Fertilizer Application: Precaution, Rate and Time

After reading this article you will learn about:- 1. Precautions of Fertilizer Application 2. Rate of Fertilizer Application 3. Time.

Precautions of Fertilizer Application:

i. Note that there is sufficient moisture in the fields before applying fertilizers.

ii. Ensure uniform distribution of fertilizer on the entire area of operation.

iii. Avoid hot-hours or the day while applying (broad-casting) a fertilizer.

iv. Choose a fair weather day preferably for broadcasting.

v. Do not top dress the fertilizer when the crop leaves are wet otherwise burning and scorching of leaves may occur.

vi. Confirm the compatibility of fertilizers before mixing.

vii. Place the fertilizer at least 5-8 cm below the soil surface.

viii. Cover the fertilizer furrow immediately.

ix. In double band placement open the bands by keeping nitrogen the planted row in centre.

x. In ring placement open the ring near the active root zone of fruit plants (corresponding to the circumference of shoot system).

xi. Avoid drilling of fertilizers and seed together especially of legumes as even a small amount of fertilizer may damage germination.

xii. Check choking of the tube from time to time.

xiii. Select only spray-grade urea for foliar spray.

xiv. Prepare fresh solution for each spray.

xv. Avoid spraying during hotter period of the day. Spraying in the evening is preferred. Spray again if it rains immediately after spraying.

xvi. Urea used for foliar application must not contain more than 1.5% biurate, a compound which is highly harmful to the plants.

xvii. Foliar application of fertilizers should be avoided on the crops having very small leaves i.e. compound leaf system.

xviii. Bulky organic manures should be applied to the field soil one month before sowing while cakes 8-10 days before sowing so that decomposition may take place properly and, nutrients are available for crop growth.

Rate of Fertilizer Application:

Best management practices for nitrogen fertilizer application rate are poorly developed, but some promising new practices are on the horizon. Nitrogen fertilizer rate is one of the most important N management variables, both economically and environmentally.

The amount of N fertilizer needed to optimize crop yield often differs significantly from one field to another and from one part of a field to another part. Unfortunately, the tools available to predict how much N is needed are not yet very satisfactory for most crops.

Yield goal is the main tool for predicting N fertilizer rate in most crops, but yield level seems to play only a small role in determining how much N fertilizer is needed. Variation in the ability of the soil to supply N to the crop is the main factor that determines how much N fertilizer is needed to optimize yields.

Nitrogen application rates based on yield goal supply enough N to maximize crop yield in almost all situations. If N application timing does not expose N to loss, there is not much potential to improve crop yield by increasing N rates, but there is potential in many fields to save on the nitrogen fertilizer bill without losing yield.

This is increasingly important to profitability as N prices go up. Fertilize for normal yields. Even in years with excellent yield potential, increasing N rates above rates associated with normal yield is rarely needed. Conditions that are good for corn growth are also good for microbial activity that releases N from soil and the soil tends to supply more N to the crop in these years.

Crop colour appears to be the most reliable indicator of how much N is needed for a range of crops. Lighter colour indicates more N stress and a need for higher N rates. This approach only works for fertilizer applications made during the growing season.

Most producers’ make-in-season applications of N to wheat, rice, cotton, and forage grasses, but not to corn which receives about half of the recommended N fertilizer applied.

Although corn colour is the best predictor of how much N fertilizer is needed, it does not fit with the pre-plant N management systems. As nitrogen prices and environmental pressures increase, the usefulness of colour-based N side dressing for corn may increase. Sensors can be mounted either on tractor-based or high-clearance side dressing equipment and can control application rates of side dress N.

This approach is also being tested in wheat and cotton and may turn out to be useful for minor millets and grasses as well. Nitrogen components of phosphorus (P) fertilizers can also be safely credited if they are applied in rabi season.

Crediting half the N is safer if the P was applied in the fall before growth of a summer crop. Nitrogen components of starter fertilizers and nitrogen applied with herbicides should be included as part of the total intended N rate.

Time of Fertilizer Application:

Fertilizer should be applied when plants need it, when it will be most effective, and when plants can readily take it up. A split application may be beneficial, applying half the yearly rate in early spring and the rest in the fall as or after plants go dormant.

