CHARACTERISTICS, CONSTRAINTS AND MANAGEMENT OF MANGROVE SOILS FOR SUSTAINABLE CROP PRODUCTION

Six representative soil profiles were studied to characterize and assess the constraints and management of mangrove soils for sustainable crop production in the Niger Delta of Nigeria. Profiles were sited at Urua--Essien Etuk (KS10), Okobo Ebughu I (DR11) and II (DR18), Oron I (RN12) and II (RN13) and Ikot Akpan Udo (KS14). Results indicate soil texture varied widely from sandy (KS10) to predominantly silty loam (RN12, RN13 and KS14) and sandy clay loam (DR11) with a mixed clayey/silty loam (DR18) texture. The high silt (388 -- 528gkg-1) and clay (188.8 -- 448gkg--1) contents indicate high water--holding capacity. Soil colour values were dominantly dark grayish brown (2.5 Y 3/2) to black (2.5 Y 2/0). Soil pH (H2O-, dry) ranged from strongly to moderately acid (3.1 - 5.5) --while pH in field moist soil varied from slightly acid to slightly alkaline (6.6 - 7.5). Organic C (12.4 -180.5gkg--1), total N (0.5 - 7.7 gkg--1) and exchangeable Mg (0.6 - 5.33cmolkg-1) levels were high while exchangeable Ca, cation exchange capacity (CEC) and available P contents were low. Poor drainage, high acidity (low pH), high electrical conductivity, loamy texture, low P, Ca and CEC levels were the major constraints of the soil against sustainable crop production. Management measures to be adopted should include reduction of excess water (drainage), application of soil amendments (gypsum/lime), cultivation of promiscuous soybean variety and planting of Al--resistant and Al-tolerant crops such as tea, cassava, rice, cowpea, mango, guava and rubber. Addition of both organic and mineral fertilizers after reclamation are also recommended.