Dự án nông nghiệp " Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders - Southern Central Coast " pdf

009/06 VIE Six-monthly Report- October 2008 Attachment 1 009/06 VIE: Improving capability of provincial extensionists for assessing soil constraints to sustainable production through the use of the SCAMP decision support system. Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders 2. Southern Central Coast PW Moody A and Phan Thi Cong B A Queensland Department of Natural Resources and Water, Indooroopilly, Qld 4068, Australia B Institute of Agricultural Sciences of Southern Vietnam, Ho Chi Minh City, Vietnam 2 1. Introduction The Soil Constraints and Management Package (SCAMP) has been developed to identify soil constraints to crop production by considering a range of key soil properties (Moody and Phan Thi Cong 2008; Moody et al. 2008). Once these constraints have been identified, management practices that ameliorate or modify these constraints can be formulated. Crops vary in their tolerance to soil constraints and a soil property limiting the productivity of one crop may not be a limitation to the productivity of another crop. Therefore, once the constraints of a particular soil type have been identified, the soil can then be assessed for its ability to potentially support the production of specific crops. The objectives of this series of reports are to:  review existing information on the identification and extent of upland cropping soils in focus provinces of Vietnam.  identify the major soils used for smallholder cropping in the focus provinces, and determine their constraints by the application of SCAMP.  identify the major crops/cropping systems used by smallholders in the focus provinces, and document the specific soil requirements of these crops/cropping systems.  link soil constraints to the soil requirements of the major upland crops and develop management guidelines for the management of specific soil types for specific crops. Part 2 focuses on the soils and cropping systems of the Southern Central Coast comprising Quang Nam, Quang Ngai, Binh Dinh, Phu Yen, Khanh Hoa, Ninh Thuan, and Binh Thuan Provinces. 2. Climate and Landforms The region has a typical tropical monsoon climate with an annual temperature of around 24 o C-27 o C on average (minimum 20 o C-21 o C and maximum 31 o C-32 o C). Total heat accumulation per annum is 8,000 o C– 9,500 o C, with annual solar radiation of 140 Kcal/cm 2 . Annual rainfall ranges from 500 mm to 2,500 mm with an average humidity of 70-80%. Differences in regional rainfall have resulted in the identification of 3 major agri-ecological zones: • Nam-Ngai (Quang Nam & Quang Ngai): 2000-2600 mm ; • Binh–Phu (Binh Dinh & Phu Yen): 1500-1700 mm; and • Southern Ca Pass (Khanh Hoa, Ninh Thuan): < 600 mm. The landforms of the Southern Central Coast comprise: (i) mountains and midlands, (ii) river deltas, and (iii) coastal sand dunes, floodplains and swamps. 3 3. Major Soils used for Smallholder Cropping Acrisols, Fluvisols and Arenosols comprise the major soil types of the South Central Coast of Vietnam. The areal extents of the soils are given in Table 1. Of the total land area of the Southern Central Coast, about 19% comprises land that is suitable for agriculture (of which about 21% is cultivated), 39% comprises forestry land, and 35% comprises unused land, rivers and streams. Table 1. Areas of major soil groups in the South Central Coast of Vietnam Soil type Area Proportion (ha) (%) Ferralitic grey soils (Ferric Acrisols) 299,512 54.9 Acidic alluvial soils (Dystric Fluvisols) 59,466 10.9 Grey soils with yellowish red mottles (Plinthic Acrisols) 53,465 9.8 Humus grey soils (Haplic Acrisols) 39,280 7.2 Sandy soils (Haplic Arenosols) 19,640 3.6 Others 74,196 13.6 Total 545560 100.0 Source: Nguyen thi Ngoc Hue et al. (2008) 4. Soil Constraints and Management Practices for Sustainable Crop Production The following general constraints to agricultural productivity have been identified for the Southern Central Coast: • the soils are generally low in nutrients and are acidic (low water and nutrient retention capacity); • drought is common due to irregular rainfall and high evaporation during the dry season; • wind and water erosion is common as a result of the sloping topography with limited groundcover; • soil degradation and desertification are common particularly in Quang Ngai and Binh Dinh Provinces; • flooding often occurs in the wet season; • sand encroachment occurs inland due to strong winds and limited groundcover. It is evident from Table 1 that Acrisols, Fluvisols and Arenosols occupy the greatest proportion of the land surface of the South Central Coast. Constraints and management strategies for Acrisols in the Central Highlands have already been discussed in Part 1 of this series of reports (Moody and Cong 2008), and these constraints and strategies would be equally applicable to the Acrisols of the South Central Coast. Consequently, this report will consider the constraints and management strategies for Fluvisols and Arenosols. 