The Crucial Role of Soil Organic Matter in Satisfying the Phosphorus Requirements of Olive Trees (Olea europaea L.)

Under high organic matter content, even under low extractable soil P concentrations, sufficient or over-sufficient foliar P levels may be found. This multi-year study aimed at examining the effects of organic matter content and irrigation management on (a) soil fertility, (b) P-cycle related soil enzymes (acid and alkaline phosphatase, pyrophosphatase) and (c) foliar nutrient concentrations. Irrigated and non-irrigated groves of fully productive trees of the cultivar “Chondrolia Chalkidikis” with low organic matter (LOM < 1.5%), medium organic matter (1.5% < MOM < 2.5%) and high organic matter (HOM > 2.5%) were selected for the experimentation. It was hypothesized that olive groves receiving high inorganic fertilization and irrigation inputs (usually with medium to relatively low organic matter content) would show higher soil and foliar P concentrations compared to the non-irrigated groves with higher organic matter content receiving manure applications. Most of the soil variables (including the three enzymes’ activities) were affected by differences in organic matter content. However, organic matter content did not show a significant influence on foliar nutrient concentrations. Olive trees, especially those cultivated in soils with high organic matter content (receiving organic fertilization), can over-satisfy their P nutritional needs, even though soil analyses show low soil extractable P concentrations, probably due to the high enzymatic activity of acid and alkaline phosphatases. The practical conclusion of this study is that P fertilizer recommendations should be primarily based on foliar P rather than on extractable soil P.

Toward Standardized Leaf Sampling for Foliar Nutrient Analysis in Breadfruit

Breadfruit (Artocarpus altilis) cultivation is gaining momentum throughout the tropics due to its high yield and nutritious fruit. One impediment to expanding production of breadfruit is the lack of agronomic research related to production management. We examined foliar nutrient concentrations of different leaf positions and leaf parts to assess within- and between-tree variance to inform an effective sampling protocol. We further validated the sampling protocol on 595 trees at 87 sites that were assessed for yield and productivity. Foliar nutrients differed significantly by categories of productivity. For the first time, breadfruit-specific standards of foliar nutrient concentrations are presented for consideration. In conclusion, we recommend that foliar sampling use petioles harvested from leaves in the third position from the branch tip using sun-exposed leaves in the midcanopy of each tree.

GROWTH AND NUTRITION OF CACAO SEEDLINGS INFLUENCED BY ZINC APLICATION IN SOIL

ABSTRACT Levels of Zn in tropical soils profoundly influences growth and nutrition of tree crops. Research was undertaken to assess the effect of soil Zn on growth and nutrition of clonal cacao tree seedlings of PH 16. Three acidic Oxisol soils differing in texture were used with nine doses of Zn (0, 1, 2, 4, 8, 16, 32, 48, and 64 mg dm-3). Rooted clonal seedlings were grown in plastic pot with 11 dm-3 of the soils at varying Zn levels for 240 days. At harvest growth (dry matter mass of leaves, stems, shoots, roots, and total) and nutrient concentrations were determined. The clonal cacao seedlings showed differences for production of dry matter mass and foliar nutrient concentrations for P, K, Ca, Mg, Mn, Fe, Zn, and Cu. There was Zn toxicity in all soils.