Tài liệu Study on site specific nutrient management (ssnm) for sugarcane (saccharum officinarum l.) in the mekong delta

CHAPTER 1 INTRODUCTION 1.1 Rationale Sugarcane (Saccharum officinarum L.) is an annual crop producing the most biomass then it requires a large amount of nutrient inputs for its life cycle. There are some methods to assess nutrient status of sugarcane in order to determine correct rate of fertilizer, such as: (i) the Critical Nutrient Concentration (CNC) method has developed table of critical nutrient value and optimum range of sugarcane leaf that is considered as standard for diagnosis; however, this way will be not precise when other nutrient concentrations vary in tissue (Walworth and Sumner, 1986; Bailey, 1989, 1991 and 1993); (ii) the Diagnosis and Recommendation Integrated System (DRIS) is suggested by using at least 3 ratios (normally 6 to 7) of nutrient concentration for diagnosis (Walworth and Sumner, 1987). The DRIS has been applied successfully to explain result of leaf analysis in many kinds of crops, including sugarcane (Beaufils and Sumner, 1976; Elwali and Gascho, 1984; Beverly, 1991; Reis, 1999 and Hundal et al., 2005). Nevertheless, it seems to be as a “qualitative method” by showing “lack or excess of nutrients” situation but not providing fertilizer application rates to crop; (iii) the Site-Specific Nutrient Management (SSNM) is based on crop yield at a particular plot gained from two main sources: soil nutrient-supplying capacity and fertilizer application. Determining amount of fertilizer input will reduce nutrient loss on one hand and improve fertilizer use efficiency on the other hand. The SSNM approach has been applied successfully for rice crop (Dobermann et al., 2002) and hybrid corn over the world (Pasuquin et al., 2014), but the application for sugarcane is limited. Besides the need to determine fertilizer rate, timing of fertilization for increasing nutrient use efficiency by crops need to be considered as well. Using leaf colour chart (LCC) to diagnose nitrogen content in crop was considered a simple, easy method and have been popularly applied to rice. However, the study of LCC in sugarcane is still limited. 1 1.2 Research objectives (i) To assess current sugarcane farming and use of NPK fertilizer in alluvial (Soc Trang province) and acid sulfate soils (Hau Giang province). (ii) To determine effect of NPK fertilizer inputs to the nutrient uptake, growth and yield of sugarcanes under the two soil types. (iii) To determine recovery efficiency (RE) and agronomic efficiency (AE) in order to suggest NPK application for sugarcane cultivation. (iv) To evaluate LCC application for nitrogen timing on sugarcanes in two soils. 1.3 Object and scope of research  Object of research: NPK application for sugarcane (Saccharum officinarum L.)  Scopes of research:  Field experiments were carried out on sugarcane farmers in Cu Lao Dung district of Soc Trang province and Long My district of Hau Giang province.  Research period: January 2011 to January 2013.  Omission plot experiments were implemented to evaluate the omission of N, P, K nutrients  Study on growth and N, P, K uptake of sugarcane aims at improving scientific knowledge having a database for calculating “soil nutrient-supplying capacity” and fertilizers rate to achieve “target yield” based on SSNM principle. 1.4 Limitations of research  About fertilizer: only study N, P, K nutrients by inorganic fertilizer for sugarcane; the sugarcane pressmud was introduced as “improved treatment” according to the SSNM recommendation. 2  About location and experimental design: to minimize variation in statistical analysis, the experiments were designed as randomized completely block with 4 replications at two soil conditions. The research did not apply “on-farm research” in several locations as recommended by SSNM.  About soils: limited in two soil types in the Mekong delta such as: (i) alluvial soil (Dystric Fluvisols) in Cu Lao DungSoc Trang and acid sulfate soil (Thionic Gleysols) in Long My-Hau Giang. 