RESPONSE OF CASSAVA (Manihot esculenta crantz.) TO POTASSIUM ON ACIDIC DRY LAND IN INDONESIA

PROJECT REPORT

RESPONSE OF CASSAVA (Manihot esculenta crantz.) TO POTASSIUM ON ACIDIC DRY LAND IN INDONESIA Abdullah Taufiq, Subandi and Suyamto

COLLABORATIVE PROJECT BETWEEN INDONESIAN LEGUMES AND TUBER CROPS RESEARCH INSTIRUTE (ILETRI) AND BELARUSIAN POTASH COMPANY (BPC)

Indonesian Legumes and Tuber Crops Research Institute (ILETRI) Jl. Raya Kendalpayak km 8, PO Box 66 Malang 65101 East Java – Indonesia www.balitkabi.litbang.deptan.go.id; e-mail: [email protected]

2013

EXECUTIVE SUMMARY Cassava in Indonesia is mainly cultivated on dry land as monocrop or intercropped with upland rice or palawija crops (maize, groundnut). During the last ten years (2000-2011), cassava harvested area reduced by 7.7% but yield increased by 62.4%. Due to multiple end-uses of cassava, the demand as well as the price of this crop tends to increase. This situation encouraged farmer to increase productivity by planting higher yielding variety and improving crop management practices. Lampung is the largest cassava producers in Indonesia that contributed 26.3% of the national area. Majority of cassava in this region is planted as monocrop. Soil in this region dominated by acidic soil of Ultisol and Oxisol with very low soil fertility, very erosive and so that nutrient, especially K, rapidly goes down. Therefore, potassium may become an important role to improve production. Objectives of the research were to find out the response of cassava to potassium application on dry land, to show and communicate the role of potassium and to deliver a reference to control potassium deficiency on cassava to farmers and extension workers, and to create awareness to them on balanced- nutrient management and cost and benefit ratio analysis. The field trial had been conducted in farmer’s field at Sukadana Ilir Village, Sukadana Subdistrict, East Lampung District (5o2’38.63” S, 105o32’27.98” E; 46 m above sea level) and at Restubaru Village, Rumbia Subdistrict, Central Lampung District (4o46’15.30” S, 105o34’12.40” E; 47 m above sea level), Lampung Province, Indonesia from November 2012 to June 2013 (7 months). The experiment consisted of seven treatments that were laid out in a randomized complete block design, and replicated three times. The treatment consisted of six rates of K fertilizer (0, 30, 60, 90, 120 and 180 kg K2O/ha), and one farmers’ practice. All potassium fertilizer treatments were combined with 135 kg N/ha and 36 kg P2O5/ha, except one treatment with 200 kg N/ha and 60 kg P2O5/ha. Urea (46% N), SP36 (36 kg P2O5), and KCl (60% K2O) use as source of N, P, and K fertilizer respectively. Soil at the experimental site had a sandy loam to clay loam texture, acidic, low organic-C content, medium to high available P, and very low exchangeable K (0.05-0.09 me/100 g soil). Cassava of c.v UJ3 or UJ5 was planted on highly population density (28,500-33,000 plants/ha) and it harvested on 7 months after planting. Result showed that potasium (K) fertilizer dosage of 30-60 kg K2O/ha was optimum for cassava grown on acidic soil with very low exchangeable soil K. This K dosage improved vegetative growth of cassava as indicated by improvement of plant height, dry weight of stem and leaf. The K fertilizer at 30 to 60 kg K2O/ha increased fresh tuber weight by 9-47% compared to control, and increased starch content by 7-14% (wet basis). Agronomic effeciency (AE) from application of 30-60 kg K2O/ha was 83-207 kg FTY/kg K2O (FTY=fresh tuber yield). Application of 30 to 60 kg K2O/ha was economically feasible as indicated by benefit to cost ratio of 12-17. Farmers usually sell as fresh tuber,

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so that application of 30-60 kg K2O/ha is suggested as it will provide more yield and more income. It can be concluded that potassium fertilization has important role in increasing cassava yield grown on acidic dry land with very low soil potassium status. The optimum K dosage in this agroecology was 30-60 kg K2O/ha depending on variety. Potassium fertilization improved tuber quality as indicated by increasing starch content.

Keywords: potassium, cassava, acidic dryland, Indonesia

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TABLE OF CONTENTS

EXECUTIVE SUMMARY .................................................................................. 2 TABLE OF CONTENTS ................................................................................... 4 LIST OF TABLES ........................................................................................... 5 LIST OF FIGURES ......................................................................................... 6 LIST OF APPENDIX ....................................................................................... 6 INTRODUCTION ........................................................................................... 7 ObjectiveS ........................................................................................... 9 Material and Method ............................................................................. 9 Location and Planting Date ................................................................... 9 Experimental set up .............................................................................. 9 Implementation .................................................................................. 10 RESULT AND DISCUSSION .......................................................................... 11 Soil Characteristics ............................................................................. 11 Crops Growth ..................................................................................... 13 Tuber (storage roots) yield.................................................................. 17 Agronomic and Economic Efficiency ..................................................... 18 K and Starch Content .......................................................................... 20 CONCLUSION ............................................................................................. 22 ACKNOWLEDGMENT ................................................................................... 22 REFERENCES ............................................................................................. 22 APPENDIX .................................................................................................. 24

