Use of Sub-Surface Soil Water in Robusta Coffee Field Through Organic Matter Wicks

Pelita Perkebunan 27(3) 2011, 191-203 soil water in Robusta coffee field through organic matter wicks Use of sub-surface

Use of Sub-Surface Soil Water in Robusta Coffee Field Through Organic Matter Wicks Pemanfaatan Air Tanah Lapisan Bawah di Kebun Kopi Robusta Menggunakan Sumbu Bahan Organik Pujiyanto*1) Summary Coffee trees are susceptible to water strees which occurs during dry season. Coffee production is strongly influenced by actual rainfall a year before crop year and rainfall during crop year. Inadequate water supply during those period would reduced production significantly. To mitigate the negative impacts of water stress, it is justified to find technology for maximum utilization of in-situ available water resources. This research was an effort to optimize soil water reserve in the soil profile. The objective of this study is to evaluate the effectiveness of organic matter wicks to facilitate coffee trees use the soil water reserve in the deeper soil layer. The experiment was carried out on Robusta coffee field of 10 years old located in Kaliwining Experimental Station in Jember District, East Java. The experiment was conducted during four consecutive years. The experiment site is a flat area of Inceptic hapludalf soil family. Organic matter wicks was selected as device to cope retardation problems of water capillary rise and downward growth of coffee roots. The wicks were set up by establishing soil hole(s) at 10 cm diametre through drilling located 10 cm beside coffee trunks. The holes was then filled with organic matter originated from cow dung of 0.313 g/cm 3 bulk density up to the soil surface. The experiment was set according to randomized completely block design with four replications to evaluate the depth of wicks and number of wick holes. Depth of wick was at four levels, namely: 0, 50, 100 and 150 cm, while number of wick holes was at three levels, namely: 1, 2, and 3 holes/tree. Reserch findings revealed that organic matter wicks effectively mitigated negative effect of water stress on coffee. Organic matter wicks at 50–150 cm deeps reduced leaf water deficit and increased soil water content during dry season, increased root density, new node formation and coffee production. The number of wick holes had linear relationship with variables of leaf water deficit and production. Increasing number of holes would reduced leaf water deficit and increased production.

Ringkasan Tanaman kopi tergolong cukup peka terhadap cekaman air yang terjadi selama musim kemarau. Realisasi produksi kopi sangat dipengaruhi oleh curah hujan dalam tahun berjalan dan tahun sebelumnya. Ketidakcukupan suplai air dalam periode tersebut menurunkan produksi secara nyata. Guna mengurangi dampak negatif cekaman air, dipandang perlu untuk memperoleh cara pemanfaatan air tersedia di dalam tanah pada lapisan bawah melalui penggunaan sumbu bahan

Naskah diterima (received) 6 Juni 2011, disetujui (accepted) 24 Agustus 2011. 1) Pusat Penelitian Kopi dan Kakao Indonesia, Jl. PB. Sudirman No. 90, Jember, Indonesia. *) Alamat penulis (Corresponding Author) : [email protected]

PELITA PERKEBUNAN, Volume 27, Nomor 3, Edisi Desember 2011

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organik sampai pada kedalaman air tersedia tersebut. Tujuan penelitian ini adalah untuk mengetahui pengaruh sumbu bahan organik dalam memfasilitasi tanaman kopi memanfaatkan cadangan air tanah pada jeluk yang lebih dalam. Penelitian ini dilaksanakan di kebun kopi Robusta umur 10 tahun yang terletak di Kebun Percobaan Kaliwining, Jember – Jawa Timur. Penelitian dilakukan selama empat tahun berturutturut. Lokasi penelitian merupakan wilayah dataran dengan jenis tanah Inceptic hapludalf. Sumbu bahan organik diharapkan dapat mengatasi masalah hambatan pergerakan kapiler air dari tanah lapisan bawah ke lapisan atas dan memfasilitasi pertumbuhan akar tanaman kopi ke lapisan tanah yang lebih dalam. Sumbu bahan organik dibuat dengan cara membuat lubang bor sampai kedalaman tertentu pada jarak 10 cm dari pokok tanaman kopi dan selanjutnya diisi sampai penuh dengan bahan organik berupa pupuk kandang yang telah matang dengan kerapatan jenis 0,313 g/cm3 . Penelitian ditata menurut rancangan acak kelompok dengan empat tingkat perlakuan kedalaman sumbu bahan organik, yaitu: 0, 50, 100 dan 150 cm dan tiga tingkat perlakuan jumlah lubang sumbu bahan organik, yaitu: 1, 2, dan 3 lubang/pokok tanaman kopi. Masing-masing perlakuan diulang empat kali. Hasil penelitian menunjukkan bahwa sumbu bahan organik efektif mengurangi dampak negatif cekaman air pada tanaman kopi. Sumbu bahan organik sampai kedalaman 50 - 150 cm menurunkan defisit kejenuhan air daun kopi selama musim kemarau, meningkatkan kadar air tanah, meningkatkan kepadatan akar, meningkatkan pembentukan buku baru, meningkatkan jumlah buah kopi, dan meningkatkan produksi kopi. Jumlah lubang sumbu bahan organik per pokok tanaman kopi menurunkan defisit kejenuhan air daun dan meningkatkan produksi biji kopi. Key words:

