Mary Wk Mburu

Influence of line-planted trees and phosphorus application on water use of maize in sub-humid western Kenya

ABSTRACT Planting of trees in rows is common on farms in western Kenya where phosphorus deficiency is also a major constraint to maize production. The influence of soil P status and simultaneous agroforestry systems on water use have, however, not been reported for the region. Effects of line-planted Grevillea robusta (upperstorey trees), Calliandra calothyrsus and Senna spectabilis (both managed as hedges) and P application on water use efficiency were investigated in maize. The experiment was laid out as a splitplot with tree species forming main plots while 250 kg P/ha and no P applications formed subplots. Seasonal evapotranspiration was greater under Grevillea by 40.8 mm (5.2%) in the Long Rains and by 49.3 mm (10.2%) in the Short Rains. Application of P significantly increased seasonal evapotranspiration (ET) by 1.7% in Long Rains and 2.4% in the Short Rains. Maize water use efficiency was higher with P (6.9 kg/ha/mm in Long Rains and 9.5 kg/ha/mm in the Short Rains) than without P (0.8 kg/ha/mm in the Long Rains and 2.1 kg/ha/mm in Short Rains). The results revealed enormous potential for increasing maize WUE in these soils by overcoming P deficiency. Combining Grevillea trees with P enhanced use of seasonally available water.

Effects of nitrogen and phosphorus fertiliser on growth and yield of ironweed ( Vernonia galamesis )

ABSTRACT Ironweed (Vernonia galamensis) is a promising new crop for industrial oil but information on its response to fertiliser is scanty. A field experiment was conducted at the University of Nairobi Field Station farm during 2 seasons (January to May 1998, season 1 and March to August 1998, season 2) to determine the effects of nitrogen (N) and phosphorus (P) fertiliser rates on growth, photosynthetically active radiation (PAR) interception and seed yield of 2 Vernonia galamensis cultivars (ethiopica and gibbosa). N was applied at 0, 75 and 150 kg N/ha, and P at 0, 45 and 90 kg P2O5/ha. The experiment was a 2 × 3 × 3 factorial laid out in a randomized complete block design with 3 replications. N and P application significantly increased total dry matter (TDM), photosynthetically active radiation (PAR) interception and leaf area index (LAI) of both varieties in late vegetative and reproductive stages. Gibbosa had consistently higher TDM, LAI, PAR and was taller compared to ethiopica throughout the growing season. Average seed yield of gibbosa was 2.3 times higher than that of ethiopica in both experiments. The highest TDM, LAI and seed yields were obtained at the highest N and P levels. Gibbosa had a significantly higher number of capsules/plant but a lower harvest index (HI) compared to ethiopica.