An experiment was conducted in factorial split design in the Agricultural Research farm of BHU, Varanasi for two years 2018-19 and 2019-20 in the rabi seasons to study the effect of sowing time, nitrogen, and zinc management. To study the effect of sowing time crop was sown in the second fortnight of November and the first fortnight of December and a similar dose of 150 kg of nitrogen was applied to the crop at various growth stages like basal, CRI stage, and flag leaf visible stage in both treatments but one of the nitrogen treatments included the application of urea 2% at anthesis stage where 9.2 kg urea was saved from 150 kg nitrogen for spraying. Zinc management included four levels of treatments: Z1: 0 kg ha-1 Zn, Z2: 5.0 kg ha-1 Zn as basal, Z3:1.7 kg ha-1 Zinc as basal + 0.50% ZnSO4 spray at Z31 (stem elongation) + 0.50% at Z75 (milking), Z4: 1.7 kg ha-1 Zinc as basal + 0.50% ZnSO4 spray at Z60 (Anthesis) + 0.50% ZnSO4 spray at Z85 (Dough stage). Chlorophyll content was found to be maximum in Z2 up to 60 days after sowing and after foliar application with 0.5% zinc sulfate, chlorophyll content was found to increase in Z3 as compared to Z4. The number of spikelet formations was also affected by Z3. Two of the parameters showed a significant result in the second fortnight of November and the effect of nitrogen was found to be non-significant.

Chlorophyll content, number of spikelet, sowing time, foliar application, zinc.

Wheat being the most important cereal crop, it grown in vast areas of Indian geography and various cropping systems. The time left after harvesting of kharif crop and changing climatic scenario has been a matter of concern in order to maintain yield. It has been proved that delayed sowing decreases the yield up to a significant level due to less period for optimum vegetative growth and high temperature during anthesis and grain filling leading to poor grain quality and less yield.

Since nitrogen is a component of protoplasm, protein, chlorophyll, alkaloids, hormones, and vitamins, a sufficient level of nitrogen is required for efficient crop production. It is well-known fact that nitrogen is highly essential for the Crown root initiation stage and flag leaf stage to nourish crop vegetative as well as reproductive growth. Increased dry matter synthesis from nitrogen ultimately leads to higher yields (Reena et al., 2017). A common micronutrient shortage in humans is dietary zinc (Zn) insufficiency. Zinc fertilization has been shown to be a successful strategy for increasing wheat's grain Zn concentration and reducing human Zn insufficiency. It is vital to use the right Zn fertilizer forms and application techniques in order to optimize the benefits of Zn fertilization. Though soil application is highly essential for crop establishment and proper growth, for quality concerns as well as yield attributing characters, zinc foliar application is a suitable option (Zhao et al., 2020).

To study the effect of sowing time, nitrogen, and zinc management on rabi wheat, field experimentation was conducted for two years 2018-19 and 2019-20 on the agricultural farm of the Institute of Agricultural Sciences, Banaras Hindu University. Experimentation was conducted in factorial split design where the main plot carried two factors i.e., sowing time and nitrogen management while the subplot carried one factor i.e., zinc management. Sowing time had two levels i.e., Sowing in the second fortnight of November (D1) and Sowing in the first fortnight of December (D2). Nitrogen management also had two levels i.e., a) N1:150 kg ha-1 Nitrogen [75 kg basal + 37.5 kg at Z20 (main shoot only) + 37.5 kg at Z37 (flag leaf visible)] and b) N2: 150 kg ha-1 Nitrogen [70 kg basal + 35.5 kg at Z20 (main shoot only) + 35.4 kg at Z37 (flag leaf visible) + 9.2 kg as 2% urea application at Z60 (beginning of anthesis stage)]. In subplot zinc management consisted of (Z1) Control i.e., 0 kg Zn ha-1, (Z2) 5 kg ha-1 Zinc as basal, (Z3) 1.7 kg ha-1 Zinc as basal + 0.50% ZnSO4 spray at Z31 (stem elongation) + 0.50% at Z75 (milking), (Z4) 1.7 kg ha-1 Zinc as basal + 0.50% ZnSO4 spray at Z60 (Anthesis) + 0.50% ZnSO4 spray at Z85 (Dough stage) as subplot treatment. The experiment was repeated in three replications and each replication had sixteen treatments. The sowing date remained the same for both years. 30th November and 14th December were assigned to D1 and D2, respectively. 100 kg ha-1 seed rate was applied keeping the line-to-line spacing 20.0cm. Phosphorus and potassium were applied at the rate of 60 kg ha-1. Standard cultural practices like irrigation and weed management were followed as per requirement.