Soil water, organic matter wick, water stress mitigation, Robusta coffee (Coffea canephora).

INTRODUCTION During the last decade, it was noticed a trend of deminishing coffee yield of the existing Robusta coffee in several production center in Indonesia. It was supposed due to degradation of environment qualities induced by over-exploitation, either within the coffee farm or area surrounding the farm. Land degradation was remarkably noticed by reduction of soil capacity to supply water and nutrients for the crops. To achieve high yield, it had been applied for decades an intensive crop management by application of high external inputs, especially in large coffee farms. External inputs, such as pesticides and inorganic fertilizers giving rise to greater nutrient losses from soil. Due to steady increase of inputs leading to profit mar-

gin reduction, coffee growers have to adopt low external inputs technology and rely most on in-situ organic inputs, such as farmyard manures and composts. To cope degradation problems of coffee farms, implementation of sustainable coffee management is inevitable. Coffee trees are susceptible to water stress which occurs during prolong dry season. During water stress period, several visible symtoms can be observed, inisiated by leaf wilting followed by leaf fall. At more severe stress, flowers, shoots and juvenile fruits was shed. Water stress reduce harvested crops in the on going year and the next following year. It may extent to the next several following years due to slow vegetative recovery which may occured for several years. During severe


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Use of sub-surface soil water in Robusta coffee field through organic matter wicks

prolong dry season in 1982, Robusta coffee production in Java deminished up to 27% and caused 31.6% death of immature plants (Soerotani & Soenardjan, 1983). To mitigate negative impacts of water stress, it is justified to find method for maximum utilization of in-situ available soil water. During dry season, water content in the uppermost soil layer (0—20 cm deep) droped up to permanent wilting point, meanwhile in the subsurface layer (more than 100 cm deep) of soil in flat area was still saturated with water. At this condition, coffee trees in the field had showed wilting symtoms followed by leaf fall (Pujiyanto, 1994). Firstly, it is due to incapability of coffee roots to utilize available water in deeper soil layer. Most feeder roots of coffee are distributed at the first 40 cm soil deep (Nur et al., 2000). Therefore, the roots do not have capability to absorb water from deeper soil. Secondly, soil profile is consisted of several layers leading to uncontinuous capillary pores which impair upward capillary movement of water. Different composition and texture of each soil layer may stop capilary rise of water. This research is an effort to optimize in-situ soil moisture reserve located in deeper soil layers to minimize yield loss of cofffee due to water stress during dry season. The objective of this study is to evaluate the effectiveness of organic matter wicks to facilitate coffee trees use the soil water reserve in the deeper soil layer.

MATERIAL AND METHOD The experiment was carried out on Robusta coffee field of 10 years old located in Kaliwining Experimental Station in Jember District, East Java province. The experiment was conducted during four consecutive years. The experiment site was

