The following points highlight the four nutrients required for maize production and which were considered as the major plant nutrients for enhancing the crop productivity: 1. Nitrogen 2. Phosphorus 3. Potassium 4. Secondary and Micronutrients.
As a general rule, provided other conditions are not limiting, maize responds favourably to large applications of nitrogen. Lower the inherent soil fertility, greater will be the response. The expected yield sets the minimum amount of nitrogen to be applied.
As a rule of thumb, it is assumed that for every 100 kg of grain yield, 1.8 kgN in the grain and 1.0 kg in the above ground parts of the plant are required and must be supplied by soil and fertiliser.
Slow initial growth, yellowish green leaves and premature senescence of the lower leaves are the principal symptoms of nitrogen deficiency in maize. The discoloration usually commences at the tip of leaves and progress along the midrib. Older leaves are the first to show symptoms, which spread progressively to younger leaves.
Response to Nitrogen:
Response of maize to nitrogen depends of availability of nitrogen in the soil, cultivar, available soil moisture and other management practices. Maize hybrids on an average yielded 14.2 kg grain kg-1 N applied, while traditional varieties gave 9.16 kg grain kg-1 N applied. However, 15.4 kg grain kg-1 N was obtained from hybrids for the first 45 kg N ha-1.
At most places in India, 120 kg N ha-1 was optimum with a response of 12.3 kg grain kg-1 N. Response of traditional varieties to nitrogen varied from 40-60 kg ha-1. Economic optimum level was between 125 and 175 kg N ha-1 at Almora (UP), Bajaura (HP), Delhi, Dholi (Bihar), Hyderabad (AP) and Udaipur (Rajasthan). Economic response up to 240 kg N ha-1 had been obtained under favorable conditions at Solan (HP), Srinagar, Pantnagar, Arabhavi (Karnataka) and Godhra in Gujarat.
Based on the results of experiments conducted at several locations in the country, the ICAR (2006) has recommended the following fertiliser schedule for hybrids:
Fertiliser schedule for maize vary from state to state depending manly on the adequacy of rainfall/irrigation and yield potential of the cultivar.
Time and Method of Application:
Nitrogen content of young plants is higher than it is at any other time during growth cycle of maize. However, the actual requirement is very low. A deficiency when the plant is about 20 cm height, however, will cause a reduction in the number of rows of kernels per ear, thereby, lowering the yield-an effect that cannot be overcome by an adequate supply at later stage.
The ICAR (2009) is now recommending five split applications of N as against earlier three equal splits at seeding, knee-height and tasseling for high yield and use efficiency. Five split applications appear ideal for irrigated maize since soil moisture is not a problem for fertiliser application and is efficient use.
The five splits schedule is:
Top dressing should be as side dressing (10 cm away from the row and 6-8 cm deep into the soil) for improving nitrogen use efficiency.
Higher yield can be obtained when maize follows a legume with considerable nitrogen economy in maize fertiliser schedule. The amount of nitrogen contributed by legume depends on the environment in which it is grown. In general, about 25 kg N ha-1 can be saved when a legume precedes maize.
Studies at Karnal and Pantnagar indicated that Azospirillum inoculation along with 40 kg N ha-1 was equivalent to 60 kg N ha-1 for maize, indicating a saving of 20 kg N ha-1. Application of FYM at 12 t ha-1 alone increased maize yield by 700 kg ha-1. Application of 120 kg N as fertiliser and 60 kg N ha-1 through fertiliser along with FYM at 12 t ha-1 resulted in comparable yield.
There was no need for fertiliser phosphorus to maize crop when 12 t ha-1 of FYM was applied. The FYM containing 0.5 per cent nitrogen and 0.25 per cent phosphorus will, therefore, contain 60 N and 30 P2O5 kg ha-1. About 33 per cent nitrogen and 66 per cent phosphorus is likely available to maize in the first year (direct effect).
