RSS | Register/註冊 | Log in/登入
Site search:
Home>FFTC Document Database>Extension Bulletins>NITROGEN LEACHING OF THE LONG-GERM CROP ROTATION SYSTEM IN TAIWAN
facebook分享

Chi-Ling Chen1, Chong-Yi Liao1, His-Chia Wu2, Chia-Jen Liu2 ,Horng-Yuh Guo1
1Agricultural Chemistry Division,
Taiwan Agricultural Research Institute,
Taichung 41301, Taiwan

2Farm Management Division,
Taiwan Agricultural Research Institute,
Taichung 41301, Taiwan

ABSTRACT

Appling fertilizers can increase crop yield evidently. However, the surplus nutrient, especially nitrogen not absorbed by plants, may increase its negative impact on the environment. As nitrogen cycling in farmlands is a complex mechanism, in order to realize rational use of fertilizer, there is a need for better understanding of the transformation and leaching of nitrogen. In this study, four different rates of fertilizer conducted in rice and maize cultivation explores the fertilizer use efficiency of different forms of nitrogen, and the effects of nitrogen uptake efficiency with different management practices. In addition, the amount of nitrogen leaching and other nitrogen impacts or pathways in the environment are estimated from eight representative soils of Taiwan by the use of lysimeters designed not to break or disturb soils. The results from the measurement of leachate sampled below one meter of surface soil reveal that nitrogen leaching during the crop growth stage can reach the 20 % of applied nitrogen in some crop; the others are less than 5 % roughly. The extent of nitrogen leaching is similar as the measured data from lysimeters installed in field at long-term ecological research sites. From the investigation of groundwater in some of agricultural regions, there are less 1% and 6% of wells sampled of which NO3-N contents are higher than the limit of second type groundwater pollution monitoring standard (25 mg/l) and drinking water quality standard (10 mg/l). However, the nitrate contamination has been getting gradually serious in some agricultural regions, such as Mingchien area located in head recharge area of Choshui alluvial fan with few mud layers in the geological profile, even the soil texture is clay under heavy rate of fertilization by local farmers.

Keywords: Nitrogen leaching, crop rotation system, lysimeter. 

INTRODUCTION

Appling fertilizers can increase crop yield evidently. Therefore, farmers in the pursuit of yield and lower total cost considerations, often practice excessive fertilization. The surplus nutrient, especially nitrogen which is not absorbed by plants may affect the soil, surface water and groundwater quality.

The nitrogen cycling in farmlands is a complex mechanism. Transformation and transport processes of nitrogen in soil-plant systems include soil fixation, mineralization, immobilization, ammonia volatilization, nitrification, denitrification, plant uptake, runoff and leaching et al. According to the research, the nitrogen application rate is lower than 50% in paddy field and much less in upland than in paddy field and only 11% in vegetable land in Taiwan (Lian et al.1996; Lian and Wang, 1997). It means that more than 50% nitrogen losses to the environment. The transport processes of nitrogen were affected by climate, soil properties, crop, management, irrigation, and fertilizer application (Cameron and Haynes, 1986; Hill, 1991; Aranibar et al., 2004; Zhou et. al., 2006). There are about 10-70% nitrogen uptake by plant, 5-40% by soil fixation, 10-60% by ammonia volatilization and 0-20% by leaching in upland (Mahmood et. al., 1998).

The investigation of the monitoring wells set by EPA and WRA had high percentages exceeded the NH4+-N limit of the second type groundwater pollution monitoring standard (0.25 mg/L) and less than 10% of the monitoring wells which exceeded the NO3-N limit of the second type groundwater pollution monitoring standard (25 mg/L) (Chen et al. 2008).

As nitrogen cycling in farmlands is a complex mechanism, in order to realize rational use of fertilizer, better understanding of the transformation and leaching of nitrogen is needed. In this study, four different rates of fertilizer conducted for rice and corn cultivation was done to explore the fertilizeruse efficiency of different forms of nitrogen. In addition, the amount of nitrogen leaching and other nitrogen impacts or pathways in the environment were estimated from eight representative soils in Taiwan through the use of lysimeters which were designed not to break or disturb soils. The results have been compared with the data from the lysimeter which was installed also in the field.