a flat area of Inceptic hapludalf soil family. The clay fraction in the experiment site was classified as superactive haloisitic clay. Sand fraction was dominated by plagioclas and volcanic class. Soil temperature regime of the study area is isohypertermic. Soil analyses indicated that C content is 1.64%, N of 0.25%, available P of 36 ppm, K of 1.49 cmolc/kg, Na of 0.9 cmolc /kg, Ca of 19.97 cmolc / kg, Mg of 4.73 cmolc /kg, CEC of 28.86 cmolc /kg, pH of 6.3. Physical analyses indicated sand content of 13%, silt of 57% and clay of 30%. Rainfall type of the study area is C, average rainfall of 1855 mm/year, average temperature of 25.9 O C, humidity of 82.8% and wind speed of 0.8 km/hour. The experiment was set factorially according to randomized completely block design with four replications to evaluate application depth of organic matter wicks and number of wick holes. Organic matter wicks were establised by setting up holes through soil drilling at 10 cm distance from coffee trunk followed by organic matter filling. The holes were made by using soil driller of 10 cm diameter. The holes was then filled with organic matter up to the soil surface. Dry cowdung of 0.313 g/cm 3 bulk density was used as wick filler. Depth of organic matter wicks was evaluated at four levels, namely: 0, 50, 100 and 150 cm, while number of wick holes was at three levels, namely: 1, 2, and 3 holes/tree. Variables of plant growths and soil characteristics were observed periodically, namely: leaf water content, number of new shoot, coffee production, root density, and soil water content. Leaf sample for determination of water content was taken at the third leaf from the tip during dry season. From every tree sample was taken 8 leaves. Relative water content was cal-


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culated based on the different between leaf water content at field condition and the water content at saturated condition. Coffee production was calculated based on number of coffee cherries and their outturn. Root density was determined by weighing coffee roots in a certain volume of soil sample. The soil samples were derived from 10 cm distance from the trunk at 0–10 cm and 10–20 cm soil deep. Soil water content was determined by oven method at 105OC. The roots in the soil sample were seperated from soil media. The roots were determined their fresh weight and dry weight by oven method at 70OC.

RESULT AND DISCUSSION Leaf water deficit Leaf water deficit illustrates real time water status in coffee trees in response to soil water condition. Therefore, leaf water deficit could be used as variable for the water status in plant. Based on observation during dry season for four consecutive years in the field, there was an indication of better water status in coffee leaves due to organic matter wicks. Figure 1 indicated that leaf water deficit declined as the depth organic matter wicks increased. The deeper the organic matter wicks, the better their leaf water status. Average leaf water deficit at wick depths of 0, 50, 100 and 150 cm were 32%, 27%, 25%, and 23% respectively. At wick depth of 150 cm, organic matter wicks reduced leaf water deficit 28% compared to the control treatment. It was supposed due to better water absortion from the soil profile of the coffee trees. Firstly, the organic matter wicks increased soil water reserve around the wicks, either directly and indirectly. Organic matter has high water

holding capacity. According to Oades (1984) the capacity of organic matter to retain water is up to 20 times their weight, while soil particles are much less. Secondly, organic matter wicks improved soil aggregation and stabilization of aggregates leading to stabilization of macro and meso soil pores (Pujiyanto et al., 2003) in which most available water retained in the soil profile. Organic matter with larger C/N ratio is more stable against microbial decay (Scheel et al., 2007), therefore it will have longer effect on aggregate stabilization. Better soil aggregation enable coffee trees to absorb more quantity of water. Froberg et al. (2007) indicated that transport of the added organic matter was small, therefore addition of organic matter did not have a major impact on deeper soil layers. To ameliorate deeper soil layer, the organic matter should be incorporated in deeper layer as well. Veenstra et al. (2007) indicated the important of organic matter addition for carbon accumulation in soil of arable land. Feeder roots of Robusta coffee were predominantly (63%) distributed in the uppermost soil layer of 0–20 cm deep, and less than 17% were distributed in the soil layer of more than 40 cm soil deep (Nur et al., 2000). Soil water which was retained in the macro and meso soil pores is readily accesible for plant roots. While soil water in the micro pores is mostly not available for plants. The increasing water absorbtion due to better soil pores may be considered as indirect effect of organic matter application on soil water status. Visual observation indicated that the better water status of coffee plants was also an effect of the increasing absorbtion area of roots due to increasing root growth, especially on area at the surrounding organic matter.


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4040

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Leaf water deficit, % Defisit kejenuhan air daun, %

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Figure 1.

3rd year

2nd year 2nd ke-2 year Th.

1st Th. year ke-1

4th year 4th year Th. ke-4

3rd Th. year ke-3

Relationship between depth of organic matter wicks and average of leaf water deficit of Robusta coffee during four consecutive dry seasons.

Gambar 1. Hubungan antara kedalaman sumbu bahan organik dengan defisit kejenuhan air daun kopi Robusta selama empat masa musim kering.

40

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Leaf water deficit, % Defisit kejenuhan air daun, %

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a No hole (Tanpa lubang)

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55 00

Figure 2.

