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Growth and Yield of Rabi Maize (Zea mays L.) at Different Planting Densities and N-Levels

Maize is one of the major staple food in India. It has evolved from a purely subsistence to a successful commercial crop. Its production has increased over the years as people change their consumption trends. Maize recorded the highest annual growth rate of 2.5 per cent in the area as well as 5.5 per cent in production during the period 2004-05 to 2013-14. Maize production is dominated by Andhra Pradesh and Karnataka, producing approximately 38 per cent of India’s maize in 2010-11. Andhra Pradesh has the highest yield followed by Tamil Nadu due to majority of the area being covered under Hybrids. Yield has also seen a high growth rate of 2.8 per cent as compared to other cereals. Maize production has improved with the adoption of improved technologies by farmers. These technologies include improved seeds like hybrid, open pollinated varieties, timely planting, proper spacing, timely weeding and harvesting. Maize crop bears high yield potential and responds to various agro-management practices. Low yield of maize is due to many constraints but among them, imbalanced use of fertilizers and lack of optimal crop stand are the factors of prime importance. This variable response is mainly due to differences in plant morphology (Benga et al., 2001) intraspecific competition in maize plants (Maddonni and Otegui, 2004). Increasing level of nitrogen has increased yield International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 6 Number 12 (2017) pp. 2047-2053 Journal homepage: http://www.ijcmas.com


Introduction
Maize is one of the major staple food in India. It has evolved from a purely subsistence to a successful commercial crop. Its production has increased over the years as people change their consumption trends. Maize recorded the highest annual growth rate of 2.5 per cent in the area as well as 5.5 per cent in production during the period 2004-05 to 2013-14. Maize production is dominated by Andhra Pradesh and Karnataka, producing approximately 38 per cent of India's maize in 2010-11. Andhra Pradesh has the highest yield followed by Tamil Nadu due to majority of the area being covered under Hybrids. Yield has also seen a high growth rate of 2.8 per cent as compared to other cereals. Maize production has improved with the adoption of improved technologies by farmers. These technologies include improved seeds like hybrid, open pollinated varieties, timely planting, proper spacing, timely weeding and harvesting. Maize crop bears high yield potential and responds to various agro-management practices. Low yield of maize is due to many constraints but among them, imbalanced use of fertilizers and lack of optimal crop stand are the factors of prime importance. This variable response is mainly due to differences in plant morphology (Benga et al., 2001) intraspecific competition in maize plants (Maddonni and Otegui, 2004). Increasing level of nitrogen has increased yield A field experiment was conducted during rabi season 2014-15 at Agricultural College Farm, Bapatla to study the "Growth and yield of rabi maize at different planting densities and nitrogen levels". The experiment was laid out in a split plot design and replicated thrice. The results revealed that planting density of M 1 (1,00,000 plants ha -1 ) and foliar application of ZnSO 4 with nitrogen at tasseling i.e., S 8 (300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling) recorded highest growth, yield attributes and yield which was on par with M 1 (1,00,000 plants ha -1 ) and S 4 (300 kg N ha -1 ). The interaction between planting densities and nitrogen levels was found to be non-significant. components of maize during different research studies (Bangarwa et el., 1989) resulting in remarkable increase in grain yield. Maize grain yield is more affected by variations in plant population density than other members of the grass family due to its low tillering ability, its monoecious floral organization and the presence of a brief flowering period (Vega et al., 2001).

Materials and Methods
The experiment was conducted during rabi season 2014-15 at Agricultural College Farm, Bapatla, Andhra Pradesh. The experimental site is situated at 80 0 25' E longitude, 15 0 54' N latitude and at an altitude of 5.49 m and 7 km away from the Bay of Bengal. The experimental soil was sandy loam in texture, slightly alkaline in reaction (pH 6.6), medium in organic carbon (0.52%), low in available nitrogen (206 kg ha -1 ), medium in available phosphorus (24.1 kg ha -1 ), high in potassium (301.5 kg ha -1 ) and low in zinc (0.3 ppm). Nitrogen was estimated by Modified Micro Kjeldahl's method (Piper, 1966), phosphorus by Vanado Molybdate Phosphoric Acid method (Jackson, 1973), potassium by Flame Photometer method (Jackson, 1973) and zinc by DTPA extraction method (Lindsay and Norvell, 1978). The mean maximum and mean minimum temperatures were 30.0 0 C and 18.3 0 C.
The maize hybrid, Laxmi-2277 was sown in 2 nd week of November 2014. Thinning and gap filling was done at 15 DAS by keeping one seedling per hill -1 . Entire dose of phosphorus were applied as basal dose through single super phosphate and nitrogen was applied as per treatments in three equal splits through urea as basal, at 30 DAS and at 60 DAS. Potassium was applied twice as basal and at 60 DAS, through muriate of potash. Whereas 0.5% ZnSO 4 was applied as foliar spray at tasseling as per treatments.

