Macronutrient status and yield stability of arecanut ( Kahikuchi ) under integrated nutrient management practice in Assam

A long term field experiment was carried out in clay-loam soil at ICAR-CPCRI, Kahikuchi campus, Guwahati, Assam during 2000-2012 with arecanut variety Kahikuchi with seven nutrient combinations. The treatments included control (T1), 100 per cent vermicompost (T2), 200 per cent vermicompost (T3), 100 per cent chemical fertilizer (T4), 50 per cent vermicompost + 50 per cent chemical fertilizer (T5), 1/3 rd vermicompost + 2/3 rd chemical fertilizer (T6) and 2/3 rd vermicompost + 1/3 rd chemical fertilizer (T7). The treatment T7 produced highest fresh ripened arecanut yield of 16.7 kg i.e., about 3.6 kg dry chali per palm. Positive correlations were obtained between yield of arecanut and soil available N, P and K content. Significant and positive correlation was found between leaf N, P, K and available N, P and K content in surface and sub-surface soil. Available N, P and K content increased over the years under nutrient applied plot that reflected in yield of arecanut. The average yield in various treatments followed in the order of T7 > T5 = T6 > T2 = T3 > T4 > T1. The application of targeted, sufficient and balanced quantities of organic and inorganic fertilizer will be the need of the hour to make nutrients available for higher yield, soil fertility maintenance and agricultural sustainability without polluting environment.


Introduction
Arecanut is grown in an area of 90,000 hectares in North East (NE) India, comprising seven states with an average productivity of 1.2 tonnes per hectare. Nearly 82 per cent arecanut cultivation in the NE lies in Assam with an estimated area of 74,000 hectare producing 62,700 tonnes (NHB Database, 2010). It is grown in almost all households, which is literally called 'Bari' system of planting. General practices of non-application of manures, lack of awareness on technological development and absence of large scale plantation lead to poor production of arecanut in Assam. In a state where arecanut is part of economy and used in religious and social functions, application of manure is of utmost important for the crop which provides economic return for 60 to 70 years. For good yield and maintenance of soil fertility, it is therefore, pertinent to adopt integrated nutrient management (INM) practices depending upon the local availability of nutrient resources. INM refers to the maintenance of soil fertility and plant nutrients supply at an optimum level for sustaining the desired productivity through optimisation of the benefits from all possible sources of organic, inorganic and biological components in an integrated manner. Effect of INM practices in enhancing native soil nutrients, providing balance nutrient lost and increasing yield have been enumerated by many research workers in different agricultural crops (Reddy and Upadhyay, 2002;Mohandas, 2012;Singh et al., 2004). However, hardly any literature is available on nutrient management in arecanut cultivation in North Eastern India, particularly in Assam. So, a field study was conducted to develop a farmer-friendly INM practices in arecanut for achieving sustainable crop production for long term period.