1st year Th. ke-1

2nd year Th. ke-2

3rd year Th. ke-3

4th year Th. ke-4

Relationship between number of holes of organic matter wicks and average of leaf water deficit of Robusta coffee during four consecutive dry seasons.

Gambar 2. Hubungan antara jumlah lubang sumbu bahan organik dengan defisit kejenuhan air daun kopi Robusta selama empat empat masa musim kering.


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The effect of number of wick holes was similar with the effect of wick depth (Figure 2). The increasing number of wick holes implied the icreasing rates of applied organic matter. The higher organic matter application rates, the more bulk soil media ameliorated, and the more water reserve available in the soil.

Soil water content Sampling for soil water determination was taken from soil profile of 0-20 cm deeps. Figure 3 indicated that water content during dry season at the organic matter treated soil samples were higher than the control treatment with no organic matter.

Soil water content during dry season, % Kadar air tanah selama musim kemarau, %

3535

a

3030 2525

y = -0,000 X2 + 0,068 X + 24,12 Y=-0.000x +0.068x+24.12 = 0,991** RR² =0.991** 2

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Soil water content during dry season, % Kadar air tanah selama musim kemarau, %

Kedalaman sumbu bahan organik, cm

3535 b

3030 2525

+4x+24.3 y Y=-0.9x = -0,9 X2 + 4 X + 24,3 R =0.983** R² = 0,983** 2

2

2020 1515 1010 55 00 0

0 Figure 3.

1

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Number of holes of organic matter wicks Jumlah lubang sumbu bahan organik

3

3

Relationship between (a) depth of organic matter wicks and (b) number of wick holes and soil water content during four consecutive dry seasons.

Gambar 3. Hubungan antara (a) kedalaman sumbu bahan organik dan (b) jumlah lubang sumbu dengan kadar air tanah selama empat masa musim kering.


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Average soil water content at organic matter wicks of 0, 50, 100 and 150 cm deeps were 24.2%, 26.7%, 28.8%, and 28.9% respectively. Among the treated soil, there was no significant different among application depth of organic matter wicks (Figure 3a). The same case was also valid for the effect of wick-hole number, among the three evaluated hole number indicated no significant different (Figure 3b). The soil samples on the treated soil of organic matter wick were a mixture of soil particles and organic matter, that have comparable composition among them. Therefore they have comparable water holding capacity. It was not the case on the untreated soil, due the absence of added organic matter, the water retention capacity was merely determined by soil particles which was lower than that of organic matter treated soil. The increment of water retention capacity was quite important for the survival of coffee plants. It reduced water stress on the plants which will

affect to less severe adaptation of plant physiology during dry season period. During water stress, plants adapted by reducing water evapotranspiration rate through stomatal enclosure.

Root density Root density was calculated based on root-biomass determination in the soil samples. Observation during four cosecutive years indicated that organic matter wicks increased root biomass around the wick site. Average roots biomass for non-treated soil was 40.1 mg/g soil, while in the treated soil samples was 109.8 mg/g soil. Higher root density and root biomass was due to accelerated root proliferation around the applied organic matter. Organic matter made available more nutrient and induced favour chemical and physical soil properties (Pujiyanto et al., 2004). Better soil properties may stimulate better biological activities in the

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Root density, mg/g soil Kepadatan akar, mg/g tanah

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100 +110.5x-52.5 Y = -17,5 X2Y=-17.5x + 110,5 X - 52,5 R =0.998** R² = 0,998** 2

80

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Depth of organic matter wicks, cm Kedalaman sumbu bahan organik, cm

Figure 4.

Relationship between depth of organic matter wicks and average root density of Robusta coffee.

Gambar 4. Hubungan antara kedalaman sumbu bahan organik dengan kepadatan akar kopi Robusta.


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soil. The positive effect of organic matter was due to improvement of the soil media related to their physical, and chemical characteristics; especially improvement of available water and nutrients derived from decomposition of organic matter.The beneficial effect of organic matter application on plant growth have been demontrated by many researchers (Baon & Soenarjo, 1983; Cobo et al., 2002a; Cobo et al., 2002b; Erich et al., 2003; Salas et al., 2003).

