Question

Which macronutrient is required by wheat crop/rice crop?

Answer 1

Macronutrients

In temperate regions, 25 kg N are required per tonne of grain containing 15 percent

protein. Therefore, a yield of 10 tonnes will need 250 kg/ha N for the grains alone,

and about 30–40 percent more for the total plant biomass, which results in a total

amount of 350 kg N/ha. However, as fertile soils generally provide one-third of

this amount, fertilizer amounts can be adjusted to N removal in grains. Ideally, N

fertilizer applications to winter wheat (200–250 kg N/ha for high yields) should

be split into several dressings as follows:

¾ in autumn: only 30 kg N/ha (or none where sufficient N is left from the

previous crop);

¾ in early spring: about 120 kg N/ha (minus mineral N in soil, e.g. 30 kg/ha

N);

¾ at beginning of tillering: about 30–50 kg N/ha;

¾ at ear emergence: 40–60 kg N/ha – this can be divided into two portions

to enable a late foliar spray to improve protein content for better baking

quality.

Wheat needs no special N fertilizer. However, for applications in spring with

cold weather, quick-acting nitrate is superior to ammonium or urea. Placement of

N fertilizers brings little or no advantage on most soils, except perhaps under low

rainfall and in the absence of irrigation. One kilogram of fertilizer N produces

about 15–25 kg of grain. Where yields are limited by climate or other constraints,

the fertilization rate can be reduced in view of the lower requirements and the

respective soil nutrient status.

Under subtropical conditions, the generally recommended amounts of N are

120–150 kg N/ha to irrigated HYVs, and about half of this to traditional varieties

or where irrigation is not available. N application is generally recommended in

2–3 splits at planting, and one month and two months after planting. The basal

dressing is generally given in the form of urea or through NP/NPK complexes.

For top-dressing, any of the common N fertilizers are suitable but ammoniumsulphate performs better than others on S-deficient soils. To unirrigated wheat
depending solely on stored soil moisture and seasonal rainfall, N rates varying
from 40 to 120 kg N/ha can be applied depending on stored soil moisture as
described above (Figure 36).
Because an optimal supply of P and K is required for high yields, even during
periods of water stress, these nutrients should be applied before sowing in spring
or autumn unless there is danger of K leaching on sandy soils. As a rule, on
fertile soils, nutrients applied to offset nutrient removal with grains and straw are
sufficient. For a yield of 8 tonnes/ha of winter wheat, the recommended rates are:
90 kg/ha P2O5, 160 kg/ha K2O and 25 kg/ha Mg. On deficient soils, the amounts
added should be at least 30 percent higher, and on soils containing high amounts,
about 50 percent lower than the values given above.
Deficiencies of nutrients other than NPK are likely to occur in poor soils, at
high yields and with persistent use of NPK. S and Mg are the two most likely
nutrients to be limiting. These can be applied prior to sowing or, in the case of S,
through an S-containing N fertilizer in the standing crop. Where visible deficiency
symptoms appear, water-soluble fertilizers or foliar sprays can be applied.