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LIST OF TABLES

Table 1. The details of the treatment combinations between N, P and K fertilizer. ....................................................................................... 10 Table 2. Soil characteristis of the experimental site at Sukadana and Rumbia. ........................................................................................ 12 Table 3. Effect of potassium (K) fertilization on available K in the top soil layer (0-20 cm) at harvest. Lampung, 2012-2013. ........................... 13 Table 4. Efect of potassium fertilization on above ground biomass of cassava at Sukadana and Rumbia. Lampung, 2012-2013.................. 16 Table 5. Efect of potassium fertilization on tuber yield and harvest index of cassava of UJ3 variety at Sukadana site. East Lampung, 20122013. ............................................................................................ 17 Table 6. Efect of potassium fertilization on tuber yield and harvest index of cassava of UJ5 variety at Rumbia site. Central Lampung, 20122013. ............................................................................................ 18 Table 7. Agronomic efficiency of potassium fertilization on cassava at Sukadana and Rumbia sites. Lampung Province, 2012-2013. ............ 19 Table 8. Simple economic analysis of potassium fertilization on cassava at Sukadana site. East Lampung, 2012-2013. ...................................... 19 Table 9. Simple economic analysis of potassium fertilization on cassava at Rumbia site. Central Lampung, 2012-2013. ..................................... 20 Table 10. Effect of K fertilization on K content of tuber, leaf, and starch content of tuber at harvest. Sukadana - East Lampung, 20122013. ............................................................................................ 20 Table 11. Effect of K fertilization on K content of tuber, leaf, and starch content of tuber at harvest. Rumbia - Central Lampung, 20122013. ............................................................................................ 21 Table 12. Simple correlation among K fertilization, K content of tuber, leaf, stem, and starch content of tuber at harvest. Rumbia, 2012-2013. ... 21 Table 13. Simple correlation among K fertilization, K content of tuber, leaf, stem, and starch content of tuber at harvest. Sukadana, 20122013. ............................................................................................ 21

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LIST OF FIGURES

Figure 1. Efect of N, P and K fertilization on plant height of cassava of UJ3 variety at Sukadana, East Lampung during planting season of 2012-2013..................................................................................... 14 Figure 2. Efect of N, P and K fertilization on plant height of cassava of UJ5 variety at Rumbia, Central Lampung during planting season of 2012-2013..................................................................................... 15

APPENDIX

Appendix 1. Efect of potassium fertilization on plant height of cassava of UJ3 variety at Sukadana site. East Lampung, 2012-2013. ................. 24 Appendix 2. Efect of potassium fertilization on plant height of cassava of UJ5 variety at Rumbia site. Central Lampung, 2012-2013. ................ 25

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RESPONSE OF CASSAVA (Manihot esculenta crantz.) TO POTASSIUM ON ACIDIC DRY LAND IN INDONESIA Abdullah Taufiq, Subandi, and Suyamto Indonesian Legumes and Tuber Crops Research Institute

Jl. Raya Kendalpayak km 8, PO Box 66 Malang 65101 East Java - Indonesia www.balitkabi.litbang.deptan.go.id; e-mail: [email protected]

INTRODUCTION Indonesia is the fourth cassava producers in the world after Nigeria, Brazil, and Thailand. BPS data (http://www.bps.go.id) showed that cassava harvested area during the last ten years (2000-2011) reduced by 7.7% from 1.28 million hectare to 1.18 million hectare, but productivity increased by 62.4% from 12.5 t/ha to 20.3 t/ha. Lampung, East Java, and Central Java Provinces are the main cassava producers which consecutively covering 26.3%, 17.7%, and 16.2% of the total area. Soil type in the main area was dominated by Ultisol, Alfisol, and Inceptisol which are commonly marginal in soil fertility (Suryana 2007). Cassava has a multiple end-uses such as food, feed, and raw material of many industries, so that the demand tends to increase. Cassava has a strategic role for food security because 64% of total consumption is for food. Cassava also developed as raw material for bio-fuel. Lampung Agricultural Office data showed that cassava area in year 2012 was 366,830 ha or increased by 42.6% compared with last year, and the production increase by 121%. The area mainly distributed in Central Lampung, East Lampung, and North Lampung District. Majority of farmer in Lampung grow cassava on dryland as monocrop. Cassava in this region is mainly prosessed to cassava flour. Ministry of Industrial and Trade reported that in year 2013 there are 66 cassava flour industries in Lampung (http://www.kemendag.go.id). Cassava in Lampung had significant added value and wellfare impact (Nugroho and Hanani 2007). This is the reasons why cassava area in this region increased rapidly. Cassava price varied over location and season. Average lowest price in 2011 in major cities of Indonesia was IDR 1,200/kg and highest was IDR 138/kg (Cakrabawa and Sabarella 2011). FAOs tatistics showed that the price of fresh root at producer level in 2001 was IDR 395/kg and in 2010 was IDR 2,022/kg (FAOSTAT data base, http://faostat.fao.org). However, the price at farmer’s level in South Malang and Tulungagung (East Java) at harvest (September-Oktober) 2012 was IDR 750/kg up to IDR 1,200/kg (nett price, personal communication). In year 2013, fresh root price at harvest in East and 7