Amelioration of the soil properties stimulated root growth, especially within the zone of organic-matter affected area in which all the necessary inputs for root growth (nutrient, water and air) were readily available. Among the tree evaluated depth of organic matter wicks, the root biomass were camparable. The soil samples were taken from around the wicks holes. Therefore, the composition of the soil samples were similar, giving rise to the similar effect on root growth. Beside

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a

Number of new nodes, tree Jumlah buku baru, tanaman

140 120 Y=0.2732x+94.742

100

Y = 0.2732 X + 94.742R˛=0.7824* R² = 0.7824* Y =R˛0.2732x+94.742 = 0.7824*

80 60 40 20 0 0

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Depth of organic matter wicks, cm Kedalaman sumbu bahan organik, cm 160

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Number of new nodes, tree Jumlah buku baru, tanaman

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Y = 0.2732 X + 94.742 Y=13.6x+95.1 R² = 0.7824*R˛=0.7799*

80 60 40 20 0 0

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Number of holes of organic matter wicks Jumlah lubang sumbu bahan organik

Figure 5.

Relationship between (a) depth of organic matter wicks and (b) number of wick holes and average number of new nodes of Robusta coffee during four consecutive dry seasons.

Gambar 5. Hubungan antara (a) kedalaman sumbu bahan organik dan (b) jumlah sumbu bahan organik dengan rata-rata jumlah buku baru tanaman kopi Robusta selama empat masa musim kering.


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induced favourable soil condition and made available nutrients, organic matter application would increase phytohormones which was assumed produced by microorganisms (Pujiyanto et al., 2004). The presence of the hormones within soil aggregates was presumably affected roots growth.

Formation of New Nodes Production of Robusta coffee is related directly with formation of new nodes at one year before the crop year. The cherries are set only on new nodes. Nodes which had cherries in previous year are hardly bearing cherries in the following years. Therefore, vegetative growth rate to form new nodes during a certain year is decissive for production in the following year. Figure 6 showed that the increased depth of organic matter wicks lineary correlated with number of newformed nodes. The deeper the organic matter wicks, the more nodes will be formed. The new-formed nodes on treatment of organic matter wick up to 150 cm deep was 143.6 nodes/tree, while on the control treatment was only 102.4 nodes/ tree. Wick of organic matter increased new-formed nodes by 40%. Higher new nodes formation was due to the better soil qualities, in term of nutrients and water supply, and growth condition as well. Growth acceleration of coffee trees that was indicated by higher number of new nodes was a resultant of improvement effect on soil-media; not only on their chemical properties but also on their physical and biological properties. Pujiyanto et al. (2003) reported better aggregate stability due to organic matter application. Annabi et al. (2007) showed the increasing water repellency within the aggregates as an indicator for better stability. Frac-

tion of organic matter that responsible for aggregate stability was associated with the biochemical characteristics of the organic products such as water-extractable polysaccharide, cellulose and hemicellulose, and lignin contents (Abiven et al., 2008). Nutrients derived from organic matter will be taken up by coffee roots to boost growth. Organic matter had much higher CEC than bulk soil. Higher CEC values of the media indicated higher capability to retain and to supply nutrients (Pujiyanto, 2007). Therefore, much more nutrients especially cations, can be retained in the soil and will avoid losses by leaching. The retained nutrients gradually can be absorbed by plant roots through exchange processes. Following decomposition of the organic matter, nutrients and organic acids will be released to soil solution. The nutrients will be available for plants, while the organic acids may favour better condition for coffee growth. Research findings showed that organic acids capable to increase solubility of Cu & Zn (Wu et al., 2002), and reduced aluminum toxicity (Hu et al., 1985) which eventually may be absorbed by coffee roots.

Number of Cherries Figure 8 showed relationship between depth of organic matter wicks and number of coffee cherries during four consecutive crop years. The number of coffee cherries increased lineary as the increassed of wick depth of organic matter. It is imply that the deeper the wick depth, the better the soil support for coffee. The applied organic matter in the wicks would undergo decomposition gradually so that the volume would deminished. The former space for organic matter would be replaced gradually by nearby soil particles from the wick wall to form continu-


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Number of coffee cheries per tree Jumlah buah per pohon

Pujiyanto

a

1500 1200 900 = 3,466x+ 710,2 + 710,2 y =y 3,466x = 0,924 R²R˛ = 0,924

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Depth of organic matter wicks, cm Kedalaman sumbu bahan organik, cm Number of coffee cheries per tree Jumlah buah per pohon

b 1500 1200 900

y = 228,9x + 597,4 y =R² 228,9x + 597,4 = 0,919* R˛ = 0,919*

600 300 0 0 0

Figure 6.

