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MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY LE HONG VIET STUDYING ON SETTING - UP SUITABLE CROPPING SYSTEMS ON SALINE - AFFECTED ACID SULFATE SOILS: Case studies in Luong Nghia, Vinh Vien A and Hoa Tien communes of Hau Giang province SOIL SCIENCE 62 62 01 03 THESIS SUMMARY 2019 The work is conducted in Can Tho University Scientific Supervisor: Assoc Prof Chau Minh Khoi Opponent 1: Opponent 2: This thesis will be defensed in Can Tho University: At: , date: This thesis will be submitted to: + Vietnamese National Library + National Center for Information and Reference + Can Tho University’s Library LIST OF PUBLICATION Le Hong Viet, Ho Minh Phuc, Tran Van Dung, Chau Minh Khoi and Pham Thanh Vu (2014) Land evaluation for salinity affected acid sulfate soil areas in Hau Giang Province Can Tho University Journal of Science Special issue on Agriculture (2014) (3): 158-165 Le Hong Viet, Chau Minh Khoi, Do Ba Tan (2015) Investigation of saline intrusion in irrigating canals and agricultural soils in Long My District, Hau Giang Province Can Tho University Journal of Science Vol 38 (2): 48-54 Le Hong Viet, Chau Minh Khoi, Do Ba Tan, Tran Huynh Khanh (2016) Analyzing economical efficiency of alternative rice-based cropping systems adapting to salinity intrusion in Hau Giang province Can Tho University Journal of Science Special issue on Agriculture (2016)(4): 22-28 Le Hong Viet, Vu Van Long, Thi Tu Linh, Do Ba Tan, Chau Minh Khoi (2018) The effect of rice-watermelon rotation on soil nitrogen, phosphorus availability and rice yield in the acid sulfate soil in Hau Giang province Can Tho University Journal of Science Special issue on Agriculture (2018)(54): 235-240 CHAPTER INTRODUCTION 1.1 Rationale Climate change (CC) has been a challenge to human beings, directly affecting socio-economics and environment worldwide Vietnam, as similar to some of other countries, is anticipated to be severely affected by the extreme conditions of CC Of which, the Mekong Delta, as a consequence, will face increased temperature, flooding and sea level rise (IPCC, 2013; MRC, 2010; Nguyen Van Thang et al., 2010) According to the these report, national land resources will be deteriorated as follows: (i) lost agricultural land due to saline intrusion and (ii) changed soil quality In the coming years, it is anticipated that saline intrusion will be more severe because of fresh water scarcity and earlier drought events This would bring more disadvantages for agricultural production in the region In the Mekong Delta, saline intrusion has been adversely affecting rice yield, crop-growing areas and cropping calendar For instance, in 2015 Winter-Spring season there were 104,000 of paddy fields affected by saline intrusion This effect increased up to 140,000 in the later year In Hau Giang province, as similar to other coastal provinces in the Mekong Delta, it’s agricultural production sector is being challenged by saline intrusion In 2015, there were 20,000 of paddy fields in the province affected by drought and saline intrusion in Spring-Summer and Summer-Autumn seasons The areas, where were mostly suffered, are Long My district and Vi Thanh city (Hau Giang DARD, 2015) To overcome these challenges, finding suitable integrated management practices for soil, water, crop nutrients and manageable cropping calendar for saline-affected areas is of necessity This aims at improving soil properties and increasing land use effectiveness so as to adapt to the extreme conditions of CC in the region 1.2 Aims of the study: Overall aim: To setting-up suitable cropping systems on the rice-based cropping systems formed on acid sulfate soils and affected by saline intrusion in Hau Giang province Specific aims: - To investigate current saline intrusion situations in rice-cropping areas in Hau Giang province - To determine suitable land use types under the extreme conditions of CC in order to strategize and plan for sustainably agricultural production in the presence and future - To setting-up trials for suitable cropping systems adapting to saline intrusion conditions in the study areas - To test some promising soil management practices for improving saline affected soil quality 1.3 Study contents: - Investigating saline intrusion effects on soil, water and agricultural production coinciding with defining suitable land use types in the study areas - Setting-up