Materials and methods
The field experiment was laid out at ICAR-Central Plantation Crops Research Institute, Research Centre, Kahikuchi, Guwahati, Assam, following randomized block design during 2000. The experimental site, Kahikuchi is located in sub-humid area at 20 0 18' N latitude and 91 0 78' E longitude. It receives an average annual precipitation of 2500 to 3000 mm. The mean maximum temperature varies between 15 0 C and 34 0 C and mean minimum temperature varies from 8 0 C to 22 0 C and is located at 50 m above MSL. The soil of experimental site was clay loam in texture and was acidic in nature with initial pH range between 4.4 and 5.4 at surface soil and 4.5 and 6.7 at subsurface soil. Initial organic carbon as well as available N, P and K content varied from 0.98 to 1.37 per cent and 194.0 to 249.5, 21.9 to 43.8, 173.6 to 268.8 kg ha -1 , respectively at surface soil and subsurface soil contains 0.67 to 0.99 per cent organic carbon, 166.3 to 212.5 kg N ha -1 , 14.0 to 30.9 kg P ha -1 and 159.6 to 205.8 kg K ha -1 . The arecanut crop variety considered was Kahikuchi. The arecanut palms were planted following a spacing of 2.7 m in both the ways. The different integrated nutrient management treatments include: control (T1), 100 per cent vermicompost (T2), 200 per cent vermicompost (T3), 100 per cent chemical fertilizer (T4), 50 per cent vermicompost + 50 per cent chemical fertilizer (T5), 1/3 rd vermicompost + 2/3 rd chemical fertilizer (T6) and 2/3 rd vermicompost + 1/3 rd chemical fertilizer (T7). Absolute control was maintained for comparison. Fifty g borax per plant per was applied every year in two splits at the base of each treated palm to maintain the homogeneity due to less or limiting content of boron in soil.
The response of different treatments was observed since 2007, at nut bearing stage and carried on upto 2012. The treatments were imposed in two splits and each treatment was replicated thrice with six palms per replication. Vermicompost was prepared from arecanut leaf with Eudrilus eugenae earthworm and it contained 1.8 per cent N, 0.46 per cent P and 0.61 per cent K with a pH of 7.2 and organic carbon of 19.6 per cent. Fresh nut yield and number of fresh nuts per palm at ripening stage was observed. The nuts were dried in two split and chali yield was recorded. The soil and leaf samples were collected from two palms in each replicated plot during April. Soil samples were taken from two opposite sides of the base of the palm, from the circular basins 75 cm away from the bole at two different depths i.e., 0-30 cm and 30-60 cm. The soil samples were dried in shade, sieved (2 mm sieve) and analysed for pH, organic carbon, available nitrogen, available phosphorus and available potassium content. pH (soil:water 1:2.5) was measured with the help of pH meter (Jackson, 1973); organic carbon by Walkley and Black (1934) chromic acid digestion method. Available nitrogen in soil was determined by using Kel-plus nitrogen distillation unit (Subbiah and Asija, 1956). The available phosphorus was determined following the procedure described by Bray and Kurtz (1945) and potassium was determined flame photometrically by neutral normal ammonium acetate extraction method (Hanway and Heidel, 1952). The leaf samples were collected from 4 th leaf from the top by cutting 4-5 leaflets from the middle of the leaf on both sides. Leaf samples were washed with distilled water, oven dried at 65-72 0 C and then powdered. The nitrogen content in leaf sample was estimated by using Kel-plus digestion and distillation method described by Jackson (1973). The powdered fraction (0.5 mm) of leaf sample was digested in HNO 3 :HClO 4 (3:1) di-acid mixture and analysed for phosphorus and potassium content (Jackson, 1973).

Yield parameters
Different INM treatments had a significant influence on fresh ripened nut weight, number of nuts per palm and chali yield per palm (Table 1 & 2) for six consecutive years (2007 to 2012). The average mean data of single fresh ripened nut weight (42.2 g) was recorded maximum in the palms under treatment T7 which was 19 per cent increase over the control. During 2012, fresh ripened nut weight increased over control by 20.6 per cent under T7 treatment. Fresh ripened nut weight increased upto 2008 (8 th year of age) and then remained almost static in the subsequent years in all the treatments barring control (Table 2) where it remained almost stagnant over the study period. Number of nuts per palm differed significantly among various INM treatments during study period except T2 and T3 which were at par. Nut yield per palm differed among the treatments but it increased upto 2008 i.e., 8 th year of age under the treatments of T1, T2, T3 and T4 and remained at par in the subsequent years. Remaining treatments T5, T6 and T7 showed highest nut number in 2009 i.e. and remained at par in the subsequent years. Production capacity of arecanut (Var. Kahikuchi) reached the highest in 8 th years of age (in 2008) under single form (organic/ inorganic) of nutrient application and in 9 th year of age under integrated nutrient supply (in 2009). However, significantly more number of nuts (420 per palm) was produced under the treatment T7 at the end of sixth year of study compared to control treatment i.e., 58.6 per cent over the control in 2012. It was on par during 2009 to 2011 and 58.5 to 63.5 per cent over control. The mean pooled data described the superiority of the treatment T7, T6 and T5 over other treatments. Statistically T5 and T6 were at par, but T7 significantly differed from other treatments. Maximum per cent increase in ripened nut number was observed under T6 in 2012 (75.1%) which was at par in 2009 (72.3%) over the initial yield.
Almost similar trend was observed in chali yield per palm where it was highest under T7 treatment and it significantly differed from the other treatments. Among the other treatments, T6 and T5 were at par but significantly higher than T1, T2, T3 and T4. It clearly showed that blending of inorganics and organics had more positive effect on the yield and yield characters of arecanut. Kalpana et al. (2006) reported that the highest coconut yield palm -1 year -1 was recorded in the treatment receiving 50 per cent organics + 50 per cent inorganics compared to 100 per cent organic treatment.