MATERIALS AND METHOD

Nitrogen uptake of crop under various application rates of fertilizer and manure

The experiments have been conducted in the farmlands of Taiwan Agricultural Research Institute (TARI). The soil properties are enumerated in Table 1. Rice and maize have been cultivated with four levels of nitrogen application of swine manure and chemical fertilizers in 2009 and maize in 2010, separately. The varieties of rice and sweet maize are Tainung 71 and Bau Mi, respectively. The swine manure is sampled from high bed livestock house without flushing. The chemical fertilizers used as straight fertilizer are ammonium sulfate, calcium superphosphate and potassium chloride. P and K of each treatment was supplied with chemical fertilizer to the amount of treatment with the highest fertilization. The nitrogen levels of fertilizer for rice are CK (without N-fertilizer), F1 (50 kg-N /ha), F2 (100 kg-N /ha), F3 (150 kg-N /ha) as basal application and with/without top dressing (25 kg-N/ha) at panical initiation. The nitrogen levels of fertilizer for maize are CK (without N-fertilizer), F1 (80 kg-N /ha), F2 (160 kg-N /ha), F3 (240 kg-N /ha) as basal application. Since the nutrient concentration in manure is variable and the analyzed data is obtained after three days of application, the nitrogen levels of manure are not the same as those of the fertilizer. The plant tissue was sampled at harvest, then dried, ground, digested and analyzed by phenate method (APHA, 1998).

Nitrogen leaching from various soils after manure application - lysimeter study

This study focused on using lysimeter to estimate the nitrogen leaching from various soils after manure application. To make lysimeter without disturbing the soils, a designed cubic meter stainless steel frame has been used to sample the soils. Eight kinds of representative soils have been sampled from different locations in Taiwan. The soil properties of eight representative soils in Taiwan are shown in Table 2. The applied nitrogen rates are 100-140 and 160 kg/ha for rice and maize, separately. The ammonia and nitrate concentration in leachate have been analyzed by phenate method and cadmium reduction method (APHA, 1998). Shuiling, which caused a long-term wet condition, resulting in higher ammonia volatilization.

According to the results of plant analysis, nitrogen distribution in various parts of maize as Fig. 2 Stems and leaves occupied the first place, about 50-60%. Secondly, 40-50% of nitrogen distributed into fruits; around 50-60% nitrogen of fruit was allocated to kernels especially. Comparing non-fertilized treatments of two experimental sites, the yield and nitrogen uptake in Shuilin were higher than those in Wufeng. The better fertility retained from previous crop is the major factor to cause the higher yield in Shuilin. As for fertilized treatments, the highest yield and the highest crop nitrogen uptake, whick were 98.9 and 172 .1 kg/ha respectively, were reached under 160 kgN/ha and 185kgN/ha applications in Wufeng and Shuilin (Fig. 2).

The results reveal the nitrogen uptake by crops is related to soil fertility, decomposition of soil organic matters and growth potential etc. The factors which affect the growth of crop and decomposition of soil organic matter, such as climate, soil and water management etc., also affect the nitrogen uptake of the crop. Therefore, the recommended fertilization should consider and adjust all of the previous discussed factors. In addition, strategies that reduce the nitrogen loss caused by the climatic dramatic change, such as the heavy rainfall should be considered as well.

Nitrogen leaching from various soils after manure application - lysimeter study

In order to understand the pathway and ratio of nitrogen losses from fields to environment, the lysimetric experiments to cultivate rice and maize were conducted at the Taiwan Agricultural Research Institute in 2009 and 2010. Here, manure was applied and data such as nitrogen input, nitrogen uptaked by plants and nitrogen losses including leaching and runoff were all recorded. The rates of leachate and nitrogen leaching are showed as Fig. 3 and 4. The daily leachates from paddy and upland are showed as Fig. 5 and Fig. 6.

Even though paddy had a layer called plow pan, it contained higher water content under continuous irrigation. Compared to upland, lowland (first season, 2009) had higher leachate rate, from 16 to 60% (Fig. 3), and nitrogen leaching rate from 1 to 18% (Fig. 4). The extent of nitrogen leaching is affected by soil texture evidently. Same as sandstone-shale alluvial, both Shenkang and Jente series with fine sand and sandy loam textures have serious water leachate and nitrogen leaching. Oppositely, Chiangchun and Taikang series (Taiwan clay) with fine texture had slower rate of water leachate and lower nitrogen leaching (Fig. 4). As for water leachate rate, higher leachate rate always happened to lowland compared to upland (Fig. 3). It was suspected that the amount of nitrogen leaching was affected by the amount of water leachate. On the other hand, around 8-13% of input nitrogen lostfrom runoff of lowland. Since this lysimetric study was operated in an open space, nitrogen content in the runoff could be influenced by the peripheral environment easily, which will also be discussed.