Central Java was IDR 550-700/kg and in Lampung was IDR 860-910/kg depending on variety. In case of Lampung, the price of UJ5 variety was higher than UJ3 variety due to lower moisture content. In Indonesia, cassava yield could attain 25-40 t/ha with good cultural practices (Wargiono et al. 2006). Taufiq et al. (2009) reported that cassava yield of 63 t/ha can be achieved by application of 70 kg N/ha, 30 kg P2O5/ha and 115 kg K2O/ha. The nutrient uptake by cassava is high. At yield level of 21 t/ha of fresh tuber, cassava uptake 87 kg N, 37.6 kg P, and 117 kg K/ha (Howeler, 1981), 136 kg N, 17.6 kg P, and 131.9 kg K/ha (Amanullah et al. 2007). Wargiono et al. (2006) reported that at yield level of 30 t/ha, cassava uptake 147.6 kg N, 20.7 kg P, and 148.8 kg K/ha. These data reveal that potassium (K) uptake is as high as nitrogen (N). Potassium removed by cassava in harvested product was as high as maize and peanut (Putthacharoen et al. 1998). Application of 60 kg K2O/ha on Alfisol at South Malang (East Java) with exchangeable K of 0.07 me/100 g, increased fresh-tuber yield by 92% from 11.9 t/ha to 22.8 t/ha compared with no K (Suyamto 1998). On Ultisol at Metro and Tulangbawang (Lampung) with exchangeable K of 0.06-0.12 me/100 g, optimum yield of 31.4 t/ha and 24.4 t/ha, respectively, was gained from combination of NPK fertilizer at dose of 90 kg N/ha, 36 kg P2O5/ha, and 60 kg K2O/ha (Ispandi and Munip 2005). On Inceptisol at CIAT with exchangeable K of 0.18 cmol/kg, cassava yield reduced by 61% from 13.6 t/ha in the first year to 5.3 t/ha in the fifth year without K fertilizer, but the application of 100 kg K/ha reduced yield by 36.8% from 15.5 t/ha in the first year to 9.8 t/ha in the fifth year (El-Sharkawy and Cadavid 2000). In Ultisol at Nigeria with exchangeable K of 0.11 me/100 g in the top 15 cm and 0.05 me/100 g in 13-30 cm soil depth, optimum K rate for cassava was 105 kg K/ha, and K should be applied 3-4 months after planting for high efficiency (Maduakor 1997). Yield responses to added K were large and consistent over nine years of study in Vietnam (Nguyen et al. 2002). These data revealed that potassium has an important role in increasing cassava production on soil with K level below a critical level. Critical level of soil K for cassava was 0.15 me K/100 g (Howeler 1981). Majority of farmer in Indonesia usually do not apply fertilizer for cassava (FAO 2005), but some farmers apply much N, less P, and no K fertilizer. Almost all of cassava plant parts are taken out from land at harvest, and hence make soil fertility, especially K, rapidly goes down. Therefore, it is important to verify the optimum dose of K fertilizer, and to give better understanding to farmer about the role of K in increasing cassava yield.

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OBJECTIVES 1. To confirm response of cassava grown in dry land to potassium application. 2. To show and communicate the role of potassium and to deliver a reference to control potassium deficiency on cassava to farmers and extension workers. 3. To create awareness among farmers and extension workers on balancednutrient management and cost and benefit ratio analysis. MATERIAL AND METHOD Location and Planting Date The field experiment had been conducted at farmers’ field in two locations: 1. Site 1: Sukadana Ilir Village, Sukadana Subdistrict, East Lampung District (5o2’38.63” S, 105o32’27.98” E; 46 m above sea level), Lampung Province. The crop was planted on 22 November 2012 and harvested on 20 June 2013. 2. Site 2: at Restubaru Village, Rumbia Subdistrict, Central Lampung District (4o46’15.30” S, 105o34’12.40” E; 47 m above sea level), Lampung Province. The crop was planted on 16 November 2012 and harvested on 14 June 2013. Experimental set up The trial consisted of seven treatments that were arranged in a randomized complete block design, and replicated three times. The treatment consisted of six doses of K fertilizer (0, 30, 60, 90, 120, and 180 kg K2O/ha), and one treatment attributed as farmers’ practice (Table 1). All potassium fertilizer treatments were combined with 135 kg N/ha and 36 kg P2O5/ha, except one treatment with 200 kg N/ha and 60 kg P2O5/ha. Urea (46% N), SP36 (36 kg P2O5), and KCl (60% K2O) were used as source of N, P, and K fertilizer respectively. KCl fertilizer used in Lampung is imported from Russia by Lautan Luas Tbk., Jakarta.

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Table 1. The details of the treatment combinations between N, P and K fertilizer. No.

Fertilizer treatment

1)

Remark

N (kg/ha)

P2O5 (kg/ha)

K2O (kg/ha)

1

Farmer2)

Farmer

Farmer

2

135

36

0

3

135

36

30

4

135

36

60

5

135

36

90

6

135

36

120

7

200

60

180

K fertilizer was applied at 15 DAP, dibled at two side of plant stand and covered

1): P fertilizer in all treatments was applied at planting and 3 months after planting (MAP) with proportion of 50% each. 25% of N fertilizer was applied at 1 MAP, 50% at 3 MAP, and 25% at 4 MAP. 2): Farmer at Sukadana site (East Lampung) applied 300 kg/ha Phonska (15-15-15-10) and 300 kg/ha Urea (46% N). Farmer at Rumbia site (Central Lampung) applied 200 kg/ha Phonska (15-15-15-10) and 200 kg/ha SP36 (36% P2O5). All fertilizer applied at one MAP.

Implementation Soil was cultivated twice without ridgeding. Stem cuttings of cassava of in situ variety was planted with planting distance according to existing farmers’ practice (farmer commonly grows a short maturing cultivar that can be harvested in 6 to 7 months after planting). In East Lampung site, cassava of UJ3 variety was planted on plot measuring of 7.2 m x 8 m at distance of 60 cm between row and 50 cm within row (plant density 33,333 plants/ha). In Central Lampung site, cassava of UJ5 variety was planted on plot measuring of 7 m x 8 m at distance of 70 cm between row and 50 cm within row (plant density 28,570 plants/ha). Farmer in all location usually plant cassava twice a year as monocrop. The crops had been harvested at 7 months after planting (MAP). Soil characteristic at two sites was presented in Table 2. Bud reduction to maintain two buds per plant was done at one MAP. Hand weeding at 1, 2, and 3 MAP (depends on weed condition). Insect and disease controlled using chemical pesticides, according to their kind and intensity. Data collected consisted of: 1. Initial composite soil analysis at 0-20 cm and 20-40 cm soil depth: soil texture, pH, available P, exchangeable K, Ca, and Mg, and organic C. Nine soil subsamples were collected sistematically from experimental land using

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soil auger. The subsample from each depth mixes togather and then took one sample for laboratory analysis. 2. Plant height at 30, 60, 90, 120, 150, 180 days after planting, and at harvest. Plant height was measured on stem starting from base of the stem. The measurement applied on five plants representing crop growth performance in each plot. 3. Dry weight of leaves, stem, and tuber at harvest. Number of sample was three plants per plot. The samples dried in the oven at 105 oC for at least 48 hours (untill constant weight). 4. Potassium concentration in the leaf (including petiole), stem and tuber at harvest (7 MAP). 5. Soil potassium analysis at harvest. The soil sample at each plot was randomly taken from the root (tuber) zone. 6. Fresh tuber yields in harvested-plot (middle of 6 rows along 8 m). 7. Starch content of tuber at harvest. Analysis of variance and mean comparison of collected data were proceded using statistical software of Statistix 3.0 (N.H. Statistical Software). RESULT AND DISCUSSION Soil Characteristics