1.5 Scientific and practical significances + Scientific significance This study is based on the principle of SSNM. Fertilizer recommendation for small scale where soil, crop, climate, weather, cultural practice should be the same. Therefore, recommendation based on crop need at specific field will get higher fertilizer use efficiency. Principally, calculation of fertilizer rates based on the SSNM method comes from nutrient balance which is manifested by crop yield. According to this approach, there are two sources of nutrient, such as soils and fertilizers to create optimum yield of crop. In this research, NPK fertilizer rates have been extrapolated based on the difference between sugarcane nutrient requirements and the soils nutrient supplying capacity. In addition, the database on growth and nutrient uptake of sugarcane in Mekong delta soils has been constructed in this study, which would be useful to assess crop growth and nutrient balance on the sugarcane soils. + Practical significance The results can be applied for sugarcane farming in the Mekong delta. By simple and easy practice, the study results help to reduce production costs then increase price competition in the region. In the coming crops, determination of NPK fertilizers rates can be updated by extension workers or farmers through “omission plot technique” at some representative sugarcane fields in the Mekong delta. 3 The result from LCC application for sugarcane is important reference to help farmers estimate when to test leaf color and apply nitrogen exactly as crop need in the two soil types. 1.6 Innovativeness - SSNM and LCC have been applied first time in the Mekong delta, the results showed that the method is helpful for determining NPK fertilizers rates and nitrogen application timing for sugarcane in the Mekong delta. - Soil-supplying capacity of N, P, K for sugarcane have been determined. Percent ratio of N, P, K from soils to total crop requirement in order to achieve target yield were recorded as 32.6%N, 46.2%P2O5, 56.1%K2O in Cu Lao Dung and 32.9%N, 59.6% P2O5 và 63.4% K2O in Long My. - At the same NPK fertilizer application rates, response to sugarcane yield in Long My was about 89% compared to Cu Lao Dung. Using “improved treatment” by using sugarcane pressmud at 10 tons/ha made sugarcane yield increased at both study sites. - Farmers in the research areas almost have not applied K for sugarcane. The application of potassium made Brix degree of sugarcane increased in both Cu Lao Dung and Long My. CHAPTER 2 LITERATURE REVIEW 2.1 Sugarcane farming in Soc Trang and Hau Giang Soc Trang and Hau Giang are located in the lower Mekong delta. According to Hua Thanh Xuan (2008), Soc Trang is one of the largest sugarcane producers in the Mekong delta in term of planted areas. Most sugarcanes are planted in the island of Cu Lao Dung and Long Phu formed by alluvial deposition. Currently sugarcane yield in Cu Lao Dung is higher than average of the world. Hau Giang has the highest ranks of sugarcane planted area as well as production in the Mekong delta, annual planted area of sugarcane in Hau Giang is situated after rice with 13,063 ha and yield of 82,60 tons per ha (Statistical Year Book, 2010). 4 2.2 Botanical requirement characteristics, growth and nutrient 2.2.1 Botanical characteristics of sugarcane 2.2.2 Periods of growth 2.2.3 Nutrient requirement Sugarcane is a long crop that belongs to C 4 pathway creating big amount of production and needs high humidity, nutrients, sunshine to optimize its productivity. It is estimated that one ton of sugarcane production requires 0.56-1.20 kgN, 0.38-0.82 kgP 2O5, 1.00-2.50 kgK2O, 0.25-0.60 kgCa, 0.20-0.35 kgMg, 0.02-0.20 kgNa and 2.0-2.7 kgS together with micronutrients (Zender, 1990). On average, one sugarcane crop takes away 208, 53, 280, 30, 3.4, 1.2 and 0.2 kg N, P, K, S, Fe, Mn and Cu respectively from soils to achieve yield of 100 tons per ha (Singh and Yadav, 1996). Nutrient requirements are different by soil conditions from place to place (Natesan et al., 2007). 2.2.4 Quality parameters of sugarcane 2.3 Characteristics of K88-92 sugarcane variety 2.4 Fertilizer 2.4.1 Fertilizer recommendation for sugarcane Fertilizer is the most important factor of nutrient supply for sugarcane, accounting for about 50% of yield increase. Fertilizer recommendation is higher in the tropical than sub-tropical regions. Saini et al. (2006) recommended fertilizer for sugarcane production as 400 kgN, 170 kgP and 180-190 kgK depending on time and soil conditions. 