The following points highlight the seven nutrients required for wheat production and which were considered as the major plant nutrients for enhancing the crop productivity. The nutrients are: 1. Nitrogen 2. Phosphorus 3. Potassium 4. Sulphur 5. Zinc 6. Manganese 7. Boron.
Nutrient # 1. Nitrogen:
Response to Nitrogen:
The morphological framework and the developmental rethym of traditional tall varieties is such that they cannot respond to high doses of nitrogen without lodging. The dwarf varieties, in general, are responsive to higher rates of nitrogen application. Response of tall and dwarf varieties to grades levels of nitrogen (0,40,80,100,120 kg ha-1) was studied in 69 field trials in major wheat ecosystems of the country.
On an average, the response of tall and dwarf wheats was 990 and 1280 kg ha-1, respectively at 40 kg ha-1. At 80 and 120 kg ha-1, double dwarf wheats gave very high response of 2470 and 3250 kg ha-1, respectively.
Main conclusions from the trials were:
1. The dwarf varieties gave higher grain yield than tall varieties at low as well as higher rates of nitrogen application.
2. The tall varieties lodged at 80 kg N ha-1. Hence, it is not advisable to apply more than 40 kgN ha-1.
3. The dwarf wheats showed significant and very high economical response up to 120 kgN ha-1.
4. Single and double dwarf wheats also showed lodging tendency at doses higher than 120 kg ha-1. A dose of 100-120 kg ha-1, depending on soil fertility, has been recommended for dwarf wheats.
5. Triple dwarf wheats responded up to 200 kg ha-1 without lodging.
6. Contrary to common belief that nitrogen requirement vary from zone to zone, the optimum dose for different zones did not show wide variation and was in all cases more than 130 kgN ha-1.
New varieties with chromosomal translocation IB/IR, such as PWB 343, WH 542, HD 2826 and several others have distinct yield advantage over earlier varieties due to longer maturity period. The extended vegetative period makes these varieties respond linearly up to 180 kg N ha-1. In view of greater response, farmers apply 150 kg N ha-1. This is one of the reasons for the all-time high wheat production during 1999.
Time and Method of Application:
Results of 23 field experiment all over major wheat growing areas in the country conclusively proved significant increase in grain yield of irrigated wheat due to split application of nitrogen. Two split applications, half as basal and the remaining at crown root initiation, (first irrigation) was effective and convenient under all situations.
If the rate of application is more than 120 kg N ha-1, it would be better to apply in three equal splits, especially in light soils. Broadcasting and drilling are the usual methods of fertiliser application. Placement 5 cm below seed and 5 cm away from seed did not prove effective against drilling.
Rainfed (barani) wheat, in majority of cases, is not fertilised owing to economic reasons. It is desirable that 2-3 t ha-1 of form yard manure or some other organic matter is applied 5-6 weeks before sowing. Nitrogen at 40 kg ha-1 gives considerable boost to yield, if applied 10 cm deep (3-4 cm below the seed) at or before seeding.
Cropping Systems Based Nitrogen Management:
Rice-wheat is the major system in irrigated wheat zones of north India. Wheat gave significantly highest yield at 180 kg N ha-1 at Punjab and Kanpur but rice gave highest yield at 120 kg N ha-1 indicating no residual beneficial effect of nitrogen applied to wheat on rice. Almost similar trend was noticed in cereal-cereal systems at several places.
Results of cropping systems research emphasised the need for nitrogen application to each crop in the sequence, as there was no scope for residual effect of nitrogen on succeeding crops. Results of limited experiments on wheat based cropping systems indicate scope for saving around 25 per cent nitrogen if wheat crop follows a leguminous crop.
Nutrient # 2. Phosphorus:
Balanced nutrient application is essential for maximising the crop yield. Significant increase in grain yield of irrigated wheat was obtained due to application of phosphorus. The magnitude of response to 60 kg P2O5 ha-1 ranged from 111 kg ha-1 at Pantnagar (UP) to 375 kg ha-1 at Bichpuri. At Ludhiana, highest response was 433 kg ha-1 at 40 kg P2O5 ha-1. Highest wheat yield was due to combined application of 120 N along with 40 P2O5 kg ha-1.
Critical level of available phosphorus for wheat has been reported as 16 and 50 P2O5 ha-1 for alluvial and black soils, respectively. For rainfed wheat, application of phosphorus at 25 kg P2O5 ha-1 over basal dressing of 25 and 50 kg N ha-1 indicated that a balanced combination of nitrogen and phosphorus at a lower level leads to higher response than application of nitrogen alone. Phosphorus should be applied as basal dose both for irrigated and rainfed wheat. Placement is essential for good response to applied fertiliser.
Cropping Systems Based Phosphorus Management:
Studies on management of phosphorus in cropping systems were more concentrated on rice- wheat system due to differences in the environment in which these two crops are grown. Land submergence increases the availability of phosphorus to rice crop. Because of this phenomenon, wheat responded tremendously to the applied phosphatic fertiliser while relatively lower response was observed in rice on the same piece of land.
