Yoshida - 1981 - Fundamentals of Rice Crop Science

MINERAL NUTRITION OF RICE 147
where N F is amount of nitrogen applied (kg/ha), and Y o represents nitrogen
fertility levels in the soil. Y o varies with soil type and perhaps with variety. Values
of 2 t/ha and 3.5 t/ha are assigned to Y o so that the first value represents the average
nitrogen fertility level of paddy fields and the second represents a high fertility
level. Yield increases obtained by fertilizer application can be computed from the
second term of equation 3.24.
As shown in Figure 3.15, grain yield is determined by soil fertility level, amount
of nitrogen applied, and percentage of nitrogen recovery. At Y o = 2 t/ha, 50 kg of
fertilizer nitrogen can produce yields of 2.75–3.25 t/ha. To produce 6 t/ha, a
minimum of 160 kg N is needed. These computations illustrate the relationship
between the target yield and fertilizer requirements.
3.8. PHOSPHORUS
3.8.1. Occurrence of deficiency
Phosphorus deficiency occurs widely in soils of low or high pH: acid latosolic
soils, acid sulfate soils, calcareous soils, and alkali soils. Ando soils, which have a
high capacity to fix applied phosphorus, need much larger amounts of phosphorus
than usual. For example, the optimum for acid Ando soils in northern Japan is
about 200 kg P 2 O 5 /ha; that for calcareous soils at Dokri, Pakistan, about 45 kg
P 2 O 5 /ha; and that for calcareous soils at Rajendranagar, India, about 80–100 kg
P 2 O 2 /ha.
3.8.2. Phosphorus in soil solution
Depending on soil type, submergence increases the concentration of phosphorus in
the soil solution from less than 0.05 ppm to about 0.6 ppm and subsequently
decreases it (Fig. 3.16). The increase of phosphorus solubility in submerged soils
3.15. Simplified models for relationship between fertilizer nitrogen and rice yield. 30% and 50%
are minimum and maximum nitrogen-recovery percentages.