sw—soil and water: nitrogen and phosphorus losses due to soil erosion during a typhoon, japan

J. agric. Engng Res. (2001) 78 (2) 209}216

SW*Soil and Waterdoi:10.1006/jaer.2000.0643, available online at http://www.idealibrary.com on

Nitrogen and Phosphorus Losses due to Soil Erosion during a Typhoon, Japan

Machito Mihara

Tokyo University of Agriculture, Faculty of Regional Environment Science, 1-1-1 Sakuragaoka Setagaya-ku, Tokyo 156-8502, Japan;e-mail: [email protected]

(Received 6 December 1999; accepted in revised form 6 September 2000; published online 6 December 2000)

The objectives of this study are to observe soil, nitrogen and phosphorus losses under di!erent amounts offertilizer during the typhoon of 20 June 1997, and to evaluate the e!ects of soil and nutrient losses associatedwith the typhoon on the annual loads. Cumulative rainfall of 143)5 mm was recorded during the typhoon of 20June 1997.

At the onset of surface runo!, the concentration of ammonium nitrogen was dominant among inorganicnitrogen, and gradually decreased with cumulative surface discharge. After 4 h of surface runo!, nitrate nitrogenconcentration became higher than that of ammonium nitrogen. According to the loads of nutrient losses, itbecame clear that the total nitrogen and phosphorus losses in the most fertilized plot (6285 kg ha~1), were thehighest among plots. Additionally, total nitrogen and phosphorus loads during the typhoon ranged from 20 to49% and from 35 to 45% of the annual loads, respectively. It was concluded that the typhoon largely a!ectedthe annual nutrient losses.

( 2001 Silsoe Research Institute

1. Introduction

Heavy rainfall during typhoon causes severe soil ero-sion on upland "elds in the semi}mountainous regions ofJapan. There are many studies concerning the predictionof soil losses based on the universal soil loss equation(USLE) (Wischmeier & Smith, 1978) or water erosionprediction project (WEPP) (Nearing et al., 1989). InJapan, USLE has been applied to predict soil erosionloss. Additionally, a large number of studies have investi-gated eutrophic components, pesticides, herbicides, andagricultural chemicals transfer (Sharply & Halvorson,1994). However, little is known about the e!ects of soilerosion on these chemical transfers in Japan. Soil erosiona!ects not only soil productivity of upland "elds but alsothe water environment in streams further down thecatchment. Severe eutrophication in reservoirs and ca-nals is associated with nitrogen and phosphorus losses insurface runo!, and these have recently been the focus ofintense research in Japan.

In the Kasumigaura lake basin of Ibaraki Prefecture,the loads of eutrophic components in the surface runo!were estimated to be 68 and 81% of the annual loads for

0021-8634/01/020209#08 $35.00/0 209

nitrogen and phosphorus, respectively. It was reportedthat soil conservation practices had an important role inreducing the nitrogen and phosphorus out#ow (Suzuki& Tabuchi, 1984). Also, in the Suwa lake basin of NaganoPrefecture, eutrophic components out#ow in surface ero-sion processes was investigated through laboratory experi-ments using a slope model, and through the water qualityresearch in the watersheds of the same lake (Mihara& Sakamoto, 1996; Mihara et al., 1997). The seasonalchanges in nitrogen and phosphorus loads in relation withsoil losses under di!erent amounts of fertilizer were inves-tigated in the same upland "eld of this paper (Mihara& Ueno, 1999). It was concluded that nitrogen and phos-phorus loads were proportional to soil losses and the loadsincreased with the amounts of fertilizer. Additionally, thee!ects of tillage type on soil and nutrient losses werediscussed to determine a suitable tillage system (Gaynor& Findlay, 1995; Richardson & King, 1995). However,little work has been done to investigate the nitrogen andphosphorus losses due to soil erosion processes duringa typhoon accompanied with heavy rainfall.

The objectives of this study are to observe the soil,nitrogen and phosphorus losses under di!erent amounts

( 2001 Silsoe Research Institute

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of fertilizer during a typhoon, and to evaluate the e!ectsof soil and nutrient losses associated with the typhoon onthe annual loads.

2. Methods

Four USLE plots were constructed in an upland "eldat the Rolling Land Laboratory, Tokyo University ofAgriculture and Technology located in the hilly area ofTama (Fig. 1). Each experimental plot measures 1)8 m by22)1 m, and the average gradient was 2)733 (Mihara& Ueno, 1999). The soil type of the upland "eld isa Andosol. A synthetic fertilizer was spread uniformly at0, 5 (1257 kgha~1), 10 (2514 kg ha~1) and 25 kg(6285 kg ha~1) covering with surface soil at the end ofJuly 1996 on plots I, II, III and IV, respectively. Thefertilizer was granulated and included nitrogen, phos-phate and potassium at the same mass concentration of8%. Observations were conducted under conditionswithout weeds or any other vegetation. As herbicideswere not applied to the plots, any weeds were cut oncea week using a mower. Surface runo! was dischargedinto a water tank, then water samples of 1 l were collectedafter stirring. Sampled surface runo! was called suspen-sion in this paper, so sediment, suspended solids andsolution were included in the suspension.

