CASSAVA AGRONOMY RESEARCH IN VIETNAM

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1 T Institute T Thai T University T Hue T National FT and FT 4 CASSAVA AGRONOMY RESEARCH IN VIETNAM Nguyen Huu HyF FT, Nguyen The DangF FT, ham Van Bien, 3 4 Tran Thi DungF FT, Nguyen Thi CachF Thai hienf ABSTRACT During e last decade to e year 2, cassava agronomy research in Vietnam has been supported by CIAT and e Nippon Foundation. Research has been conducted roughout e country wi e objectives of developing new and well adapted technologies, which require only low inputs and result in high net incomes for farmers, while maintaining soil fertility and reducing erosion. The results of is research indicate e following: -In fertilizer trials, e response of cassava depends on e type of soil and e kind of fertilizer used. In ree sites cassava showed strong responses to e annual application of N and K and only slight responses to. In long-term NK trials conducted in Thai Nguyen University and in Hung Loc Agricultural Research Center e application of and kg/ha of N-B2BOBB-KB2BO, respectively, gave higher yields and economic returns an oer treatments. -In long-term intercropping trials conducted on flat land at Hung Loc Research Center, cassava intercropped wi grain legumes and wi application of fertilizers increased net incomes, but cassava grown between hedgerows of Leucaena leucocephala and Gliricidia sepium (alley cropping system) gave e highest yields and net incomes, bo wi and wiout fertilizer application. -In sloping areas, intercropping cassava wi peanut and/or planting contour hedgerows of vetiver grass or Leucaena reduced soil losses by erosion and maintained or improved soil fertility. INTRODUCTION In Vietnam cassava is e ird most important food crop, after rice and maize; it is used mainly for human consumption and for animal feed. In e last decade of e century, e crop has changed from a subsistence food crop to a cash crop; e planted area is ranked in fif position, after rice, maize, sweet potato, vegetables and legume crops. According to e national statistics, in 2 e area under cassava in Vietnam was 246,172 ha, wi e estimated total production of 2. million tonnes fresh roots and an average yield of 8 t/ha. The Norern Mountainous Region, e Soueastern region, e Nor Central Coast and e Sou Central Coast are e four ecological zones of greatest cassava production in Vietnam. Alough cassava is a crop wi a capacity to produce high yields, until now e average yield of cassava production and e economic returns for e farmers in Vietnam has been low, as e areas under cassava production were not quite suitable. The main reasons are at cassava was usually grown by small farmers in very marginal areas or on sloping lands and poor soils, using local varieties and wiout any improved technologies or external inputs. From 1989 and up to now, cassava breeding and agronomy research in Vietnam of Agricultural Sciences (IAS) of Sou Vietnam, Ho Chi Minh city, Vietnam. Nguyen University of Agriculture and Forestry, Thai Nguyen, Vietnam. of Agriculture and Forestry, Thu Duc, Ho Chi Minh city, Vietnam. University of Agric. and Forestry, 2 hung Hung Street., Hue city, Vietnam. Inst. of Soil and Fertilizers, Tu Liem, Hanoi, Vietnam.

2 have been strengened and supported by CIAT and e Nippon Foundation wi e following objectives: to develop new cassava technologies which require low inputs but result in higher yields and incomes while maintaining soil fertility. RESEARCH RESULTS Soil Fertility Maintenance rough Fertilizer Application Since 199 two long-term NK experiments have been conducted, one on e red latosol clay soil in Hung Loc Agricultural Research Center in Sou Vietnam, and one on yellow sandy clay loam soil in Thai Nguyen University of Agriculture and Forestry in Nor Vietnam. Bo experiments have 12 treatments, consisting of 4 levels each of N, and K in an incomplete factorial design. Two cassava varieties were planted in subplots, wi fertilizer treatments in main plots. In e red latosol soil at Hung Loc Agricultural Research Center, e response of cassava to any of e ree nutrients was initially not clear, even after four years. But, starting in e fif year, e response to K application became significant and is response increased year after year. After 12 years of continuous cropping on e same plots e response to N, and K was very clear, especially e response of cassava to K and N. Among e 12 treatments, e treatment wi 8 kg N+4 B2BOBB+8 KB2BO/ha gave e highest yield and net income (Figure 1A). In e yellow clay loam soil in Thai Nguyen University of Agriculture and Forestry, e response of cassava to K was clear even in e first and second years. And after 12 years e response of cassava to all ree nutrients was very clear, but specially to e application of K. The root yield of cassava was t/ha in e treatment wiout K applied, and was more an t/ha in e treatment wi adequate K applied. Again, application of 8 kg N+4 B2BOBB+8 KB2BO/ha gave a high yield and produced e highest net income (Figure 1B). Figure 2 shows at e exchangeable K level of e soil after 12 years of continuous cassava cultivation was markedly reduced when no K was applied. The soil K level increased wi increasing levels of applied K, but remained below e critical level of.1 me K/ g even wi e application of 8 kg KB2BO/ha in Hung Loc Center and of 16 kg KB2BO/ha in Thai Nguyen (Figure 3). Soil Fertility Maintenance by Intercropping An experiment on cassava intercropping and alley cropping has been conducted at Hung Loc Center for ten years. The experiment has eight treatments, two wi intercropping of grain legumes, ree wi intercropped green manures and two wi leguminous trees planted as hedgerows in alley cropping system, and a check. The objective of e research is to determine e long-term effect of intercropping, green manuring and alley cropping on soil fertility and cassava root yields. Table 1 shows at e annual yield of cuttings of leaves and stems and e nutrients returned to e soil were highest in case of e two legume tree species, Leucaena leucocephala and Gliricidia sepium, planted in hedgerows. Also, e soil K levels were highest in ese two treatments while soil was not much affected by any of e treatments except at hedgerows of Leucaena leucocephala increased e available -content of e soil (Figure 4).