4 In a limited assessment of the soils of Binh Thuan Province, Moody et al. (2005) identified several constraints of the sandy soils (Arenosols) and the alluvial soils (Fluvisols) (Table 2). Table 2. SCAMP descriptors for 4 Arenosols and 5 Fluvisols of Binh Thuan Province, Vietnam. The number of sites with the attribute is in parentheses. Attribute Arenosols Fluvisols Texture S (4) L (1); C (4) Water pathway drainage (4) drainage + runoff (1); runoff/ponding (4) Acidity surface a (1) surface a (2) Acidification hazard ar(high) (2); ar (very high) (2) ar(low) (3); ar(moderate) (2) Low nutrient retention e (4) e (1) Low organic C om (3) Low K reserves surface k (4) surface k (3) Hard-setting hs (4) Compaction comp (2) These assessments indicate that the Arenosols are sandy in texture, with low organic matter content, low CEC, and high to very high acidification hazard. Potassium status is low. Drainage is the main pathway of water movement. Compaction is a constraint in those Arenosols that have a predominantly fine sand component (20-200 µm). The Fluvisols are predominantly clayey in texture. Depending on site slope, runoff or ponding is the main pathway of water movement. Acidity constraints are not common. Low soil K reserves and hard-setting surfaces are common. With these constraints, the SCAMP database would indicate the following management strategies for sustainable productivity: e: CEC should be increased by increasing soil organic matter content (retaining crop residues, adding organic residues, growing cover crops or companion green manure crops) in association with a liming program to increase soil pH and therefore the variable charge component of CEC (e.g., Aitken et al., 1998; Phan and Merckx, 2005). The practicality of adding high activity clays to increase permanent charge could be assessed (e.g., Noble et al., 2004). om (low): Increasing the levels of organic matter in these soils would improve nutrient supply, increase CEC, increase water holding capacity and increase pH buffer capacity. The management of soil organic matter in tropical soils involves mulching and incorporation of ‘green manure’ crops such as legumes or forage grasses, retaining all crop residues in the field where the crop has grown, not burning crop residues, minimum or zero tillage farming systems, strip or alley cropping and application of organic materials (such as animal manure, composted municipal waste, sewage sludge, and locally available industrial organic wastes) obtained from off-site. k: Potassium fertilisers or organic amendments having a significant content of K will need to be applied. In soils with low K reserves in the subsurface layer, it is likely that crops will exhibit K deficiency during periods of drought. In these circumstances, placement of K fertilisers below the seed at sowing or mixing K fertiliser through the soil in the planting hole is a more efficient management strategy than sidedressing K fertilisers on the soil surface. Crops should be closely monitored for K deficiency symptoms. 5 hs, comp: Hard-setting surfaces reduce infiltration rate and cause poor crop establishment, while compaction layers restrict root growth and limit rooting depth causing drought stress to crops. Retaining crop residues and applying surface mulch should be used to maintain soil surface moisture thus minimising hard-setting. To minimise compaction risk, soils should only be cultivated when drier than their plastic limit, and tillage and machinery traffic should be avoided when soil is wetter than its plastic limit. 5. Major Upland Crops grown by Smallholders Agricultural census data (1999) were used to identify the major crops grown by smallholders in the Southern Central Coast. Where available, crop areas are presented in Table 3. Smallholder crops with significant areas are rice, maize, cassava, sugarcane, and peanut. In general, coconut, cashew and rubber are grown in commercial plantations. 