A. Dobermann et al., MANAGEMENT OF PHOSPHORUS, POTASSIUM, AND SULFUR IN INTENSIVE, IRRIGATED LOWLAND RICE, Field crops research, 56(1-2), 1998, pp. 113-138
Management of soil phosphorus (P), potassium (K) and sulfur (S) resour
ces in intensive, irrigated rice systems has received less attention t
han increasing cropping intensity and yields with new cultivars, irrig
ation, and fertilizer N. Crop requirements, input-output balance, and
soil supplying capacity of P, K and S in irrigated lowland rice are re
viewed. Based on projected rice production requirements, we estimate t
hat the total annual nutrient demand for irrigated rice will be about
9 to 13 X 10(6) t N, 9 to 15 X 10(6) t K, 1.2 to 2.4 X 10(6) t P and 0
.9 to 1.5 X 10(6) t S in 2025, amounts that represent an increase of 6
5 to 70% above 1990 requirements. At present, negative K balances are
widespread and K deficiency has become a constraint to increasing yiel
ds, even on heavy-textured lowland soils with high inherent fertility.
Because opportunities are limited for breeding cultivars that acquire
more P, K or S from soil or have higher internal nutrient-use efficie
ncies, long-term management strategies must focus on maintaining adequ
ate nutrient balances in the topsoil layer. Interactions among nutrien
ts have a large influence on physiological and agronomic efficiency th
at result from nutrient applications. Strategies that only aim at incr
easing P or K application rates without considering the indigenous sup
ply from soil reserves are inefficient; they may not sustain yield inc
reases to meet rice demand. Little improvement in fertilizer use effic
iency can be expected from the present system of providing blanket rec
ommendations for a given production domain. Instead, site-specific nut
rient-management approaches will be needed to accommodate the tremendo
us variability in indigenous nutrient supply found in the irrigated lo
wlands of Asia. (C) 1998 Elsevier Science B.V.