As the irrigation is limited, the leachate and nitrogen leaching are lower from upland than from lowland roughly as showed Fig.3 - Fig. 6. However, results revealed that in 2010, higher leachate rate (14-33%) and nitrogen leaching can reach to 8% on upland from Pingchen, Chengtsuoliao, and Taikang series with higher clay content. Although the irrigation were not applied, it rained often during the growing stage, leading to times of alternating wet and dry. Under this condition, soil with fine texture got cracked easily so that nitrogen was leached along the slits together with rainfall. Fig. 6 illustrates this situation clearly; one to two days after a heavy rain, water leachate of Chentsuoliao series soil increased evidently.

Based on different field water capacities of different soil textures (Table 4), the available water of one-meter-deep plants in fine sand to clay loam could be about 60-180mm. When taking actual water status of fields into consideration, the highest amount of irrigation, 24-72 mm was recommended when field water capacity was 60%. Since Chentsuoliao series soil is clay loam, leaching should not happen if rainfall or amount of irrigation was lower than 72 mm theoretically. In this study, leaching water of upland could be collected only after continuous rainfall over 70mm (Fig. 6). Additionally, the nitrogen loss from runoff was monitored about 1-4%.

According to the result of this study, it was observed that the yield of rice could still be achieved to more than 3 Mg/ha without any fertilizer applications. The yield from treatment without manure application was about half of that from treatment of manure application. This result indicated that nitrogen supplied by mineralization of soil organic matter was equal to the total nitrogen provided by fertilizer, irrigation and rainfall.

From this results, except for the amount of leaching from sandy soil (Shenkang series) under paddy, which was over 18% of total nitrogen application, the amount of leaching from fine texture soil were even lower than 2%. These results reveal one-meter-deep soil layer could intercept applied nitrogen up to approximately 80%. So, it is predicted that groundwater two meters below topsoil had little risk to be contaminated under recommended fertilization. The risk should lower for groundwater below upland.

An experiment has been conducted to assess the impact of compost, manure and inorganic fertilizer on nitrate leaching and yield using undisturbed drainage lysimeters for a 6-year maize-alfalfa rotation in Michigan (Basso and Ritchie, 2005). The results reveal the highest amount of NO3-N leaching was observed in the treatment with manure, followed by compost, inorganic and control treatments. Moreover, Bakhsh et al. (2005) also indicated that greater nitrate nitrogen leaching occurred under manure application rather than urea or ammoniacal nitrogen fertilizer application in soybean-maize rotation cropping system. In this study, only manure experiments were set because of the equipment limitations. According to the conclusions of previous studies, it was speculated that lower nitrite nitrogen leaching could occurred if application of manure was replaced with synthetic fertilizer. Previous studies mentioned above also emphasized on the relationship among rainfall, irrigation, and nitrate nitrogen leaching. Therefore, besides rational fertilization, water management was important as well.

Nitrogen leaching in field under various cropping systems

The rates of nitrogen leaching from paddy in Chi-Ko branch farm were less than 5 % of total applied nitrogen under both application rates of fertilizer as Table 5. Serious leaching of nitrogen contaminating groundwater can be predicted not to occur under the application rate of 180 kg N/ha/crop on paddy field with silt clay loam. The rates of nitrogen leaching from lowland-upland cropping system are higher than those of double rice cropping system. But they are still among 6-7 %. Comparing to the silt lay loam of Chi-Ko farm, the higher leaching from sandy loam is evident in Yuin-lin farm (Table 6). The rates of nitrogen leaching from lowland-upland cropping system are similar to those of double rice cropping system Yuin-lin farm.

According to the results of lysimeters and field monitoring, the extents of nitrogen leaching are similar between two kinds of measurement from middle soil texture.

Groundwater quality in some agricultural regions in Taiwan

There are two main groundwater monitoring systems in Taiwan, water resources agency (WRA) and Environmental Protection Administration (EPA). The wells of WRA were installed with a depth of 25-300 m to monitor lower aquifer, and wells of EPA were installed with depth of 10-20 m monitor the uppermost aquifer. As for maintaining convenience, the monitoring wells of both networks were installed at school or public organization, hence, monitoring sites might be far from agricultural regions.

