Influence of irrigation on maize growth, yield and nitrogen uptake in a semi-arid environment in Kenya

A field study was carried out for two seasons (November to February 1999 and April to August 2(00), to investigate the influence of irrigation on maize growth, nitrogen uptake and yield. The experimental design was randomised complete block design laid out as split plot with water regime as main plots (irrigated, rainfed), and factorial combinations of N (0, 50, 100 kg N ha,l) and P (0, 25 kg P2Os) as subplots. Data collected included leaf area index (LA!), photosynthetically active radiation (PAR) interception, total dry matter (TDM), nitrogen uptake and maize grain yield. Phosphorus had no effect on growth and yield, therefore the data were pooled for P. In season I with 350 mm rainfall, irrigation had no effect on LA! and fractional PAR interception but it significantly increased total N uptake, TDM and grain yield. The mean total N uptake, TDM and grain yield in irrigated treatments were 103, 10,472 and 4,896 kg ha'l respectively while under rainfed treatments they were 47, 4,891 and 2,180 kg ha,l respectively. In water stressed rainfall conditions of season 2 (143 mm rainfall), irrigation significantly increased LAI, PAR interception, N-uptake, TDM and grain yield. Under irrigation the mean LA! were 0.29 and 2.2 during establishment and flowering phases respectively and 0.17 and 1.1 under rainfed treatment respectively. The mean PAR interception under irrigated treatments were 15.3 and 63.6 % while under rainfed treatments they were 10.5 and 29.4 % respectively during the same phases. The mean N uptake, TDM and grain yield under irrigated treatments were 143.1, ll,nO and 5,197 kg ha-I respectively and 14.1, 1,081 and 151 kg ha,l respectively under rainfed treatments. In season 1 nitrogen application significantly increased LA!, fractional PAR interception, N-uptake, TDM and grain yield. The mean LA! with N were 0.37 and 2.67 during establishment and flowering phases respectively and 0.14 and 1.83 respectively without N. The mean fractional PAR interception were 54.6 % with Nand 43.3 % without N during flowering. Under irrigated treatments and with N, the mean N uptake, TDM and grain yield were 121, H,SSI and 5,396 kg ha-l while without N they were 67, 7,M4 and 3,897 kg ha'l respectively. Under rainfed treatments with N the mean N uptake, TDM and grain yield were 56, 5,779 and 2,547 kg ha'i respectively and 28, 3,115 and 1,447 kg ha.l respectively without N, In season 2 nitrogen significantly increased N uptake, TDM and grain yield in irrigated treatments only. The mean N uptake, TDM and grain yield in irrigated treatments with N were 168, t2,965 and 5,929 kg ha-I respectively and 94.1, 9,231 and 3,734 kg ha'l respectively without N. The optimal N application was 50 kg ha'l above which there was no improvement in growth performance and yield. Supplementary irrigation can therefore increase maize yield even at low fertilizer input level in semi-arid Kenya.