suitable cropping systems on the rice-based cropping systems formed on acid sulfate soils and affected by saline intrusion - Identifying soil management practices applicable for rice production in the study areas 1.4 Targets and areas of study This study was implemented on the rice paddy soils affected by saline intrusion in Hau Giang province The studies were focused for three communes mostly affected by annual saline intrusion, including Hoa Tien commune in Vi Thanh city and Luong Nghia and Vinh Vien A communes in Long My district 1.5 Impact of the results The findings from this study revealed the current salinity in soil and water in the study areas in Hau Giang province, recommended suitable cropping systems and effective soil management practices in particular conditions of saline intrusion Results on economic benefits of the alternative cropping systems help improve land use effectiveness, sustain rural livelihoods of the rice farmers to adapt with the climate change and saline intrusion in the region 1.6 Highlighted results - Current effect of salinity, with particular of Na+ adsorbed on soil colloids, present in soil and water in the acid sulfate soils in dry season in Hau Giang province - Suitable land use types for the study areas under the conditions of acidity and saline intrusion Based on the target areas, different suitable upland crops were introduced to rotate with rice to sustain agricultural soil uses under salinity intrusion conditions - Amendment of lime (CaCO3) or gypsum (CaSO4) at a rate of tons/ha in combination with freshwater from canals or rainwater was proved to be significantly effective as remediating saline-affected acid sulphate soils However, this result needs to be validated in the field conditions CHAPTER METHODOLOGY OF STUDY 2.1 Investigating current agricultural production and saline intrusion in the study area 2.1.1 Investigating current agricultural production and saline intrusion in the study area Time and location: the study was carried out during the dry season in 2013 in three communes affected by saline intrusion, including Luong Nghia and Vinh Vien A in Long My district and Hoa Tien in Vi Thanh city Data collection: - Primary data was collected for the information regarding agricultural production, cropping systems, saline intrusion and farming technologies to adapt to climate change Available thematic maps of soil types, soil uses, flooding and saline intrusion were also collected - Expertise interview: this activity aimed to quick access on agricultural production, focusing on benefits and challenges under saline intrusion - Household survey: this activity applied Participatory Rural Appraisal approach – PRA (Nguyễn Duy Cần et al., 2009) The survey was conducted in 135 households located in the studied communes 2.1.2 Investigating saline concentrations in soil and water in the study area Sample collecting sites: the study was carried out in three communes as mentioned above The locations of the study areas are shown in Figure 2.1 Figure 2.1 Map of soil and water sample collection in the study areas Note: ALS: Alluvial soil; ASS: Actual acid sulfate soil; PASS: Potential acid sulfate soil; SM: soil material Collection of water samples: water samples were collected in dry season in 2012 and 2013, starting from February to May Water samples were measured for pH and EC Values of EC would tell the amount of salinity dissolved in inrrigating water Collection of soil samples: soil samples were colletced at the same time as sampling water samples Soil samples were collected manually by a core at a depth in between and 20 cm There were five locations in the same field sampled and composited to obtain a representative sample Soil samples were air-dried in room temperature, crushed and sieved through 1-mm mesh for soil chemical analyses The soil parameters were analysed including EC, cation exchangeable capacity (CEC), exchangeable Na+, soluble Na+ These parameters would help analyse the accumulation of Na+ in soil Soil sodic characteristics was analyzed based on the proportion of the adsorbed Na+ and CEC values Methods applied for soil analyses are described in Table 2.3 2.1.3 Contouring suitable soil use types Investigation was carried out at 45 locations evenly distributed in three study communes Typical soil profiles were described up to meters Special data on soil properties were then recorded so as to mapping soil units and