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RICE

Upland Rice Response to Phosphorus Fertilization in Asia

^a Univ. of Hawaii, 1955 East West Rd., Agric. Sci. 205, Honolulu, HI 96822 and Int. Rice Res. Inst. (IRRI), DAPO Box 7777, Metro Manila, Philippines
^b IRRI, DAPO Box 7777, Metro Manila, Philippines
^c Renewable Nat. Resources Res. Cent., Bumthang, P.O. Jakar, Bhutan
^d Lab. of Soil Fertil. and Soil Biol., KU Leuven, 3001 Leuven, Belgium
^e Centre de coopération internationale en recherche agronomique pour le développement (Cirad-ca), Montpellier, France

* Corresponding author (t.george{at}cgiar.org)

Upland rice (Oryza sativa L.) yields on infertile, acid soils in the Asian uplands average only 1 Mg ha^-1. Phosphorus deficiency is considered a major soil constraint to increased yield, but little quantitative information is available. We analyzed P responses of traditional rice on farm in Laos, Thailand, and the Philippines and improved varieties in researcher-managed trials in the Philippines. Treatments in on-farm trials were a control and 50 kg P ha^-1 ± 100 and 50 kg ha^-1 N and K, respectively. Treatments in researcher-managed trials were P rates on an unlimed and limed Ultisol. Mehlich-1 extractable P correlated with on-farm grain yield (r = 0.47). Phosphorus fertilization increased average grain yield (1 Mg ha^-1) by 20%, total biomass (4 Mg ha^-1) by 27%, and P uptake (4.1 kg ha^-1) by 53%. Yield increased 37% with P + N + K, but only 16% of the 2.4 Mg ha^-1 biomass increase was grain. Improved rice in researcher-managed trials responded to P, with a larger proportion of biomass partitioned to grain [i.e., higher harvest index (HI)]. Grain yield of ‘UPLRi-5’ increased from 3.2 to 4.6 Mg ha^-1 in limed soil while that of ‘IR55423-01’ increased from 3.4 to 4.0 Mg ha^-1 in unlimed soil. Phosphorus fertilization always increased the frequency of higher yields averaged across trials, soils, varieties, and growing conditions. Yield gain from on-farm P fertilization of traditional rice was small because of low HI, unlike in improved varieties, which had a HI. We infer that increasing upland rice yield in Asia would require genotypes with higher HI in addition to P fertilization.

Abbreviations: BC, buffer coefficient • HI, harvest index • M1P, Mehlich-1 extractable P

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