MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURE SCIENCE DOAN VINH PHUC STUDY ON HYBRID SELECTION AND FARMING TECHNIQUES TO CULTIVATE MAI[.]
MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURE SCIENCE - DOAN VINH PHUC STUDY ON HYBRID SELECTION AND FARMING TECHNIQUES TO CULTIVATE MAIZE HYBRIDS (ZEA MAYS L.) ON RICEGROWING LAND ROTATED WITH MAIZE IN LONG AN AND DONG THAP PROVINCES Specialization Code : Plant Science : 62 01 10 SUMMARY OF THE DOCTOR THESIS IN AGRICULTURE SCIENCE HO CHI MINH CITY – 2022 The work was completed at VIETNAM ACADEMY OF AGRICULTURE SCIENCE Scientific supervisors: Dr Le Quy Kha Prof Dr Ngo Ngoc Hung Reviewer 1: Reviewer 2: Review : The thesis will be defended in the Institute-level Thesis Judging Committee meeting at The Institute of Agricultural Sciences for Southern Vietnam on month , 2022 The thesis can be found at: - Hanoi National Library - Vietnam Library of Agricultural Sciences - Library in the Institute of Agricultural Sciences for Southern Vietnam INTRODUCTION Necessity of the thesis In Vietnam, maize plays an important role in the lives of farmers Eighty percent of maize is utilized for the livestock industry (Nguyen Hong Tin, 2017) Statistical data shows that maize yields in Vietnam in 2020 are only 4.56 million tons and Vietnam has imported 12.07 million tons of maize to meet the country's consumption demand (General Statistics Office, 2020) It is reported that the demand for maize will increase while the maize area in Vietnam is currently on a downward trend Mekong Delta is the largest rice granary in Viet Nam, however, it is facing the severe effects of climate change Some crops are lack water due to drought, some crops are flooding due to excess rainfall Moreover, the cultivation of up to rice crops per year on the same land, so the interval of resting time between crops is too short it is not enough to cut off the life cycle of pests and diseases Therefore, the necessity of switching to upland crops that require less water is the current sustainable development solution In particular, the growing area of maize can be expanded in unfavorable areas in the Mekong Delta because currently, the maize growing area in the Mekong Delta accounts for only 2.92% of the whole country, but the maize grain yield in this region ranks second in the country Dong Thap province (alluvial soil, heavy mechanical composition) and Long An (gray soil, light soil texture, alkaline soil) are two provinces that possess different soil characteristics typical in the Mekong Delta with potential for development maize under current climate change conditions Statistical data from 2014 2020 show that the maize area in Dong Thap province fluctuated slightly but it tended to decrease while maize grain yield increased during this period In 2020, the maize area in Dong Thap reached 4.9 thousand and got the highest yield in the whole country (9.02 tons.ha-1) While, in Long An province, the maize planting area decreased sharply from 2014 to 2020 By 2020, the maize area in Long An only reached 0.4 thousand ha, but maize yield reached 6.25 tons.ha-1, ranking third in the region Data for Mekong Delta (General Statistics Office, 2020) shows that the potential for the growth of maize crops in the rice lands rotated with maize in the Mekong Delta is great if an appropriate set of hybrids and farming techniques are selected However, the development of hybrid maize in this area still faces many difficulties Influenced by the long tradition of rice cultivation, maize farming is new to farmers Maize hybrid seeds depend on multinational companies with high costs, leading to high production costs, while domestic maize hybrids are few and they have low competition capacity in market share for the Mekong Delta Moreover, the technical package of maize farming is still in general, there is no specific guide for each different ecological region when