To realize the present status of groundwater quality under agricultural region, the main agricultural region in middle and south Taiwan are planned to be investigated. There are over 1100 groundwater samples which have already been collected from Chunghua, Yunlin and Pingtung. The investigation of Chiayi and Tainan are still being conducted.

The result of the investigation shows that about 73% of samples which NH4+-N concentration exceed second type groundwater pollution monitoring standard (0.25 mg/l) in Chunghua, 82% and 29 % of those in Yunlin and Pingtung, respectively. There are only 5 samples (about 0.4% of samples) which NO3-N concentration exceed the second type groundwater pollution monitoring standard (25 mg/l) in three countyies (Table 7 ). As to drinking water quality standard, there are more than 90% of samples which NH4+-N concentration exceed limit (0.1 mg/l) in Chunghua amd Yunlin counties, but less than 5 % of samples which NO3-N concentration exceed limit (10 mg/l). Different from Chunghua amd Yunlin counties, there are about 42% of samples which NH4+-N concentration exceed drinking water quality tandard, but about 11.4% of samples which NO3-N concentration exceed standard.

Among all of the samples, there are about 61% samples which NH4+-N concentration exceeded the limit of the second type groundwater pollution monitoring standards, and about 76% of those exceeded the criteria of the drinking water quality standard. There are only 0.4% of samples which NO3-N exceed the second type groundwater pollution monitoring standard, and about 6% of samples exceed drinking water quality standard. The NH4+-N contaminations in Changhua and Yunlin counties are more serious than that in the Pingtung area.

To better understand the correlation between the nitrogen leaching and soil texture, five classes for soil profile texture of soil management group in soil database established by the agricultural research institute are used in this study. The five classes are defined as follows: 1. fine texture; 2. medium and fine texture; 3. medium and coarse texture; 4. coarse texture; 5. shallow soil layer. However, the correlation is not significant between the nitrogen content NH3-N or NO3-N content in groundwater and classes of soil profile texture in this investigation (Fig. 7). The results reveal that the potential of the NO3-N leaching will increase in sandy soil or shallow soil layer field. Besides, one of the reasons might as well be attributed to the heavy rate of fertilizer used by local farmers. The depth of groundwater layer is also important effect, but the investigation wells of agricultural groundwater which are civil-use well depths of agricultural wells are unknown.

The distribution of inorganic nitrogen in groundwater was illustrated with Fig. 7. Samples from Donggang, Linbian, and Shinyuan three towns that are near the seaside of Pingtung all had higher concentration of NH4+-N. The areas with higher NO3--N contents are located in Zhuoshuixi alluvial fan and the fan top of the Pingtung plain. Because the soil layer of alluvial fan top is shallow and its geology layer belongs to gravel, which lacks clay layer to hinder leachate from the surface, groundwater is easily contaminated by fertilizers and other factors. (Chen and Lu, 2008). There are more than 10 wells were used for tap-water in Mingjian, Nantou. The NO3-N contents of groundwater from some wells increased fiercely from 0.05mg/? in 1980s to 20mg/? or even more recently. According to the survey, groundwater pollution in this case should be resulted from the excessive fertilizer applications (Chang et al., 2002; Chen and Liu, 2003).

In Mingjian, Nantou, main crops such as tea, pineapple, and ginger are planted on the laterite, having high tolerance to acidity. This kind of red soil has high leaching potential so that causes the serious deficiency of nutrient and organic matter. In order to promote the yield and quality of crops, farmers used to apply a lot of manure. Generally speaking, they applied 30-50Mg manure (about 300-500kgN/ha) and mixed with 45cm-deep soil together, then applied top-dress with chemical fertilizer, and maintain the soil wet with spray irrigation. The available nitrogen in soil usually is 40-50 mg/ml here. In addition, soil layer of this area is relative thinner, only 1-2 meters even 30cm. Furthermore, the geology layer belongs to gravel, combination of above factors making the nitrogen easy to leach into groundwater through irrigation and rainfall. Without plants absorption, groundwater would be contaminated easily, especially by NO3--N.

The convenient and low-cost farming ways described above were concluded from farmers' rich experiences. To prevent the NO3--N pollution from being worse, some strategies are suggested, such as increase the times of application with less amount each application, amount control of irrigation and foliar fertilizer is suggested. The rate of application can be decreased more than 50% if foliar fertilizer is applied. However, the inconvenient management and higher cost will be needed if the strategies are applied. Farmers will not accept these strategies unless they replace current ones with economic crops to cultivate.

