Use of wheat straw, soybean trash and nitrogen fertiliser for maize production in the Kenyan highlands

Abstract

Making best use of available crop residues is an important component of integrated nutrient management. A field study was conducted over two seasons (1997 and 1998) in Kenya that examined use of wheat straw, soybean trash and nitrogen fertiliser as nutrient inputs for maize (Zea mays L.) production. The organic inputs were applied at the rate of 2 t ha-1 per season and urea was added at rates of 0, 20, 40, 80 and 100 kg N ha-1 in an incomplete factorial treatment structure that also included a complete control (no inputs) and 80 kg N ha-1 as urea without organic inputs. Maize grain yield ranged between 751 and 6836 kg ha-1 with lowest yields observed in the treatment receiving wheat straw alone and higher yields associated with soybean residue incorporation and during the second, wetter growing season. The 1998 crop benefited from more favourable rainfall, providing grain yield increase of 141% above control treatment as a result of combining 2 t ha-1 soybean trash and 100 kg N ha-1 urea. The generally high yields from soybean trash are explained in terms of its higher quality, faster decomposition and nutrient release compared to the lower quality wheat straw. A positive effect in increases of soil pH, C, N and P status as a result of cumulative use of crop residues was observed. Larger yields were obtained when organic and inorganic inputs were applied to soils, particularly when soil moistue was adequate and the organic inputs higher in mineralisable nutrients. Early indications of additional longer-term benefits through soil quality improvement were also measured. These findings suggest that better use may be made of crop residues than the burning following harvest as is currently practiced by many farmers in this area of western Kenya.

Effects of conservation tillage, crop residue and cropping systems on changes in soil organic matter and maize–legume production: a case study in Teso District

“…Application of organic amendments under conservation tillage systems is expected to provide a long-term source of N and reduce the need for N fertilization. In western Kenya, incorporation of crop residues (maize stover, wheat straw, bean trash and improved fallows) into soils have been associated with improved N levels in soils and subsequent high maize and bean yields (Palm et al 1997;Okalebo et al 1999;Kifuko 2002;Ndung'u et al 2006;Waigwa 2002). Cropping systems had no significant effect on total N content in all cropping seasons.…”

Available technologies to replenish soil fertility in East Africa

“…Table 7. Effect of continued application of crop residues and nitrogen fertilizer on maize grain yield (t/ha) in a Chepkoilel ferralsol, Eldoret, Kenya (after Okalebo et al 1999 particularly when soil moisture was adequate and from addition of organic inputs higher in mineralisable nutrients. These findings suggest that better use may be made of crop residues than the burning following harvest as is it currently practiced by many farmers in this wheat growing area of western Kenya .…”

Chickpea‐Wheat Rotation for Higher Production in a Humid Tropical Region

“…Nutrient depletion, coupled with the inability of farmers to apply inorganic fertilizers and the practices of grazing and burning plant residues, has been indicated as the major cause of declining agricultural production in Africa (Kikafunda et al, 2001; Sanchez et al, 1997). Several studies in tropical regions have shown that application of grain legume residues, such as chickpea, Hyacinth bean ( Dolichos lablab L.), soybean ( Glycine max ), and tropical forage legumes, increased soil N content (Njunie et al, 2004; Okalebo et al, 1999; Onwonga 1997). In previous studies, no attempt was made to test the mature chickpea and green manure and to relate their measured residue parameters with N dynamics in soil.…”

“…Onwonga (1997) reported that mature chickpea residue could return 54 kg N ha −1 when the DM yield was 1.7 Mg ha −1 , which is equivalent to a fertilizer replacement value of 38 kg N ha −1 for wheat. Okalebo et al (1999) reported higher maize yields after application of soybean residues.…”