Soil nutrient status
The soil available N, P, K, pH and organic carbon content at two different depths i.e., 0-30 cm and 30-60 cm are shown in Table 3 for three alternate years (2008, 2010 and 2012). The soil available nitrogen in surface soils differed significantly by different INM treatments in every year of study. Build up of available nitrogen in soil was observed in all the treatment except the absolute control where there is a gradual decrease in available nitrogen content of soil. Available nitrogen content significantly increased gradually in surface soils over the initial content by 3.7 (2010) and 7.4 per cent (2012) in the 200 per cent vermicompost applied plots. Available phosphorus and potassium content in the soil showed significant variation among the treatments. Continuous application of 100 per cent inorganic fertilizer (T4) resulted in the build up of more available phosphorus and potassium in the soil, as the other integrated treatments consisting of vermicompost contains less phosphorus (0.46%) and potassium (0.61%). Similar trend was also noticed in sub surface soils.
In the 100 per cent chemical fertilizer applied plot, available P content increased significantly over the years by 4.3 in 2010 and 5.2 per cent in 2012 in surface soil. The treatments which received chemical fertilizers resulted in excess deposition of available K in both surface and subsurface zone. The significantly higher deposition was observed under 100 per cent chemical fertilizer applied plots. The sub-surface soils contained comparatively less available N, P and K content.
Data on soil pH in surface soil showed that under the treatment T4 and T6, the pH was less when compared to other treatments. Continuous application of inorganic fertilizer might be the reason for more acidic nature of soil in the above treatments. High rainfall and humid conditions in the experimental soil leads to the binding of cations and organic acids resulting in leaching of soluble solids, increasing acidity the soil. In the treatment T7, soil pH showed an equal or increasing trend justifying the application of integrated nutrient management in true proportion. The sub-surface soils were comparatively less acidic irrespective of   This effect may be ascribed to the direct addition of water-soluble carbon through vermicompost application (Singh et al., 2009). Maheswarappa (2008) and Bopaiah and Shetty (1991) reported similar phenomenon that integrated approach not only has the advantage of improving nutrition, but recycling of organic substances play major role in organic matter build up which is the site of all chemical and biotic activity in the soil.

Leaf nutrient content
The leaf N, P and K content as influenced by different treatments is listed in Table 4. This indicated that foliar content of N, P and K varied from 1.32 to 1.54, 0.18 to 0.26 and 0.97 to 1.22 per cent respectively in 2012. Similar results were also reported by Bhat and Mahapatra (1989). The leaf nutrient content either increased or remained stable during the course of study in all the INM treatments. However, maximum leaf nitrogen content (1.71%) was recorded in the palms that received 200 per cent vermicompost (T3) followed by T2 (1.69%). Among all the treatments, highest yield was obtained in T7 where, comparatively less leaf N, P and K content was recorded. This shows the utilization of applied manures to maximum extend and a little luxury consumption of N, P and K by the palms under T7. The corelation between soil available N and leaf N (r = 0.96** and r = 0.91**) soil available P and leaf P (r = 0.91** and r = 0.95**) and soil available K and leaf K (r = 0.78* and r = 0.89**) were positive and significant at both the depth of the soil, which suggests that plant can uptake P and K from the soil when soil bears good quantities of its available form. Arecanut yield might be attributed to this phenomenon as P and K content in plant plays major role determining the yield potential of the crop. Singh and Ram (1992) reported that the significant improvement in plant growth, yield attributes and yield of chickpea on account of vermicompost application along with inorganic sources of NPK resulted in translocation of nutrients from soil and enhanced supply of macro and micro-nutrients during entire growing seasons and microbial decomposition. Mishra et al. (2011) suggested that the addition of manures add sufficient amount of organic matter to the soil and solubilise plant nutrients and improve physical conditions of the soil by accelerating porosity, aeration and water holding capacity. It is also well documented fact that incorporation of organic manures with inorganic fertilizers in the soil not only acts as store house of macro-and micro-nutrients but also favourably affect physical and chemical characteristics of soil and plant (Bhriguvanshi, 1988).