cultivating maize on rice-growing land Therefore, the study was carried out to select domestic maize hybrids that can be well adapted to rice land with different soil conditions in Dong Thap province (alluvial soil, heavy mechanical composition) and Long An province (infertile gray soil, light texture) The implementation seasons are Winter-Spring and Spring-Summer from 2014 to 2018 Objectives of the thesis 2.1 General goals Selection of domestic maize hybrids that are suitable to ecological conditions on ricegrowing land rotated with maize for two groups of alluvial soils (Fluvisols) and gray soils (Acrisols) in the Mekong Delta is examined; identification of technics for maize cultivation on rice-growing land rotated with maize for the two representative soil groups of the above ecological sub-regions in the Mekong Delta is studied 2.2 Specific goals - Selection of - domestic maize hybrids that are suitable to ecological conditions on rice-growing land rotated with maize for two groups of alluvial soils (Fluvisols) and gray soils (Acrisols) in the Mekong Delta is investigated; - Determination of nitrogen fertilizer dosage, agronomic efficiency of nitrogen, phosphorus, and potassium fertilizers is studied; Planting density and tillage techniques serve as the basis for developing a technical package for maize cultivation on ricegrowing land rotated with maize for the two representative soil groups of the ecological sub-regions mentioned above in the Mekong Delta - Determination of the economic efficiency of maize cultivation on rice-growing land rotated with maize in the above ecological sub-regions in the Mekong Delta is also observed Scientific and practical significance of the thesis 3.1 Scientific significance The adaptability and stability of hybrid maize in the Mekong Delta depend not only on yield but also on tolerance and ear aspect The results of the selection of maize hybrids are present in the growth, development, and resistance criteria, productivity in combination with the application of the selection index, selected domestic maize hybrids suitable for cultivation conditions in two ecological sub-regions in Dong Thap and Long An The results of research on maize cultivation techniques on rice-growing land rotated with maize have confirmed that trenching is mandatory in Dong Thap during the rainy SpringSummer crop In Long An, it is necessary to dig trenches and raise beds for all maize crops Attention should be paid to lowering the groundwater level when the maize plants are young, the growing point is below the ground It is necessary to have large enough jumps in density and nitrogen dosage, to have lower, equal, and higher levels, significantly different from the control treatment when studying planting density and nitrogen dosage for hybrid maize in Mekong Delta region The study result contributes to the theoretical basis for improving the yield of maize cultivated on alluvial and gray soils by increasing the reasonable planting density and the appropriate dose of fertilizer 3.2 Practical significance The results of the study have provided practical information on two domestic hybrid maize hybrids, LCH9A and MN585 In which, the maize hybrid MN585 was officially certified by the Ministry of Agriculture and Rural Development (according to Decision No 5097/QDTT-CLT, December 31st, 2019) Results of the study on nitrogen fertilizer dosages, agronomic efficiency of nitrogenous, phosphorus, and potassium fertilizers, planting density, and tillage techniques are an important basis for developing a suitable hybrid maize farming package for the ecological sub-region in the Mekong Delta Object and scope of research 4.1 Objects New maize hybrids and promising hybrids are provisionally certified for production compared with some foreign hybrids being produced in the Mekong Delta Technical measures: studying the influences of tillage technique, planting