Influence of Mycorrhiza, Nitrogen and Phosphorus on Growth, Yield and Economics of Hybrid Maize

Field experiment was conducted at Agricultural

Maize (Zea mays L.) is one of the most versatile crops and can be grown in diverse environmental conditions and has diversified uses as human food and animal feed.Besides its use as food and fodder, maize is now gaining importance on account of its potential uses in manufacturing of starch, resins, syrups, ethanol, etc.It has got immense potential and is therefore called as "miracle crop" and also "queen of cereals".Maize, being a C4 plant is an efficient converter of absorbed nutrients into food.
The productivity of any crop is the ultimate result of its growth and development.Plant population, inorganic and organic fertilization are the important prime factors that determine the yield of maize crop.Among the essential nutrients, macro-nutrients such as, nitrogen, phosphorus and potassium play a crucial role in deciding the growth and yield.Many workers have indicated that nitrogen is the foremost limiting factor for maize production.On the other hand, intensive cultivation only results in considerable removal of nutrients from the soil and their replenishment through organic manure is very limited and thus newly evolved hybrids with good yield potential show positive response to high levels of NPK fertilizers.The response of crops to nitrogen varies widely from place to place, depending upon the fertility level of soil and other environmental conditions.This necessitates the study on the response of crop to different levels of fertilizer.
Arbuscular mycorrhiza fungi are considered as obligate symbionts to crop plants for better utilization of P and other essential elements.The readily available form of N to any crop plant is NO3which is highly labile in soil solution and thus the role of mycorrhiza is insignificant.Conversely, drought stress impedes the mobility of NO3-ions in soils due to its low concentration and diffusion rate (Azcon et al., 1996).Under such environmental condition, AM fungi may play a crucial role in transporting N from the soil to the root surface, thereby contributing to plant growth and nutrition.
Phosphorus is generally available in small quantities in soil solution because most of inorganic phosphate ions are bound to soil colloids or fixed as iron aluminium PO4 (Larsen, 1967).Nearly 98 percent of the Indian soils are deficient in P and about 10-15 percent of P from soil is utilized by plants.Moreover, less than 15-25 percent of P from PO4 fertilizer applied to soil is normally available to plants and a large quantity of P remains unavailable due to its fixation (Bradey, 1990;Singh and Singh, 1992).Under such circumstances AM fungi can be effectively utilized to enhance the P mobilization.
Increased use of NPK fertilizers generally devoid of micronutrients and soil fertility has brought about several problems related to nutrient deficiency by depleting finite beneficial organisms reserve of the soil.Hence, it becomes, important to maintain proper balance of major nutrients with organic fertilizers for *Corresponding author email: aman_agron@yahoo.co.in sustaining the crop production.Keeping this in view, a field investigation was carried out to find out the effect of mycorrhizal inoculation and different nitrogen and phosphorus levels on growth, yield and economics of hybrid maize.

Materials and Methods
Field experiment was conducted at Agricultural Research Station, Bhavanisagar during kharif 2009 to study the influence of mycorrhizal inoculation and fertilizer levels on growth, yield and economics of hybrid maize under irrigated condition.The experiment was laid out in a factorial randomized block design with four replications.Four fertilizer levels viz., 200:100:100, 150:100:100, 200:75:100 and 150:75:100 NPK kg ha -1 were the treatments under factor 'A'. Two mycorrhizal treatments viz., no inoculation of mycorrhiza (control) (M -) and inoculation of mycorrhiza (M + ) were included under factor 'B'.The soil of the experimental field was red sandy loam in texture belonging to Typic Paleustalfs.The nutrient status of soil was low in available nitrogen (229.6 kg ha -1 ), medium in available phosphorus (20.2 kg ha -1 ) and medium in available potassium (268.2 kg ha -1 ).Maize hybrid, COH (M) 5, a high yielding single cross hybrid released by Tamil Nadu Agricultural University, Coimbatore was chosen for the study.
Seeds of maize hybrids were sown on the side of the ridges by adopting a spacing of 75 x 20 cm along with vermiculite based mycorrhizal inoculum at a depth of 5 cm below the seeds.The inoculum with the spore density of 200 spores g -1 was applied as a thin layer beneath the seeds prior to sowing @ 100 kg ha -1 .Seeds were dibbled at the rate of one seed hill -1 .
Well decomposed farm yard manure at the rate of 12.5 t ha -1 was applied uniformly over the field before last ploughing.ZnSO4 @ 37.5 kg ha -1 was applied uniformly as basal to all the plots.As per the treatment schedule, nitrogen was applied in three splits viz., 25: 50:25 per cent as basal and on 25 and 45 DAS, respectively.The entire dose of phosphorus was applied basally.The potassium was applied in two equal split doses viz., basal and at 45 DAS.The N, P and K fertilizers were applied in the form of urea (46 % N), single super phosphate (16 % P2O5) and muriate of potash (60 % K2O), respectively.