evaluating soil quality 2.2 Setting-up suitable cropping systems on salinity-affected acid sulfate soils 2.2.1 Criterias for selecting suitable cropping systems Suitable cropping systems selected to introduce into the intensive ricebased systems must meet the criteria as below: - The selected alternative crops must be suitable to the specific the soil use types affected by saline intrusion in presence and future - The selected alternative crops must be suitable to local climate, soil properties and hydrological regimes, which can be evaluated based on the parameters of growth, yield, quality, low requirement for water consumption and short growing duration so as to rotate with a rice crop in the dry season - The selected cropping systems must be higher economical benefits than the existing mono rice cropping system in the study areas 2.2.2 Methodology for setting-up the alternative cropping systems Selecting suitable cropping systems and designing on-field trials: the cropping pattern of sweet potato-rice-sticky maize was set-up in Luong Nghia commune, that of rice-water melon-rice was in Vinh Vien A commune and two cropping systems of mung bean-rice-water melon and maize-rice-sticky maize were conducted in Hoa Tien commune There totally were four cropping systems of rice in rotation with upland crops were implemented on 12 farms, of which three farms represented as replicates of each cropping pattern Each farm had an approximately area of 1,000 m The field trials were started from 2012, each cropping pattern were run continuously two or three crops in SummerAutumn, Winter-Spring and Spring-Summer seasons Method for water collection: water samples were taken in a total of times at the start, middle and end of each crop (Table 2.1) At the experimental farms, water samples were taken at three locations and were composited to obtain a representative sample Samples were reserved at 40C for analysing EC Method for soil collection: soil samples were collected at two stages during the experiment, including (1) at the start of establishing the trials to analyze soil properties and soil nutrient-supplying capacity at the study sites and (2) at the start of the rice crop, which followed an upland crop, to analyze the changes in soil nutrients caused by introducing an upland crop in rotation with rice crops To these aims, soils were sampled and treated followed the methods described above The soil samples taken at the start of the experiment were analyzed for pH, EC, soluble Na+, exchangeabe Na+, K+, Ca2+, CEC, available P, total P, total N, NH4+, NO3- and organic C Table 2.1 Timing of water and soil sample collection Crop Summer-Autumn 2012 Winter-Spring (2012 - 2013) Spring-Summer 2013 Sampling time within a crop Month of sampling Water sampling Soil sampling Start 06/2012 x x Middle 07/2012 x x End Start Middle End Start Middle End 08/2012 11/2012 12/2012 01/2013 02/2013 03/2013 04/2013 x x x x x x x x x x x x x x The soil samples taken at the start of the rice crop followed an upland crop were analyzed for changes in pH, EC and main nutrients, e.g available N and P In addition, soil samples were also collected for salinity monitoring at the start, middle and end of each crop (Table 2.1) Methods for soil analyses are presented in Table 2.3 Methods for yield records and economical analyses for the cropping systems: The yields of rice and mung bean were records on 14% and 15.5%-moisture basis, respectively On the other hand, the yields of water melon, sweet potato and sticky maize were recorded as fresh weight Formula for calculating economic income generated from the cropping systems: - Income (VND/ha) = sum of selling cost – sum of investing cost - Investing benefit: Total income Investing benefit = Total investing cost - Marginal benefit cost ratio (MBCR): Marginal benefit cost ratio = Total income – Total income Total investing cost – Total investing cost In which, Total investing cost 1: total grant from tested model; Total investing cost 2: total grant from farmer practice 2.3 Methods for remediating salinity-affected soil by salinity washing in combination with adding lime (CaO) and gypsum (CaSO4) This experiment was carried out with an assumption that salinity intrusion will be expanding in the future This scenario needs suitable practices to manage the soil and remediate the accumulation of salinity in soil 2.3.1 Time and location Lab experiments were run from