Soil texture in topsoil (0-20 cm) and in subsoil (20-40 cm) layers at two sites was dominated by sand fraction (Table 2). From the texture point of view, it was indicated that the soil had good structure that favorable for tuber development. However, the soil might have low cation exchange site because of low clay fraction, and therefore cation losses including potassium (K) might be high. Soil pH at all sites was acidic to very acidic. Low soil pH was couple with low availability of Ca and Mg (Table 2). Critical Ca level in soil for cassava is 0.25 me/100 g (Howeler 1981). It was indicated that increasing soil pH and improving Ca and Mg status migh have benefecial effect in improving cassava growth and productivity. Soil organic matter as indicated by organic-C content was very low at all sites even in the topsoil layer (Table 2). This fact indicated that organic matter addition might become huge effect on increasing cassava growth and productivity. Phosphorous (P) availability in the topsoil was high, but in contrast for subsoil. Potassium (K) avalilability at all sites was very low, and it was below a 11

critical level (Table 2). Howeler (1981) mentioned that critical level of P for cassava is 8 ppm P (18 ppm P2O5, Bary 1) and K is 0.15 me K/100 g. It was indicated that K migh be as limiting factor for cassava at all locations, and therefore K fertilizer application will have significant effect on cassava growth and productivity. Table 2. Soil characteristis of the experimental site at Sukadana and Rumbia. Soil variables

Sukadana-East Lampung

Rumbia-Central Lampung

0-20 cm

20-40 cm

0-20 cm

20-40 cm

Sand (%)

40

61

81

79

Silt (%)

26

39

8

3

Clay (%)

34

0

11

18

Texture class

Clay loam

Silty loam

Loamy sand

Sandy loam

pH-H2O (1:2.5)

4.5

4.7

5.1

4.9

pH-KCl (1:2.5)

3.9

4.1

4.2

4.2

C-organic (%)

0.95

0.72

1.18

0.79

P Bray 1 (ppm P2O5)

27.8

8.45

49.2

11.4

Exch-K (me/100 g)

0.05

0.09

0.07

0.12

Exch-Ca (me/100 g)

0.36

0.54

0.75

0.48

Exch-Mg (me/100 g)

0.20

0.30

0.28

0.20

Soil potassium (K) status in top layer at harvest (7 MAP) did not consistently increase by increasing K fertilizer dose. Exchangeable K (exch-K) did not increase at dose of 30 kg K2O/ha, but it increased by 0.02 unit at dose of 60 kg K2O/ha (Table 3). However, exch-K at dose of more than 60 K2O/ha was relatively same as at 60 K2O/ha. Increasing exch-K positively correlated (r=0.79*) with K fertilizer rate. It means that increasing exch-K was due to K fertilizartion. High sand fraction and low organic carbon content may cause the soil have low cation exchange capacity, so that have low ability to adsorb K. Hence, it might be better to apply K fertilizer several time instead of one time.

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Table 3. Effect of potassium (K) fertilization on available K in the top soil layer (0-20 cm) at harvest. Lampung, 2012-2013. Fertilizer treatment (kg/ha)

Exchangeable K (me/100 g Rumbia Sukadana

N

P2O5

K2O

Farmer1)

Farmer

Farmer

0.06

0.07

135

36

0

0.04

0.06

135

36

30

0.04

0.06

135

36

60

0.06

0.08

135

36

90

0.05

0.07

135

36

120

0.06

0.08

200

60

180

0.07

0.08

Note: 1) Farmer at Sukadana applied 300 kg/ha Phonska (15-15-15-10) and 300 kg/ha Urea (46% N), while farmer at Rumbia applied 200 kg/ha Phonska (1515-15-10) and 200 kg/ha SP36 (36% P2O5). All fertilizer applied one MAP.

Crops Growth Cassava growth significantly response to fertilization treatments at both

sites as indicated by plant height (Figure 1 and Figure 2), and above ground biomass accumulation (Table 4). Plant height data was presented in Appendix 1. Plant height increased as potassium (K) rate increased from 0 to 120 kg K2O/ha. Plant height at farmer treatment did not significantly different compared with treatment 135-36-60 (N-P-K), and it might be due to farmer at both sites applied N-P-K fertilizer. Farmer in Sukadana applied 300 kg/ha Urea and 300 kg/ha Phonska (183 N, 45 P2O5, and 45 K2O kg/ha), and in Rumbia applied 200 kg/ha SP36 and 200 kg/ha Phonska (45 N, 117 P2O5, and 45 K2O kg/ha). Plant height data indicated that significant response of cassava to potassium (K) fertilizer started at diferrent plant age. The response to K fertilizer at Sukadana observed on 90 days after planting (DAP), while at Rumbia on 180 DAP (Appendix 1), and it could be related to different variety between the two location. The plants without K fertilizer grow shorter than that with K fertilizer (Figure 1 and Figure 2), and the best plant height attained at dose of 120 and 180 kg K2O/ha. However, application of 60 kg K2O/ha did not significantly different compared with the higher one. Potassium fertilizer in this trial was applied at 15 DAP, and there was no response even on 60 DAP. Alves (2002) mentioned that up to 30 DAP, shoot and root growth depends on the reserve of stem cutting, and after that the fibrous roots start to grow and penetrate into the soil and function in water and nutrient absorbtion. 13

