Root Growth and Nutrient Uptake of Rice as Affected by Planting Methods and Green Manures

Abstract

Field experiment with rice was conducted at IRRI during 1989 wet season. The experimental design was a two factor randomized complete block with 12 treatments and four replications. Fertilizer N was applied at 60 kg N/ha as 2/3 basal incorporated (B&I) + 1/3 N topdressed at 5-7 days before panicle initiation (DBPI) except for pure green manure treatments where the full N dose as Sesbania rostrala (Sesbania) or Aeschynomene afraspera (Aeschynomene) was basally incorporated. Root length density was determined at the flowering and plant nutrient uptake was determined separately by calculating from the product of dry matter, straw dry weight, grain yield and % N, P, K content. Results showed that root growth of broadcast seeded flooded rice (BSFR) was higher at all soil depth than transplanted rice (TPR) as per unit area due to higher plant density and root growth was not disturbed by uprooting. However, on a per tiller basis, root length was significantly lower in BSFR than in TPR at 0-10 cm soil depth which could have partly caused more lodging in BSFR. There were no significant differences among N treatments and no interaction between planting method and N treatment on root growth. However, nonfertilized control gave significantly higher root-to-shoot ratio than did N-treated plots. Total N uptake in BSFR was higher than that in TPR. Topdressing urea in PU-green manure treatments resulted in higher N uptake at maturity than did green manure applied alone. Phosphorus and K uptake were not significantly differ among the fertilized treatments in both TPR and BSFR at 5-7 DBPI.