February 2013 to April 2014 at the College of Agriculture, Can Tho University Soil samples used for the experiments were collected at Luong Nghia commune Soil is classified as Epi-OrthiThionic Fluvisol (FAO) and was sampled at depth of 0-20 cm on a paddy rice field The area is usually affected by salinity intrusion from February to April, annually 2.3.2 Method The experiment consisted of five treatments with replicates for each (Table 2.2) and was laid out in a completely randomized design Table 2.2 Treatments of salinity washing to remediate salinity-affected soil Treatment TT Treatments code NT1 Control (no salinity washing) NT2 Salinity washing after 1-d soil submergence NT3 Salinity washing after 2-d soil submergence NT4 NT3 combined with CaO (equivalent to tonnes CaCO3/ha) NT5 NT3 combined with tonnes CaSO4/ha NT1: Control (no salinity washing) NT2 and NT3: 20-g soil was added into a syringe and submerged with 40 ml deionized water for or days, respectively After submergence, the submerged water was decant NT4: 20-g soil was mixed with 0.0224 g CaO in an equivalent of tonnes CaCO3/ha Soil was maintained in moist condition for day to accelerate chemical reaction happened The 40 ml deionized water was added, mixed and decant as NT2 and NT3 NT5: 20-g soil was mixed with 0.04 g CaSO4 in an equivalent of tonnes/ha The treatment was manipulated as the other treatments Soil samples at the end of salinity washing were collected to analyze as follows: pH, EC (1:2,5), cations exchange capacity, exchange sodium percentage, exchangeable and dissolved Na+ and Ca2+ concentration This data was used to evaluate various salinity washing methods on improvement of salinity soil The details of analysis methods of each parameters were summarized in Table 2.3 2.4 Methods for soil and water analyses Table 2.2 Methods for soil and water analyses No Sample Parameter Unit EC Water + Na and Ca 2+ Analytical method mS/cm EC meter ppm Atomic Absorption Spectrometry pH-H2O EC-H2O mS/cm Organic C %C 1:25 water extract and measured by pH meter 1:2.5 water extract and measured by EC meter Walkley – Black (1934) Total N Soil %N Available N (NH4+ and NO3-) mg/kg Total P %P2O5 Kjeldahl distillation 1:10 soil:2M KCl extract and analyzed by colorimetric method at 650 nm for NH4+ and 540 nm for NO3- Digestion used concentrated H2SO4 HClO4 Analysis used colorimetric method at 880 nm Available P mgP/kg Bray II 10 CEC meq/100g 11 Soluble Na+ and Ca2+ 12 Exchangeable Na+ Ca2+ meq/100g 13 ESP Unbuffered BaCl2 exchange meq/100g Water extract and measured by atomic absorption spectrometry Using BaCl2 exchange and measured by atomic absorption spectrometry % ESP = Exchangeable Na+ CEC CHAPTER RESULTS AND DISCUSSION 3.1 Present situation of agricultural production, salinity intrusion and suitable land use types at the study areas 3.1.1 Present situation of agricultural production at the study areas In recent years, salinity intrusion becomes one of the most challenges for agricultural production in the region, especially in dry season Household surveys revealed that the main constraints in the region are acid sulfate soil temporally affected by salinity intrusion, that hampers crop yields and farmer’s income The survey recorded that there were five main cropping systems in the study areas, including (1) double mono-rice crops, (2) triple mono-rice crops, (3) pine apple, (4) sugar cane and (5) water melon The results from economical analyses for each cropping system indicated as below: - The double mono-rice cropping system: yields were low with an average of around 5.72 tonnes/ha, the B/C value was in an average of 0.86 - The triple mono-rice cropping system: average yield was recorded to be around 5.21 tonnes/ha and B/C value was low with an average of 0.58 - The pine apple cropping system: the farm has an average area of 1.58 with a yield gained 13.9 tonnes/ha in average The B/C value of this cropping system was higher than that of mono-rice system, with an average value of 1.83 - The sugar cane cropping system: the survey recorded the average area of this type of farm varied around 1.31 ha, with an average yield of 79.4 tonnes/ha The B/C value was 1.34, which was higher than that in the mono-rice cropping systems - The water melon cropping system: the total area growing water melon in the study areas was small compared with other cropping systems The average yield of water melon in the area was 18.81 