density, and amount of nitrogen fertilizer contributing to adjusting the technical techniques from general recommendations to recommendations for each type of soil and different crops on rice-growing land in the Mekong Delta 4.2 Research scope Hybrid maize hybrids: including 50 maize hybrids and promising maize hybrids, of which 24 hybrids are certified at ministerial level (including foreign hybrids as a check) and 26 other hybrids are promising hybrids that are tested in other regions Technical measures: study the effects of tillage technique, planting density, and amount of nitrogen fertilizer for gray soil group in Long An and alluvial soil group in Dong Thap over different seasons on rice land in the Mekong Delta Location: on the group of rice-growing land in Tan My commune, Duc Hoa District, Long An province (gray soil), An Phong commune, Thanh Binh district, Dong Thap province (alluvial soil) Time: in Winter-Spring and Spring-Summer crops from 2014 - 2018 Contributions of the thesis Selected two single maize hybrids with high grain yield, suitable for rotation on rice land in ecological sub-regions in Long An and Dong Thap In which, hybrid maize MN585 is officially certified for the Mekong Delta Results of the study on nitrogen fertilizer dosages, agronomic efficiency of nitrogenous, phosphorus, potassium fertilizers, planting density, and tillage techniques are an important basis for developing a suitable hybrid maize farming package for the ecological sub-region in the Mekong Delta Dissertation layout The thesis is presented on A4 paper size with 203 pages, in which the thesis content has 143 pages divided into parts: (i) Introduction from page to page 5; (ii) Literature review from pages to 47; (iii) Materials, Contents and Methods section on pages 48 to 64 (iv) Results and discussion sections on pages 65 to 141; (v) Conclusions and recommendations page 142 to 143 From page 144 to page 203 is presented a list of published works related to the thesis, references to the thesis appendix The thesis content is presented with 57 tables of data and images with 190 Vietnamese and foreign references cited (56 documents in Vietnamese, 120 documents in English, and 14 websites) The appendix includes statistical tables; soil analysis results; climate and weather changes; decision on the certification of hybrids, characteristics of maize hybrids participating in the experiment, and some illustrations during the implementation of the thesis CHAPTER LITERATURE REVIEW According to Prasanna et al (2018), maize production accounts for about 50% of global grain production According to a report by the US Department of Agriculture, in the 2019/2020 crop year, the global maize area reached 192.55 million hectares, the average yield reached 5.79 tons.ha-1, and the output reached 1,113.50 million tons (USDA, 2020) The US produces the most maize in the world with 360,233 million tons China, Indonesia, and the Philippines are also among the countries with the highest maize production in the world In Vietnam, it is reported that from 2014 to 2020 although the maize yield has increased, the area planted to maize has decreased gradually, leading to a sharp decrease in maize production Some studies also showed that in 2020 in Viet Nam, maize production reached 4.56 million tons, whereas the amount of maize that was imported to meet the domestic demand was 12.07 million tons (General Statistics Office, 2020) Vietnam is strongly affected by climate change, severe drought, and saltwater intrusion, especially in the Mekong Delta The transition to upland crops requiring less water is the current sustainable development solution for this region The maize area can be expanded in the Mekong Delta, with an average maize grain yield of 6.24 tons.ha-1, ranking second in the country; however, at the present, the maize area in this region is only 27.5 thousand (accounting