CONCLUSION

The results of this study reveals the nitrogen uptake efficiency of rice and maize are only around 40 % of applied nitrogen under rational fertilizer application of 150-170 and 160-200 kg N/ha in soil with middle texture in Central Taiwan, respectively. Nevertheless, it was observed that lower uptake efficiency can occur if application of synthetic fertilizer was replaced with manure. The nitrogen loss from leaching is about 20 % of applied nitrogen from sandy soil under paddy and about 10 % from clay soil with slits caused by alternating dry and wet during rainy season. The nitrogen losses from leaching are much lower than 5 % of applied nitrogen from other soil. Because nitrogen is not accumulated in soil, it is speculated that there is more than 50% of applied nitrogen loss to the environment by other fate such as ammonia volatilization, denitrification and runoff etc. The nitrogen loss would be more serious if heavy fertilization is practiced. However, from the investigation of groundwater in some of agricultural regions, there are less 1 % and 6% of wells sampled of which NO3-N contents are higher than the limit of second type groundwater pollution monitoring standard (25 mg/l) and drinking water quality standard (10 mg/l). Nevertheless, the nitrate contamination has been getting gradually higher in some agricultural regions, such as Mingchien area located in head recharge area of Choshui alluvial fan with few mud layers in the geological profile. Even the soil texture is clay under heavy rate of fertilization by local farmers. To prevent the sequential deterioration of groundwater quality, it is recommended to increase the frequency of fertilizer application with less amount for each application. The foliar spreading and water management could also be helpful. However, the cost of application could be increased.

REFERENCE

  • Aranibar, J.N., Otter L., Macko S.A., Feral C.J.W., Epstein H.E., P Dowty.R., Eckardt F., Shugart H.H., and Swap R.J. 2004. Nitrogen cycling in the soil_plant system along a precipitation gradient in the Kalahari sands. Global Change Biology. 10(3): 359-373.
  • American Public Health Association. 1998. American Water Works Association & Water Pollution Control Federation. Standard method for the examination water and wastewater, 20th ed., Method 4500-NO3 -I , pp.4 - 121 ~ 4 - 122, APHA, Washington, DC., USA.
  • American Public Health Association, American. 1998. Water Works Association & Water Pollution Control Federation, Standard Methods for the Examination of Water and Wastewater , 20th ed., Method 4500 - NH3 , pp. 4-103 ~ 4-109, APHA , Washington ,D.C.,USA.
  • Bakhsh A., Kanwar R.S., and Karlen . D.L. 2005. Effects of liquid swine manure applications on NO3_N leaching losses to subsurface drainage water from loamy soils in Iowa. Agriculture, Ecosystems and Environment .109. 118_128.
  • Basso, B. and Ritchie J. T.. 2005. Impact of compost, manure and inorganic fertilizer on nitrate leaching and yield for a 6-year maize-alfalfa rotation in Michigan. Agriculture, Ecosystems and Environment 108:329-341.
  • Cameron, K.C. and Haynes R.J. 1986. Retention and movement of nitrogen in soils. pp.166-241. In: R. J. Haynes et al.(ed.) Mineral nitrogen in the plant-soil system. Academic Pressing.
  • Chen W. F and Liu T. K., 2003. Dissolved oxygen and nitrate of groundwater in Choshui Fan-delta, weatern Taiwan. Env. Geol., Vol. 44, pp. 731-737.
  • Chen C.L., Guo H.G., Chu C.l., Lin C.C., and Huang W. 2008. Nitrogen and Phosphorus Contamination of Groundwater in Some Agricultural Area of Taiwan. Proceedings of Conference on Non-point Pollution from Agriculture. P103-120
  • Chang C.L., Huan R.T., Jian H.B., Hung S. J. and Su J.L. 2002. Denitrification mode testing research of Shinjie water purification plant in Nantou. The eighth international symposium of drinking water quality management and processing technology. pp.3-1~3-29. (In Chinese)
  • Chen W.F. and Lu H.Y. 2008. Nitrate pollution of groundwater in recharge area of alluvial fans, Taiwan. Symposium on non-point pollution from agriculture, p.92-121
  • Hill, M. J. 1991. Origins of nitrate in water. 99.59-76. In: H. Michaell (ed.) Nitrates and nitrites in food and water. Ellis Horwood Ltd.
  • International Atomic Energy Agency. 2008. Field Estimation of Soil Water Content: A Practical Guide to Methods, Instrumentation and Sensor Technology.
  • Lian, S. and Wang C.H. 1997. Measurement and application of available nitrogen on the management of vegetable cultivation. Annual report. Taiwan agricultural research institute.(In Chinese).
  • Lian, S., Wang C.H., and Lee S.C. 1996. Tracing of the labelled urea-N flood-fertigated with different depths of water at knee-high stage under no-till conditions. Jour. Agric. Res. China. 45: 47-56. (In Chinese, with English abstract, figures and tables).
  • Mahmood T., Tahir G..R., Malik K. A. and Shamsi S. R. A. 1998. Denitrification losses from an irrigated sandy-clay loam under a wheat-maize cropping system receiving different fertilizer treatments. Biol Fertil Soils26:35_42.
  • Zhou J.-B., XI J.G., Chen Z.J. and LI S.X. 2006. Leaching and Transformation of Nitrogen Fertilizers in Soil After Application of N with Irrigation: A Soil Column Method. Pedosphere. 16(2):245-252.


