Phosphate potential of acidic and limed soils and its relation to corn yield / by Leonardo Vidamo Crizaldo.

Thesis (D.P. - - Soil Science) University of the Philippines, College, Laguna.

Includes bibliographical references.

CRIZALDO, LEONARDO V, March, 1981, University of the Philippines at Los Banos, College, Laguna, Phosphate Potential of Acidic and Limed Soils and Its Relation to Corn Yield, Major Professor: Dr, Henry P, Samonte,

Wide variations in the sorptive capacity due to high reactivity of P to many soil constituents and the inherent differences of soil's physical and chemical properties make it difficult to establish P fertility index, Improvement of diagnosis and prediction of responses to P fertilization requires consideration of the energy level or intensity of phosphorus since this directly affects the absorption of P from the soil solution, This study was conducted with the following objectives: (1) to determine P fertilizer rates needed to adjust the phosphate potential (PP) of some acidic and P deficient soils in the Philippines and (2) to evaluate the effects of PP based fertilization on the relative dry matter yield, P concentration in tissues and P-uptake of corn,

The effects of PP based fertilization on corn yield, nutrient content and P-uptake were investigated using five acidic and P deficient soils under limited and unlimited conditions.

The soils used were Tagaytay clay loam, Guadalupe, Lipa, Luisiana and Alaminos clays, The respective Pof unlimited, unfertilized soils were; 7.79, 7.99, 7.61, 8.31 and 7,48, All of these intensity levels are considered low, After liming, the respective PP increased to 7.49, 7.72, 7.13, 7.92 and 7.46, In terms of P increase due to liming, these are equivalent to 3,28, 1,69, 5,96, 1,60 and 9,17 kg Py Os per 2 x 105 kg soil respectively,

Five levels of PP were established for each soil based on the relation of PP, soil solution P and rete of P fertilization. Over-all soil and lime treatments the PP are; 7,69, 7.30, 6.90, 5.86 and 5.12 corresponding to 0, 5.60, 13,60, 72.86 and 135.80 kg PoO05 per2x 106 kg soil respectively.

The mean dry matter yield, F concentration in tissues and P-uptake of corn varied significantly among soil types even at the same treatment, This suggests a larger influence of the inherent mineralogical and chemical properties of the soil on P absorption as compared with PP, Liming resulted in significantly higher yield, % P in corn tissues and Pe uptake among soil types. Liming thus increased P in solution subsequently the energy status to withdraw P was less,

To produce significantly higher yield over the unfertilized soils, the PP must be adjusted to 5.86 over-all soils corresponding to a soil solution P of 0.10 ppm by applying 72.86 kg Po O05 per 2 x 10° kg soil, With respect to P-uptake, however, aPP of 6,90 resulted in significantly higher yield, Further increment of PP to 5.12 corresponding to a soil solution P of 0.20 ppm and an application of 135.80 kg PyCs per 2 x 10° kg soil further increased the yield and P-uptake significantly.

Phosphate potential based P fertilization, therefore, must be soil and lime status specific as shown by the significant differences among soil types and between limited and unlimited soils within the soil type with respect to yield of corn variety DMR-2.,

Submitted to the University Library April 10, 1989 T-1117