for 2.92% of the total maize area of the whole country) (General Statistics Office, 2020) The development of hybrid maize in the Mekong Delta faces many challenges that need to be resolved as follows: 1) Breeding: Although some suitable maize hybrids are selected for different soil conditions and crop rotation on rice land in the Mekong Delta (Dao Ngoc Anh, 2013; Le Quy Kha et al., 2015), the number of selected hybrids is still very small The study aimed to select domestic maize hybrids to participate deeply in the maize hybrid market share for the Mekong Delta region 2) Technical measures: There are no packages of maize farming techniques for all regions In addition, maize farming techniques on rice land are not the same as on upland fields, with many biotic and abiotic stresses The study was carried out to serve as a basis for building a technical package for maize cultivation on rice-growing land on different soil groups 3) Maize needs a lot of nutrients to achieve a high grain yield The study evaluates the effectiveness of some biological products and slow-release fertilizers to reduce the number of chemical nitrogen fertilizers and reduce environmental pollution 4) Domestic maize market: Output for maize production is currently facing many obstacles due to high maize production costs and competitive prices from maize exported countries Ho Cao Viet (2015) showed that maize farmers suffered losses due to high production costs, low maize prices, and low yields The study aimed to evaluate the efficiency of maize cultivation on rice land and the economic efficiency of maize crop rotation CHAPTER RESEARCH MATERIALS, CONTENTS AND METHODS 2.1 Research materials and facilities 2.1.1 Experimental materials Research materials include promising hybrids or hybrids (in the process of being certified for production in ecological regions outside the Mekong Delta or already certified for production and trade) from research institutes and organizations, domestic institutions, and companies Hybrids that were used as control include NK6 (Syngenta company), DK9901, and DK6919 (Dekalb company) depending on different ecological regions (Table 2.2) With the expectation of a quick selection of maize hybrids that are suitable for each different ecological sub-region, some hybrids are adjusted to change over seasons and years; some promising hybrids in the previous crop were kept and followed up with other hybrids in the following seasons In the same crop, the experimental sets were similar across the experimental sites Table 2.2 Maize hybrids in the hybrid selection experiment over the growing seasons from 2014 to 2016 Hybrids SummerNo Summer-Spring Winter-Spring 2014 Winter-Spring Spring/Autumn 2014 - 2015 2015 - 2016 Summer 2015 HLB1104 QL6 VS7672 VS7672 VS71 VS686 VS1499 VS1499 LCH9A Highway 12 VS6721 VS6721 NSC87 MN585 CNC97 CNC97 KK2 VS26 MN585 CNC123 MN1 TB15 CNC234 CNC234 LVN8960 TB16 CNC366 CNC366 KK1 Highway 13 SSC068 CN13-12 NL13-1 LCH9A SSC443 NL131A 10 SSC474 MN1 SSC946 GS9989 11 LVN61 SSC2095 SSC672 GS6869 12 HN46 HLB1103 CN13-12 SSC443 13 SSC2095 VS8 GS6869 SSC120946 14 LCH9B VS71 GS9989 SSC946 15 VS36 New MN1 LCH9A LCH9M2 16 H818 SSC474 HLB1402 MN585 17 V118 CNC366 HLB1404 LCH9A 18 VS26 HLB1104 30T60 DK6919 (E/C3) 19 NK67 (D/C1) NK67 (D/C1) NK67 (D/C1) 20 DK9901 (D/C2) DK9901(D/C2) DK9901 (D/C2) D/C1, 2, 3: Controls 1, 2, 3; XH: Spring-Summer crop; HT: Summer-Autumn crop; DX; Winter Spring IAS: Institute of Agricultural Science for Southern Vietnam; SSC: Southern Seed Company; NMRI: Maize Research Institute; D/C: Check hybrids; A brief profile of the hybrids is included in Appendix 2.1.2 Experimental materials Fertilizers including Phu My nitrogen (46% N), Long Thanh Superphosphate (16% P2O5), Phu My potassium chloride (61% K2O), Amistar top 325SC insecticide (composition: 200g.L-1 Azoxystrobin 125g.L-1 Difenoconazole), Anvil 5SC (composition: 50g.L-1 