Cumulative rainfall of 143)5 mm was recorded duringthe typhoon from 3:00 to 15:00 h of 20 June 1997. The

Fig. 1. Experimental erosion plots located in the hilly area ofTama, Japan

rainfall intensity higher than 17)5 mmh~1 continuedfrom 5:00 to 8:00 h, and the peak rainfall intensity over30 min of 46)0 mmh~1 was recorded from 7:30 to 8:00 h.As the plots were located in a valley in the hilly area ofTama, surface runo! from each plot was caused not onlyby rainfall but also by groundwater. During thistyphoon, surface discharge per unit time was measured.The concentration of soil loss, suspended solids, totalnitrogen and phosphorus in both suspension andsolution and inorganic nitrogen were analysed in thelaboratory. To separate the solution from the suspension,sediment and suspended solids such as soil particles andorganic matters were removed by centrifugal separation.

Total nitrogen (total N) and total phosphorus (total P)of the water samples were analysed by means of theabsorption spectrophotometry after decomposition withpotassium peroxodisulphate (K

2S2O

8). Ammonium

nitrogen (NH4-N) was analysed by the Nesslar method,

nitrate nitrogen (NO3-N) by the cadmium reduction

method, and nitrate nitrogen (NO2-N) by the diazot-

ization method, while suspended solids (SS) were mea-sured by the photometric method (Buurman et al., 1996;Hach Company, 1994). Particles larger than 0)02 mmwere removed by sedimentation in analysing processes ofsuspended solids. Particles of all sizes were included inthe soil loss analysis.

The chemical properties of the upland soils were ana-lysed in July 1996 before fertilization, in December 1996and in July 1997 after fertilization. The synthetic fertilizerwas spread uniformly at the end of July 1996 on the plots.For making clear the typhoon e!ects on nutrient losses,soil chemical properties in July 1997, about a month afterthe typhoon, was compared with that in December 1996before the typhoon. Total nitrogen of the upland soil wasanalysed by the Kjeldahl method and inorganic nitrogenby the two normal potassium chloride extractionmethod. Meanwhile, total phosphorus was calculated onthe basis of the amounts of phosphate analysed by theBray II method (Japanese Society of Soil Science andPlant Nutrition, 1986).

3. Results and discussion

3.1. Changes in soil properties before and after thetyphoon

The physical properties of the soils sampled in July1996 are shown in Table 1. The soil texture of the investi-gated upland "elds was clay loam or light clay. Theorganic matter content measured by ignition loss rangedbetween 13)7 and 14)9%. The dispersion ratio (Middle-ton, 1930) was from 18)0 to 22)6%, also there was nosigni"cant di!erence in the dispersion ratio among plots

Table 1Physical properties of soils sampled in July 1996

Plot Specixc Particle size distribution*, % Soil Dispersion Organic mattergravity texture ratio, % content, %

Gravel Coarse Fine Silt Claysand sand

I 2)68 1)0 7)7 32)7 33)7 24)9 CL 22)6 14)6II 2)64 0)4 7)3 31)7 34)7 25)9 LiC 18)0 14)9

III 2)67 0)3 7)0 30)8 35)9 26)0 LiC 22)2 14)0IV 2)68 0)5 8)5 32)6 32)5 25)9 LiC 18)2 13)7

*International methods; CL, clay loam; LiC, light clay.

211NITROGEN AND PHOSPHORUS LOSSES DURING A TYPHOON

in July 1996 at the 0)05 level on the basis of normaldistribution test. However, in December 1996 before thetyphoon and 5 month after the fertilization, the disper-sion ratio of plot IV was lower than for the other plots(Table 2). There was a tendency for the dispersion ratio todecrease with the amount of fertilizer applied. On theother hand, electrical conductivity increased with theamount of fertilizer. As the fertilizer increased, the higherelectrical conductivity of the soil water shortened thedi!use electrical double layer of soil particles (vanOlphen, 1963), so that the dispersion ratio was inverselyproportional to the amount of fertilizer.

Chemical properties of the soils are shown in Table 3.Total nitrogen of the soils in December 1996 ranged from2942 to 5114 mg kg~1, and this tended to be greater thanbefore fertilization for all the fertilized plots. Total nitro-gen in July 1997, about a month after the typhoon, waslower than that in December 1996 for all plots. Also totalnitrogen and phosphorus in each plot became re-markably similar in July 1997 compared with those inDecember 1996. It was considered that fertilizer appliedwas washed out due to rainfall associated with surfaceruno!.