Stem and shoot dry weight of cassava significantly increased due to K fertilizer application. Stem dry weight at both sites increased by 23% due to application of 30 K2O/ha, and increased by 57-61% due to application of 60 kg K2O/ha compared with no K (Table 4). Stem dry weight tended to increase on 90 and 120 kg K2O/ha, but not significantly different compared with that on 60 kg K2O/ha (Table 4). Shoot dry weight at both sites significantly increased by 21-23% due to application of 30 kg K2O/ha and increased by 47-50% due to application of 60 kg K2O/ha compared with no K, but not significantly increased on higher dose compared with that on 60 kg K2O/ha (Table 4). Leaves dry weight at harvest (7 MAP) was 0.4-0.5 t/ha at Sukadana site and 0.6-0.8 t/ha at Rumbia site. The rest leaves at harvest was about 15% to 20% of total leaves. It means that 80% to 85% of the leaves fall before harvest, and application of K fertilizer up to 180 kg K2O/ha could not retard the leaves to fall. Potassium availabality at both sites were very low, and so that application of K fertilizer improved cassava growth as indicated by increasing plant height, stem, and shoot dry weight. Application of K fertilizer at rate of 60 kg K2O/ha seem to be optimum for growth of cassava. No deficiency symptoms appeared on leaves at 30 DAP in all treatments at both sites. At 60 DAP, plants in plots without K fertilizer had smaller leaves than that of fertilized plot, but there was no chlorosis symptom appeared on leaf margins. At 90 DAP, plants in plots without K fertilizer grows shorter with smaller leaves than that of fertilized plot, and there was chlorosis symptom appeared on leaf margins. This indicated that there was K deficiency on crops without K fertilizer.

Plant height (cm)

150 1 2

100

3 50

4 5

0 0

30

60

90

120 150 180 210

Plant age (DAP)

6 7

Figure 1. Efect of N, P and K fertilization on plant height of cassava of UJ3 variety at Sukadana, East Lampung during planting season of 2012-2013 (treatment codes as described in Table 1).

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Plant height (cm)

300 250 200 150 100 50 0

1 2 3 4 5 0

30

60

90 120 150 180 210

Plant age (DAP)

6 7

Figure 2. Efect of N, P and K fertilization on plant height of cassava of UJ5 variety at Rumbia, Central Lampung during planting season of 2012-2013 (treatment codes as described in Table 1).

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Table 4. Efect of potassium fertilization on above ground biomass of cassava at Sukadana and Rumbia. Lampung, 2012-2013. Fertilizer treatment (kg/ha) No.

N

P2O5 2)

1 Farmer 2 135 3 135 4 135 5 135 6 135 7 200 CV (%)

Farmer 36 36 36 36 36 60

K2O Farmer 0 30 60 90 120 180

Dry weight (t/ha)1) Sukadana – East Lampung Rumbia – Central Lampung Stem Leaves Shoot Stem Leaves Shoot 1.7 bc (31)3) 1.3 c 1.6 bc (23) 2.1 ab (61) 2.7 a (108) 2.8 a (115) 2.5 a (92) 20.5

0.4 a 0.4 a 0.5 a 0.5 a 0.4 a 0.5 a 0.4 a 23.9

2.1 bc (23) 1.7 c 2.1 bc (23) 2.5 ab (47) 3.2 a (88) 3.2 a (88) 2.9 a (71) 9.3

5.5 bc (31) 4.2 c 5.2 bc (24) 6.6 ab (57) 5.4 bc (29) 6.7 ab (59) 8.2 a (95) 15.9

0.6 a 0.6 a 0.6 a 0.6 a 0.7 a 0.8 a 0.7 a 18.9

6.1 bc (27) 4.8 c 5.8 bc (21) 7.2 ab (50) 6.1 bc (27) 7.4 ab (54) 8.9 a (85) 15.4

Notes : 1): Numbers in one coloum with the same letter means not significantly different according to LSD test at 5% level; 2):Farmer at Sukadana site applied 300 kg/ha Phonska (15-15-15-10) and 300 kg/ha Urea (46% N), while farmer at Rumbia site applied 200 kg/ha Phonska (15-15-15-10) and 200 kg/ha SP36 (36% P2O5). All fertilizer applied at one MAP; 3): Numbers in the parenthesis were difference percentage from no K treatment.

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Tuber (storage roots) yield K fertilization on soil with very low K status had a positive effect on tuber yield improvement. In Sukadana site, application of 60 kg K2O/ha significantly increased fresh tuber weight from 26.1 t/ha to 38.5 t/ha (47%) and dry tuber weight (without bark or periderm) from 7.5 t/ha to 11.1 t/ha (48%) compared with no K fertilization. Increasing dose of K fertilizer more than 60 kg K2O/ha did not significantly increase tuber weight (Table 5). Average dry tuber weight at this site was 28% of fresh weight. Comparing with farmers’ practice, application of 60 kg K2O/ha increased fresh and dry tuber yield by 23% and 18%, respectively (Table 5). Table 5. Efect of potassium fertilization on tuber yield and harvest index of cassava of UJ3 variety at Sukadana site. East Lampung, 2012-2013. Tuber weight (t/ha)1)

Fertilizer treatment (kg/ha)

Harvest index

No. N

P2O5

K2O

Fresh

Dry

1

Farmer2)

Farmer

Farmer

31.3 bc (20)3)

9.4 abc (25)

0.8 a

2

135

36

0

26.1 c

7.5 c

0.8 a

3

135

36

30

31.4 bc (20)

8.6 bc (15)

0.8 a

4

135

36

60

38.5 a (47)

11.1 a (48)

0.8 a

5

135

36

90

37.8 a (45)

10.4 ab (39)

0.8 a

6

135

36

120

35.0 ab (34)

10.6 ab (41)

0.8 a

7

200

60

180

36.5 ab (40)

9.5 abc (27)

0.8 a

9.3

11.7

4.3

CV (%)

Notes : 1): Numbers in one coloum with the same letter means not significantly different according to LSD test at 5% level; 2): Farmer applied 300 kg/ha Phonska (15-15-15-10) and 300 kg/ha Urea (46% N) at one MAP. 3): Numbers in the parenthesis were difference percentage from no K treatment.