2.4.2 Role of N, P and K 2.4.2.1 Nitrogen (N) Nitrogen is a key nutrient affecting yield and quality of sugarcane. Nitrogen increases sugarcane yield through increases of shoots, stalk height, diameter of internode (Abayomi, 1987). Seasonal nitrogen use efficiency is estimated at 0.841 tons sugarcane kg-1N (Chattopadhyay et al., 2004). Quantity of nitrogen fertilizer in the world ranges from 50 to 300 kgN ha -1 and 1 kg of nitrogen can create 0,5-1,2 tons ha-1 (Hunsigi, 1993). 5 2.4.2.2 Phosphorous (P2O5) Phosphorus is an essential element to promote creation of roots and increase of branches but its availability depends on local soils and fertilizer application. Increase of sugarcane yield after phosphorus use is results of sucker development, biomass, and density. At optimum phosphorous level, sugar concentration and juice purity are also better (Elamin et al., 2007). 2.4.2.3 Potassium (K2O) Potassium nutrient plays important roles in plant growth and metabolism. Potassium fertilizer application often increases sugar concentration and juice return, especially the case of late harvest (Hunsigi, 2011). 2.5 Site-specific Nutrient Management approach 2.5.1 Definition Site-specific nutrient management (SSNM) is an approach to feeding crop with nutrients as and when needed. The application and management of nutrients are dynamically adjusted to crop needs of the location and season. This method helps farmers adjust fertilizers to address lack of nutrients between required nutrients to maximize crop yield and nutrient reserve of the soils, organic materials, and irrigation water. The SSNM approach aims to increase farmers profit through higher yield, application of nutrients (mainly N, P and K) locally and seasonally, and optimal use of existing indigenous nutrient source such as crop residues and organic fertilizers. 2.5.2 Principles of SSNM 2.5.2.1 Principles of SSNM According to Witt et al. (2006) the SSNM provides maize farmers knowledge to maximize fertilizer use and profit by balance of required nutrients for high yield and indigenous nutrient supply from soils, organic matters, crop residues, fertilizers and water. This new method is based on model of QUEFTS (Quantitative Evaluation of the Fertility of Tropical Soils) developed in Africa for maize crop (Janssen et al., 1990; Smaling và Janssen, 1993) and later for rice crop (Witt et al., 1999; Wang et al., 2001; Dobermann et al., 2002). Technology of omission plots is useful to determine fertilizers required to meet target yield (Witt and Doberman, 2002). In this method N, P and K fertilizers are applied in sufficient amounts to 6 overcome deficiencies and ensure high yield. The target yield can be determined from plots without limitation of NPK. In other words, the SSNM is an approach based on the plant that utilizes the omission plot technique to determine the yield obtained with only the soil reserves (omission plots) compared to the attainable yield obtained when nutrients are not limiting. 2.5.2.2 Steps of SSNM Step 1: Determine target yield Step 2: Estimate soil nutrient-supplying capacity Step 3: Calculate N, P and K nutrient inputs to meet deficiencies between crop need and soil supply 2.5.2.3 Parameters in the SSNM 2.5.3 Agronomic efficiency of N, P and K Agronomic efficiency of N, P or K (AEN, AEP or AEK) is the increase in yield per unit of fertilizer N, P2O5 or K2O applied. Fertilizer recommendation based on yield response and agronomic efficiency is an alternative approach where soil testing is not used regularly. This sounds good approach compared to other supportive decision making tools. 