Fertiliser Application: Precaution, rate and time

Precautions of fertiliser application:

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

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

iii. Avoid hot-hours of the day while applying (broad-casting) a fertiliser.

iv. Choose a fair weather day preferably for broadcasting.

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

vi. Confirm the compatibility of fertilisers before mixing.

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

viii. Cover the fertiliser 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 fertilisers and seed together especially of legumes as even a small amount of fertiliser 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 fertilisers 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 fertiliser application rate are poorly developed, but some promising new practices are on the horizon. Nitrogen fertiliser rate is one of the most important N management variables, both economically and environmentally.

The amount of N fertiliser 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 fertiliser rate in most crops, but yield level seems to play only a small role in determining how much N fertiliser is needed. Variation in the ability of the soil to supply N to the crop is the main factor that determines how much N fertiliser 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 fertiliser bill without losing yield.

This is increasingly important to profitability as N prices go up. Fertilise 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 fertiliser 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 fertiliser applied.

Although corn colour is the best predictor of how much N fertiliser 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) fertilisers 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 fertilisers 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, fertilisers 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) fertiliser applications is to apply fertiliser 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 fertilisers should be so timed as to ensure its supply to the plant throughout its growth period especially during grand growth period. Nitrogenous fertilisers are very soluble in water, hence liable to be leached.

As such it is necessary to apply nitrogenous fertilisers in split doses of two-four, depending on the type of soil and the duration of the crop. When the fertiliser 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 fertiliser 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. 

Source: Soil Management.com