3 6 A = Hung Loc Center = KM 6 = SM Root yield (t/ha) O 8 K 2 O 8 N 8 K 2 O 8 N 4 2 O B = Thai Nguyen Univ. = KM 6 = Vinh hu. Root yield (t/ha) O 8 N 8 N 8 K 2 O 8 K 2 O 4 2 O Kg N/ha kg 2 O /ha kg K 2 O/ha kg N- 2 O -K 2 O/ha Figure 1. The effect of annual applications of various levels of N, and K on e root yields of two cassava varieties planted in Hung Loc Agric. Research Center (top) and at Thai Nguyen Univ. of Agric. and Forestry. Data are average values for 1999 to 1 ( to 12 cycle).

4 7 Cassava root yield (t/ha) 4 Hung Loc = N K = N 2 K 2 = N 2 K 2 = N 2 2 K = N 2 2 K Relative yield (%) Soil K (me/g)..1.. Critical K-level Soil (ppm) Critical -level Crop cycle Figure 2. Effect of annual applications of N, and K on cassava root yield, relative yield (yield wiout e nutrient over e highest yield wi e nutrient) and e exchangeable K and available (Bray content of e soil during twelve years of continuous cropping in Hung Loc Agric. Research Center, Dong Nai, Vietnam.

5 year 8.2 = HARC = TNUAF.2 Soil K (me/g) kg K 2 O/ha applied Figure 3. The effect of annual application of four rates of K on e K level of e soil in two long-term NK trials conducted in Thai Nguyen University of Agriculture and Forestry (TNUAF) and in Hung Loc Agricultural Research Center (HARC), Vietnam in 2 after 12 years of continuous cassava cultivation. Table 1. The amount of annual cuttings of legume leaves and stems and e nutrients which returned to e soil in 1999/ during e 8 of continuous cropping in a long-term soil improvement experiment conducted at Hung Loc Agric. Research Center in Dong Nai, Vietnam. Crop residues Nutrient Nutrients or leaf/stem content (%) returned (kg/ha) cuttings Treatment (t DM/ha) N K N K 1. Cassava monoculture C+pigeonpea green manure C+Mucuna green manure C+peanut intercrop C+cowpea intercrop C+Canavalia green manure C+Leucaena alley crop C+Gliricidia alley crop Table 2 shows at e cassava root yields in e Canavalia green manure and e two alley cropping treatments were significantly higher as compared to cassava grown in monoculture. And among e eight treatments, cassava planted as an alley crop wi Leucaena leucocephala and Gliricidia sepium hedgerows, gave e highest yields and economic benefits, while cassava intercropped wi peanut and Mucuna produced e lowest yields and net income.

6 9 Soil-K (me/g) = check 2 = pigeonpea GM 3 = mucuna GM 4 = peanut IC = cowpea IC 6 = Canavalia GM 7 = Leucaena AC 8 = Gliricidia AC Soil- (ppm) Treatments Figure 4. The effect of green manures (GM), intercropping (IC) and alley cropping (AC) on e exchangeable K and available (Bray II) -content of e soil after ten consecutive years of cassava cultivation wiout fertilizers at Hung Loc Agric. Research Center in sou Vietnam in 2. Erosion Control In Vietnam, mountainous areas occupy about 7% of e total area. According to estimates of Nguyen Tu Siem and Thai hien, deforestation, and e practice of slash-andburn for growing upland rice and cassava wiout control of erosion, resulted in one million ha of soil being eroded and degraded wi little or no production capacity. Table 3 indicates at on sloping land in Hung Loc Agricultural Research Center cassava intercropping wi mungbean or peanut, or e planting of contour hedgerows of vetiver grass, Leucaena or Gliricidia reduced e soil loss and gave higher yields an cassava grown in monoculture. Also, intercropping cassava wi peanut or planting hedgerows of Leucaena produced e highest economic benefits.