If water is unavailable, fertilizers should not be applied at all as plants will not be able to absorb nutrients. The best management practices (BMP) for timing of nitrogen (N) fertilizer applications is to apply fertilizer as close as possible to the period of rapid crop uptake.

Managing N in this way will minimize losses of N from the field and sill ensures adequate N availability to the crop during critical growth periods. These benefits, however, must be balanced against the risks associated with a smaller time window for N application, and against other time-sensitive field operations that may be necessary at the same time that N applications would be most efficient.

Most of the crop plants generally require nitrogen throughout their growth period. Irrespective of the crop, all plants tend to grow at a slow pace in the beginning, rapidly in the “grand growth period” (the period at which elongation of cells, tissues and formation of organs take place) and again slow during maturity. Accordingly, nitrogen is also taken up by the plants in keeping with the pace of plant growth.

Hence use of nitrogenous fertilizers should be so timed as to ensure its supply to the plant throughout its growth period especially during grand growth period. Nitrogenous fertilizers are very soluble in water, hence liable to be leached.

As such it is necessary to apply nitrogenous fertilizers in split doses of two-four, depending on the type of soil and the duration of the crop. When the fertilizer is applied at sowing time, it is called basal dressing; and the dose applied in standing crop is called top dressing.

When the application of N is not synchronized with crop demand, N losses from the soil-plant system are large resulting in low N fertilizer use efficiency. The chlorophyll meter also known as Soil Plant Analysis Development (SPAD) can quickly and reliable assess the N status of a crop based on leaf area.

Alternatively, the Leaf Colour Chart (LCC) is an inexpensive and hence it can be used by farmers of Asian countries. Keeping in view, a need based evaluation for the N management in wheat using LCC and SPAD meter to save the applied N without compromising the yield of crops. Experimental evidence is given in Table 24.1.

Levels of nitrogen:

T₁ = 0 kg ha^-1, T₂ = 60 kg ha^-1, T₃ = 100 kg ha^-1, T₄ = 120 kg ha^-1 (60: 60: 0), T₅ = 120 kg ha^-1 (45: 45: 30), T₆ = 150 kg ha^-1 (75: 75: 0), T₇ = 150 kg ha^-1 (60: 60: 30), T₈ = SPAD (35) with no basal N, T₉ = SPAD (35) with basal N @ 20 kg ha^-1, T₁₀ = SPAD (37) with no basal N, T₁₀ = SPAD (37) with no basal N,T₁₁ = SPAD (37) with basal N @ 20 kg ha^-1, T₁₂ = LCC (4) with no basal N, T₁₃ = LCC (4) with basal N @ 20 kg ha^-1, T₁₄ = LCC (5) with basal N and T₁₅ = LCC (5) with basal N @ 20 kg ha^-1, Minimum support price (MSP) of wheat = Rs. 6200.00 t^-1, Urea = Rs. 4.80 kg^-1, Labour charge = Rs. 60.00 labour^-1, Irrigation = Rs. 300.00 ha^-1 and cost of plant protection chemicals PPC = Rs. 1,000.00 ha^-1 season^-1.

From the results, it may be concluded that the amount of N can be preserved at 40-67.5 and 57.5-72.5 kg ha^-1 through the use of LCC and SPAD in wheat over fixed timing N treatment T₇, 150 kg ha^-1 (60: 60: 30) where N was applied in three splits without reduction in the yield. The overall results show that SPAD value of 37 and LCC value of 5 are better than SPAD, 35 and LCC, 4 for the management of N in wheat.

Plants require phosphorus mainly during the early root development and early growth period. Besides, almost all phosphatic fertilizers release phosphorus very slowly to the plant growth unlike nitrogenous fertilizers. They are, therefore, applied only at the time of sowing i.e. basal dressing.

Intake of potash by plant is similar to nitrogen whereas time its availability is like that of phosphorus. Soils rich in so clay fix the applied potassium and release it very slowly. As such, it is advisable to apply the entire quantity of potassic fertilizer at sowing time. However, mixtures of nitrogen and potassium can be applied in standing crop as well.