W. J. Horst et al. (Eds.), Plant nutrition – Food curity and sustainability of agro -ecosystems. 876~877, 2001© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
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Spatial variability of available phosphorus and site specific P fertilizer recommendations in a wheat fieldscr脱硝
M. R. Karaman, S. Ersahin and A. Durak
Agricultural Faculty, Department of Soil Sci., Tokat-Turkey, 党的什么是党的根本性建设
Key words : phosphorus, site specific, spatial variability, wheat Abstract
Knowledge of the spatial variability in soil available phosphorus content is esntial in determining the local P needs of crops. This study was conducted to determine spatial variability in available P content of topsoils and subsoils on a 8.5 ha alluvial wheat field. Phosphorus values were more variable in topsoils than in subsoils since the topsoils have been frequently mixed with plowing activities and appli
ed P fertilir. Contour maps for available P contents further indicated that available P deposited differed in the subsoils.Introduction
Soil physical and chemical characteristics greatly affect the P nutrition of plants. The utilization of P fertilirs by crops generally is low (10-30 %), and fixation of phosphorus significantly affect P accumulation in the soil (Tisdale et al., 1993). The accumulation of P fertilir in the soil leads to the environmental pollution and economical loss. Also, a great variability in available P values occurs in agricultural areas. Therefore, in large broadcast applications of P, soil analys are esntial for effective P fertilir recommendation and incread P u efficiency. In the soil fertility analysis, considering local needs of crops for P fertilir depending on spatial variability of soil available P will make valuable contributions to the beneficial u of field soil (DeCourt et al., 1996).
Materials and methods
This study was conducted to determine spatial variability in available phosphorus content in topsoils (0-30 cm) and subsoils (30-60 cm) on a 8.5 ha alluvial wheat field near Tokat Airport, 25 km north of downtown Tokat,
西安钟楼简介Turkey. Topsoil and subsoil samples were taken on a 25 x 25 m grid. Available P contents in the soil
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samples were determined by the method from Oln et al. (1954).Other analys were made by routine methods, and statistical values were calculated with the computer program (StatMost, 1995).Results and discussion
Maximum, minimum, coefficient of variance (C.V.),kurtosis and skewness values revealed that a great spatial variability occurred in available P content, C.E.C. and O.M. content for both topsoil and subsoil (Table 1).Coefficients of variation were 32, 29 and 22% for available phosphorus, C.E.C. and O.M. content for topsoil,respectively. Of the subsoil characteristics, O.M. had the greatest C.V. (63%). All other lected soil properties generally exhibited a medium variability in both topsoil and subsoil. Wilding and Dress (1983) also showed that the soil properties such as soluble P and exchangable cations were commonly more variable than many other soil properties. A three-dimensional map of available phosphorus contents in the topsoil is prented in Fig.
1.
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According to boundary values from General Directorate of Rural Services (Ulgen and Yurtver, 1984),the topsoil was 1% very low, 47% low, 41% medium, and 11% high in available P; the subsoil was 3% very low,36% low, 38 % medium, and 23 % high (Fig. 2).
Three-dimensional maps and contour plots for available P indicated that considerable variability in available P content occurred in the experimental area.Available P contents of topsoil were greater than tho of subsoil due to continuous addition of available P to topsoil.Mallarino (1996) and Borges and Mallarino (1997) also emphasized that the problems for soil sampling caud by spatial variability are aggraveted for relatively immobile nutrients such as P and K becau of the limited mix of soil and the high residuality of the nutrients. A significant variability occurred in P fertilir ra
te recommendations,and depended on the available P content each grid-sampling point. Thus, the classical P fertilir recommendation program would lead to over fertilisation in and underfertilisation in of
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total experimental field. Site-specific P fertilir recommendation which would consider the spatial variability would supply more realistic P fertilir rates for optimal crop production, and it would benefit both the environment and production economics. But, as a result of economical limitations, one of veral interpolation methods can also be ud for gridding by estimating values for non-measured locations between sampled points (Wollenhaupt et al., 1994). The results further indicated that available P deposited existed in the subsoil. Thus,deep plowing could be performed every four to five years to mix P from this source with the topsoil and enhance P uptake by the crop.References
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Borges R and Mallarino AP 1997 Soil Sci. Soc. Am. J. 61,846.
卫风硕人DeCourt H, Darius PL and Baerdemaeker JD 1996Computers and Electronics in Agriculture 14, 179-196.Mallarino AP 1996 Soil Sci. Soc. Am. J. 60, 1473.
Oln SR, Cole CV, Watanable FS and Dean LA 1954Estimation of available phosphorus in soils by extraction with sodium bicarbonate. U.S. Dept. of Agriculture, Cir. No 939, Washington DC.
StatMost 1995 Dataxiom Software Inc. Ur’s Guide:StatMost. Ed. Dat. Soft. Inc., LA, CA. USA.
Tisdale SL, Nelson WL, Beaton JD and Havlin JL 1993Soil Fertility and Fertilirs. Macmillan Publishing Company, New York, USA.
Ülgen N and Yurtver N 1984 General Directorate of Soil-Water Service. Publishing No 47, Fertilir Guidebook No:8, Ankara, Turkey.
Wilding LP and Dress LR 1983 In Application of geostatistics to spatial studies of soil. Eds. BB Trangmar, RS Yost and G Uehara. Advances in Agr.Vol:38.
Wollenhaupt NC, Wolkowski RP and Clayton MK 1994 J.Prod.
Agric. 7, 441-448.
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