Wan JIANG,Yong WU,Ding JIANG,Jinhui YANG,Yong SONG,2*

1.College of Horticulture and Landscape,Hunan Agricultural University,Changsha 410128,China;2.Hunan Provincial Engineering Research Center for Potato,Changsha 410128,China

Manihot esculenta(cassava)is a woody shrub of the spurge family,Euphorbiaceae.Native to South America,it is an annual crop in tropical and subtropical regions and one of the three largest tuber crops worldwide,known as"underground granary""the king of starch"and"energy crop"[1].With high adaptability,cassava takes advantages in terms of high yield,high starch content,drought and soil infertility tolerance[2-3].

International Center for Tropical Agriculture (CIAT)and International Institute of Tropical Agriculture(IITA)are engaged in breeding,cultivation technology,collection and preservation of germplasm,physiology and biochemistry characters,and agricultural economy of cassava[4],as well as optimal planting time,different plant densities,planting methods and tuber length[5-6].

Currently,China is devoted to research on highly-yielding cultivation technology of cassava,which plays a key role in protecting eco-environment,reducing production cost,improving perunitarea yield and starch content.Meanwhile,it is of great importance to select suitable cultivation cultivars and modes,and enhance field management in order to improve cassava yield and economic benefits[7-9].Mulching technology not only improves soil and water use rates,but also enhances agricultural yields.Wei[10]researched that mulching technology increased cassava yield and starch content per unit area,as well as farmers’incomes.At present,mulching technology has been widely applied in more than 80 crops,such as vegetables,crops,cottons,oil crops,fruit trees and medicinal materials,with huge economic and social benefits[11].

Considering from climate and soils,Hunan enjoys a promising prospect of cassava development,for most areas in Hunan are suitable for it growth[12].However,high humidity caused by frequent rains in early cassava stage and frost caused by low temperature in later stage should be taken into consideration,which have influenced cassava growth significantly[13].Besides,foundation of cassava industry is not so solid in Hunan and cultivation technology falls behind,which both prevent cassava industry from further development.

The research,therefore,investigated the effects of cultivation methods on cassava growth,yield and quality to improve cassava yield and quality based on climate and soils in Hunan,in order to provide technology supports for cassava production in Hunan.

Materials and Methods

Test cultivars

South China No.9(SC9),without bitter taste,is characterized by low toxicity,high starch content,and low cellulose.What’s more,it is abundant with protein,carotene,and Vc.With a short growth term,it is suitable to be cultivated in tropics and subtropics,which can be harvested after7 months.It is an ideal raw material for cassava and starch processing industries[14].

Test time and location

The test was conducted in a teaching and scientific research base of Hunan Agricultural University at 28°07′58″N,113°17′32″E,with an elevation of 57 m from March-December of 2014.The soil fertility there is satisfied.

Test design and methods

The test was started from March 20,2014,and direct seeding and seedling cultivation with mulches proceeded simultaneously.Specifically,the test included two sowing methods(direct seeding and transplanting after mulching cultivation)and two planting methods (exposed cultivation and mulching cultivation),as follows:treatment A where cassava was cultivated exposed as per direct seeding(CK),treatment B where cassava was exposed and transplanted after seedling grew,treatment C where seeds were mulches as per direct seeding,and treatmentD where seeds were mulches and cultivated,followed by transplanting.Everytreatmentwas with three replications,according to randomized block design.There were totalling 12 test plots and every test plot had an area of 50 m2.

At land consolidation,NPK compound fertilizers were applied at 750 kg/hm2.Afterfertilizers were fully mixed with soils,furrows were established with width of 1.0 m,and height of 25 m.Subsequently,seedlings were planted in a single row,and prow spacing was 80 cm (0.8 m×1.0 m).Therefore,12 495 plants can be planted per unit area(hm2).It is notable that protected areas surrounding the test plots should be built and health cassava should be cut into stems of 15-17 cm for sowing.After cassava was planted with mulches,furrows should be covered with thin films,and margins werecompactedwithsoils.When seedlings grew,mulches should be artificially broken for seedling growth.

Observed items and methods

Seedling stage and rateThe date should be recorded when 50%seedlings grew.Besides,the proportion of seedling number in test plot should be surveyed,followed by statistical work.

Plant growth vigorFive plants were tagged and sampled in succession in every test plot to measure plant height,and stem diameter,to get means.Furthermore,the measurements should be conducted once on the 16thfrom May to November successively.

YieldIn every test plot,growth vigor of the tagged plants was sampled to get average tuber weight per plant,the number of tuber per plant and groundpart weight.

Quality analysisStarch content and dry matter content of cassava were compared and analyzed.Specifically,starch content was measured by anthrone method and dry matter content was measured by drying and constant weight method.

Results and Analysis

Effects of different cultivation methods on seedling of cassava

The testwas conducted on March 20,2014 and direct seeding and seedling cultivation with mulches proceeded simultaneously,followed by transplanting on April 13,2014(Table 1).

