3. MATERIALS AND METHODS

Transcription

1 41 3. MATERIALS AND METHODS The present study entitled, Long-term effect of integrated nutrient management on dynamics of nitrogen, phosphorus and potassium in rice-wheat system was undertaken in an ongoing long-term fertilizer experiment initiated in kharif, 1991 at Bhadiarkhar experimental farm of College of Agriculture, Palampur. The present investigation has been undertaken during the two cropping cycles viz. Kharif (rice) 2008 to rabi (wheat) The details of field experiment and methodology adopted have been described under the following heads: 3.1 General description of study area 3.2 Field studies 3.3 Laboratory studies 3.4 Statistical analysis 3.1 General description of study area Experimental site The Bhadiarkhar farm of College of Agriculture, Chaudhary Sarwan Kumar Himachal Pradesh Krishi Vishvavidyalaya, Palampur is located at N latitude, E longitude and m altitude in North-West Himalayas. The site lies in the Palam Valley of Kangra district of Himachal Pradesh Climate Agro-climatically, Palampur falls under sub-temperate humid zone of Himachal Pradesh, which is characterized by mild summers, severe winters and experiences occasional snowfall during winters. The region receives an average rainfall of 2600 mm per annum, major portion of which (80 %) is received during June to September. Winter rains are received during December to February. October, November, April and May are dry months and usually receive very low or no rainfall. Mean monthly meteorological data recorded at the meteorological observatory of the Department of Agronomy Forage and Grassland Management during the crop season has been presented in Fig 3.1 and 3.2 (Appendix I & II).

2 Rainfall (mm), Relative humidity (%) Maximum and Minimum Temp ( o C) 42 Maximum Temperature ( C) Minimum Temperature ( C) Rainfall (mm) Relative Humidity (%) June July Aug Sep Oct Nov Dec Jan Feb March April May Standard Month 0 Fig. 3.1 Mean monthly weather data at Palampur during

3 Rainfall (mm), Relative humidity (%) Maximum and Minimum Temp. ( o C) 43 Maximum Temperature ( C) Minimum Temperature ( C) Rainfall (mm) Relative Humidity (%) June July Aug Sep Oct Nov Dec Jan Feb March April May Standard Month 0 Fig. 3.2 Mean monthly weather data at Palampur during

4 Soil characteristics Taxonomically, the soil of the study area falls in the order Alfisols and sub group Typic Hapludalf (Verma 1979). In the genetic system of classification, the soils of the area have been classified as Grey Brown Podozols and have been developed from fluvioglacial parent material. These soils owe their origin to rocks like slates, phyllites, schists, quartzites and gneisses. The soil of the experimental site at initiation of experiment (1991) was acidic in reaction and silty clay loam in texture. The surface soil of the experimental field was categorized as high in available nitrogen and medium in available phosphorus and potassium. The organic carbon content was also medium in status. Some important physico-chemical characteristics of the surface soil ( m) of the experimental site are given in Table 3.1. Table 3.1 Initial physico-chemical properties of experimental soil ( m) Soil property Value A. Particle Size analysis Sand (%) Silt (%) Clay (%) Textual class Silty clay loam B. Chemical analysis Soil ph 5.5 Organic carbon (g kg -1 ) 6.0 Available Nutrients (kg ha -1 )

5 45 o Nitrogen o Phosphorus 21.9 o Potassium CEC [ c mol(p + ) kg -1 ] Field studies Experimental details The field experiment was conducted on a pre-established long-term field experiment which comprised of 12 treatments, each replicated four times with a gross plot size of m 2 in randomized block design was continued for the purpose of present investigation. The treatment detail was as under: Treatments Kharif Rabi T 1 Control Control T 2 50% NPK 50% NPK T 3 50% NPK 100% NPK T 4 75% NPK 75% NPK T 5 100% NPK 100% NPK T 6 50% NPK+50% N through FYM 100% NPK T 7 75% NPK+25% N through FYM 75% NPK T 8 50% NPK+50% N through wheat cut straw 100% NPK T 9 75% NPK+25% N through wheat cut straw 75% NPK