Potassium fertilization at Rumbia site at dose of 30 kg K2O/ha significantly increased fresh tuber weight from 27.9 t/ha to 30.4 t/ha (9%) and dry tuber weight (without bark or periderm) from 11.7 t/ha to 13.3 t/ha (14%) compared with no K fertilization. Application of K fertilizer more than 30 kg K2O/ha did not significantly increase tuber weight (Table 6). Average dry tuber weight at this site was 44% of fresh weight. Fresh and dry tuber yield with application of 30 kg K2O/ha did not significantly different compared with farmers’ practice (Table 6), and this was because of farmer applied 30 kg K2O/ha from Phonska fertilization.

17

Table 6. Efect of potassium fertilization on tuber yield and harvest index of cassava of UJ5 variety at Rumbia site. Central Lampung, 2012-2013. Tuber weight (t/ha)1)

Fertilizer treatment (kg/ha) No.

N

P2O5

Fresh

K2O

Dry 3)

Harvest index

1

Farmer2)

Farmer

Farmer

30.9 a (11)

13.9 ab (19)

0.7 a

2

135

36

0

27.9 b

11.7 c

0.7 a

3

135

36

30

30.4 ab (9)

13.3 b (14)

0.7 a

4

135

36

60

30.3 ab (9)

13.5 ab (15)

0.6 a

5

135

36

90

31.6 a (13)

14.0 ab (20)

0.7 a

6

135

36

120

32.1 a (15)

14.6 a (25)

0.7 a

7

200

60

180

32.7 a (17)

14.7 a (26)

0.6 a

4.8

5.4

7.8

CV (%)

Notes : 1): Numbers in one coloum with the same letter means not significantly different according to LSD test at 5% level; 2): Farmer applied 200 kg/ha Phonska (15-15-15-10) and 200 kg/ha SP36 (36% P2O5) at one MAP. 3): Numbers in the parenthesis were difference percentage from no K treatment.

Soil available K in sub soil layer at Rumbia site (0.12 me K/100 g) was higher than at Sukadana (0.05 me K/100 g), so that the optimum dose of K fertilizer at Rumbia site (30 kg K2O/ha) was less than at Sukadana site (60 kg K2O/ha). Root of cassava crop could absorb soil K from sub soil layer, and therefore need less K fertilizer dose to attain optimal growth. Farmers in Sukadana prefer to grow cassava of UJ3 variety (farmer called Thailand), and in Rumbia prefer UJ5 variety (farmer called Kasetsart). In Lampung Province farmer usually sell fresh tuber, and UJ3 produced higher fresh tuber than UJ5, and also tuber develompment of UJ3 is faster than UJ5. In contrast, UJ3 produced dry tuber less than UJ5 because water content of tuber of UJ3 was higher (64.3%) than in UJ5 (55.7%). Difference in tuber water content causes difference in the price. Fresh tuber price at collector trader level at harvest in this season was IDR 880/kg for UJ3 and IDR 910/kg for UJ5. Crop performance of UJ3 was smaller than UJ5, and therefore harvest index of UJ3 (0.8) was higher than UJ5 (0.7) (Table 5 and Table 6). Agronomic and Economic Efficiency Agronomic efficiency (AE) of potassium fertilization at Sukadana site at dose of 60 kg K2O/ha was higher (207 kg yield/kg K2O) compared with the other one. At Rumbia site, application of 30 kg K2O/ha had higher AE (83 kg

18

yield/kg K2O) compared with the other one (Table 7). It means that optimum dose K fertilization for cassava at Sukadana was 60 kg K2O/ha, and at Rumbia was 30 kg K2O/ha, and both had high economic efficiency (Table 8 and Table 9). Table 7. Agronomic efficiency of potassium fertilization on cassava at Sukadana and Rumbia sites. Lampung Province, 2012-2013. K2O rate (kg/ha) 0 30 60 90 120

Sukadana – East Lampung FTY ∆FTY AE (kg (kg/ha) (kg/ha) FTY/kg K2O) 26,100 – – 31,400 5,300 177 38,500 12,400 207 37,800 11,700 130 35,000 8,900 74

Rumbia – Central Lampung FTY ∆FTY AE (kg (kg/ha) (kg/ha) FTY/kg K2O) 27,900 30,400 2,500 83 30,300 2,400 40 31,600 3,700 41 32,100 4,200 35

Notes: FTY=Fresh tuber yield; AE=agronomic efficiency

Table 8. Simple economic analysis of potassium fertilization on cassava at Sukadana site. East Lampung, 2012-2013. K fertilizer (kg/ha) K2O Equivalen to KCl (A) (B) 0 0 30 50 60 100 90 150 120 200

Cost of KCl (IDR/ha) (C) 0 300,000 600,000 900,000 1,200,000

FTY (kg/ha) (D) 26,100 31,400 38,500 37,800 35,000

∆FTY Quantity Return (kg/ha) (IDR/ha) (E) (F) – – 4,664,000 5,300 12,400 10,912,000 11,700 10,296,000 7,832,000 8,900

Benefit (FC) (IDR/ha) (G)

Ratio benefit to cost (G/C)

– 4,364,000 10,312,000 9,396,000 6,632,000

– 15 17 10 6

Notes: IDR=Indonesian rupee; KCl contain 60% K2O; KCl price IDR 6,000/kg; FTY=fresh tuber yield; yield price IDR 880/kg; $US 1=IDR 10,860.

The value of benefit to cost ratio of application of 60 kg K2O/ha (100 kg KCl/ha) at Sukadana site was 17 (Table 8), and at Rumbia site at dose of 30 kg K2O/ha (50 kg KCl/ha) was 7 (Table 9). Means that application of K fertilizer on these doses was economically feasible.