2.5.4 Use of “improved treatment” in SSNM for sugarcane 2.5.5 Managemnet of nitrogen in sugarcane farming 2.5.5.1 Determine timing to apply nitrogen fertilizer 2.5.5.2 Manage nitrogen nutrient to balance supply and demand 2.5.5.3 Diagnose nitrogen by LCC technique Leaf color is considered as an indicator to diagnose requirement of nitrogen fertilizer for crop. Previous studies show that rice genotype and nitrogen management based on LCC affected yield and yield components (Nagappa et al., 2002). Farmers believe that when the leaves shift from dark to light green or yellow, crop needs more nitrogen. Similarly, LCC is applied for sugarcane too (Gaddanakeri et al., 2007). Chandrashekara (2009) reported that application of nitrogen at 50 and 60 kgN/ha with LCC=6, sugarcane yields were high (150.5 and 151.7 tons/ha in the first crop and 123.8 and 125.0 tons/ha in the second crop respectively), CCS, juice, Brix, Pol and fructose, total uptake of N, P, K less than traditional practice. 7 2.6 Method of soil nutrient assessment in sugarcane 2.7 Nutrient interaction in sugarcane farming CHAPTER 3 RESEARCH METHODOLOGY This study consists of four main activities: 3.1 Activity 1: Survey on current sugarcane farming and fertilizer application in the research areas Household survey was conducted in sugarcane areas of Cu Lao Dung (Soc Trang) and Long My (Hau Giang) districts to understand farming techniques such as veriety, quantity of fertilizer use, yield. 3.2 Activity 2. Study effects of fertilizers on sugarcane growth, NPK uptake, and yield This is a factorial experiment in a randomized complete block design with 2 factors, 4 replications, and 8 treatments as NPK, NP, NK, PK and NPK, NP, NK, PK in combination with sugarcane pressmud in Cu Lao Dung (Soc Trang) and Long My (Hau Giang) to assess effects of nutrient omission application (N, P, K) and sugarcane pressmud to growth, nutrient uptake, and yield of sugarcane. The experiment was carried out from January 2011 to January 2012. 3.3 Activity 3. Determine return efficiency (REX) and agronomic efficiency (AEX) to recommend fertilizer (N, P, K) application for sugarcane There were two field experiments including sugarcane cultivated by planting (January 2011 to January 2012) and by ratooning (January 2012 to December 2012) which is a practice of growing a crop from the stubbles of previous crop at the same field in Activity 2 to determine AE and RE for NPK fertilizer recommendation of sugarcane at two research sites. 3.4 Activity 4. Diagnose for nitrogen application timing by LCC technique 8 The experiment was randomized complete block design with 4 replications and four treatments as PPB-1, PPB-2, PPB-3 and PPB-4 in Cu Lao Dung-Soc Trang and Long My-Hau Giang (Table 3.5). The experiment was carried out from January 2012 to January 2013 to diagnose timing for nitrogen application by LCC technique. Table 3.5: Treatment of nitrogen application timing Treatment PPB-1 PPB-2 PPB-3 PPB-4 Nitrogen application timing (Day after cultivation) 10-20 60 90 120 150 1/5 1/5 1/5 1/5 1/5 1/5 1/5 2/5 LCC LCC 1/5 1/5 LCC Weekly measurement, applied N when LCC<2 Note: Treatments with LCC application, applied N when LCC<2 with amount of 1/5N CHAPTER 4 RESULTS AND DISCUSSIONS 4.1 Activity 1: Survey on current sugarcane farming and fertilizer application in the research areas In Cu Lao Dung, most farmers applied nitrogen fertilizer at level of 250-300 kgN/ha (36.1%) and 300-350 kgN/ha (31.1%). Similarly, farmers in Long My used nitrogen fertilizer at level of 300-350 kgN/ha (34.5%). For phosphorus fertilizer, common dosage were 100-150 kgP2O5 (37.7%) in Cu Lao Dung whereas in Long My most cases were below 100 kgP 2O5. Farmers payed less attention on potassium application in both of study sites. According to Nguyen Huy Uoc (2001) it is necessary to apply potassium fertilizer at 140200 kgK2O/ha to reach 70-80 tons/ha sugarcane and sugar concentration above 10 CCS. On average, at household level sugarcane yield were 158 tons/ha in Cu Lao Dung and 135 tons/ha in Long My if farmers applied NPK sufficiently. 4.2 Activity 2. Study effects of fertilizers on sugarcane growth, NPK uptake, and yield 9 4.2.1 Effects of nutrient omission application in combination with sugarcane pressmud use on growth and development of sugarcane Nitrogen omission application (Treatment PK) resulted in plant height, diameter, and density lower than nitrogen application treatments (NPK, NK, NP) at 40, 120, 150, 210 and 330 days after cultivation. However, phosphorus omission application (Treatment NK) and potassium omission (Treatment NP) such above yield parameters were neglibigle decrease. The efficiency of sugarcane pressmud application increased the stalk height in Cu Lao Dung but not in Long My. The stalk height is an important parameter of growth and yield. 