On this basis, 20 kg ha-1 each of nitrogen and phosphorus would be made available from the application of 12 t ha-1 of FYM. In addition, FYM improves soil physical condition for better crop growth. These studies clearly indicated the benefits of INM for improving maize yield with fertiliser economy and improved soil health.
Maize accumulates phosphorus throughout the growing season, with maximum uptake between third and sixth week of growth. At maturity, 75 per cent of the total phosphorus of the above ground parts has been translocated to grain. Phosphorus content of leaves tends to reach a maximum about middle of the season and then decreases as the plant matures.
Slow growth of the seedlings and dark green colour with a purplish tinge are fairly typical but may be caused by factors other than phosphorus deficiency. The purplish tinge of leaves and stem of young plants may be due to formation of anthocyanin pigments or insect damage to seedling. During pollination, the silk emerges slowly and defective ears are produced on phosphorus deficient plants.
Response to Phosphorus:
A marked response will be obtained on soils that have been intensively cropped without application of the deficiency caused by crop harvests. Application of phosphatic fertilisers over the years continuously leads to build up soil phosphorus leading to negligible response.
Experimental results across the country indicated the need for 60 kg P2O5 ha-1 when the rates of nitrogen application are around 100 kg ha-1. Average increase in grain yield at 60 kg P2O5 ha-1 was around 110 kg ha-1. Response up to 17 kg grain kg-1 phosphorous has been obtained on phosphorus deficient soils.
Time and Method of Application:
The most efficient method of phosphorous fertiliser application is drilling in continuous brand, 10 cm to the side and 5 cm below the seed level. Recommended rate should be applied at sowing.
The amount of potassium taken up by maize plant is only somewhat less than that of nitrogen. A crop of 10 t ha-1 of grain may require about 200 kg ha-1 of potassium. However, most of it does not move into the grain and move back into the soil through root system. Relative rate of potassium uptake is more rapid than that of nitrogen or phosphorus and reaches its peak about 30 days earlier.
It ceases several weeks before plant matures, while nitrogen and phosphorus uptake continue until the plant reaches its maximum dry weight. Potassium content of the leaves decreases from very high level at the beginning of the season to very low content at the end.
Potassium deficient plants develop slowly. Leaves are light green or striped with yellow and their tips and margins become necrotic. Though, the plants are stunted, they will tend to lodge because of poorly developed root system and susceptibility to stalk rot. The ears are small, pointed and barren at the tip.
Response to Potassium:
In general, when soil contains over 200 kg exchangeable K ha-1, there may not be much response to applied potassium. The average yield increase to added potash was 560 kg ha-1 at 50 kg K2O ha-1 in the Kulu valley. At many places in India, no response has been obtained with the application of potash. For hybrids and composites, the ICAR (2006) recommended 40 kg K2O ha-1, especially in intensive cropping systems.
Time and Method of Application:
Potassium is absorbed by maize crop, relatively at higher rate during the early stage. As such, it should be applied as basal dose at sowing by placement along with phosphorus and basal dose of nitrogen.
4. Secondary and Micronutrients:
Increasing soil acidity is associated with decreased availability of S, Ca, Mg and Mo. At very low pH levels (below 5. 0) Bo, Mn, Cu and Zn decline in availability. Response of maize to secondary and micronutrients has not been reported from maize growing areas, except for zinc to a limited extent.
Deficiency of zinc has been associated with nutritional disorder known as white bud. The external signs of zinc deficiency are stunted growth and chlorotic fading of leaves. Zinc deficiency is expected in calcareous soils. Evidence of zinc deficiency in maize is more frequently observed during cool and wet seasons.
A level of less than 15 ppm in the sixth leaf at silking can serve as a deficiency guideline. Soil application of zinc sulphate at 25 kg ha-1 before sowing is adequate to correct the zinc deficiency. Foliar treatment at 1.0 per cent Zn SO4 can correct the deficiency in standing crop.