Abstract

Key Words

Soil erosion, Water balance, Soil texture, Crop management

Introduction

The topography of the land in Korea consists of approximately 65% mountainous terrain. Uplands are distributed widely in valleys, alluvial fans, mountain foot slopes, hills, and mountainous areas, and are mainly located in areas with a slope above 2 %, which can result in accelerated soil erosion. In Korea, average rainfall for 30 years (1971-2000) is 1,310mm, which mostly occur in summer so that there is a potential for soil erosion and nutrient loss on upland on hillslope in the early rainy season because of incomplete coverage of the soil surface. Damages by soil loss lead to a decrease of productivity by arable land loss (Jung et al. 1998, Lee et al. 1998) and burying of waterways or reservoirs by sedimentation of lost soil (Oh et al. 1995, Kim et al. 2003) and river pollution induced by nutrients loss (Kim et al. 1997, Jung et al. 1998, Jung et al. 2000). An appropriate crop management to reduce soil and nutrients loss is a main key for land conservation and non-point pollution management so that agricultural practice methods for soil erosion control have to be developed. But, the control of soil erosion is not easy because it appears differently with rainfall intensity, cultivation period and season of crop, ground coverage, surface roughness and soil water content. Therefore, this study was carried out to assess the effect of soil texture and crop on soil erosion and nutrient loss from arable land using lysimeter during rainfall.

Methods

This study was carried out in NIAST (National Institute of Agricultural Science & Technology) in Suwon, located in middle part of Korea. The site has lysimeters constructed with L, SL, CL soils, with 15% gradient, 5m length, 2m width and 1m depth. Crops grown were maize and peanut with three replicates and bare soil is used as control treatment. The runoff and sedimentation tank for measurement of runoff, percolation, soil and nutrient loss was made, and rainfall gauge (Model 260-2501, NovaLynx Corp., USA) was set up for measurement of precipitation. FDR sensors (Model EnviroSCAN, Sentek Sensor Tech., Australia) were installed for soil water content and the other weather data were obtained from weather station. 500 mL of outflow water from sedimentation tank was and filtered for analysis. Nitrate was determined by distillation method, phosphorous by Lancaster method, and cations by ICP (GBC Integra XMP, Australia). Soil loss was measured by dry soil weighting method after 500mL～1L of outflow water filtered. Soil characteristics of experimental field are shown in Table 1. Fertiliser applications for maize were (N-P-K) 343-285-313 ㎏ ha^-1, for peanut were 280-193-258 ㎏ ha^-1, . An component quantity(N-P-K) of compost for bare soil were 170-20-148 ㎏ ha^-1 .

Table 1. Characteristics of experimental field

Results

  The annual rainfall during experiment period was 1146.9mm, and 76% (874.4mm) of the rainfall was received from July to September. Annual erosion indices (EI₃₀) expressing soil erosion factor showed also values focused on July to September as 263(83%). Erosion index in Table 2 used data above 12.7mm per one rainfall event in this study. If there was no rainfall event longer than 6 hours, the precipitation was calculated as one rainfall event. Soil erosion factors were estimated from Nomograph developed by Wischmeir (1981).

Table 2. Erosion index by monthly and annual rainfall characteristics

Effect of soil texture on runoff, drainage, water balance and soil loss by rainfall are shown in Table 3.. Total precipitation to occurrence period of runoff was 956.3mm. In the case of quantity of outflow water, bare soil was 30% more than cultivation area on all soil texture so that soil loss from crop cultivation area existed hardly but soil loss depths of bare soil were 1.37mm on SL, 3.73mm on L and 4.97mm on L soil. This implies that crop cultivation has an advantage in reducing runoff and soil loss.

Table 3. Effect of soil texture on runoff, drainage, water balance and soil loss
(Unit: ton ha^-1)

ET : Evapotranspiration  CSW: Change of soil water content  RE : Rainfall excess(including interception)

Nutrients loss by soil texture and crops are shown in Table 4. Nutrients loss from bare soil were entirely heavier than cultivation area. When maize was compared with peanut, nutrients loss of upland with maize were more than those of peanut on SL and CL soil, but those of peanut cultivation area was bigger than maize on L soil. SL was more than CL and L in the case of nutrients loss on maize cultivation area. Nutrients loss of L was more than those of CL and SL on peanut cultivation area. The order of nutrient loss on bare soil was CL>L>SL.

Table 4. Aspect of soil loss by each soil texture and crop

Conclusion

Crop cultivation reduced runoff during rainfall and the runoff decrease on SL soil with peanut cultivation was far superior than on other soil texture and crop. Crop with great ground coverage had an advantage for decrease of soil loss and runoff. The quantity of drainage water of CL bare soil was similar to cultivation area on CL soil because electronic characteristics of clay and soil pore filled by very small size particles suppress drainage of rainfall. Nutrients loss on bare soil during high rainfall was two times bigger than soil with crops cultivation so that there was a high potential for nutrient contamination of rivers or streams. Therefore, agricultural practices avoiding bare soil situation during rainfall is recommended for arable land. The total nutrients loss from soil growing peanut on L and CL soil was similar to that of maize except for SL soil with peanut. Therefore, cultivating peanut on SL soil will result in lower nutrient loss than cultivating maize, thus reducing nutrient pollution of rivers or streams. However, nutrients loss from L or CL soil showed similar trends. Consequently, crop cultivation having high ground cover during rainfall is a recommended agricultural practice to reduce runoff, soil and nutrient loss.

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