Hexaconazole 50g.L-1) were used Microbiological and slow-release fertilizers were utilized in the study Equipment such as moisture meter (Kett Grainer PM 400), electronic scale, caliper, tape measure, sprayer, and water pump were also employed 2.2 Research content - Content 1: Selecting domestic maize hybrids suitable to ecological conditions on ricegrowing land rotated with maize in Long An and Dong Thap provinces - Content 2: Studying some farming techniques for hybrid maize on rice-growing land rotated with maize in Long An and Dong Thap provinces + Experimenting with soil preparation techniques; + Experiments to evaluate the efficiency of fertilizer use for hybrid maize on converted rice land; + Experiments to determine the appropriate dose of nitrogen fertilizer and planting density; + Study on the effectiveness of microbiological and slow-release fertilizers on maize - Content 3: Building a model of maize cultivation on rice-growing land rotated with maize in ecological sub-regions in Long An and Dong Thap provinces + Evaluation of production efficiency of promising maize hybrids applying synchronous technical measures; + Evaluation of the effectiveness of modified farming models in the local production structure 2.3 Research Methods 2.3.1 General farming techniques The row length of maize in the experiment was 5.0 m, the distance between rows was 0.7 m Wide of the alley: 1.0 m Distance of repetitions: 1.0 - 1.5 m Sowing plant in each hole Trenching technique: only dig trenches 25 - 30 cm wide, 20 - 25 cm deep The bed is 1.1 - 1.2 m wide, ensuring that rows are 0.7 m apart Fertilizer method: Base fertilizer: 100% phosphate + 1/4 nitrogen First side application at the stage of maize plants with - leaves: 1/4 of nitrogen + ½ of potassium 2nd side-dress of fertilizing: maize stage - leaves: ½ amount of protein + amount of potassium Care: Monitor pest control, weeds Trimming or compensating plants at the 1st stage of maize plants with - leaves Trimming, or compensating plants for 2nd times when maize plants with - leaves Weeding control and slightly adding soil to the root zone at the stage of - leaves Additional watering, ensuring enough moisture for maize plants, especially 10 - 15 days before and after flowering 2.3.2 Experimental layout 2.3.2.1 Content 1: Experimental design in a randomized complete block (RCBD), three replicates The plot area is 18 m2, each plot is sown in rows 2.3.2.2 Content 2: Promising maize hybrid MN585 in the selection experiment was selected to carry out the experiments in content - Testing of soil preparation measures: randomized complete block design (RCBD), three replicates, four treatments: 1) Soil preparation + Trenching (LĐ + ĐR); 2) No tillage + Digging trenches (KLĐ + ĐR); 3) Soil preparation + No trench digging (LĐ+KĐR); 4) No soil preparation + No trench digging (KLĐ+KĐR) The plot area is 120 m2, each plot is sown in 30 - 35 rows Amount of fertilizer (kg.ha-1): 200 N – 90 P2O5 – 90 K2O - Experiment to evaluate the efficiency of fertilizer use for hybrid maize on converted rice land: randomized complete block design (RCBD), three replicates, four treatments: 1) NPK: Provide adequate amounts of fertilizer N, P, K; 2) PK: Provide adequate P, K but not apply N; 3) NK: Provide adequate N, K but not apply P; 4) NP: Provide enough N, P but not apply K The plot area is 21 m2, each plot is sown in rows Amount of fertilizer (kg.ha-1): 200 N - 90 P2O5 - 60 K2O - Experiment to determine the appropriate dose of nitrogen fertilizer and planting density: arranged in subplot format, three replicates Main plot factors: five levels of nitrogen (kg N.ha-1): 120, 160, 200, 240 and 280 kg N.ha-1 on fixed P and K dosage: 90 kg P2O5.ha-1 and 60 kg K2O.ha-1 Sub-plot factor: density Winter-Spring crop: four density 5.7; 7.1; 8.4 and 11.0 thousand plants.ha-1 (row spacing 70 cm x plant to plant spacing 25; 20; 15 and 13 cm) SpringSummer