The concentration of ammonium and nitrate nitrogenin July 1997 was lower than that in December 1996.Additionally, total phosphorus in July 1997, abouta month after the typhoon, was lower than that in De-cember 1996 for all plots. It was considered that the

Table 2Dispersion ratio and electrical conductivity of soils sampled in

December 1996

Plot Dispersion ratio Electrical conductivity,% kS cm!1

I 20)2 471II 19)7 565

III 17)4 626IV 15)7 954

typhoon a!ected the concentration of nitrogen and phos-phorus in soils.

3.2. Soil and nutrient losses during the typhoon

Soil and nutrient losses associated with the typhoonare shown in Figs 2}5. The concentration of total nitro-gen and phosphorus in the suspension was comparedwith that in the solution. There was a tendency for thetotal nitrogen and phosphorus concentration in the sus-pension to be greater than that in the solution. It followsthat sediment and suspended solids transported the ni-trogen and phosphorus components.

At the onset of surface runo!, ammonium nitrogenconcentration was dominant among inorganic nitrogen,and gradually decreased with cumulative surface dis-charge. This tendency was similar to the previous study(Mihara & Sakamoto, 1996). After 4 h from the onset ofsurface runo!, the concentration of nitrate nitrogenbecame higher than that of ammonium nitrogen.

Ammonium nitrogen concentration of the surface soilin each plot was higher than nitrate nitrogen concentra-tion as shown in Table 3. So, it was considered thatammonium nitrogen was concentrated in the surface soildue to ammoni"cation, and washed out at the onset ofsurface runo!. Then, nitrate nitrogen was supplied to thesurface #ow with #owing out the groundwater.

3.3. ¸oads of soil and nutrient losses during the typhoon

The loads of soil and nutrient losses were shown in Fig. 6.Soil and nutrient loads were calculated on the basis ofsurface discharge and the concentration. In fertilizedplots, there was a tendency that soil loss decreased withthe amount of fertilizer applied. As shown in Table 2, thedispersion ratio also decreased with the amount of ferti-lizer. It was considered that dispersion properties of soilsa!ected soil loss during the typhoon.

Table 3Chemical properties of soils

Date Plot Total N, Total P, NH4-N, NO3-N, NO2-N,mg kg!1 mg kg!1 mg kg!1 mg kg!1 mg kg!1

July 1996 3366 98 160 134 0)36Dec 1996 I 2942 70 181 132 0)58

II 3520 106 192 148 0)48III 3398 122 204 166 0)34IV 5114 628 221 196 0)36

July 1997 I 2858 86 59 48 0)16II 2595 84 72 66 0)14

III 3141 65 65 50 0)16IV 3291 148 68 60 0)16

Fig. 2. Soil and nutrient losses in plot I during the typhoon of 20 June 1997: (a) rainfall; (b) accumulative surface runow; (c) soil loss( ) and suspended solids ( ); (d) total phosphorus in suspension ( ) and in solution ( ) (e) total nitrogen in suspension

( ) and in solution ( ); ( f ) inorganic nitrogen as NH4-N ( ) as NO3-N ( ) and as NO2-N ( )

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Fig. 3. Soil and nutrient losses in plot II during the typhoon of 20 June 1997: (a) rainfall; (b) accumulative surface runow; (c) soil loss( ) and suspended solids ( ); (d) total phosphorus in suspension ( ) and in solution ( ) (e) total nitrogen in suspension



According to nutrient loads, it became clear that thetotal nitrogen and phosphorus loads from plot IV, themost fertilized plot (6285 kg ha~1), were the highest of allplots. Total phosphorus in the suspension for plot IV wasalmost 2 times higher than for plot III.

Total nitrogen and phosphorus loads in the suspen-sion were much larger than in the solution, so it wasconsidered that soil particles and organic matters trans-ported nitrogen and phosphorus components. Due tothe fact that the phosphate absorption coe$cient of an-dosol is high (Kawaguchi, 1987), the transport of phos-phorus with soil particles was much larger than that ofnitrogen. It follows that soil conservation practices, such

as settling ponds or "lter strips, become important notonly for reducing soil loss but also for water qualityconservation.

3.4. E+ects of the typhoon on annual nutrient losses

Total annual rainfall from August 1996 to July 1997was 1245)5 mm of which 11)6% was contributed by thetyphoon of 20 June 1997. Soil and nutrient losses duringthe typhoon can be expressed as proportions of theannual losses to evaluate the e!ects of the typhoon onsoil and nutrient losses. The annual loads of soil and

Fig. 4. Soil and nutrient losses in plot III during the typhoon of 20 June 1997: (a) rainfall; (b) accumulative surface runow; (c) soil loss( ) and suspended solids ( ); (d) total phosphorus in suspension ( ) and in solution ( ) (e) total nitrogen in suspension


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nutrient components were explained in a previous paper(Mihara & Ueno, 1999).

