EPC₀ (0.33 mg L^?1) had remained unchanged and P depletion (P₀) had caused a decrease to 0.12 mg L^?1. These results demonstrate that P sorption and desorption properties respond strongly to both P fertilization and null fertilization treatments and that in a long‐term field experiment only a low proportion of the residual fertilizer P can be recovered from soil.     

玉米细根形成和土壤中无机磷分级平衡对缺磷的特异性响应

Plants have diverse strategies to cope with phosphorus (P) deficiency. To better understand how maize responds to P deficiency, a field experiment with two P levels, 0 and 100 kg P2O5 ha-1 (P0 and P100, respectively), was carried out as a part of a long-term Pfertilizer field trial. Plant and soil analyses showed that P-deficient maize reduced its growth rate, increased P use efficiency, and formed more thin roots with the diameter less than 0.6 mm at jointing and silking stages, compared to the plants treated with P100. Further, there were no differences in major inorganic P fractions (Ca 2 -P, Ca 8 -P, Al-P, Fe-P, occluded P and Ca 10 -P) between the rhizospheric and bulk soils at each harvest, even when soil Olsen-P was only 1.38 mg kg-1 . These results suggested that maize responded to P deficiency by reducing the internal P demand for growth and increasing P acquisition ability by favorable root morphological alteration at low carbon cost.     

Soil organic matter status of Chernozem soil in North Kazakhstan: effects of summer fallow

In North Kazakhstan there is concern about the degradation of Chernozem soil and agricultural sustainability by the inclusion and frequency of summer fallows in crop rotations in terms of their influence on the changes of soil organic matter (SOM) quality and quantity. We examined five fallow-wheat (Triticum aestivum L.) cropping systems with different frequencies of the fallow phase in Chernozem soil of North Kazakhstan; continuous wheat (CW), 6-y rotation (6R), 4-y rotation (4R), 2-y rotation (2R) and continuous fallow (CF). Soil samples were collected from the two phases of each rotation, pre- and post-fallow, and analyzed for potentially mineralizable C (PMC) and N (PMN), ‘light fraction’ organic matter (LF-OM), C (LF-C) and N (LF-N). Potentially mineralizable C was inversely proportional to the frequency of fallow and was highest in CW. Mineral N (min-N) and PMN were more responsive to rotation phase than other indices of SOM. Mineral N was higher in the post-fallow phase while PMN was higher in the pre-fallow phase. Light fraction organic matter was negatively correlated to the frequency of fallow and was higher in the pre-fallow than in the post-fallow phase in a rotation. The results suggested that the yearly input of plant residue in a less frequently fallowed system built up more PMC, whereas PMN was closely correlated to recent inputs of substrate added with plant residues. We conclude that a frequent fallow system may deplete SOM via accelerated mineralization. Also that LF-OM, PMC and PMN are more sensitive to detect subtle changes in SOM quality than total SOM. Our results may provide prediction of SOM response to fallow frequency in wheat-based rotation systems in Chernozem soils of semi-arid regions.     

Changes in soil organic carbon and nutrient pools in aggregate-sized fractions along a chronosequence of wolfberry (Lycium barbarum L.) plantations in arid areas of Northwest China

Different land use and management actions can affect soil aggregates (SAs) and nutrient stocks, which are crucial for sustainable agriculture. The impacts of various chrono-sequences on the soil aggregate structure, soil organic carbon (SOC) and nutrients associated with aggregate fractions in wolfberry (Lycium barbarum L.) plantations are still not fully understood. This study examined the composition and stability of SAs, SOC, total nitrogen (TN), available phosphorus (AP) and exchangeable cations (K⁺, Na⁺, Ca²⁺ and Mg²⁺) in bulk soil and various aggregate-size fractions from five wolfberry plantations with varying ages (1, 4, 6, 10 and 13 years) and a corn field (0 years) in the arid region of northwest Ningxia in China. The results indicated that silt–clay (<53 μm) fractions were dominant in the soil, accounting for 51%–66%, under different plantation ages. The proportion of the macro-aggregates (>250 μm) increased significantly, by 40%–47%, over the 4 years of wolfberry plantation. Likewise, the soil aggregate stability was improved, and total exchangeable bases (TEB) along with numerous cations concentrations (K⁺, Na⁺, Ca²⁺ and Mg²⁺) in SAs were significantly reduced as the wolfberry plantings became older. Both concentrations of SOC and TN in the soil aggregates peaked in the 13th year. The silt–clay fractions stored a considerable amount of SOC and nutrients. However, short-term (under 6 years) cultivation of wolfberry reduced the stocks of SOC, TN and AP in the soil, while long-term (over 10 years) cultivation increased them, particularly in macro-aggregates. These findings indicated that long-term wolfberry farming had several advantages, such as enhancing soil structure, accumulating SOC and nutrients and ameliorating alkaline soils, especially after 10 years, in the arid northwest of China.     