19

Table 9. Simple economic analysis of potassium fertilization on cassava at Rumbia site. Central Lampung, 2012-2013. K fertilizer (kg/ha) K2O Equivalen to KCl (A) (B) 0 0 30 50 60 100 90 150 120 200

Cost of KCl (IDR/ha) (C) 0 300,000 600,000 900,000 1,200,000

FTY (kg/ha) (D) 27,900 30,400 30,300 31,600 32,100

∆FTY Quantity Return (kg/ha) (IDR/ha) (E) (F) – – 2,275,000 2,500 2,184,000 2,400 3,367,000 3,700 3,822,000 4,200

Benefit (FC) (IDR/ha) (G)

Ratio benefit to cost (G/C)

– 1,975,000 1,584,000 2,467,000 2,622,000

– 7 3 3 2

Notes: IDR=Indonesian rupee; KCl contain 60% K2O; KCl price IDR 6,000/kg; FTY=fresh tuber yield; yield price IDR 910/kg; $US 1=IDR 10,860.

K and Starch Content Increasing potassium (K) fertilization from 0 kg K2O/ha up to 60 kg K2O/ha increased K content of tuber (storage root), leaf, and stem, and also starch content of tuber at both locations (Table 10 and Table 11). Table 10. Effect of K fertilization on K content of tuber, leaf, and starch content of tuber at harvest. Sukadana - East Lampung, 2012-2013. K content (%)

Fertilizer treatment (kg/ha)

Starch content (% wet basis)

N

P2O5

K2O

Tuber

Leaf

Stem

Farmer1)

Farmer

Farmer

0.37

1.37

0.63

29.1

135

36

0

0.26

1.10

0.39

25.9

135

36

30

0.25

1.12

0.46

26.5

135

36

60

0.32

1.73

0.66

29.6

135

36

90

0.34

1.51

0.62

25.4

135

36

120

0.40

1.79

0.67

26.1

200

60

180

0.34

1.84

0.96

26.3

Note: : Farmer applied 300 kg/ha Phonska (15-15-15-10) and 300 kg/ha Urea (46% N) at one 1)

month after planting.

Application of 60 kg K2O/ha at Sukadana site increased starch content of tuber by 24.5% from 25.9% to 29.6% (wet basis) compared with no K fertilization (Table 10). At Rumbia site, starch content of tuber also increased by 6.8% from 31.9% to 34.0% (wet basis) compared with no K fertilization (Table 11). Increasing K content in these plant parts positively correlated with dose of K fertilization, and increasing K content in the tuber correlated with K 20

content in the leaf and stem (Table 12 and Table 13). This result indicated that K fertilization did not only improve crop growth and productiveness, but it also improved starch content. Table 11. Effect of K fertilization on K content of tuber, leaf, and starch content of tuber at harvest. Rumbia - Central Lampung, 2012-2013. K content (%)

Fertilizer treatment (kg/ha)

Starch content (% wet basis)

N

P2O5

K2O

Tuber

Leaf

Stem

Farmer1)

Farmer

Farmer

0.24

1.96

0.49

31.7

135

36

0

0.18

1.37

0.49

31.8

135

36

30

0.22

1.57

0.53

34.0

135

36

60

0.29

1.94

0.51

33.8

135

36

90

0.35

2.02

0.51

34.1

135

36

120

0.30

2.27

0.73

34.1

200

60

180

0.30

2.35

0.81

30.5

: Farmer applied 200 kg/ha Phonska (15-15-15-10) and 200 kg/ha SP36 (36% P2O5) at one month

1)

after planting.

Table 12. Simple correlation among K fertilization, K content of tuber, leaf, stem, and starch content of tuber at harvest. Rumbia, 2012-2013. Variables K2O rates (kg/ha) K leaf (%) K stem (%) K tuber (%) Starch (%)

K2O rates (kg/ha) 1.00 0.95** 0.67* 0.74* 0.53

K leaf (%) 1.00 0.60* 0.65* 0.61*

K stem (%) 1.00 0.23 0.09

K tuber (%)

1.00 0.38

Starch (%)

1.00

Note: cases included (n)=10; ** and * significant at 1% and 5% level.

Table 13. Simple correlation among K fertilization, K content of tuber, leaf, stem, and starch content of tuber at harvest. Sukadana, 2012-2013. Variables K2O rates (kg/ha) K leaf (%) K stem (%) K tuber (%) Starch (%)

K2O rates (kg/ha) 1.00 0.71* 0.85* 0.86** –0.01

K leaf (%) 1.00 0.84** 0.68* 0.40

K stem (%) 1.00 0.78** 0.32

Note: cases included (n)=10; ** and * significant at 1% and 5% level.

21

K tuber (%)

1.00 0.04

Starch (%)

1.00

CONCLUSION 1. Cassava grown on acidic dryland with very low soil potassium status response positively to potassium (K) fertilization. 2. The improvement growth and yield of cassava could be achieved by application of K fertilizer at rate of 30 kg K2O/ha with cassava of UJ3 variety, and 60 kg K2O/ha with cassava of UJ5 variety. Fertilization on these doses also increased starch content of tuber by 6.8% (UJ3 variety) and 14.5% (UJ5 variety). Potassium fertilization on these doses was agronomically and economically efficient. ACKNOWLEDGMENT This research carried out in cooperation between Indonesian Legumes and