tonnes/ha, with B/C value rather high up to 2.22 3.1.2 Status of salinity intrusion in soil and water in the study area a Salinity in canal water in the study area The results from analyses of salinity in water indicated that most of the study areas had experiences with salinity intrusion at different levels as depicted in Figure 3.1 Figure 3.1 Levels of salinity intrusion in the study area Monitoring salinity in canal water indicated that lower salinity was recorded in 2012 than in 2013 However, the concentrations of salinity in irrigating water were lower than the threshold of having negative effects on crop growth Compared between the communes, salinity in the canal water in Luong Nghia and Vinh Vien A in 2013 was higher than that in Hoa Tien (Figure 3.2) Impressively, there were 85% of water samples analyzed in dry season 2013 having EC > 2mS/cm, which were risky for agricultural production in the study area Figure 3.2 EC values of canal water at the study sites in dry season 2012 and 2013 *: values beyond the normal distribution range of the analyzed values b Soil salinity and pH at the study area Results from analyzing soil EC indicated that 84% of analyzed samples having EC values of lower than 1.8 mS/cm, which may give negative effects on agricultural production in dry season in the study area However, the remaining areas had lower EC values, which were in a range not affect crop growth (Table 3.1) Results from analyzing soluble Na+ existing in soil indicated that the contents of Na in soil varied in a range of 0.7-2.2 meq/100 g recorded in 2012 and 1.0-2.1 meq/100g in 2013 + Exchangeable Na+ contents were low in 93% of the samples analyzed, mostly lower than meq/100g ESP values were recorded below 15% in most of the analyzed samples, revealing that the soils in the study area have not been sodic yet Table 3.1 Soil EC, Na+ and ESP measured in dry seasons 2012 and 2013 in the study area Site Year Numeral EC (mS/cm) Luong Nghia Vinh Vien A Hoa Tien Early dry season Last dry season Soluble Exchange Na+ Na+ (meq/100g) Soluble Exchange EC Na+ Na+ (mS/cm) (meq/100g) ESP (%) ESP (%) Highest 2,8 2,9 1,3 8,7 1,5 2,7 1,0 6,4 2012 Medium 1,1 1,3 0,6 3,6 0,7 1,1 0,4 1,9 Lowest 0,3 0,5 0,1 0,8 0,2 0,2 0,0 0,0 Highest 3,4* 5,5* 3,2* 22,7* 3,8* 6,2* 3,6* 25,1* 2013 Medium 1,0 2,1 1,4 9,7 0,8 1,9 1,1 7,4 Lowest 0,4 0,6 0,2 1,1 0,3 0,5 0,1 1,1 Highest 0,7 3,6 0,7 3,1 0,6 2,0 0,8 3,5 2012 Medium 0,5 2,2 0,5 2,4 0,4 1,4 0,2 1,1 Lowest 0,4 0,5 0,4 1,9 0,2 0,6 0,0 0,1 Highest 3,0 3,0 1,6 8,0 2,0 2,6 1,9 12,7 2013 Medium 1,4 1,1 0,5 3,0 1,1 1,4 1,2 6,8 Lowest 0,6 0,0 0,1 0,2 0,5 0,1 0,1 0,4 Highest 1,2 1,5 1,9 14,3 0,7 0,3 0,9 6,6 2012 Medium 0,7 0,7 1,0 7,3 0,6 0,2 0,5 3,8 Lowest 0,4 0,4 0,5 4,1 0,6 0,2 0,3 2,1 Highest 2,3 2,8 2,2 14,6 2,1 0,5 2,1 12,9 2013 Medium 1,2 1,0 1,3 9,9 0,7 0,2 0,9 7,3 0,3 0,1 0,3 2,3 0,2 0,0 0,2 1,9 Lowest 10 3.1.3 Contouring suitable soil use types Suitable soil use types were evaluated and contoured based on their natural characteristics a Mapping main soil groups Based on the depth, where exists the depth of actual acid sulfate soil and potential acid sulfate soil, soils in the study area were contoured in four main groups: (1) no acid sulfate soil, (2) actual acid sulfate soil exists within 50 cm from the soil surface, (3) potential acid sulfate soil exists below 50 cm and (4) potential acid sulfate soil exists within 50 cm (Figure 3.3) Of them, acid sulfate soils were mainly dominant, accounting for 72.11% of the total agricultural land area In most area, acid sulfate soil appears within 50 cm from the soil surface, so hampering agricultural production in the area Figure 3.3 Map of main soil groups classified based on the depth of existing acid sulfate horizons Note: AASS: Actual acid sulfate soil; PASS: Potential acid sulfate soil; SM: soil material b Contouring suitable soil use type Map of soil units were created based on the map of main soil groups and overlapped different thematic maps of soil pedology (mainly the depths of existing acid sulfate soil horizon), hydrology (timing of salinity intrusion and flooding) The result generated a map of 17 soil units (Figure 3.4 and Table 3.2) 11 Figure 3.4 map of soil units in the study area Table 3.2 Soil units in the study area Soil Depths of existing Timing of salinity Flooding units ASS horizon intrusion (month) (cm) Alluvial soil No salinity < 30cm Alluvial soil No salinity 30 - 60cm Alluvial soil