Effects of repeated manure and fertilizer phosphorus additions on soil phosphorus dynamics under a soybean-wheat rotation

 Soil P availability and efficiency of applied P may be improved through an understanding of soil P dynamics in relation to management practices in a cropping system. Our objectives in this study were to evaluate changes in plant-available (Olsen) P and in different inorganic P (P_i) and organic P (P₀) fractions in soil as related to repeated additions of manure and fertilizer P under a soybean-wheat rotation. A field experiment on a Typic Haplustert was conducted from 1992 to 1995 wherein the annual treatments included four rates of fertilizer P (0, 11, 22 and 44 kg ha^–1 applied to both soybean and wheat) in the absence and presence of 16 t ha^–1 of manure (applied to soybean only). With regular application of fertilizer P to each crop the level of Olsen P increased significantly and linearly through the years in both manured and unmanured plots. The mean P balance required to raise Olsen P by 1 mg kg^–1 was 17.9 kg ha^–1 of fertilizer P in unmanured plots and 5.6 kg ha^–1 of manure plus fertilizer P in manured plots. The relative sizes of labile [NaHCO₃-extractable P_i (NaHCO₃-P_i) and NaHCO₃-extractable P₀ (NaHCO₃-P₀)], moderately labile [NaOH-extractable P_i (NaOH-P_i) and NaOH-extractable P₀ (NaOH-P₀)] and stable [HCl-extractable P (HCl-P) and H₂SO₄/H₂O₂-extractable P (resisual-P)] P pools were in a 1 : 2.9 : 7.6 ratio. Application of fertilizer P and manure significantly increased NaHCO₃-P_i and -P₀ and NaOH-P_i, and -P₀ fractions and also total P. However, HCl-P and residual-P were not affected. The changes in NaHCO₃-P_i, NaOH-P_i and NaOH-P₀ fractions were significantly correlated with the apparent P balance and were thought to represent biologically dynamic soil P and act as major sources and sinks of plant-available P. Received: 23 October 1997     

栽培方式与施磷量对水稻养分累积、分配及磷素平衡的影响

针对宁夏引黄灌区水稻磷肥施用不合理的问题,探索水稻增产与养分高效的磷肥供应与相应的栽培模式之间的关系,以指导该地区水稻生产。通过在宁夏引黄灌区进行的田间试验,研究插秧和直播两种栽培模式下不同供磷水平(P2O50、45、90、135、180 kg/hm2)对水稻产量、不同器官氮磷钾养分含量、累积量及其分配比例、水稻磷肥利用效率及磷素平衡的影响。结果表明:插秧栽培较直播栽培水稻实粒增产15.6%,瘪粒产量降低184.0%。两种栽培方式下,水稻产量随着施磷量增加而增加,插秧栽培增产幅度为64.6%~68.7%,直播栽培增产幅度为24.2%~42.6%。施磷量和水稻籽粒产量之间有极显著的二次曲线关系,插秧水稻最高产量施磷量为158.5 kg/hm2,最佳经济产量施磷量为146.7 kg/hm2,比直播处理降低11.42%、8.9%。与直播处理相比,插秧处理实粒、地上部的氮素累积量分别提高12.3%、12.01%,磷素累积量降低6.39%、2.61%,钾素累积量提高了11.67%、17.87%。直播处理100 kg籽粒氮磷钾消耗比例为1∶0.35∶0.6,插秧处理为1∶0.30∶0.64。插秧处理水稻磷肥利用效率、偏生产力、农学利用效率、生理利用效率较直播处理分别提高了17.4%、8.6%、38.4%、4.6%,两种栽培方式下,当施磷量超过135 kg/hm2后水稻磷素携出量开始下降,施磷处理磷肥表观平衡均表现为盈余。综合考虑提高水稻产量、效益、磷肥当季回收率及维持土壤磷素平衡等因素,在本试验条件下,插秧处理最佳施磷范围为P2O5146.7~158.5 kg/hm2,直播处理为P2O5159.8~176.6 kg/hm2较为适宜。