Index of Images

  • Fig. 1 (a) Yield ,(b) nitrogen uptake and (c) nitrogen uptake efficiency of rice cultivated with various applied nitrogen on farm at Taiwan Agricultural Research Institute.

    Fig. 1 (a) Yield ,(b) nitrogen uptake and (c) nitrogen uptake efficiency of rice cultivated with various applied nitrogen on farm at Taiwan Agricultural Research Institute.

  • Fig. 2 (a) Yield ,(b) nitrogen uptake and (c) nitrogen uptake efficiency of maize cultivated with various applied nitrogen on farm at Taiwan Agricultural Research Institute.

    Fig. 2 (a) Yield ,(b) nitrogen uptake and (c) nitrogen uptake efficiency of maize cultivated with various applied nitrogen on farm at Taiwan Agricultural Research Institute.

  • Fig. 3 Rate of applied water from leaching from paddy and upland in 2009 and 2010.

    Fig. 3 Rate of applied water from leaching from paddy and upland in 2009 and 2010.

  • Fig. 4 Rate of applied nitrogen from leaching from paddy and upland in 2009 and 2010.

    Fig. 4 Rate of applied nitrogen from leaching from paddy and upland in 2009 and 2010.

  • Fig. 5 Daily rainfall, irrigation and leachate from paddy with soil of Chengtsuoliao series during the first crop of rice in 2009.

    Fig. 5 Daily rainfall, irrigation and leachate from paddy with soil of Chengtsuoliao series during the first crop of rice in 2009.

  • Fig. 6 Daily rainfall, irrigation and leachate from upland with soil of Chengtsuoliao series during the first crop of maize in 2010.

    Fig. 6 Daily rainfall, irrigation and leachate from upland with soil of Chengtsuoliao series during the first crop of maize in 2010.

  • Fig. 7 Nitrogen distribution of groundwater in some of agricultural regions.

    Fig. 7 Nitrogen distribution of groundwater in some of agricultural regions.

  • Table 1 Soil properties and weather condition of experimental fields.

    Table 1 Soil properties and weather condition of experimental fields.

  • Table 2 Soil properties of representative soils.

    Table 2 Soil properties of representative soils.

  • Table 3 Soil properties of the sites of long term ecological research on agricultural ecosystem.

    Table 3 Soil properties of the sites of long term ecological research on agricultural ecosystem.

  • Table 4 Typical field capacity and wilting point values (m3/m3) for different soil textures.

    Table 4 Typical field capacity and wilting point values (m3/m3) for different soil textures.

  • Table 5 The leachate and nitrogen leaching of various cropping system at Chi-Ko branch station.

    Table 5 The leachate and nitrogen leaching of various cropping system at Chi-Ko branch station.

  • Table 6 The leachate and nitrogen leaching of various cropping system at Yuin-Lin branch station.

    Table 6 The leachate and nitrogen leaching of various cropping system at Yuin-Lin branch station.

  • Table 7 Groundwater quality in some of agricultural regions.

    Table 7 Groundwater quality in some of agricultural regions.

Download the PDF. of this document (540), 1,514,042 bytes (1 MB).