As shown in Table 1,seedling emergence stages tended to be volatile upon cultivation methods.Compared with treatment A,treatments C,B and D performed significantly in shifting seedling emergence stage to an earlier time.What’s more,the treatment C proved the earliest in seedling emergence and the highest in germination rate,which were 36 d earlier than that of CK and 19.24%higher.Besides,seedling emergence stage and germination rate of treatments B and D proved 31 d earlier and 14.29%compared with treatment CK.It can be concluded from Table 1 that mulching and transplanting function well in improving seedling germination rate of cassava,which is related to weather of Hunan in the term.As shown in Table 2,it was rainy in most time in March and April,when soils were scoured by rains directly,resulting in soil hardening,poor permeability,oxygen deficit and even root rot.Consequently,germination rate went down.In contrast,mulching treatmentprevented rain scouring and seedling transplanting guaranteed seedling growth in a greenhouse,avoiding the bad weath-er.Therefore,treatments B,C and D are effective ways in improving germination rate of cassava.

Effects of cultivation methods on cassava growth in different stages

Plant height and stem diameter were measured once on the 16thfor every month during May-November,and 5 plants were sampled in succession in every test plot to get means(Table 3).

As shown in Fig.1 and Fig.2,mulching advanced cassava growth significantly,for example,both of plant height and stem diameter increased of cassava in the treatment by direct seedling in fields or the treatment with transplanting.As shown in Fig.3,plant height and stem thickness kept over 15 cm and 7 mm,respectively,by mulching from May,which showed considerable differences compared with treatment without mulches.In August,plant height grew dramatically of cassava by mulching,and kept over 140 cm.Besides,stem thickness maintained over 24 mm,showing significant differences with the treatments without mulches.These have demonstrated that mulching plays a key role in increasing plant height and stem diameter,because mulching increases ground temperature,preserves soil moisture,improves soil physical properties,as well as enhance efficiency for solar energy utilization[15].

Effects of cultivation on cassava yield

Test plants were harvested onNovember 17,2014 and the tagged plants were sampled to measure average tuber weight per plant,the number of tuber per plant,and weight of ground part(Table 4).

Table 2 Weather in the test term

Table 3 Effects of cultivation methods on SC9 growth

As shown in Table 4,compared with CK,treatments C and D played an important role in increasing cassava yield by 41.98%and 26.72%,respectively.As for treatment B,yield increased just 11.45%.The cause is that mulching actually improves tuber weight per plant.On the other hand,direct seeding proves much more popular than transplanting in cultivation,because it is prone damaging roots even scrupulously and it is hard for the roots to be recovered.But tubers are produced based on roots,and the number of tuber would reduce if root decreases.In general,treatment C performed better in terms of the number of tuber per plant,tuber weight per plant,economic coefficient,and yield.

Effects of cultivation methods on quality of tuber

Starch content and dry matter content of cassava were compared and analyzed. Specifically, starch content was measured by anthrone method and dry matter content was measured bydrying and constant weight method(Table 5).

As shown in Table 5,compared with exposed treatment,the mulching treatment performed better in terms of the ratio of dry matter,starch yield,starch content,and yield.Specifically,treatment C proved the best,with the ratio of dry mater of 47.72%and yield of 38 725.20 kg/hm2.What’s more,starch content grew by 3.50%compared with CK.It is obvious that mulching makes contribution to formulation and expansion of tubers,increasing tuberyield and affecting starch content and dry matter ratio.On the other hand,with cultivation method the same,direct seeding and transplanting played insignificant role in improving tuber quality.Therefore,the mulching treatment mainly increases dry matter and starch contents of cassava.In practice,it is recommended to apply the mulching treatment by direct seeding for convenience.

Discussion and Conclusion

Treatment C performing the best in cultivation

Of the four treatments,treatmentC performed the best, whose seedling emergence stage was 36 d ahead of that of CK,and germination rate reached 98.41%.Besides,the ratio of dry matter achieved 47.72%,starch contentwas as high as 28.08%and cassava yield reached 38 725.20 kg/hm2.

Table 4 Effects of cultivation methods on SC9 yield

Table 5 Effects of cultivation methods on SC9 quality

Mulching in improving cassava yield

Compared with exposed treatments,mulching treatment is characterized by earlier seedling germination,highergermination rate,and higher yield and starch content.Because temperature keeps lower in early sowing stage in Hunan,mulching would notonlyincrease earth temperature,conserve water and fertilizer,but also bring germination stage forward,which extends cassava growth stage,advances plant growth and tuber formulation.Meanwhile,such practice increases contents of dry matter and starch,and improves tuber weight per plant and cassava yield. Additionally, direct seeding proves saving labor cost and time,improving work efficiency.

The mulching treatment by direct seeding suitable for cassava production

The mulching treatment by direct seeding saves labor cost and time,and improves cassava yield and starch yield per unit area,as well as increases farmer's incomes,so that it is conductive to supplying of raw materials for cassava processing industry and sustainable development of the industry.Therefore,it is much suitable to be applied in Hunan,with a promising future.

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