6 Table 3. Crop areas of the Southern Central Coast. All crops except rubber are grown by smallholders. Crop Area (ha) Rice 540000 Sugarcane 71067 Maize 41300 Cashew 32426 Cassava ? Coffee 5196 Peanut ? Cotton 1787 Pepper 988 Coconut ? Rubber ? 6. Soil Suitability for Major Upland Crops grown by Smallholders SCAMP assessments of the Arenosols and Fluvisols (Section 4 above) have identified several soil constraints to crop productivity. Some of these constraints have effects on crop productivity, irrespective of the crop grown: low CEC (e); low organic carbon (om); K deficiency (k); hardsetting characteristics (hs) and compaction layers (comp). However, crops vary in their tolerance to other constraints such as drainage and acidity; while a particular soil attribute or constraint might be a major limitation to the productivity of one crop, it may pose only a minor limitation to another. The FAO (1976) framework for land evaluation uses five classes to categorise the suitability of a specific soil/landscape unit for growing a particular crop (Table 4). To facilitate the use of SCAMP for this application, individual soil attributes/constraints identified for the Arenosols and Fluvisols have been rated according to their effects on the sustainable production of the major crops grown by smallholders in the Southern Coastal Region (Table 5). Ratings are based on collation of information in Williams (1975), Landon (1984), Page (1984), Schaffer and Andersen (1994), Robinson (1996) and Dierolf et al. (2001). 7 Table 4. Soil suitability classes [Source: FAO 1976] Suitability Class Criterion Description 1 Highly suitable Soil is suitable for sustainable production of the crop without ameliorative measures. 2 Moderately suitable Soil is suitable for sustainable production of the crop if minor ameliorative measures are applied (e.g. liming, mounding to improve local drainage). 3 Marginally suitable Soil is only suitable for sustainable production of the crop if major ameliorative measures are undertaken (e.g. large scale drainage works). 4 Currently not suitable Soil is not suitable for sustainable production of the crop. Table 5. Suitability class of soil attributes/constraints for production of specific crops. SCAMP descriptor Paddy rice Maize Cassava Sugarcane Coffee Peanut Texture S 4 2 2 2 2 2 L 1 1 1 1 1 1 C 1 1 2 1 1 3 O 4 3 2 3 3 3 Drainage 1 (g) 2 4 4 4 4 4 rating 2 (g - ) 1 4 3 3 4 3 3 3 3 3 2 3 3 4 4 1 2 1 2 2 5 4 1 1 1 1 1 6 4 1 1 1 1 1 Slope (%) 0-2 1 1 1 1 1 1 2-5 2 1 1 1 1 1 5-10 3 2 2 2 2 2 >10 4 3 3 2 3 3-4 Soil pH a - 1 2 1 1 2 1 a 2 3 2 2 3 2 Salinity s - s 2 3 3 4 3 4 2 4 3 4 3 4 Drought tolerance L L H L L M Main nutrient /water uptake zone (cm) <50 80- 100 >100 >100 >100 50- 100 Nutrient needs High N req'd High N, K req'd Tolerates low fertility High N req'd High N, K req'd Ca in pegging zone The following comments apply to the management practices that may need to be undertaken to meet the requirements of individual crops in addition to those already outlined in Section 4 above. 8 Texture S: Because of the low inherent plant available water content of sandy soils, irrigation may be required for crops of low drought tolerance such as maize, sugarcane and coffee. Using surface mulches of plant residues will reduce evaporation and conserve soil moisture. For crops with high nutrient demands such as maize, sugarcane and coffee, the low ECEC of sandy soils requires that nutrient cations such as potassium are applied in split applications at rates in accord with crop demand. Growing green manure crops or applying plant material from these crops (eg. Tithonia) will temporarily increase the nutrient holding capacity (i.e. CEC) of the soil. C: Root crops such as cassava are not suited to clayey soils because of harvesting difficulties. Clayey soils are unsuitable for crops that do not tolerate prolonged soil wetness such as coffee; the low permeability of clayey soils causes them to remain wet for a longer period than soils of lighter texture. Drainage Soils with imperfect or poor drainage are unsuitable for crops that cannot tolerate waterlogged conditions such as coffee and maize, and raised beds and large scale drainage works must be undertaken if such crops are to be