Growth parameters
In the present study, plant height was not significantly influenced by planting densities and nitrogen levels (Table 1). Drymatter accumulation was influenced by planting densities. Significantly highest drymatter was produced with closer spacing of M 1 (1,00,000 plants ha -1 ) which was significantly superior to M 2 (83,333 plants ha -1 ) and M 3 (66,666 plants ha -1 ). Maximum drymatter at higher planting densities is due to more biomass accumulation with more number of plants per unit area. Similar observations were reported by Suryavanshi et al., (2009).
Days to 50% tasseling and silking was not influenced by planting densities and nitrogen levels. Planting density of 66,666 plants ha -1 recorded less per cent barrenness than 83,333 plants ha -1 and 1,00,000 plants ha -1 . More barrenness at high densities was due to the absence of the usual sink for the assimilate supply which inhibited the plants to produce viable ears. These results are in agreement with Dawadi and Sah (2012).   Table.3 Kernel yield, stover yield and harvest index of maize at different planting densities and nitrogen levels Significantly highest drymatter was produced with S 8 (300 kg N ha -1 as foliar spray at tasseling) which was on par with S 4 (300 kg N ha -1 ) and S 7 (240 kg N ha -1 ) and significantly superior to the other doses. Adequate supply of N with Zn might have helped to increase their growth which in turn put forth more photosynthetic surface, thus resulting in higher drymatter accumulation. These results are in agreement with the findings of Aruna et al., (2006). Per cent barrenness was found to be significantly less (1.28 %) with S 8 (300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling) which was significantly superior to other levels. Adequate supply of nitrogen together with zinc reduced barren plants at higher doses of N. These results are in accordance with Aruna et al., (2006) and Dawadi and Sah (2012).

Yield attributes
Among yield components of maize, no. of cobs plant -1 , cob length (cm), number of kernels cob -1 were significantly influenced by planting densities and nitrogen levels while kernel weight cob -1 (g), number of kernel rows cob -1 and 100-grain weight was not significantly influenced by planting densities but influenced by nitrogen levels.
Test weight was not statistically influenced by planting densities. Interaction between them was found to be non-significant (Table 2). Lower planting density of 66,666 plants ha -1 recorded maximum number of cobs plant -1 , cob length and number of kernels cob -1 than 83,333 plants ha -1 and 1,00,000 plants ha -1 . Greater competition between plants for resources like nutrients, solar energy and soil water might have suppressed the performance of individual plants with higher plant density as reported by Wasnik et al., (2012).
Number of cobs plant -1 , kernels rows cob -1 and kernels cob -1 recorded significantly highest with S 8 (300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling) which was on par with S 4 (300 kg N ha -1 ) but significantly superior to other levels of nitrogen with or without zinc.
Significantly highest cob length (cm), kernel weight cob -1 (g) and 100-grain weight (g) was recorded with S 8 (300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling) which was on par with S 4 (300 kg N ha -1 ) and S 7 (240 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling). This might be due to better absorption of N and Zn through foliage and their synergistic effect improved the yield parameters of maize. These results are in accordance with Tank et al., (2006).
Higher test weight was obtained with 300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray which was on par with 240 kg N ha -1 + 0.5% ZnSO 4 as foliar spray, 300 kg N ha -1 and found significantly superior to other levels tested. Increase in test weight might be due to better absorption of zinc through foliage and availability of nitrogen and their synergistic effect might have helped better grain filling and hence higher 100-grain weight. These lines are in conformity with Aruna et al., (2006).

Kernel and stover yield kg ha -1
Planting densities and nitrogen levels significantly influence the kernel and stover yields of maize and their interaction was found to be non-significant (Table 3). Maximum grain of 4767 kg ha -1 was recorded with M 2 (83,333 plants ha -1 ) and stover yield of 6120 kg ha -1 was recorded with M 1 (1,00,000 plants ha -1 ).
Significantly highest kernel and stover yields of maize was recorded with S 8 (300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling) which was on a par with only nitrogen S 4 (300 kg N ha -1 ) and significantly superior to other levels. This indicates that decline in yield components was more compensated with increase in plant density per unit area and adequate availability of nutrients and moisture. Similar results were reported by Gollar and Patil (2000).The increase in kernel yield at higher N levels together with Zn as foliar spray is due to better uptake of nutrients and zinc applied at tasseling. The results obtained are in consonance with the findings of Sekhar et al., (2012). Maximum stover yield of maize at higher plant densities might be due to variation in the crop stand per unit area. These results are in agreement with Zamir et al., (2011). As zinc plays a role in metabolism of plant as an activator of enzymes which in turn directly or indirectly affect the synthesis of carbohydrates, soil application of NPK coupled with ZnSO 4 as foliar spraying at tasseling influenced the stover yield of maize. These findings are in agreement with Tyagi et al., (1998). Harvest index was not influenced by planting densities and nitrogen levels. Application of 300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling recorded numerically more harvest index followed by other nitrogen levels.
From the present study, it was clearly indicated that growth parameters and yield attributes of rabi maize were significantly highest with M 3 (66,666 plants ha -1 ) while kernel yield was highest with M 2 (83,333 plants ha -1 ) which was on par with M 1 (1,00,000 plants ha -1 ). Stover yield was significantly superior with M 1 (1,00,000 plants ha -1 ) compared to M 2 (83,333 plants ha -1 ) and M 3 (66,666 plants ha -1 ). Nitrogen levels had significant effect on growth and yield of rabi maize, maximum growth and yield was obtained @ 300 kg N ha -1 + 0.5% ZnSO 4 as foliar spray at tasseling which was on par with 300 kg N ha -1 alone.