crop: density 5.7; 7.1; 9.5 and 14.3 thousand plants.ha-1 (row spacing 70 cm x plant to plant spacing 25; 20; 15 and 10 cm) Area of plot is 21 m2, each plot has rows - Experiment to evaluate the effectiveness of microbiological and slow-release fertilizers on maize: Experimental layout: The experiment was arranged in a randomized complete block (RCBD), with three replications Experimental plot area: 21 m2 (6 rows.plot-1, row length: m, row spacing: 0.7 m, plant spacing: 0.2 m) Distance between plots: 1.0 m, interval between repetitions: 1.0 - 1.5 m Sow one plant in each hole The tillage technique was similar in the tillage experiment Promising hybrid MN585 was used in the experiment The amount of fertilizer N: P: K (kg.ha-1) respectively 220 N: 90 P2O5: 90 K2O An experimental treatment: including 15 treatments, three replicates, including treatments that reduce 25%, 50%, 75%, and 100% N; 50% reduction of P2O5 and K2O combined with the treatment of biological products or the use of advanced fertilizers 2.3.2.3 Content 3: Building a model of hybrid maize cultivation on rice-growing land rotated with maize in ecological sub-regions in Long An and Dong Thap provinces - Evaluation of the production efficiency of promising maize hybrids with the synchronous application of technical measures: synchronously apply technical measures such as tillage, trenching, fertilizer dosage, care, and fertilization (similar to experiments in tillage techniques and assessment of fertilizer use efficiency) The experimental maize hybrid was the promising hybrid maize MN585 in Experiment and the locally grown control hybrid - Evaluate the effectiveness of converted farming models in the local production structure: maize cultivation techniques performed similarly to tillage techniques and to evaluate the efficiency of fertilizer use The maize hybrid used is a promising hybrid MN585 in the hybrid selection experiment (experiment 1); hybrids and technical measures of rice cultivation applied according to the production practices of local farmers 2.3.3 Data collection for criteria Depending on the nature of the experiment, the monitoring criteria include days from sowing to tasselling, silking, growth duration from sowing to harvest; plant height, ear height, plant aspect, ear aspect, stay green leaf; rate of dead and fallen plants Stem borer (Chilo partellus), Banded leaf and Sheath blight (Rhizoctonia solani f sp sasakii), grain yield composition (ear length, ear diameter, number of kernels.row-1, number of rows.cob-1, the weight of 1000 kernels, and actual grain yield Response of maize yield with N, P, K fertilizers; agronomic efficiency of N, P, K Collect all input accounting costs including seeds, fertilizers, pesticides, labor (land preparation, sowing, tending, fertilizing, spraying, collecting planning, transportation), energy in maize production to calculate the economic efficiency of the experimental maize hybrid compared with the control hybrid; calculate total income from transformation models in the farming system in 2017 Calculate profit and profit ratio according to the formula: Profit margin (%): Total revenue – Total cost Profit margin = x 100 total revenue Observation, collection, and evaluation criteria according to the National Technical Regulation on testing the value of cultivation and use of maize hybrids (QCVN 0156:2011/BNNPTNT) (2011); applying the Guidelines for Survey, Comparison and Testing of maize hybrids (Le Quy Kha, 2013) and the guidance of CIMMYT (1999) 2.4 Data processing Collected data were analyzed by Excel 2010 software Analysis of variance of experimental results by Stagraphics XV Using the selection index software of Nguyen Dinh Hien (1996) to select maize hybrids over the seasons in ecological regions based on target and intensity for each monitored trait (Table 2.4) Table 2.4 Targets and selection intensity of the selection criteria