grown. Acidity a: Soils with this constraint are unsuitable for crops with a low or moderate tolerance to Al and/or Mn toxicity such as maize and coffee unless a comprehensive liming program is undertaken. a - : These soils require a liming program if they are being used to grow crops of low tolerance to Al toxicity such as maize and coffee. Applying Tithonia residues to acidic soils has been shown to ameliorate soil acidity by increasing soil pH. An added benefit of using fused magnesium phosphate (FMP) as a P fertiliser is that it also has a liming effect. Main nutrient/water uptake zone Crops with a comparatively shallow active rooting depth will not be as sensitive as deeper rooted crops such as coffee and sugarcane to constraints such as a compaction layer (comp). Conclusions Ferralsols, Acrisols, Arenosols and Fluvisols are the major arable soil groups in the Southern Central Coast. The constraints to crop production which commonly occur in the Arenosols are low plant available water capacity, low nutrient cation retention, K deficiency, acidity, low organic matter, and compaction in soils with high fine sand content. Drainage is the dominant pathway of water movement. For Fluvisols, commonly occurring constraints are low K reserves, occasional acidity, and the soil physical problem of hard-setting surfaces. Fluvisols have impeded drainage leading to runoff on slopes or ponding in low-lying areas. The crops most commonly grown by smallholders in the region are: paddy rice, maize, cassava, sugarcane, coffee and peanut. Individual crop tolerances to some of the identified constraints vary, and so soil management responses to ameliorate or 9 minimise the effects of these constraints on crop productivity will also vary. In general, however the Arenosols and Fluvisols would benefit from application of K fertilisers and reduced cultivation (to reduce the risk of compaction and hard-setting). Increasing the organic matter content of Arenosols is essential. Fluvisols may require raised beds to improve drainage in the root zone of upland crops. References Aitken, R.L., Moody, P.W. and Dickson, T. 1998. Field amelioration of acidic soils in south-east Queensland. I. Effect of amendments on soil properties. Australian Journal of Agricultural Research, 49, 627-637. Dierolf, T., Fairhurst, T. and Mutert, E. 2001. Soil Fertility Kit. Potash and Phosphate Institute: Singapore. FAO. 1976. Framework for land evaluation. Soils Bulletin No. 32. FAO:Rome. Landon, J.R. (ed.) 1984. Booker Tropical Soil Manual. Longman Inc.: New York Moody, P.W. and Cong, P.T. 2008. Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders. I. Gia Lai Province. CARD 009/06 VIE Six-monthly Report- April 2008. CARD, Hanoi. Moody, P.W., Vinh, N.C., Cong, P.T., and Legrand, J. 2008. A decision support framework for the sustainable management of sandy soils. Proceedings of 'Management of Tropical Sandy Soils for Sustainable Agriculture', pp 357-361, 27 Nov-2 Dec 2005, Khon Kaen Thailand. FAO: Bangkok. Noble, A.D., Ruaysoongnern, S., Penning de Vries, F.W.T., Hartmann, C. and Webb, M.J. 2004. Enhancing the agronomic productivity of degraded soils in northeast Thailand through clay-based Interventions. In: Water and Agriculture (eds. Seng, V., Craswell, E., Fukai, S. & Fischer, K.), ACIAR Proceedings No. 116, ACIAR, Canberra, pp. 147-160. Nguyen thi Ngoc Hue et al. (2008) Page, P.E. 1984. Tropical Tree Fruits for Australia. QDPI Information Series QI 83018. Queensland Department of Primary Industries: Brisbane. Phan, T.C. and Merckx, R. 2005. Improving phosphorus availability in two upland soils of Vietnam using Tithonia diversifolia H. Plant and Soil, 269, 11-23. Robinson, J.C. 1996. Bananas and Plantains. CAB International: Oxon. Schaffer, B. and Andersen, P.C. 1994. Handbook of Environmental Physiology of Fruit Crops. CRC Press: Florida. Williams, C.N. 1975. The Agronomy of the Major Tropical Crops. Oxford University Press: London. . Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders 2. Southern Central Coast PW Moody A and Phan Thi Cong B A Queensland. Booker Tropical Soil Manual. Longman Inc.: New York Moody, P.W. and Cong, P.T. 2008. Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders. I the major soil types of the South Central Coast of Vietnam. The areal extents of the soils are given in Table 1. Of the total land area of the Southern Central Coast, about 19% comprises land