I. NAGARAL, V. B. KULIGOD* AND J. NIRMALNATH
Department of Soil Science and Agriculture Chemistry, College of Agriculture, UAS, Dharwad-580 005, India
A field experiment was conducted during kharif 2011 at a farmer’s field in Koliwad (Hubli taluk) village in Northern transitional Zone of Karnataka between 15° 21′ N latitude and 75° 24′ E longitudes and at an altitude of 629 m above mean sea level (MSL). In the soil test crop response (STCR) NPK dose (216:116:166, N: P2O5: K2O kg ha-1, respectively) gave higher chilli dry fruit yield. The RDF (100:50:50 kg N: P2O5: K2O kg ha-1) recorded dry fruit yield of 763 kg ha-1 and it increased to 1257 kg ha-1 under STCR dose indicating an increase of 39 per cent. The highest ascorbic acid content of 151.3 mg 100 g-1 was recorded in the STCR dose of NPK and it was on par with soil test based N and K dose modified by ± 50 per cent and P dose modified by ± 25 (149.5 mg 100 g-1). Soil phosphatase activity (14.12 µg g-1 soil h-1) was significantly higher in phosphate solubilizing bacteria (PSB) treated plot which also received N and K dose as per state soil testing laboratory recommendation + 75 per cent of RDP under medium level of P test values as compared to untreated plots.
KEY WORDS: Ascorbic cid content, Chilli, Organic carbon, Soil fertility, Soil phosphatase activity,
Chilli (Capsicum annum L.) is an important spice as well as vegetable crop grown all over India. In India, chilli is cultivated in an area of 7.67 lakh hectares in India with a production of 12.34 lakh tones. Chilli is an indispensable spice essentially used in every Indian cuisine, due to its pungency, taste, colour and aroma. Chilli fruits are rich source of vitamin C, A and E and pungency is due to crystalline and volatile alkaloid called capsaicin present in the placenta of fruit. The major chilli producing states in India are Andhra Pradesh, Karnataka, Maharashtra, Odisha, Rajasthan and Tamil Nadu. These states constitute about 86 per cent of total area under chilli and 90 per cent of the total India’s production. The important chilli growing districts in Karnataka are Haveri, Gadag, Dharwad, Koppal, Belgaum, Bellary and Raichur. Haveri and Dharwad districts make-up 72 and 60 per cent respectively of total area and production, respectively. In Karnataka, the area under chilli was 1,09,185 ha, with a production of 1,05,401 kg and productivity of 1016 kg ha-1 (Anonymous, 2009).
Among the various methods of fertilizer applications, the one based on ‘yield targeting’ is the unique in the sense that this method not only indicates soil test based fertilizer dose but also levels of yield that the farmer canhope to achieve if good agronomic practices are followed. For soil-plant system, this approach is also unique because it provides a scientific base for balanced fertilization not only among the fertilizer nutrient themselves but also soil available nutrients. The existing practice of farmers is application of general dose of fertilizers to chilli without consideration of soil fertility and crop response. Balanced nutrition is the most important in modern farming. This necessitates remodeling of our approach to the problem of economic and judicious use of fertilizers based on the soil test. Keeping these views in background, a field experiment was conducted to assess response of chilli to varied fertilizer does based on soil testing.
A field experiment was conducted during kharif 2011 in the farmer’s field at Koliwad (Gadag taluk and district) village in Northern transitional Zone (Zone – VIII). The experiment was laid-out on black clay soil. A composite soil sample was collected from the experimental site at a depth of 0 to 15 cm before sowing and was analyzed for various chemical and physical characteristics. Soil reaction was slightly alkaline (8.10), non saline (EC1:2.5 0.5 dSm-1) low in organic carbon (4.12 g kg-1 of soil), low in available N (246 kg ha-1), medium in available P2O5 (23.5 kg ha-1) and high in available K2O (392 kg ha-1).
Chilli (Dyavnur dabbi) was raised on flat bed one month before transplanting and transplanted to the main field on July 24, 2011. The field experiment was laid out in Randomized Complete Block Design (RCBD). There were six soil test based fertilizer doses as treatments and four replications. The treatment details are as follows.
Dehydrogenase activity in the soil was determined by following procedure as described by Casida et al., (1964) and results were expressed as µg of Triphenyl formazan (TPF) formed g-1 soil day-1. Phosphatase activity in soil was determined by following the procedure outlined by Evazi and Tabatabai (1979) and phosphatase activity in the soil was expressed as µg paranitrophenol formed g-1 soil hr-1.
Freshly harvested green chillies were used for ascorbic acid estimation and it was determined volumetrically by reducing 2, 6-dichlrophenol indophenols dye to get a pink red colour. Ascorbic acid was calculated and expressed in mg 100 g-1 fruit (Sadasivam and Manickam 1992).