7 and 2 Table 2. The effect of green manures, intercropping and alley cropping on e yield of cassava and intercrops, as well as on gross and net income when casssava was grown wiout fertilizer for e ten consecutive year at Hung Loc Agricultural Research Center in Dong Nai, Vietnam in 1/2. 1) Cassava Starch Intercrop Gross roduct. Net yield content yield income cost income 1) Treatments (t/ha) (%) (t/ha) ( dong/ha) 1. Cassava monoculture 12.c 26.6c -,324 3, 2, C+pigeonpea green manure 13.27bc 27.bc 8.b,839 3,7 2, C+Mucuna green manure 8.71d 2.8d 1.9d 3,832 3, C+peanut intercrop 12.21c 26.7bc 4.9c,372 3,7 1,672. C+cowpea intercrop 13.77bc 27.2b 2.41d 6,9 3,7 2,39 6. C+Canavalia green manure 1.87b 26.d 2.46d 6,983 3,7 3, C+Leucaena alley crop 21.14a 28.1a 12.67a 9,367 3,4, C+Gliricidia alley crop 21.4a 26.8bc 8.3b 9,438 3,4 6,38 CV (%) LSD (.) Cassava and intercrops were fertilized annually wi a total of kg N, 4 kg B2BOBB KB2BO/ha only for e first seven years. rices: cassava dong 44/kg fresh roots cassava cultivation wiout fertilizers or intercrops: 3.1 mil. dong/ha intercrop planting, dong/ha intercrop seed, dong/ha intercrop harvest/cutting, dong/ha weeding wi intercrop, dong/ha less an wiout intercrop kg Table 3. The effect of intercropping and contour hedgerows on soil losses by erosion, e yield of cassava and intercrops, e root starch content, and e gross and net incomes when cassava, SM937-26, was grown on 8% slope at Hung Loc Agricultural Research Center in Dong Nai, Vietnam in 1/2. Dry Cassava Starch Intercrop yield Gross roduct. Net soil loss yield content Residue Grain income cost income Treatment (t/ha) (t/ha) (%) (t/ha)----- ( dong/ha) 1. Cassava monoculture 39.1a a ,137 4,986 9,11 2. C+mungbean intercrop.9b b - - 1,197,686 9,12 3. C+peanut intercrop 2.bc a ,222,686 9,36 4. C+vetiver hedgerows 11.3d a ,819,686 9,232. C+Leucaena hedgerows 17.8c a ,28,686, C+Gliricidia hedgerows.c b ,8,686 9,422 1) CV (%) 19.2 NS 2.9 LSD (.) rices: cassava dong 44/kg fresh roots peanut,/kg dry pods Cost: cassava planting material. mil. dong/ha intercrop seed or material.2 mil. dong/ha labor for cassava cultivation 3.3 mil. dong/ha fertilizers 1,186 mil. dong/ha labor for intercropping. mil. dong/ha labor for hedgerow cutting.6 mil. dong/ha

8 Regional Regional Century: Regional Regional 211 FUTURE DIRECTION Based on e results obtained from is research, future cassava agronomy research in Vietnam will focus on e following research topics: -Maintenance of soil fertility by intercropping and fertilizer application -Erosion control in cassava areas wi sloping land in various parts of e country -Using FR and RD meods to develop practical agronomic practices and enhance e adoption of ese practices by farmers. REFERENCES Howeler, R.H Mineral Nutrition and Fertilization of Cassava (Manihot esculenta Crantz). CIAT series No. 9EC-4. Jan p. Howeler, R.H Agronomic practices for cassava production in Asia. In: R.H. Howeler and K. Kawano (Eds.). Cassava Breeding and Agronomy Research in Asia. roc. of a Regional Workshop, held in Rayong, Thailand. Oct 26-28, pp Nguyen Huu Hy, ham Van Bien, Nguyen The Dang and Thai hien Recent progress in cassava agronomy research in Vietnam. In: R.H. Howeler (Ed.). Cassava Breeding, Agronomy Research and Technology Transfer in Asia. roc. Workshop, held in Hainan, China. Nov 3-8, pp Nguyen Huu Hy, Nguyen The Dang and ham Van Bien. 1. Cassava agronomy research and adoption of improved practices in Vietnam. In: R.H. Howeler and S.L. Tan (Eds.). Cassava s st otential in Asia in e 21 resent Situation and Future Research and Development Needs. roc. 6 Workshop, held in Ho Chi Minh city, Vietnam. Feb 21-2,. pp Sittibusaya, C., C. Thiraporn, A. Tongglum, U. Cenpakdee, V. Vichukit, S. Jantawat and R.H. Howeler Recent progress in cassava agronomy research in Thailand. In: R.H. Howeler (Ed.). roc. 4 Workshop, held in Trivandrum, Kerala, India. Nov 2-6, pp Tan, S.L. and S.K. Chan Recent progress in cassava varietal improvement and agronomy research in Malaysia. In: R.H. Howeler (Ed.). Cassava Breeding, Agronomy Research and Technology Transfer in Asia. roc. 4 Workshop, held in Trivandrum, Kerala, India. Nov 2-6, pp Tongglum, A., C. Thiraporn and S. Sinuprama Cassava cultural practices research in Thailand. In: R.H. Howeler and K. Kawano (Eds.). Cassava Breeding and Agronomy Research in Asia. roc. of a Regional Workshop, held in Rayong, Thailand. Oct 26-28, pp Villamayor, F.G. Jr Agronomic research on cassava in e hilippines. In: R.H. Howeler and K. Kawano (Eds.). Cassava Breeding and Agronomy Research in Asia. roc. of a Regional Workshop, held in Rayong, Thailand. Oct 26-28, pp