1 2 1 2 Number of holes of organic matter wicks Jumlah lubang sumbu bahan organik

3 3

Relationship between (a) depth of organic matter wicks and (b) number of wick holes and average number of coffee cherries of Robusta coffee during four consecutive dry seasons.

Gambar 6. Hubungan antara (a) kedalaman sumbu bahan organik dan (b) jumlah sumbu bahan organik dengan rata-rata jumlah buah tanaman kopi Robusta selama empat masa musim kering.

ous capilers from the bottom of the wicks up to soil surface. Induced by activity of roots and soil organisms, the mixture of organic matter and soil particles will form stable aggregates (Oades, 1984) that may stabilize capillary network in the wicks. Therefore, barrier for capillary rise of water from deeper soil layer would be deminished significantly, leading to ease water supply for cofffee roots. Area within the wicks also have lower bulk density than that of bulk soil. Therefore, root penetration within the wicks would be easier which was indicated by higher root density than

in the bulk soil as indicated by this finding in Figure 4. Beside their better physical conditions, area within and around the wicks of organic matter would be better in term of chemical and biological condition. The area contained more soil nutrients which were originated either from inorganic fertilizers and mineralization of organic matter. The positive effect of organic matter application was due to improvement of the soil media related to their physical, chemical and biological characteristics; especially improvement of available


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water and nutrients derived from decomposition of organic matter.The beneficial effect of organic matter application on plant growth have been demonstrated by several researchers. Haron (2003) pointed out better soil status and oil palm respons due to combined application of organic and inorganic fertilizers, while Lorion (2004) indicated that yield of potato from organic fertilizer system were comparable with synthetic inorganic fertilizers. Previous research findings also indicated that organic matter application stimulated better soil characteristics for plant growth, namely: increased CEC and nitrogen content (Sudarsono, 1991; TirolPadre et al., 2007), increas available soilP (Laboski & Lamb, 2003), exchangable soil-K, exchangable Ca, Mg, K and Na (Situmorang, 1999), soil-pH (Irianto et al., 1993), and reduced exchangable aluminum and ferrum leading to reduction soil toxicity (Situmorang, 1999), decresed permanently fixed phosphorus by soil clay (Zhang & MacKenzie, 1997), increased content of BAP and IBA hormones in the soil (Pujiyanto et al., 2003), and increased transport of chemicals in soil solution (Heitman et al., 2007). The improvement on physical properties of the media was occured especially on the increased of water retention. Organic matter have much higher water retention compared to bulk soil. Organic matter application increased total water retention of the media. Pujiyanto et al., (2003) indicated that organic matter application significantly increased size of soil aggregates and percentage of stable soil aggregates. Organic matter acted as binding agents among soil component (sand, silt and clay fraction) to form aggregates. Organic matter may also acted as binding agent among soil agregates to form bigger and more stable aggregates (Oades,

1993). Organic matter may increase meso and macro pores, leading to improvement of soil porosity, aeration, permeability and rate of water infiltration. Organic fractions played the most important role for soil aggregate stabilization. Organic matter fractions also played an important role for biologycal soil improvement acted as energy sources for soil organisms. Activity of the soil organisms induced formation and stabilization of aggregates.

CONCLUSIONS 1. Organic matter wicks effectively reduced negative effect of water stress on coffee. Organic matter wicks at 50–150 cm deeps reduced leaf water deficit, increased new node formation and increased coffee production. 2. Best result was achieved at wick depth of 150 cm. The number of wick holes had linear relationship with variables of leaf water deficit and production. Increasing number of wick holes would reduced leaf water deficit and increased production. REFERENCES Abiven, S.; S. Menasseri; A.A. Angers & P. Leterme (2008). A Model to Predict Soil Aggregate Stability Dynamics following Organic Residue Incorporation under Field Conditions. Soil Sci. Soc. Amer. Journal, 71, 413– 423. Annabi, M.; S. Houot; C. Francou; M. Poitrenaud & Y. Le Bissonnais (2007). Soil Aggregate Stability Improvement with Urban Composts of Different Maturities. Soil Sci. Soc. Amer. Journal, 71, 413–423. Baon, J.B. & Soenaryo (1989). Penggunaan belotong sebagai sumber bahan organik untuk kopi dan kakao. II.


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Use of Sub-Surface Soil Water in Robusta Coffee Field Through Organic Matter Wicks

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