Evaluation of Bio-inoculants Enriched Marginal Soils as Potting Mixture in Coffee Nursery

Fertile jungle soil is a primary ingredient of potting mixture used in coffee nursery to raise healthy, vigorous seedlings and in recent times its availability has diminished due to the receding forest lands in traditional coffee cultivating areas. Hence a nursery trial was conducted with the objective of exploring the possibility of utilizing marginal or less fertile soils enriched with bio-inoculants in the potting mixture. Two soils, (soil-1 and soil-2), which are less fertile and marginal in characteristics compared to the jungle soil enriched with bio-inoculants consortia of Azosprillum, Pseudomonas flurosence, Phosphate Solubilising Bacteria (PSB) and Vesicular Arbuscular Mycorrihiza (VAM) were employed in the secondary nursery to raise coffee seedlings and monitored for growth parameters, nutrient uptake, soil nutrient status and colony forming units for about 200 days after sowing. The results of the study indicated that the recommended Standard Package of Practice (SPP) with jungle soil, Farm Yard Manure (FYM) and sand in the 6:2:1 proportion is a best suited potting mixture to raise the coffee nursery. But in absence of the fertile jungle soil, the marginal soils also can be utilized as an ingredient of potting mixture with due care to incorporate adequate quantity of farm yard manure and the microbial consortia is not a substitute for FYM in the potting mixture.


Introduction
Raising vigorous and healthy coffee seedlings in the nursery is a must for establishing superior coffee plantation in a long run. The recommended Standard Package of Practice (SPP) for coffee nursery includes a primary sowing bed prepared using the fertile jungle soil and mixture of jungle soil, Farm Yard Manure (FYM) and sand in the ratio of 6:2:1 [1] for the poly bag/secondary nursery. Nowadays due to dwindling of forest lands in the traditional coffee growing areas and various other associated problems, procuring of fertile jungle soil in large quantity to raise the nursery is not an easy task. Under such a situation the farmers are compelled to use the easily available marginal/ less fertile soils for raising nursery which in turn will result into weak and unhealthy seedlings. The advantageous uses of bioinoculants for boosting growth in the nursery are known in many crops and also in coffee. The individual and consortia of Azosprillum, Pseudomonas flurosence, Phosphate Solubilising Bacteria (PSB) and Vesicular Arbuscular Mycorrihiza (VAM) have been tried in coffee nursery [2][3][4] along with SPP. Hence an effort was made to improve the marginal soils by enriching with bio-inoculants and a nursery trial was conducted to study the possibility of utilizing these enriched soils in potting mixture.

Materials and Methods
A nursery trial on Chandragiri (arabica) seedlings was conducted during the year 2010-11 at Central Coffee Research Institute, Chikmagalur District to explore the possible utility of marginal soils enriched with bio-inoculants in nursery mixture. A Randomized Block Design (RBD) with seven treatments (T 1 -T 7 ), three replications per treatment and about 100 seedlings per treatment was adopted in the trial where in two types of soils namely, soil-1 and soil-2 were employed. Microbial inoculants viz., Azosprillum, Pseudomonas flurosence, Phosphate Solubilizing Bacteria (PSB) and Vesicular Arbuscular Mycorrihiza (VAM) procured from University of Agricultural Sciences, Dharwad were used to prepare bio-inoculants consortia. Adequate numbers of seeds were sown in three different primary beds prepared using jungle soil, soil-1 and soil-2 and seedlings in 'topi' stage were raised. These seedlings were transplanted during April from primary bed to the secondary nursery with the following treatments. Nursery was maintained under shade net and as per the existing package of practice all the necessary plant pest and disease care practices were followed strictly. At intervals of 100, 150 and 200 days after transplanting (DAT) observations on shoot and root length, stem girth, leaf area, dry weight of seedlings, soil chemical parameters like pH, EC, available major and secondary nutrients, organic carbon content and DTPA extractable micronutrients were determined by employing the standard methods. The soil biological properties, namely, microbial population [5], microbial respiration, Dehydrogenase activity (Incubation method) [6] and Biomass Carbon [7] were also recorded at different intervals. Nutrient uptake (N, P and K) from growth media was recorded at the end of the trial (200 DAT).

Soil characteristics
The soil physical, chemical and microbial parameters of the soils employed in the study are presented in Tables 1-3 respectively. Perusal of the data indicates that the two soils (Soil 1 and Soil 2) do not differ much from the jungle soil with respect to the sand, silt and clay contents.    Table 3: Microbial properties (Initial)

Soil
The jungle soil was far more superior to Soil 1 or Soil 2 ( Table 2) in fertility status even though all the 3 soils registered acidic soil reaction. Soil 1 and Soil 2 had low organic carbon content and were deficient with respect to available P, K, Ca and Mg contents while the micronutrient status was not below respective critical limits. Hence Soil 1 and Soil 2 were referred to as marginal compared to the very fertile jungle soil. It can also be noted that Soil 1 and Soil 2 recorded lower microbial population as well as other biological properties compared to the jungle soil.