Except for plot I, soil loss associated with the typhoonaccounted for between 40 and 70% of the annual loads(Table 4). Total nitrogen loads in the suspension rangedfrom 20 to 49% of the annual total nitrogen loads. Totalphosphorus loads in the suspension associated with thetyphoon ranged from 35 to 45% of the annual totalphosphorus loads. It follows that the proportions of totalnitrogen and phosphorus losses were much higher thanthe rainfall received from the typhoon.

The percentage of nitrogen and phosphorus compo-nents in the solution, including inorganic nitrogen, was

inversely proportional to the rate of fertilizer application.The percentage of nitrogen and phosphorus componentsin the solution from plot I was higher than 65%, whichwas except for ammonium nitrogen of 39)5%.

4. Conclusion

At the onset of surface runo!, the concentration of am-monium nitrogen was the highest of inorganic nitrogen, andgradually decreased with cumulative surface discharge.After 4 h of surface runo!, nitrate nitrogen concentrationbecame higher than that of ammonium nitrogen.

Fig. 5. Soil and nutrient losses in plot IV during the typhoon of 20 June 1997: (a) rainfall; (b) accumulative surface runow; (c) soil loss( ) and suspended solids ( ); (d) total phosphorus in suspension ( ) and in solution ( ) (e) total nitrogen in suspension


Table 4Percentage of soil and nutrient loads during the typhoon as a proportion of annual term

Plot Soil, Nutrient losses, %%

Total N Total P NH4-N NO3-N NO2-N

I 2)6 48)5 (67)8) 36)7 (73)5) 39)5 75)0 65)3II 66)8 25)3 (27)8) 35)1 (67)2) 34)7 29)9 37)9

III 69)6 32)5 (25)3) 41)7 (27)5) 10)1 26)8 23)7IV 40)7 20)4 (9)4) 44)9 (18)3) 1)5 13)0 17)7

( ), Percentage of total nitrogen and phosphorus loads in solution. NH4-N, NO3-N and NO2-N, loads in solution.


Fig. 6. Soil and nutrient losses in each plot during the typhoon of20 June 1997: (a) soil loss load; (b) suspended solids load; (c)total nitrogen loads in suspension ( ) and in solution ( ); (d)total phosphorus loads in suspension ( ) and in solution ( ); (e)organic nitrogen load; ( f ) inorganic nitrogen loads as NH4-N ( )

as NO3-N ( ) and as NO2-N ( )

M. MIHARA216

Total nitrogen and phosphorus in the suspension washigher than that in the solution. Thus, it became clearthat soil particles and organic matters transported nitro-gen and phosphorus. In the case of phosphorus, thephosphate absorption coe$cient of andosol is high, sothe phosphorus transport with soil particles was greaterthan the nitrogen transport, associated with surfaceruno!. Consequently, soil conservation measures becomeimportant not only for preventing soil losses but also forwater quality conservation.

Total nitrogen and phosphorus loads in the suspen-sion associated with the typhoon ranged from 20 to 49%and from 35 to 45% of the annual loads, respectively.Also the percentage of nitrogen and phosphorus compo-nents in the solution from plot I was higher than 65% asa proportion of annual term, which was except for am-monium nitrogen of 39)5%. It was concluded that thetyphoon largely a!ected annual nutrient loads.

Acknowledgements

I wish to express my thanks to Dr R.Yasutomi and DrM. Yoh for the discussion during the course of this work.Thanks are also due to Mr T. Ueno, Mr T. Nemoto andMr Y. Saito for their assistance in carrying out theobservation during the typhoon. This study has beensupported by a Grant in Aid for Developmental Scient-i"c Research (12760165) of Japan.

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Gaynor J D; Findlay W I (1995). Soil and phosphorus loss fromconservation and conventional tillage in corn production.Journal of Environmental Quality, 24(4), 734}741

Hach Company (1994). Spectrophotometer Procedure Manual,2.255}2.259, 2.265}2.267, 2.289}2.291. Colorado, USA

Japanese Society of Soil Science and Plant Nutrition (1986).Standard Manual for Soil Analysis, pp 105}107, 130}131 (inJapanese)

Kawaguchi K (1987). Introduction of Soil Science, pp 97}102.Yokendo (in Japanese)

Middleton H E (1930). Properties of soils which in#uence soilerosion. USDA Technical Bulletin, 178, 1}16

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sw—soil and water: nitrogen and phosphorus losses due to soil erosion during a typhoon, japan

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