for maize hybrids for ecological regions of the Mekong Delta No Variable Target Intensity Days from sowing to tasselling 0 Days from sowing to silking 0 Days from sowing to harvest 0 Stem borer -3 5 Banded leaf and Sheath blight -3 Stay green -3 Plant aspect -3 Ear aspect -3 Plant height 0 10 Ear height 0 11 Grain yield 12 Characteristics LCH9A Selected hybrids for Spring Summer 2014 LVN61 VS71 LVN8960 SSC474 NK67 DK9901 MN585 Selected hybrids for Spring Summer 2015 SSC443 CNC97 SSC946 30T60 NK67 DK9901 ) Characteristics Sowing to tasselling (day) Sowing to silking (days) Growth duration (days) Plant height (cm) Ear height (cm) Stem borer (1-5) Banded leaf and Sheath blight (1-5) Stay green (1-10) Plant aspect (1-5) Ear aspect (1-5) Grain yield (ton.ha1 ) Characteristics Sowing to tasselling (day) Sowing to silking (days) Growth duration (days) Plant height (cm) Ear height (cm) Stem borer (1-5) Banded leaf and Sheath blight (1-5) Stay green (1-10) Plant aspect (1-5) Ear aspect (1-5) Grain yield (ton.ha1 ) 51 52 51 51 51 51 51 52 53 53 52 53 53 54 94 94 95 93 95 97 94 186.2 116.7 2.7 197.2 112.0 3.1 199.5 114.2 2.8 197.3 112.7 3.3 201.8 114.8 2.9 201.3 118.2 3.3 202.2 131.2 3.3 2.3 1.9 2.0 2.4 2.4 2.6 3.0 1.8 2.4 2.3 1.9 2.5 2.8 2.1 2.8 2.9 2.1 2.8 2.5 1.8 2.4 2.8 1.8 2.3 2.3 1.9 2.0 2.0 9.13 8.41 7.97 8.57 7.83 8.44 8.14 NL131A Selected hybrids of Winter-Spring crop 2015 - 2016 VS7672 SSC120946 VS6721 MN585 DK6919 52 51 54 52 54 53 54 53 56 54 56 56 100 101 101 102 102 102 244.2 128.7 2.8 179.7 89.3 2.8 218.2 105.5 3.0 238.2 131.8 2.9 228.0 121.7 2.8 241.0 131.7 3.4 1.5 1.4 1.3 1.3 1.6 1.3 1.5 2.3 1.9 1.8 2.5 1.6 1.8 2.5 1.8 2.1 2.4 2.4 2.0 2.3 1.8 1.9 2.8 2.0 9.82 9.89 9.57 9.66 9.76 9.82 3.2 Developing some farming techniques for maize hybrid MN585 on rice-growing land rotating with maize in the Mekong Delta Promising hybrid maize MN585 which has high grain yield potential, good resistance to pests and diseases, and suitable growing duration for rice farming system was used in the next study 13 3.2.1 Determination of suitable tillage method for maize cultivation on rice land rotated with maize 3.2.1.1 Effect of tillage on plant height and ear height In both Winter-Spring crops of 2016 - 2017 and Spring-Summer of 2017, in Long An, the treatment with trenching combined with tillage resulted in the highest plant height and ear height (198.3 - 216.7 cm) and (92.0 - 104.3 cm), respectively The height of the plant and ear height is 213.8 - 265.0 cm and 89.1 - 140.8 cm in Dong Thap, respectively 3.2.1.2 Effect of tillage on the rate of dead and fallen plants In Long An, no-trenching and no-tillage treatments resulted in high plant mortality in all crops However, the treatment without trenching resulted in a higher percentage of fallen plants and dead plants compared with trenching in both crops in Dong Thap Thus, the tillage and rooting method help corn plants develop root systems deeper into the soil layer below which leads to less fall (Biana et al., 2016; Shinoto et al., 2020) and helps to reduce toxic in contaminated soil alum (Vo Thi Guong and Nguyen My Hoa, 2010) Therefore, trenching is a necessary measure in Dong Thap; the combination of trenching and tillage is necessary when cultivating maize on rice land in Long An 3.2.1.3 Effect of tillage on maize yield The trenching method resulted in a higher grain yield than the no-trenching method in the two crops at the experimental sites In Long An, the treatment of tillage combined with trenching resulted in yields of 8.15 and 4.05 tons.ha-1 in Winter-Spring and Spring-Summer crops, respectively In contrast, the no-tillage or no-trenching method resulted in very low grain yield due to very high rates of fallen and dead plants under experimental conditions In Dong Thap, maize grain yields reached 10.77 and 10.56 tons.ha-1 in the Winter-Spring crop; reached 11.20 and 10.86 tons.ha-1 in Spring-Summer