Growth parameters
Among the fertilizer levels, fertilizer dose of 200:100:100 NPK kg ha -1 and among the mycorrhizal treatments, mycorrhizal inoculation recorded taller plants, higher number of leaves, LAI and DMP (Table 1).Regarding the treatment combination, application of 150:75:100 NPK kg ha -1 along with mycorrhizal inoculation recorded significantly better growth parameters.This indicated that hybrid maize responded to NPK linearly.The increasing trend of plant height with N or NP together was probably due to the role of N in cell division and cell enlargement, which ultimately affect the vegetative growth particularly height of the plant.Similar results were reported by Srikanth et al. (2009).These results are also supported by the findings of Shahzad et al. (1996) who also have reported similar results.
The maize plants inoculated with AMF fungus have shown improved growth and development as compared to plants under control.This might due to the formation of external mycelium around the roots by AMF fungi which possibly helped to increase the availability of nutrients to the surface of the roots and thereby the nutrient uptake and height of plants.The above results of increased growth of treated plants due to mycorrhization of G. intraradices are in conformity with the findings of Karthikeyan et al. (2009).
The NP levels significantly enhanced the LAI.This might be due to the production of more number of leaves per plant by increased NP levels as reported by Srikanth et al. (2009a).Inoculation of mycorrhiza significantly increased the LAI both at 60 and 90 DAS.This might be due to the increase in the number of leaves and the leaf enlargement due to better nutrient uptake.Similar results were reported in the case of corn (Kothari et al., 1991) and maize (Subramanian et al., 1995).
The DMP increased steadily with time and reached the highest at 90 DAS.At 30 DAS, the DMP was less and at 60 and 90 DAS a steep increase was noticed.This might be due to rapid increase in plant height and leaf area at these stages.
The increase in DMP might be attributed due to the improved foraging ability; higher nutrient availability and uptake of nutrients with better assimilation which could have helped the plants to grow taller with more LAI as already reported by Verma and Joshi (1999) as plant height and LAI were directly correlated to DMP.The higher LAI, indicating the higher photosynthetic efficiency as a reflection of assimilation and dry matter production due to continuous release of nutrients by split application of nitrogen and potassium might be the plausible reason for such an increase in dry matter production.This is in accordance with the earlier findings of Jat and Balyan (2004).Kumar and Murugesh (2002) reported that mycorrhizal inoculation was more advantageous in obtaining healthy vigorous seedlings and resulted in higher biomass of maize plants.Similar results were also reported earlier by Wang et al. (2006) in Zea mays, Kelly et al. (2001) in sugar cane, maize and soybean, Omar (1995) and Subramanian and Charest (1997) in maize.