Tubers Crops Research Instirute (Iletri) with Belarusian Potash Company (BPC). This research was fully funded by BPC under coordination of International Potash Institute (IPI). Thanks and highly appreciation addressed to the Director of IPI and BPC, and in particular IPI’s coordinator for South East Asia Dr. Alexey Shcherbakov. REFERENCES Amanullah, M.M., K. Vaiyapuri, K. Sathyamoorthi, S. Pazhanivelan, A. Alagesan. 2007. Nutrient uptake, tuber yield of cassava (Manihot esculenta Crantz.) and soil fertility as influenced by organic manures. J. of Agron. 6(1):183-187. BPS, Statistik Indonesia (Statistic of Indonesia). http://www.bps.go.id. Cakrabawa, D.N and Sabarella. 2011. Perkembangan harga komoditas pertanian (Price progress for agricultural commodities). www.deptan.go.id/pusdatin. El-Sharkawy, M.A., and L.F. Cadavid. 2000. Genetic variation within cassava germplasm in response to potassium. Expl. Agric. 36:323-334. FAO, 2005. Fertilizer use by crop in Indonesia. First version. FAO, Rome. 62 pp. Howeler, R.H. 1981. Mineral Nutrition and Fertilization of Cassava. Centro Internacional de Agricultura Tropical (CIAT), Colombia. 52 pp. Ispandi, A and A. Munip. 2005. Efektifitas pengapuran terhadap serapan hara dan produksi beberapa klon ubikayu di lahan kering masam (The effectiveness of liming to nutrient uptake and yield of cassava clones on acidic dry land). Ilmu Pertanian 12(2): 125-139. Maduakor, H.O. 1997. Effect of land preparation method and potassium application on the growth and storage root yield of cassava in an acid Ultisol. Soil and Tillage Research 41:149-156.

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Nguyen, H., J. J. Schoenau, Dang Nguyen, K. Van Rees, and M. Boehm. 2002. Effects of long-term nitrogen, phosphorus, and potassium fertilization on cassava yield and plant nutrient composition in North Vietnam. J. of Plant Nut. 25(3):425-442. Nugroho, I and N. Hanani. 2007. Studi Investasi untuk Pengembangan Komoditi Pertanian di Propinsi Lampung: Pendekatan input-output (Investation study for agriculture commodity developmen in Lampung Province: Input-output approarch). J. Ekonomi 12(1):32-39. Putthacharoen, S., R.H Howler, S. Jantawat, and V. Vichukit. 1998. Nutrient uptake and soil erosion losses in cassava and six other crops in a Psamment in eastern Thailand. Field Crops Res. 57:113-126 Suryana, A. 2007. Kebijakan penelitian dan pengembangan ubi kayu untuk agroindustri dan ketahanan pangan (Research policy of cassava development dor agroindustry and food security). Hlm. 1-19. Dalam Harnowo, D., Subandi, dan N. Saleh (Peny.). Prospek, Strategi, dan Teknologi Pengembangan Ubi kayu untuk Agroindustri dan Ketahanan Pangan. Pusat Penelitian dan Pengembangan Tanaman Pangan, Bogor. 98 hlm. Suyamto, H. 1998. Potassium increased cassava yield on Alfisol soils. Better Crops International 12(2):12-13. Taufiq, A., A.A. Rahmianna, and Wisnu Unjoyo. 2009. Uji efektivitas pupuk NPK Kujang formula 14-6-23 untuk tanaman ubikayu (Evaluation of effectiveness of NPK Kujang 14-6-23 for cassava). Balai Penelitian Tanaman Kacang-kacangan dan Umbi-umbian, Malang (Project report). Wargiono, J., A. Hasanuddin, dan Suyamto. 2006. Teknologi Produksi Ubi kayu Mendukung Industri Bioetanol (Production technology of cassava for bioethanol industry support). Pusat Penelitian dan Pengembangan Tanaman Pangan, Bogor. 42 hlm.

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APPENDIX Appendix 1. Efect of potassium fertilization on plant height of cassava of UJ3 variety at Sukadana site. East Lampung, 2012-2013. Plant height (cm)1) at various days after planting (DAP)

Fertilizer treatment (kg/ha) No.

N

P2O5

K2O

30 DAP

60 DAP

90 DAP

120 DAP

150 DAP

180 DAP

210 DAP

1

Farmer2)

Farmer

Farmer

10 a

24 a

42 c

58 b

87 bc

101 bc

110 bc

2

135

36

0

7a

22 a

43 c

57 b

72 c

77 c

86 c

3

135

36

30

10 a

22 a

49 bc

73 ab

92 abc

101 bc

109 bc

4

135

36

60

8a

21 a

51 abc

72 ab

98 abc

109 b

117 ab

5

135

36

90

8a

26 a

63 ab

91 a

111 ab

112 b

133 ab

6

135

36

120

9a

29 a

60 ab

96 a

118 a

141 a

143 a

7

200

60

180

9a

25 a

64 a

87 a

115 ab

124 ab

138 ab

23.9

19.6

19.2

17.5

16.2

12.7

14.9

CV (%)

Notes : 1): Numbers in one coloum with the same letter means not significantly diferenct according to LSD test at 5% level; 2): Farmer applied 300 kg/ha Phonska (15-15-15-10) and 300 kg/ha Urea (46% N) at one month after planting.

24

Appendix 2. Efect of potassium fertilization on plant height of cassava of UJ5 variety at Rumbia site. Central Lampung, 2012-2013. Plant height (cm)1) at various days after planting (DAP)

Fertilizer treatment (kg/ha) No.

N

P2O5

K2O

30 DAP

60 DAP

90 DAP

120 DAP

150 DAP

180 DAP

210 DAP

1

Farmer2)

Farmer

Farmer

17 a

65 a

142 a

130 d

165 b

190 f

233 bc

2

135

36

0

17 a

67 a

110 a

134 cd

167 b

202 d

204 c

3

135

36

30

15 a

67 a

115 a

134 cd

162 b

196 e

223 bc

4

135

36

60

16 a

68 a

122 a

146 b

187 ab

214 c

243 ab

5

135

36

90

16 a

65 a

115 a

137 c

166 b

201 de

224 bc

6

135

36

120

15 a

65 a

131 a

159 a

200 a

237 b

273 a

7

200

60

180

17 a

74 a

140 a

163 a

209 a

243 a

272 a

14.3

8.0

14.1

8.5

8.7

8.1

7.3

CV (%)

Notes : 1): Numbers in one coloum with the same letter means not significantly diferenct according to LSD test at 5% level; 2): Farmer applied 200 kg/ha Phonska (15-15-15-10) and 200 kg/ha SP36 (36% P2O5) at one month after planting.

`

25