Nutritional assessment of steeply sloping soils from Aiyura, in the Eastern Highlands of Papua New Guinea.

Abstract

Prior to commencing long-term soil loss studies at the Highlands Agricultural Experiment Station at Aiyura in the Eastern Highlands of Papua New Guinea, the nutritional status of soils from the experimental site was assessed by soil analysis and nutrient omission pot trial. Two soils were assessed; the first, an Orthoxic Tropudult, was located on long convex slopes with northerly aspect and the second, an Umbric Tropaquult, occupied a hummocky microtopography with short slopes and a southerly aspect. Soil tests suggested both surface (0 to 0.15 m depth) soils were strongly acid (pH 5.0 to 5.4 in 1:5 soil/water suspension), contained allophane and active AI (pH 7.9 to 8.2 in 1:50 soil/NaF solution), and were strongly P fixing (P retention >70%) with low P availability (< 4 mg kg1 Olsen-P) With maize (Zea mays L.) as the test plant, short duration (35 day) omission pot trials confirmed (P < 0 05) these soils were P and S deficient. Plants suffering P and S deficiency were 8 to 24% shorter, and amounts of both fresh and dry matter produced were 15 to 43% lower, and S deficient plants were distinctly yellower in colour. No deficiency was apparent with omission of B, Ca, Cu, Fe, K, Mg, Mn, Mo, N, Ni or Zn. Also, addition of lime had little effect.