Effect of Soil Water, Nitrogen and Phosphorus on Maize Growth and Yield in a Semi Arid Environment

Abstract

A field study was carried out for three seasons from November 1999 to February 2001 to investigate the influence of ilTigation on growth, light and nitrogen use in maize under semiarid conditions in Machakos, Kenya. The study also assessed the potential and applicability of the World Food Studies (WOFOST) model in predicting maize growth and yield in the same area. The work spanned three seasons namely short rains 1999 (SR1999, Nov. 1999- March 2000); long rains 2000 (LR2000, April to August 2000) and SR2000 (November 2000 to March 2001). The rainfall received in the three seasons was 350, 143 and 534 mm respectively. The experimental design was randomized complete block design laid out as split plot with water regime as main plots (irrigated, rainfed), nitrogen (N) (0, 50, 100 kg N ha- 1 ) and phosphorus (P) (0, 25 kg P20S) factorially combined as subplots. Data collected included leaf area index (LAI), photosynthetically active radiation (PAR) interception, maize grain yield, total dry matter (TDM) accumulation, nitrogen uptake and soil moisture. Irrigation significantly increased TOM (at physiological maturity) by about 2 to 10 fold during the study period. Grain yields were lowest in driest season (LR2000) (151 kg ha- 1 ) and highest (6,027 kg ha- 1 ) in wettest season (SR2000). Irrigation significantly increased leaf a rea index (LAI) by a bout 2 fold (maximum L AI, 1 .3, 2.8 for rainfed and irrigated respectively) in the dry season but had no effect in the wetter seasons. PAR interception increased by the same factor as LAI (maximum PAR interception 33 %, 64 % for rainfed and irrigated respectively in the dry season). Maize light extinction coefficient was lower (0.30) under moderate and low water supply (rainfed SR1999 and LR2000) and higher (0.37) under high water supply (irrigated LR2000 and SR2000). The total plant N uptake was highest (175 kg ha- 1 ) in wettest season (SR2000) and lowest (14 kg ha- 1 ) in the driest