Physiological attributes
Among the fertilizer levels, 200:100:100 NPK kg ha -1 recorded higher CGR but was comparable with 200:75:100 NPK kg ha -1 (Table 2).Higher nutrient uptake associated with higher nitrogen application might have resulted in increased photosynthates accumulation.This would have lead to higher crop growth and hence the crop growth rate and relative growth rate.Similar results were reported by Banga et al. (1994).
Inoculation of mycorrhiza significantly recorded higher CGR and RGR than the control.This might be due to the better growth of plants due to better uptake of nutrients as evident by higher LAI and DMP recorded under this treatment, in this present study.
The interaction between fertilizer levels and mycorrhizal inoculation on maize grain yield was significant.The highest grain yield (7275 kg ha -1 ) was recorded under the treatment combination 150:75:100 NPK kg ha -1 with mycorrhizal inoculation followed by 200:75:100 NPK kg ha -1 .This increase in yield was probably due to effective utilization of applied nutrients, increased sink capacity and nutrient uptake by crop.The yield potential of maize is mainly governed by the growth and yield components.The positive and significant improvement in LAI and DMP noticed at different stages would have resulted in enhanced grain yield.The present findings are in line with the findings of Maddonni et al. (2006).The positive responses of hybrid maize upto 250 kg N ha -1 as reported by Srikanth et al. (2009b) lend support to the present findings.
Since N is major structural constitute of cells, as N level increased, the rate of vegetative and reproductive growth also increased in plants due to increase in assimilating surface of plants as well as total photosynthesis.In physiological terms, the grain yield of maize is largely governed by source (photosynthesis) and sinks (grain) relationship which is directly related to N.These resulted in more grain yield when N was higher.
Mycorrhiza had positive influence on grain yield of maize crop.The improved nutritional status of AM fungus-inoculated plants resulted in higher grain yields by 20% in comparison to uninoculated treatments.This yield gain in mycorrhizal plants was mainly caused by the intense flow of minerals and metabolites from the leaf to the developing kernel.The increased yields of AM fungus inoculated plants thus suggest that significant amounts of P and N were translocated from the source to the sink to support kernel development and grain yield (Subramanian and Charest, 1997).A higher yield of maize due to mycorrhizal inoculation has been reported previously by Subramanian et al. (2008).
Increasing the fertilizer levels increased the stover yield significantly. Fertilizer level of 200:100:100 NPK kg ha -1 recorded higher stover yield (9894 kg ha -1 ) followed by 200:75:100 NPK kg ha -1 .The positive and significant improvement in LAI and DMP noticed at different stages due to higher dose of fertilizer would have resulted in enhanced stover yield.These results are in confirmity with the findings of Srikanth et al. (2009b).Inoculation of mycorrhiza significantly influenced the stover yield 65 of maize.Mycorrhizal inoculated plants recorded significantly higher (10041 kg ha -1 ) stover yield.Mycorrhiza inoculation might have increased the stover yield of treated plants, due to increase in plant height, leaf area index and total biomass as evidenced in the present investigation.Similar results of increase in stover yield due to mycorrhizal inoculation were also reported earlier by Lauzon and Miller, (1997) in maize.

Economics
Economic viability of crop management is the foremost criteria in transforming new investigations to farmer's field.The results revealed that the highest gross return of Rs. 70,738 and net return of Rs. 46,587 were recorded under the fertilizer dose of 150:75:100 NPK kg ha -1 along with mycorrhizal inoculation followed by fertilizer dose of 200:75:100 NPK kg ha -1 along with mycorrhizal inoculation (Table 4).Remunerative economic returns realized under this treatment combination might be due to the reduced cost of fertilizers and increased yields obtained even though additional cost was involved in terms of mycorrhizal inoculation.Ramu and Reddy (2007) reported that regarding the N levels, 240 kg N ha -1 recorded the highest net return and BC ratio which were, however, comparable with 180 kg N ha -1 , indicating the fact that application of nitrogen beyond 180 kg ha -1 was not economical.In general this might be due to the increase in input prices decreased productivity as well as profit.Remunerative economic returns realized with 180 kg N ha -1 were obviously due to reduced cost of nitrogen with 180 kg N ha -1 compared to 240 kg N ha -1 .
In any investment economics, it is the B: C ratio which is more important to compare the profitability of the treatments to identify input technologies to improve the yield.From the study conducted, it is found that application of fertilizer at 150:75:100 NPK kg ha -1 along with mycorrhizal inoculation recorded the highest B:C ratio followed by 200:75:100 NPK kg ha -1 along with inoculation of mycorrhiza.This might be due to the very extensive hyphal network development in soil, exploiting nutrients more efficiently and improving plant uptake.Even though the initial cost of mycorrhizal inoculum was high, mycorrhizal inoculation has recorded higher yield and hence increased the B:C ratio.
Based on the above discussion, it can be concluded that application of 150:75:100 NPK kg ha -1 in combination with mycorrhizal inoculation can be recommended under irrigated condition for maximum productivity and benefit cost ratio in hybrid maize.