4.2.2 Effects of nutrient omission application in combination with sugarcane pressmud use on N, P, K uptake * Nitrogen uptake (N) On Cu Lao Dung and Long My, treatments of without N application showed that total nitrogen uptake was lower than that of nitrogen application. Table 4.20: Effects of N, P, K omission application in combination with sugarcane pressmud on total nitrogen uptake (kgN/ha) in sugarcane. Cu Lao Dung – Soc Trang, December 2011. Factor Inorganic fertilizer (A) NPK NP NK PK KBB BBM Organic (B) FA FB FAxB CV (%) 40 2.69a 2.95a 2.77a 2.33b 2.73 2.64 * ns * 9.8 Days after planting (DAP) 120 150 210 197.91a 240.9a 287.8a 171.27b 216.2b 196.1b b c 168.71 193.86 208.3b c d 107.16 117.64 101.4c y y 152.07 175.91 169.9y x x 170.45 208.39 226.9x ** ** ** * ** ** ns * ** 8.6 8.4 9.2 330 287.0a 231.4b 216.4b 93.7c 192.7y 221.6x ** * ns 13.6 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant It confirmed that soil nutrient-suppying capacity could not meet nitrogen requirement of sugarcane (Table 4.20 and 4.21). Interaction of nutrient omission application and sugarcane pressmud 10 in Cu Lao Dung showed that nitrogen was high when NPK applied in combination with sugarcane pressmud at 150 and 210 days after cultivation, the NPK+BBM treatment had the highest nitrogen uptake (as 262.8 and 362.7 kgN/ha respectively). Table 4.21: Effects of N, P, K omission application in combination with pressmud on total nitrogen uptake (kgN/ha) of sugarcane in acid sulfate soils in Long My – Hau Giang, December 2011. Factor Inorganic fertilizer (A) NPK NP NK PK KBB BBM Organic (B) FA FB FAxB CV (%) 40 45.25a 41.70ab 38.29bc 32.47c 37.05y 41.81x * * ns 15.6 Days after planting (DAP) 120 150 210 304.55a 317.01a 566.88a 258.49b 267.03b 442.75b b c 236.68 236.89 443.46b c d 137.85 118.11 272.29c 225.96 236.26 405.84y 242.82 233.26 456.85x ** ** ** ns ns * ns ns ns 12.2 10.6 13.6 330 282.7a 203.7b 180.0b 93.1c 183.8 195.4 ** ns * 12.9 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant * Phosphorus uptake (P2O5) With phosphorus omission treatment, total phosphorus uptake was lower the others in alluvial soils in Cu Lao Dung but it was not clear in acid sulfate soils in Long My (Table 4.22 and 4.23). There was an interaction between nutrient omission application and combination with pressmud on total phosphorus uptake of sugarcane in Cu Lao Dung at 120 and 150 days after cultivation (Table 4.22). 11 Table 4.22: Effects of N, P, K omission application in combination with pressmud on total phosphorus uptake (kgP 2O5/ha) of sugarcane in alluvial soils in Cu Lao Dung – Soc Trang, December 2011. Days after planting (DAP) Factor 40 120 150 210 330 NPK 0.75 59.67a 66.10a 63.5a 129.1a NP 0.76 48.20bc 58.75b 51.3b 98.9b Inorganic b c c fertilizer (A) NK 0.77 51.22 41.43 44.8 79.8c c c c PK 0.85 41.95 41.24 45.0 59.7d y y Organic (B) KBB 0.78 39.48 51.86 45.9 83.5y x x BBM 0.77 61.05 53.40 56.4 100.2x FA ns * ** ** ** FB ns ** ns ** * FAxB ns * ** ns ns CV (%) 11.5 4.3 8.5 11.1 14.9 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant Table 4.23: Effects of N, P, K omission application in combination with pressmud on total phosphorus uptake (kgP 2O5/ha) of sugarcane in acid sulfate soils in Long My – Hau Giang, December 2011. Days after planting (DAP) Factor 40 120 150 210 330 NPK 14.99a 95.97a 130.58a 168.66a 157.7a Inorganic NP 14.09ab 83.66b 118.08b 123.71b 101.9b fertilizer NK 13.59ab 73.65b 91.79c 107.96bc 93.2b (A) PK 11.24b 52.83c 70.86d 96.87c 94.0b y y Organic KBB 12.74 71.60 103.43 116.38 92.6y (B) BBM 14.22 81.45x 102.22 132.23x 129.8x FA ns ** ** ** ** FB ns * ns * ** FAxB ns ns ns ns ns CV (%) 20.8 12.8 11.5 13.6 14.2 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant * Potassium uptake (K2O) Potassium obmission application did not reduce total potassium uptake of sugarcane in Cu Lao Dung site. With potassium treatment but nitrogen omission application, absorbability of potassium