6 46 T 10 50% NPK+50%N through Green manure (Dhaincha) 100% NPK T 11 75%NPK+25%N through Green manure (Dhaincha) 75% NPK T 12 Farmers practice (40% NPK+5t FYM ha -1 ) Farmers practice (40% NPK) Use of 100 per cent N:P:K correspond to the state level recommendations for respective crops which were 90:17:33 and 120:26:25 for rice and wheat, respectively. i. Cultivation and incorporation of green manure crop Sesbania aculeata (Dhaincha) was grown as an ex-situ green manure crop during kharif, 2008 and kharif, 2009 (May to July). The crop was grown for a period of days and was chopped into small pieces of 4-6 cm and incorporated into the soil by a power operated rotavator at the time of puddling before transplanting of rice. ii. Field preparation The individual plot was prepared with the help of power operated rotavator. iii. Nursery raising, sowing/ transplanting Transplanting of rice crops during Kharif 2008 and 2009 was done with spacing of 20 x 15 cm 2 on 4 th July, 2008 and 13 th July, 2009, respectively. The variety used was HPR-2143 in both the seasons and 2-3 seedlings were transplanted per hill. The crops were irrigated only twice and thereafter it met its water requirement through rainfall. Weed control was done chemically with the application of Butachlor. Wheat crops during rabi, and were sown on 15 th November, 2008 and 28 th November, 2009 and the varieties used were HPW 155 and HPW-42 in the first and second year, respectively. iv. Application of fertilizers and organics In rice, half of N and entire quantity of P and K were applied as basal dose

7 47 through urea, superphosphate and muriate of potash, respectively. The remaining half dose of N was applied at tillering stage. The organics viz. farmyard manure, wheat cut straw and Dhaincha as green manure were applied to rice crop only in the specified treatments. In wheat 1/3 rd of N and entire amount of P and K were applied as basal dose and remaining 2/3 rd dose of N in two splits at tillering and grain filling stage through urea, superphosphate and muriate of potash, respectively. In farmers practice, FYM 5 t ha -1 was applied along with 40% NPK to rice followed by 40% NPK to wheat. v. Harvesting and threshing Rice crops (kharif 2008 and 2009) were harvested on 15 th October, 2008 and 20 th October, 2009, respectively at maturity when more than 80% of the grains had ripened. Wheat crops (rabi and ) were harvested on 7 th May, 2009 and 8 th May, 2010, respectively. The produce was dried in the field for 3 to 4 days and threshing was done to separate grains from straw. Rice was threshed manually whereas wheat using plot thresher. 3.3 Laboratory studies Soil studies i. Collection and preparation of samples Plot-wise composite soil samples from and m depth were collected after wheat harvest (rabi, ). Soil samples were also collected from m depth after rice (kharif, 2008 & kharif, 2009) and wheat (rabi, & ) harvest. The soil samples were air dried, processed and passed through 2 mm sieve and properly stored in polythene bags for further analysis. Table 3.2 Various methods used for soil analysis Soil property Parameter Method employed Physical property i) Particle Size analysis Piper 1966 ii) Bulk Density Singh 1980

8 48 iii) Particle Density iv) Porosity v) Water holding capacity Piper 1950 Gupta and Dhakshinamoorthy 1980 Gupta and Dhakshinamoorthy 1980 Chemical property i) Soil ph (1:2.5) Jackson 1973 ii) Organic carbon Walkley and Black 1934 iii) Cation exchange capacity Piper 1966 iv) Available nitrogen Subbiah and Asija 1956 v) Available phosphorus Olsen et al vi) Available potassium Jackson 1973 Microbiological property i) Microbial Biomass C Vance et al ii) Microbial Biomass N Brookes et al iii) Soil respiration Stotzky 1965 ii. Analysis of soil samples Surface soil samples collected after rice (kharif 2008 and 2009) and wheat (rabi and ) harvest were analyzed for ph, organic carbon, available N, P and K using standard methods of analysis (Table 3.2). Soil physical parameters viz. bulk density, particle density, water holding capacity and porosity and microbiological properties viz. microbial biomass carbon, microbial biomass nitrogen and soil respiration were determined after wheat harvest during rabi, The various forms of nitrogen, phosphorus and potassium were determined in soil samples collected after wheat harvest (rabi, ) as per the procedures listed below: A. Procedure for determination of N forms A brief description of the methods is given below: a) Inorganic N: For determination of inorganic fractions of N, 3 g of soil was shaken with 30 ml of 2N KCl for 1 hour and filtered. The extract was then stored in refrigerator for further use. The extraction of inorganic fractions viz. NH 4 -N and NO 3 -N using the above extract was done as per the procedure given by Black (1965).