The weekly mean maximum temperature ranged from 19.8 to 39.5oC with an average in the year 2018-19, and 13.6 to 38.1oC in the year 2019-20. The weekly mean minimum temperature varied from 3.9 to 20.5oC during the year 2018-19, and 7.0 to 21.3oC in the year 2019-20. The mean fluctuation in the maximum and minimum temperatures was very close during both years.

For determination of chlorophyll content, wheat leaves were analyzed by using a SPAD meter on the field in standing crop (ten tagged plants) at 30, 60, and 90 days after sowing. The number of spikelets per ear/spike was counted after harvesting. Reading was taken from ten tagged spikes and the total number of spikelets was averaged by ten to calculate the number of spikelets per spike. Statistical analysis was done following methods given by Gomez and Gomez (1984). To determine the growth stages for application of nitrogen and zinc application, the Zadoks scale (Zadoks et al., 1974) was followed. 

Table 1 shows the data regarding the effect of time of sowing, nitrogen, and zinc management on the chlorophyll content of wheat. Table 3 indicates the interaction among different treatments for chlorophyll content and the number of spikelets per spike.  Chlorophyll content attained maximum value when wheat was sown in the second fortnight of November (D1). Observations, taken in 30 days intervals up to 90 days after sowing, showed that chlorophyll content was lower in crops sown in the first fortnight of December as compared to the second fortnight of November (D2). In the early growth stages, D2 noticed lower temperatures than D1during the early growth phases. Lower temperature inhibits the transport, uptake, and availability of plant nutrients, especially nitrogen and zinc (Boczulak et al., 2014; Brennan et al., 1993; Kumar and Meena 2023).

It is well established that nitrogen is a major component of chlorophyll molecules surrounding magnesium in the center. The disruption of chlorophyll production by zinc shortage was studied by Hisamitsu et al. (2001). Zinc, which serves as a structural and catalytic component of proteins and enzymes as well as a co-factor for the normal development of pigment biosynthesis, is responsible for increased chlorophyll quantities (Balashouri, 1995).

Table 1: The table shows the effect of time of sowing, nitrogen, and zinc management on Chlorophyll content (SPAD value) at 30, 60, and 90 DAS in wheat.

Number of spikelets per ear (Table 2) was found to be significantly higher (23.54 mean) in plots sown in the second fortnight of November (D1) as compared to D2 (16.928 mean). The result shows a similarity with the review given by Wiersma (2021).

The effect of nitrogen on the number of spikelets per ear was found to be non-significant. The reason could be the difference in the amount of nitrogen applied did not affect the number of spikelets significantly and the nitrogen was applied at similar growth stages in both treatments up to Z37 (flag leaf visible stage). Terminal spikelet formation completes by the Z30 stage but continues up to anthesis in other effective tillers. In N2, the application of urea was carried out after anthesis which has no role in spikelet formation. This can be compared with the review of Acevedo et al. (2002).

In the case of zinc management, the effects of all the treatments were significantly different from each other. Z3 recorded the maximum number of spikelets per ear followed by Z2 treatment. Z1 where no zinc was applied gave the lowest number of spikelets. Z2 also observed fewer spikelets as the zinc foliar application was given in the later stages like the anthesis and dough stage, unlike Z3 where zinc was applied at the stem elongation and milking stage. Continuous application of zinc throughout the life cycle improves plant growth and yield-attributing characteristics (Zoz et al., 2012). This statement can be used to justify the result of the current study.

Table 2: Showing effect of time of sowing, nitrogen, and zinc management on the number of spikelets per spike.

Table 3: Showing interaction among different factors at different growth stages in both experimental years.

By a judicious application of nitrogen and zinc in the proper amount and growth stages in the optimum time of sowing, characters enhancing yields like chlorophyll content and spikelet numbers can be enhanced to get maximum return. Further studies can be done to find out the proper growth stages to increase the uptake and assimilation of nutrients and we will be capable enough to beat the adverse effect of climate change on grain yield.

Bandana Rani Barik, Yashwant Singh, Saroj Kumar Prasad and Monalisa Sahoo  (2024). Effect of Sowing Time, Nitrogen, and Zinc Scheduling on Chlorophyll content and Number of Spikelets per Spike in Wheat (Triticum aestivum L.). Biological Forum – An International Journal, 16(4): 46-49.