Dry pod yield was lower (763 kg ha-1) for RDF (recommended fertilizer dose) application as compared to all other soil test based fertilizer doses (Table 1). The STCR dose (216:116:166 N:P2O5:K2 O kg ha-1) of NPK (1257 kg ha-1) registered the highest pod yield than rest of the soil test based fertilizer doses viz., RDF, soil test based N and K ± 50 per cent and P ± 25 per cent (+ 50 per cent N, -50 per cent K and -25 per cent P), Karnataka State Soil Test Laboratory (STL) based recommended NPK dose and N and K as per STL +75 per cent of RDP +RD of PSB . But, soil test based N and K ± 50 per cent and P ± 25 per cent and N and K as per STL + 75 per cent of RDP under medium level of P test values + RD of PSB stood second and third after STCR dose with respect to pod yield (942 and 862 kg ha-1, respectively). The STL dose of NPK (855 kg ha-1) and soil test based NPK ± 25 per cent (862 kg ha-1) were on par with each other. Yield performance of chilli under soil test based NPK ± 25 per cent and soil test based N and K ± 50 per cent and P ± 25 per cent applications were significantly different. Yield increased from 763 to 1257 kg ha-1 in soil test based fertilizer application by registering an increase of 39 per cent. Nitrogen being most deficient in soils, the crop yield and growth might have been hindered predominantly by its deficiency. Higher doses of nitrogenous fertilizer (being deficient) and recommended dose of P (being medium) and reduced dose of K (being sufficient) might have made balanced availability of nutrients. Increased yield attributes viz. number of fruits per plant and fruit length had positive impact on yield under soil test based fertilizer dose application.
Dry fruit ascorbic acid content was significantly influenced by the application different doses of fertilizer. The highest ascorbic content was found in STCR dose of NPK (151.3 mg 100 g-1 ). However, it was on par with the soil test based N and K ± 50 per cent and P ± 25 per cent (149.5 mg 100 g-1). These treatments (Table 1) were followed by soil test based NPK ± 25 per cent, STL dose of NPK and N and K as per STL + 75 per cent of RDP under medium level of P test values + RD of PSB (146.5, 142.1 and 139.8 mg 100 g-1). Significantly lower ascorbic acid content was observed RDF (130.5 mg 100 g-1). Increased ascorbic acid content of fruits under higher doses of fertilizer application (STCR and ± 50 per cent soil testbased modified fertilizer dose) might be due to strong positive relationship between carbohydrate metabolism and formation of ascorbic acid (Majumdar et al., 2000).
The Highest dehydrogenase enzyme activity was recorded in the treatments that received N and K as per STL + 75 per cent of RDP under medium level (Table 2) of P test values + RD of PSB (3.94 µg g-1 day-1), followed by soil test based NPK ± 25 per cent (2.51 µg g-1 day-1). The RDF recorded the lowest dehydrogenase activity (1.19 µg g-1 soil day-1). The STL dose of NPK and STCR were found to be differing with each other (1.33 and 2.36 µg g-1 soil day-1 respectively).
The higher phosphatase enzyme activity was recorded in N and K as per STL + 75per cent of RDP under medium level of P test values + RD of PSB (14.12 µg g-1 soil h-1 ), followed by soil test based N and K ± 50 per cent and P ± 25 per cent (11.75 µg g-1 soil h-1) and RDF recorded the lowest (Table 2) phosphatase activity (10.3 µg g-1 soil h-1). However, the treatment that received STL dose of NPK (9.49 µg g-1 h-1), STL dose of NPK ± 25 per cent (10.55 µg g-1 soil h-1) and STCR dose of NPK (8.35 µg g-1 soil h-1) were statistically comparable to each other. This was mainly due to the organic acids such as acetic, citric and oxalic produced by microorganism could increase mineral dissolution. Badar et al., (2006) also recorded higher dehydrogenase enzyme activity under PSB applied plots. The results obtained in the present investigation were in concurrence with the findings of Apoorva et al. (2010).
There was no significant difference in soils pH due to application of different levels of fertilizesr. Similarly, there was no significant difference in soluble salt content (EC) in soils due to application of different levels of fertilizers. Furthermore, use of different levels of fertilizer based on soil testing did not change soil organic carbon (Table 3).
Available N was significantly higher under STCR dose of NPK (283.9 kg ha-1), followed by soil test based N and K ± 50 per cent and P ± 25 (Table 4) percent (260.5 kg ha-1) and N and K as per STL + 75 per cent of RDP under medium level of P test values + RD of PSB (256.1 kg ha-1). The lowest available N (246.7 kg ha-1) was recorded in soil test based NPK ± 25 per cent and it remained on par with all other treatments (Table 4) except STCR dose of NPK and soil test based N and K ± 50 per cent and P ± 25 per cent.
Significantly higher available P2O5 (84.6 kg ha-1) was recorded in STCR dose (Table 4) , followed by soil test based N and K ± 50 per cent and P ± 25 per cent (67.5 kg ha-1) and N and K as per STL + 75 per cent of RDP under medium level of P test values + RD of PSB (63.5 kg ha-1). However, all these treatments remained on par with each other. The lowest available phosphorus (52.3 kg ha-1) was observed by soil test based NPK ± 25 per cent.
Application of STCR dose of K2O showed significantly higher available potassium status of (372.4 kg ha-1). But soil test based N and K ± 50 per cent and P ± 25 per cent and N and K as per STL + 75 per cent of RDP (Table 5) under medium level of P test values + RD of PSB (347.0 and 343.7 kg ha-1 respectively.) were on par with STCR dose of NPK. Lower available potassium (320.9 kg ha-1) was recorded in soil test based NPK ± 25 per cent. Except treatments STCR dose of NPK and soil test based N and K ± 50 per cent and P ± 25 per cent remaining all treatments were on par with Soil test based NPK ± 25 per cent treatment. Further, available sulphur didn’t differ significantly due to different levels of fertilizer application based on soil test results.