9 49 b) Organic N: For determination of organic fractions of N, hydrolysate was prepared using 25 g of soil heated with 20 ml 6N HCl with 2 drops of octyl alcohol for 12 hours under reflux. Then the sample was filtered with the help of Buchner funnel using Whatman no. 50 filter paper. After that ph of the sample was adjusted to 6.5 with the help of 5N and 0.5N NaOH. The final volume was made up to 100 ml which was further used for the determination of different organic forms of N viz. hydrolysable NH 4 -N, amino acid-n, serine+threonine N, hexosamine N and total hydrolysable N as per the procedure given by Bremner B. Procedure for determination of P forms The sequential extraction procedure as given by Sui et al. (1999) was employed for P fractionation studies. This procedure aims at quantifying plant-available (H 2 O-P or NaHCO 3 -extractable P), Ca-associated (HCl-extractable), Fe-oxide- and Al-oxideassociated inorganic P (NaOH-extractable), as well as labile and stable organic P. A brief description of the method is given below: a) Water extractable P (H 2 O-P): 0.5 g soil was shaken on end to end shaker for 16 hours with 30 ml distilled water in the centrifuge tubes. Tubes were then centrifuged at rpm for 15 minutes. The supernatant was filtered using syringe, through 0.22 µm filter paper. b) 0.5 M NaHCO 3 extractable inorganic P: The same soil was then shaken with 0.5 M NaHCO 3 solution for 16 hours and the extracts were taken in the similar manner after centrifugation and filtration. c) 0.5 M NaHCO 3 extractable total-p: For estimating the 0.5 M NaHCO 3 extractable total P, the NaHCO 3 extract was digested using persulphate digestion method (Greenberg et al. 1992). d) 0.1 M NaOH extractable inorganic P: The soil used for NaHCO 3 extraction, was then extracted with 0.1 M NaOH solution for 16 hours. The extract was obtained after centrifugation and filtration.

10 50 e) 0.1 M NaOH extractable total-p: The 0.1 M NaOH extractable P was estimated in the similar manner as 0.5 M NaHCO 3 extractable total P after following persulphate digestion method. f) 1 M HCl extractable-p: The soil used for 0.1 M NaOH extraction was then shaken for 16 hours with 1M HCl and subsequently centrifuged and filtered. g) Residual-P: The soil left after various extractions (a to f) was then digested with H 2 SO 4 -H 2 O 2. Phosphorus in all the extracts was estimated using Murphy and Riley method (1962). Difference between total P and inorganic P represented the organic P in case of 0.5 M NaHCO 3 and 0.1 M NaOH extractions. C. Procedure for determination of K forms The various forms of potassium viz. water soluble, exchangeable and non exchangeable potassium were determined in soil samples collected after wheat harvest (rabi, ) as per the procedure listed below: a) Water-soluble K: Water-soluble K was extracted by shaking the soil water suspension in the ratio of 1:5 for one hour then filtered, and K was determined (Grewal and Kanwar 1966). b) Exchangeable K: 50 ml of 1N Ammonium acetate was added to ten grams of soil taken in a 125 ml flask, thoroughly mixed and kept overnight. Then the soil was filtered, washed with neutral 1 N NH 4 OAc until volume of 100 ml was obtained and K was determined. The amount of exchangeable K was calculated by subtracting water soluble K from K extracted with neutral 1N NH 4 OAc (Merwin and Peeech 1950). c) Non exchangeable K: Twenty five ml of 1N HNO 3 was added to 2.5 gram of soil taken in 100 ml beaker, kept for 15 minutes, the beaker was covered with watch glass and then boiled for 10 minutes. The soil was

11 51 then filtered into a 50 ml of volumetric flask washed with 0.1 N HNO 3 until the filtrate was brought to volume and quantity of K was determined. The non exchangeable K was calculated by subtracting K extracted with neutral normal NH 4 OAc from K extracted in hot 1N HNO 3 (Sutton and Seay 1958) Plant studies The total produce was dried and the total weight was taken as biological yield. The grains were then separated and plot-wise grain and straw yield was recorded. Representative grain and straw samples were collected after rice (kharif, 2008 and 2009), wheat (rabi, and ) harvest. They were dried in oven at 70 0 C. The dried samples were then ground and stored for further analysis. The analytical methods used for plant analysis have been given in Table 3.3. The nutrient uptake was calculated by multiplying per cent concentration of a particular nutrient with grain and straw yields. The uptake of the nutrients obtained in respect of grain and straw was summed up to compute the amount of total nutrient removed by each crop. Table 3.3 Analytical methods used for plant analysis S. No. Parameter Method followed 1 Nitrogen Jackson Phosphorus Jackson Potassium Black Statistical analysis The data generated from the field and laboratory studies were subjected to statistical analysis using the technique of analysis of variance for randomized block design for the interpretation of results as described by Gomez and Gomez (1984).

12 52 Correlations between various N, P and K fractions with yield, their respective uptake and soil properties were worked out following the standard procedures.