Saggar (1985) reported that 60 kg P2O5 ha-1 applied to wheat crop in alluvial soils of Punjab was sufficient to meet the requirements of both crops in rice-wheat system. Later studies, however, indicated superiority of 30 kg P2O5 ha-1 each to rice and wheat over 60 kg to either of the crops. Summerising the experimental results of AICRP on cropping systems, Goswami and Singh (1997) indicated that it is difficult to draw a conclusion as to whether phosphorus should be applied to wheat or rice or both the crops.
However, in maize-wheat, sorghum-wheat and pearlmillet-wheat systems, phosphorus application could be made to wheat only without any yield loss in kharif crops. Recent studies at Modipuram (UP) revealed that skipping phosphatic fertiliser to rice or wheat resulted in significant reduction in system productivity, although application of 10 t FYM ha-1 to rice made it possible to skip phosphatic fertiliser to either of the crops.
In general, phosphorus application to wheat may he preferred over rice in rice-wheat system on marginally deficient soils. Soils highly deficient are exceptions where all the crops in the system may require phosphorus application at recommended rate.
Nutrient # 3. Potassium:
Potassium uptake by crops is higher than that of nitrogen and phosphorus. However, response to applied potassium is only marginal in several instances because of high soil potassium. Response of wheat to potassium in wheat zones was fairly low in many cases and absent in quite a few others.
Results of 183 experiments for four years indicated that on an average, response to applied potash varied from 0.4 to 4.6 per cent with 30 to 60 kg K2O ha-1 in the presence of 120 N and 30 P2O5 kg ha-1.
In general, application of potassium is advisable only if its soil test reveal medium to low. Under such situations, 40 kg k2O ha-1 is suggested. Management of potassium in cropping systems did not receive much attention due to its adequate availability in the soil. However, there is need for assessing potash requirement in rice-wheat systems, especially under intensive cropping systems.
Nutrient # 4. Sulphur:
Response of wheat to sulphur depends on a number of factors like its availability in the soil, variety, rate of application, weather conditions and incidence of diseases and pests. Experiments under FAO network in India indicated that response of wheat to sulphur was 28 kg grain 30 kg-1 S applied with a mean uptake of 3.7 kg S t-1 of grain.
The sources include fertilisers such as ammonium sulphate (24% S) single superphosphate (12% S) and potassium sulphate (18% S) and other products such as elemental S, gypsum (13-18% S) and iron pyrites (22-24% S).
Spectacular direct and residual responses to sulphur application have been reported in wheat based cropping systems. On alluvial soils of Kanpur, residual effect of sulphur on wheat following groundnut was higher (22% yield increase) than after rice where the yield response was 7 per cent only. In groundnut-wheat system, marked direct and residual effects were obtained irrespective of the crop fertilised in alluvial soils of Punjab.
In rice- wheat system, at Kanpur, higher residual response was obtained when wheat crop received sulphur through pyrites. At Modipuram (UP), application of 90 kg S ha-1 as gypsum to wheat or 45 kg S each to rice and wheat in rice-wheat system was more beneficial compared with 90 kg S ha-1 to rice. In general, experiment evidence suggests higher sulphur use efficiency with its application to the high responsive crop in the system.
Nutrient # 5. Zinc:
Zinc deficiency in wheat is particularly reported from Punjab, Uttar Pradesh, parts of Haryana and Delhi. If zinc deficiency is acute, a dose of 50 kg Zn SO4 ha-1 is recommended. In moderately deficient soils, 25 kg of this chemical is sufficient. If the deficiency is noticed during early stages of crop growth, it can be correlated by foliar spray of Zn SO4 at 0.5 per cent.
Residual effect of 40-50 kg ZnSO4 ha-1 could he recorded only in succeeding wheat and not in subsequent third and fourth crops at different locations in Uttar Pradesh. Application of 11.0 kg Zn ha-1 as Zn SO4 was optimum for the rice-wheat cycles on zinc deficient soils of Punjab. Use of 10 kg Zn ha-1 to first rice crop followed by either repeat application of 10 kg Zn ha-1 after fourth crop or 5 kg Zn ha-1 after these crops was ideal for rice- wheat system on calcareous soils of Bihar. In general, continuous application of FYM or other bulky organic manures prevents zinc deficiency even in intensive cropping systems, except on soils severely deficient in zinc.
Nutrient # 6. Manganese:
In recent years, deficiencies of manganese in salt affected soils of Punjab have become evident. Wheat and berseem on coarse textured soils grown after rice suffered from manganese deficiency. Soil application of 5-20 kg Mn ha-1 as Mn SO4 or repeated foliar spray of 0.5 per cent Mn SO4 solution mitigated the deficiency.
Nutrient # 7. Boron:
In rice-wheat system, wheat suffered loss due to boron deficiency in acid sandy soils of West Bengal. Soil application of 21.5 kg borax ha-1 corrected the deficiency and improved wheat yield by more than 1.0 t ha-1. Similar response of wheat to boron was observed on sandy loam acid soils of Meghalaya. In calcareous soils of north Bihar, addition of 8 kg borax ha”1 each to rice and wheat was more beneficial than applying 16 kg ha-1 to rice.