was affected at both study sites (Table 4.24 and 4.25). Use 12 of pressmud showed that sugarcane uptake potassium at high level in Cu Lao Dung but not in Long My district. Table 4.24: Effects of N, P, K omission application in combination with pressmud on total potassium uptake (kgK 2O/ha) of sugarcane in alluvial soils in Cu Lao Dung – Soc Trang, December 2011. Days after planting (DAP) Factor 40 120 150 210 330 NPK 4.44 417.48a 337.23a 350.2a 811,4a Inorganic NP 4.48 362.61b 270.35b 281.7b 609,6b fertilizer NK 4.46 400.93ab 250.82b 296.1b 622,9b (A) c c c PK 4.73 296.77 183.50 229.4 455,6c y y Organic KBB 4.45 328.92 244.79 285.1 591,3y (B) BBM 4.09 409.98x 276.16x 193.5 658,5x FA ns ** ** ** * FB ns ** * ns ** FAxB ns ** ** * ns CV (%) 17.2 10.4 8.9 11.3 11.5 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant Table 4.25: Effects of N, P, K omission application in combination with pressmud on total potassium uptake (kgK2O/ha) of sugarcane in acid sulfate soils in Long My – Hau Giang, December 2011. Days after planting (DAP) Factor 40 120 150 210 330 NPK 68.20 414.69a 501.02a 771.05a 552.9a Inorganic NP 60.49 341.48b 409.22b 447.01c 330.1c fertilizer a NK 59.18 393.97 323.78c 580.17b 409.8b (A) c PK 56.27 249.14 221.96d 388.78c 350.9c y Organic KBB 56.07 325.14 367.21 521.93 407.3 (B) BBM 62.99 374.51x 360.78 571.57 414.4 FA ns ** ** ** ** FB ns * ns ns ns FAxB ns * ns ns * CV (%) 15.8 12.7 18.9 21.3 11.3 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant Sugar and starch crops require large amount of potassium than others. Their requirements can exceed 800 kg/ha including luxury consumption. According to Humbert (1968) one sugarcane crop with 100 tons takes away 500 kgK2O/ha. 13 4.2.3 Effects of nutrient omission application in combination with sugarcane pressmud use on sugarcane yield at alluvial and acid sulfate soils Table 4.26 and 4.27 indicated that NPK application increased sugarcane yield at both alluvial soils in Cu Lao Dung and acid sulfate soils in Long My. The yield could reach 176 tons/ha in alluvial soils in Cu Lao Dung (Table 4.26) and 156.9 tons/ha in acid sulfate soils in Long My (Table 4.27) when NPK applied sufficiently. N, P, and K omission applications caused lower yield than NPK use, the yield differences were recorded 14-66 tons/ha in Cu Lao Dung and 9-55 tons/ha in Long My. Treatments in combination with 10 tons/ha of sugarcane pressmud increased the stalk height, plant diameter then increased sugarcane yield. Table 4.26: Effects of N, P, K omission application in combination with pressmud on sugarcane yield in alluvial soils in Cu Lao Dung – Soc Trang, December 2011. Yield components Yield at Stalk Plant Plant Factor harvest height (m) diameter density (tons/ha) 2 (cm) (plant/m ) NPK 2.72a 2.96a 8.53 176.0a Inorganic c b NP 2.50 2.87 8.47 162.3b fertilizer ab b NK 2.63 2.80 8.32 154.2c (A) c c PK 2.38 2.60 8.31 110.2d y y Organic (B) KBB 2.50 2.76 8.43 148.6y x x BBM 2.62 2.85 8.38 152.8x FA * ** ns ** FB * * ns ** FAxB ns ns ns ns CV (%) 6.0 2.7 4.4 1.8 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant 14 Table 4.27: Effects of N, P, K omission application in combination with pressmud on sugarcane yield in acid sulfate soils in Long My – Hau Giang, December 2011. Yield components Yield at Stalk height Plant Plant Factor harvest (m) diameter density (tons/ha) (cm) (plant/m2) a NPK 2.91 2.58a 9.07 156.9a Inorganic b b NP 2.72 2.36 8.47 147.9b fertilizer ab b NK 2.83 2.33 9.27 143.3c (A) c c PK 2.61 2.16 8.52 109.1d y y Organic KBB 2.70 2.29 8.80 137.1y x x (B) BBM 2.83 2.43 8.87 141.6x FA * ** ns ** FB * * ns ** FAxB ns ns ns ns CV (%) 6.1 4.2 10.2 2.2 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant 4.2.4 Effects of nutrient omission application in combination with sugarcane pressmud use on Brix (%), CCS (%) of sugarcane at alluvial and acid sulfate soils The Brix degree increased at different age of sampling (Table 4.28). Table 4.29: Effects of N, P, K omission application in combination with pressmud on Brix and CCS at alluvial soils in Cu Lao Dung and acid sulfate soils in Long My at 330 days after planting, December 2011. Cu Lao Dung Long My Brix (%) CCS (%) (*) Brix (%) CCS (%) (*) NPK 17.9 8.3 21.4 10.6 Inorganic NP 17.1 7.8 19.6 9.4 fertilizer (A) NK 18.2 8.5 21.3 10.6 PK 18.8 8.9 21.6 10.8 Organic (B) KBB 17.8 8.2 20.8 10.2 BBM 18.3 8.6 21.2 10.5 Note: (*)CCS (%) = (Brix * 0.66) – 3.5 (Nguyen Bao Ve, 2011); increase 1 unit of CCS the price of sugarcane will increase 100 VND per kg Factor Potassium omission application decreased Brix but the nitrogen omission application was not. Qasim et al. (2003) and Shirazi et al. (2005) reported that there was a relationship between 15 sugar concentration and potassium which can increase air exchange during photosysnthesis process resulting higher yield and sugar content. The CCS was estimated according to Nguyen Bao Ve (2011) which is presented in Table 4.29. In general, both sites at 330 days after planting, fertilizer treatments increased CCS. Combination with pressmud also increased CCS at the same period. 4.3 Activitiy 3. Determine return efficiency (RE X) and agronomic efficiency (AEX) to recommend fertilizer (N, P, K) application for sugarcane 4.3.1 Determine parameters used to estimate fertilizer in the SSNM approach 4.3.1.1 Soil NPK supplying capacity in Cu Lao Dung – Soc Trang and Long My – Hau Giang Figure 4.13 showed that the sugarcane yield increase of N, P, K nutrients was recorded in the following order of 45, 17 and 11 tons/ha in Cu Lao Dung and 38, 13 and 9 tons/ha in Long My. In combination with pressmud, the sugarcane yield increase of N, P, K nutrients was recorded in the following order of 51, 21 and 11 tons/ha in Cu Lao Dung and 46, 14 and 12 tons/ha in Long My. Therefore, it is conluded that the increase of sugarcane yield was ranked as of N>P>K. (a) (b) Figure 4.13: Increase of sugarcane yield (tons/ha) when NPK application at level of 300-125-200 kg/ha in combination with sugarcane pressmud at 10 tons/ha: (a) Cu Lao Dung and (b) Long My, plant cane crop 2011-2012 and ratoon 2012 16 4.3.1.2 Determine agronomic efficiency (AE X) and return efficiency (REX) to recommend fertilizer (N, P, K) application for sugarcane at alluvial and acid sulfate soils a) Agronomic efficiency (AEX) of N, P, K fertilizers In Cu Lao Dung alluvial soils, agronomic efficiency of nitrogen (AEN) was 0.15; it means that increase 1 kg of nitrogen will increase 150 kg of sugarcane. Similarly, agronomic efficiency of phosphorus (AEP) was 0.14 and agronomic efficiency of potassium (AEK) was only 0.05. In Long My acid sulfate soils, the agronomic efficiency was lower with AEN, AEP, AEK was recorded as 130 kg sugarcane/kgN, 100 kg sugarcane/kgP2O5 and 50 kg sugarcane/kgK2O respectively. Pressmud application did not increase AEx at both study sites. b) Recovery efficiency (REX) of N, P and K In Cu Lao Dung, over the two crops the recovery efficiency of nitrogen (REN) was 49%, phosphorous (REP) 33% and potassium (REK) 93%. In combination with pressmud, the recovery efficiencies of N, P, K were recorded as 37, 17 and 53% respectively. In Long My, the recovery efficiency of nitrogen (RE N) was 48%, phosphorous (REP) 45% and potassium (REK) 77%. In combination with pressmud, the recovery efficiencies of N, P, K were recorded as 43, 13 and 82% respectively. 4.3.2 Estimate fertilizers for sugarcane in Cu Lao Dung alluvial soils and Long My acid sulfate soils Based on the household survey in Cu Lao Dung (Soc Trang) and Long My (Hau Giang) presented in Table 4.10, sugarcane yield in Cu Lao Dung (158 tons/ha) and Long My (135 tons/ha) were considered as target yield to estimate nutrient inputs for the two sites. NPK fertilizer application were estimated according to Pasuquin et al. (2014) with AEN, AEP, and AEK have been calculated above (section 4.3.1.2, part a). Thus, NPK application was recommended as 328N-156P2O5-279K2O (kg/ha) in Cu Lao Dung and 334N-168P2O5-296K2O (kg/ha) in Long My. 17 4.4 Activity 4. Diagnose nitrogen application timing for sugarcane by LCC application 4.4.1 Effect of nitrogen application timing on Brix degree Table 4.46 showed that nitrogen application methods affected Brix degree of sugarcane cultivated in Cu Lao Dung at 330 days after cultivation. The highest Brix degree (21.5%) was recorded at PPB-4, used nitrogen when LCC<2, (p<0.05). However, the