Theme 2: Forage--Oral Sessions

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The measurement of soil aggregates stability and soil microbial biomass can be used as an early indicator of long-term changes in soil quality. A study was conducted to quantify the amounts of shoots and roots biomass of Urochloa grass cultivars (commonly known as Brachiaria) and their effects on changes in the size distribution and stability of soil aggregates and on microbial biomass carbon (C), nitrogen (N) and phosphorus (P) in a structurally unstable sandy loam soil at Ithookwe and Katumani in semi-arid tropical Kenya. The Urochloa grass cultivars included Urochloa decumbens cv. Basilisk, U. brizantha cvs Marandu, MG-4, Piatã and Xaraes, U. humidicola cv. Llanero and U. hybrid cv. Mulato II. Rhodes and Napier grass were included in the treatments as controls. Roots biomass was evaluated using the soil-coring method to depths of 0 – 15 and 15 – 30 cm. Four aggregates-size fractions (> 2000 μm, 250 – 2000 μm, 53 – 250 μm, and < 53 μm) were isolated using the wet sieving method. Microbial biomass C, N and P were determined on field moist rhizosphere soil (18 - 23% by weight) from a depth of 10 cm using the chloroform fumigation-extraction technique. Shoots biomass of the Urochloa cultivars ranged from 3.0 to 11.3 t ha-1 and 5.5 to 8.3 t ha-1 at Ithookwe and Katumani sites respectively. Marandu, Xaraes, Basilisk and Piata had higher roots biomass than the controls (Rhodes grass and Napier grass). Aggregate stability differed among the grasses and was highest in soils under Mulato II and Marandu with mean weight diameters of 4.49 and 4.31 mm, respectively. Generally, microbial biomass N was higher in plots with grasses than in the bare plots. Among Urochloa cultivars, the highest microbial biomass C was recorded in plots with Mulato II and the lowest from the plots with MG-4.

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Climate Smart Urochloa Grasses Improves Soil Health in the Semi-Arid Tropics of Kenya

The measurement of soil aggregates stability and soil microbial biomass can be used as an early indicator of long-term changes in soil quality. A study was conducted to quantify the amounts of shoots and roots biomass of Urochloa grass cultivars (commonly known as Brachiaria) and their effects on changes in the size distribution and stability of soil aggregates and on microbial biomass carbon (C), nitrogen (N) and phosphorus (P) in a structurally unstable sandy loam soil at Ithookwe and Katumani in semi-arid tropical Kenya. The Urochloa grass cultivars included Urochloa decumbens cv. Basilisk, U. brizantha cvs Marandu, MG-4, Piatã and Xaraes, U. humidicola cv. Llanero and U. hybrid cv. Mulato II. Rhodes and Napier grass were included in the treatments as controls. Roots biomass was evaluated using the soil-coring method to depths of 0 – 15 and 15 – 30 cm. Four aggregates-size fractions (> 2000 μm, 250 – 2000 μm, 53 – 250 μm, and < 53 μm) were isolated using the wet sieving method. Microbial biomass C, N and P were determined on field moist rhizosphere soil (18 - 23% by weight) from a depth of 10 cm using the chloroform fumigation-extraction technique. Shoots biomass of the Urochloa cultivars ranged from 3.0 to 11.3 t ha-1 and 5.5 to 8.3 t ha-1 at Ithookwe and Katumani sites respectively. Marandu, Xaraes, Basilisk and Piata had higher roots biomass than the controls (Rhodes grass and Napier grass). Aggregate stability differed among the grasses and was highest in soils under Mulato II and Marandu with mean weight diameters of 4.49 and 4.31 mm, respectively. Generally, microbial biomass N was higher in plots with grasses than in the bare plots. Among Urochloa cultivars, the highest microbial biomass C was recorded in plots with Mulato II and the lowest from the plots with MG-4.