Growth parameters
The growth parameters of the seedlings in both the marginal soils recorded after 100 and 200 days of transplanting are presented in Tables 4 and 5 respectively. In general, the growth parameters increased in all the treatments over the period of observation. At 100 and 200 DAT, in both the marginal soils under study, the growth parameters, namely, plant height, root length, stem girth, number of leaves and leaf area were higher in seedlings receiving treatment T 3 (T 2 + 100 g consortia) compared to control T 1 (Soil 1/ Soil 2 only) at 100 DAT. The treatments T 2 (Standard package of practice-SPP) and T 4 (Soil 1/ Soil 2: FYM: Sand: 4: 2: 3), also recorded growth parameters on par with T 3 . The growth of the seedlings receiving treatments T 5 , T 6 and T 7 was poor compared to the seedlings under T 2 , T 3 T 4 . These observations are in lines of the results reported by Glory Swarupa, [4] who found significant increase in growth of coffee seedlings when treated with Azospirillum, Phosphobacteria and VAM. The potting mixtures under various treatments were subjected to analysis of nutrient status and biological properties to understand the variation in growth parameters observed under different treatments. Nutrient uptake of the seedlings was also studied.

Nutrient status of potting mixtures
At 200 DAT the potting mixtures were analyzed for the chemical properties (pH, OC) and nutrient status. The results are presented in Table 6 and 7 for Soil 1 and Soil 2 respectively. The soil reaction was near neutral in the treatments containing both the marginal soils with bio-inoculants. Per cent organic carbon and available P were significantly high in T 3 and on par with T 2 and T 4 compared to T 1 (Soil 1 and Soil 2 only). However, available K was high in T 7 and on par with T 5 , T 6 and T 2 compared to T 1 . Thus the soil analytical data clearly indicated the fact that the nutrient availability in T2 (SPP) is higher compared to the T 1 and the added microbial inoculants have the advantage of supplying nutrients in balanced and adequate quantities from the medium as seen in T 3 .

Biological properties of potting mixtures
The potting mixtures under various treatments in which the seedlings were grown for 200 days were enumerated for microbial Colony Forming Units (cfus) and biological parameters like Microbial respiration, Dehydrogenase activity and Biomass carbon. The data is presented in Tables 8 and 9.   and VAM were significantly high in T 3 (40, 20, 14 × 10 3 and 70% respectively) and on par with T 2 (35, 18, 12 × 10 3 and 70%) and T 4 (29, 17, 11 × 10 3 and 70%) compared to T 1 (15, 10, 5 × 10 3 and 40%). A similar trend has been noticed in Soil-2 also. Microbial observations like Microbial Respiration, Biomass Carbon and Dehydrogenase activity were also significantly high in T 3 (18.8, 2824 CO 2 mg kg -1 soil hr -1 and 37.4 µg of PNP g -1 of soil hr -1 respectively) and on par with T 2 (18.1, 2809 CO 2 mg kg -1 soil hr -1 and 29.8 µg of PNP g -1 of soil hr -1 respectively) and T 4 (16.1, 1783 CO 2 mg kg -1 soil hr -1 and 25.5 µg of PNP g -1 of soil hr -1 respectively) compared to T 1 (7.8, 1207 CO 2 mg kg -1 soil hr -1 and 12.2 µg of PNP g -1 of soil hr -1 respectively). Similar results have been recorded for Soil-2 also.   These results also are in support of the best suitability of the T2 (SPP) as potting mixture. In T3, the externally added bio-inoculants consortia to T2 have improved the 'cfus' as well as other biological parameters. In presence of FYM the marginal soils also have performed on par with T2 and have indicated the possibility of utilizing them as potting mixture when jungle soil is unavailable.

Nutrient uptake by seedlings
The seedlings were uprooted at 200 DAT and plant parts were analyzed for the nutrient contents and the uptake was computed. The nutrient uptake of the seedlings grown in both the marginal soils is presented in Tables 10 and 11.

Treatments
Leaf Stem Root N (mg/g) P (mg/g) K (mg/g) N (mg/g) P (mg/g) K (mg/g) N (mg/g) P (mg/g) K (mg/g)  Uptake of N, P and K by leaf, stem and root of seedlings grown in Soil 1 and Soil 2, were significantly high in T 3 and on par with T 2 and T 4 compared to T 1 . Thus the higher growth parameters observed under T 3 can be attributed to availability and uptake of balanced and higher quantum of nutrients to seedlings through FYM as well as bioinoculants consortia compared to 'control'. The poor growth of seedlings observed in the treatments T 5 , T 6 and T 7 compared to the seedlings under T 2 , T 3 , and T 4 may be due to the lack of adequate organic matter which is essential for establishment of externally supplied microbes in the form of bio-inoculants. Better growth of seedlings in T 4 confirms the fact that FYM is an inevitable ingredient of potting mixture for raising coffee seedlings as it is capable of providing the organic matter even when the soil used in the potting mixture is deficient in organic matter. N (mg/g) P (mg/g) K (mg/g) N (mg/g) P (mg/g) K (mg/g) N (mg/g) P (mg/g) K (mg/g) Table 11: Nutrient uptake of seedlings at 200 DAT in Soil-2

Conclusion
The growth parameters, nutrient status and biological parameters of the potting mixtures, and data on nutrient uptake by the seedlings under different treatments recorded in the nursery trial conducted with the objective of exploring the possibility of utilizing marginal or less fertile soils enriched with bio-inoculants in the potting mixture lead to a conclusion that the SPP (mixture of jungle soil, FYM and sand in the ratio 6:2:1) is the best suited potting mixture to raise the coffee nursery. But in absence of the fertile jungle soil, the marginal soil can be utilized as an ingredient of potting mixture with due care to incorporate adequate quantity of farm yard manure and the microbial consortia is not a substitute for FYM in the potting mixture. This is because of the fact that adequate organic matter is essential for establishment of externally supplied microbes in the form of bioinoculants and FYM is capable of providing the organic matter even when the soil used in the potting mixture is deficient in organic matter.