crop According to Bakht et al (2006), proper tillage practices combined with appropriate fertilization lead to higher maize yields than notillage 14 Table 3.15 Effect of tillage method on growth, tolerance and grain yield, Winter-Spring season 2016 - 2017 and Spring-Summer 2017 crop in Long An and Dong Thap Rate of fallen plants Grain yield (ton.haPlant height (cm) Ear height (cm) Mortality rate (%) (%) ) Experiment Dong Dong Dong Dong Dong Long An Long An Long An Long An Long An Thap Thap Thap Thap Thap Winter-Spring 2016 - 2017 LĐ-ĐR 216.7 a 216.7 92.0 a 89.3 7.3 a 3.3 1.3 c 1.3 b 8.15 a 10.77 a LĐ-KĐR 133.0 b 207.7 68.0 b 85.7 1.3 b 3.3 16.0 b 4.0 a 0.75 b 7.64 b KLĐ-ĐR 120.7 bc 220.7 70.0 b 91.3 1.3 b 2.0 25.3 ab 2.0 b 0.83 b 10.56 a KLĐ-KĐR 106.7 c 210.0 49.0 c 90.0 2.0 b 2.7 32.0 a 4.0 a 0.55 b 7.46 b Average 144.3 213.8 69.8 89.1 3.0 2.8 18.7 2.8 2.57 9.11 CV (%) 5.3 3.0 3.3 6.4 25.5 28.2 27.5 28.8 11.6 9.2 LSD0.05 15.4* Ns 4.7* Ns 1.5* Ns 10.5* 1.6* 0.6* 1.67* Spring Summer 2017 LĐ-ĐR 198.3 a 269.0 104.3 a 144.6 4.7 4.0 b 6.7 0.0 4.05 a 11.20 a LĐ-KĐR 122.0 b 262.0 55.0 c 141.0 2.0 8.0 a 48.0 0.2 0.33 b 9.17 b KLĐ-ĐR 120.7 b 263.4 75.0 b 135.7 2.7 3.3 b 41.3 0.0 0.42 b 10.86 a KLĐ-KĐR 97.0 c 265.7 49.0 c 141.7 3.3 7.3 a 66.7 0.2 0.11 b 9.21 b Average 134.5 265.0 70.8 140.8 3.2 5.7 40.7 0.1 1.23 10.11 CV (%) 4.3 3.2 7.5 3.6 23.5 25.6 11.8 50.5 50.8 6.4 LSD0.05 11.6* Ns 10.6* Ns Ns 2.9* 9.6* Ns 1.3* 1.29* LĐ-ĐR: Land preparation + Digging trenches; LĐ-KĐR: Land preparation + No trenching; KLĐ-ĐR: No tillage + Digging trenches; KLĐKĐR: No soil preparation + No trench digging In the same column, numbers followed by the same letter are not significantly different at P>P=K The grain yield response was high with nitrogen (6.08 tons.ha-1), and the grain yield response was low for phosphorus (1.54 tons.ha-1) and potassium (1.90 tons.ha-1) The agronomic efficiency of nitrogen, phosphorus, and potassium was 27.66 kg maize.kg N-1, 17.13 kg maize.kg P2O5-1 and 31.68 kg maize.kg K2O-1, respectively The report of Pasuquin et al (2010) showed that the agronomic efficiency reached an average of 25.1 kg maize.kg N-1 in Southeast Asia and reached an average of 25.2 kg maize.kg N-1 in Vietnam Research results of Ngo Ngoc Hung (2009), Trinh Quang Khuong et al (2010) conducted in the Mekong Delta show that the yield response of maize is in the order of N>>P=K 3.2.3 Determination of appropriate nitrogen dose and density for selected maize hybrids on rice-growing land rotated with maize in the Mekong Delta 3.2.3.1 Effect of nitrogen dose and planting density on the growth of maize Increasing the nitrogen fertilizer dose to 280 kg N.ha-1 resulted in an increase in plant height and ear height in both experimental sites Plant height and ear height in Winter-Spring crop of 2016 - 2017 and Spring-Summer crop of 2017 were from 175.5 to 176.2 cm and from 89.6 to 91.9 cm in Long An; while plant height and ear height reached from 215.0 to 250.5 cm and from 98.3 to 124.8 cm in Dong Thap Increasing the density from 5.7 to 7.1 thousand plants.ha-1 leads to increases in the height of the plants and the ear height in Long An In Dong Thap, the plant height increased to a density of 11.0 thousand plants.ha-1 in the Winter-Spring crop of 2016 – 2017 while a density is 9.5 thousand plants.ha-1 in the Spring-Summer crop Nour (1992); Nwogboduhu (2016) also concluded that increasing planting density leads to higher plant height 3.2.3.2 Effect of nitrogen dosage and planting density on the level of stem borer and Banded leaf and Sheath blight disease In Long An, the level of stem borer infestation was not significantly different through nitrogen fertilizer doses (P>0.05) in both crops and was assessed from moderate to good infection (2.3 - 3.7 point); The level of stem borer infestation was lowest at the density of 5.7 7.1 thousand plants.ha-1 and there was a significant difference (P