Brix degree was not significantly different by nitrogen application timing in Long My site. Table 4.46: Effects of nitrogen application timing on Brix degree of sugarcane at 8 and 11 months in Cu Lao Dung and Long My, December 2012. Methods Brix degree (%Brix) Cu Lao Dung Long My 8 months 11 months 8 months 11 months PPB-1 13.2 19.1b 16.3 20.4 PPB-2 14.1 20.6b 16.4 20.7 PPB-3 13.0 18.4b 16.8 21.1 PPB-4 13.2 21.5a 16.5 20.7 F ns * ns ns CV (%) 12.4 5.0 7.0 6.4 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant 4.4.2 Effects of nitrogen application timing on sugarcane yield and yield components Sugarcane yields at harvest in Cu Lao Dung and Long My were presented in Table 4.47 and 4.48. They showed that sugarcane yiled with PPB-4 was higher than the others (PPB-1, PPB-2 and PPB-3). It confirmed that using LCC technique (LCC<2) to apply nitrogen resulting in higher sugarcane yield. 18 Table 4.47: Effects of nitrogen application timing on sugarcane yield and yield components at 330 days after cultivation in Cu Lao Dung, December 2012. Methods Yield components Yield at Stalk height Plant Plant harvest (m) diameter density (tons/ha) 2 (cm) (plant/m ) PPB-1 2.8b 3.1 7.8b 164.9c b a PPB-2 2.8 3.0 8.2 174.4b a a PPB-3 3.1 2.8 8.2 171.6b ab a PPB-4 3.0 3.2 8.3 183.1a F * ns * ** CV (%) 4.3 6.3 2.7 1.7 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant Table 4.48: Effects of nitrogen nitrogen application timing on sugarcane yield and yield components at 330 days after cultivation in Long My, December 2012. Methods Yield components Yield at Stalk height Plant Plant harvest (m) diameter density (tons/ha) 2 (cm) (plant/m ) PPB-1 3.1b 2.4b 7.6 153.2b b a PPB-2 3.0 2.8 7.6 156.3b a ab PPB-3 3.3 2.7 7.9 159.3b a ab PPB-4 3.3 2.7 8.1 166.5a F ** ns ns ** CV (%) 1.8 7.3 3.9 2.5 Note: In a column means followed by the same letter were not significantly different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant Sugarcane yield was high with method of 300 kgN/ha in combination with LCC measurement weekly (LCC<2 applied 1/5N). 4.4.3 Leaf nitrogen content at different nitrogen application timing when LCC<2 or before fertilizer use In Cu Lao Dung, Table 4.49 showed that when LCC<2 leaf nitrogen content ranged 1.30 to 1.68%, lower than critical value significantly (p<0.05). In Long My, Table 4.50 showed that regular nitrogen application or LCC<2, the leaf nitrogen content was also lower than critical value (1.80%) (p<0.05). Therefore, we can 19 conclude that indigenous nitrogen from soils could not meet nutrient needs of sugarcane. Table 4.49: Mean comparison of leaf nitrogen content (%N leaf) at different nitrogen application timing in Cu Lao Dung, December 2012. Methods Leaf nitrogen content (%N) Time 1 Time 2 Time 3 Time 4 Time 5 PPB-1 1.42** 1.47** 1.78ns 1.57** 1.30** ** ** ns ** PPB-2 1.31 1.57 1.83 1.48 1.36** ** * * ** PPB-3 1.34 1.52 1.66 1.46 1.35** ** * ** ** PPB-4 1.39 1.63 1.68 1.52 1.45** (*) Critical value 1.80 Note: In a column: *: significant at 5%; **: significant at 1%; ns: non significant via T-test with critical value (*) ( McCray and Mylavarapu, 2010) Table 4.50: Mean comparison of leaf nitrogen content (%N leaf) at different nitrogen application timing in Long My, December 2012. Methods Leaf nitrogen content (%N) Time 1 Time 2 Time 3 Time 4 Time 5 ** ** * ** PPB-1 1.40 1.46 1.61 1.28 1.21** PPB-2 1.45** 1.55** 1.68* 1.43** 1.31** PPB-3 1.45** 1.57** 1.58** 1.45** 1.24** ** ** ** ** PPB-4 1.49 1.61 1.57 1.39 1.31** (*) Critical value 1.80 Note: In a column: *: significant at 5%; **: significant at 1%; ns: non significant via T-test with critical value (*) ( McCray and Mylavarapu, 2010) When LCC<2, leaf nitrogen content varied from 1.31 to 1.61%, significantly lower than the critical value (p<0.05). 4.5 Economic efficiency of SSMN method Results from Table 4.51 showed that SSNM method created higher net profit than traditional method, it was 17.1 million VND in Cu Lao Dung and 27.4 million VND in Long My. This economic efficiency results from yield increase by SSNM application (17.3% in Cu Lao Dung and 24.8% in Long My) and decrease of cost for fertilizer (18.5% in Cu Lao Dung and 13.9% in Long My). 20