Organic and Mineral Input Management to Enhance Crop Productivity in Central Kenya

Abstract

Organic resources (ORs) are important nutrient inputs in tropical agriculture. Combined with mineral fertilizers, they form the backbone of integrated soil fertility management. This study was conducted to determine the medium‐ to long‐term influence of OR quality and quantity on maize productivity and to evaluate the occurrence of additive benefits in terms of extra grain yield produced by the combined application of ORs and N fertilizers. Farmyard manure, high quality Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray], intermediate quality calliandra (Calliandra calothyrsus Meisn.) and maize (Zea mays L.), and low quality silky‐oak (Grevillea robusta A. Cunn. ex R. Br.) sawdust were incorporated into the soil at equivalent rates of 1.2 and 4 Mg C ha−1 yr−1 in Embu (clayey) and Machanga (sandy soil), together with a control to which no OR was added. All plots were split, with one half receiving 120 kg N ha−1 season−1 as CaNH4NO3. The ORs, except sawdust and maize, improved maize grain yields compared with the control at both sites. Greatest mean maize yields (i.e., 4.9 and 2.3 Mg ha−1 season−1, in Embu and Machanga, respectively) over 10 seasons were observed with the high rate of Mexican sunflower, but was not significantly different from calliandra and manure. Generally, maize yields were greater with higher than lower OR rates, except for maize and sawdust. Although N fertilizer additions to the ORs improved grain yields in Embu, the increase was marginal; resulting in negative interactive effects of applying ORs with N fertilizers, especially with high‐N ORs. Thus high‐N ORs should not be applied in combination with N fertilizers, especially at such high fertilizer N rates.

Trade-offs between the short- and long-term effects of residue quality on soil C and N dynamics

“…A greater retention of N in the root zone, combined with subsequent stimulation of residue-N mineralization, as observed in the microcosm experiment, could have increased N available for crop uptake in the combined treatment. The high input rates used in this field trial may have exceeded crop N requirements, especially in the tithonia + fertilizer treatment and contributed to the negative interactive effects on yield (Chivenge et al 2009). Input rates aside, the early season residue mineralization and lack of fertilizer immobilization shown by tithonia led to greater N availability ahead of crop demand.…”

“…Combining the results of mineral N dynamics from laboratory and field experiments (Gentile et al 2008a;Gentile et al 2009), long-term crop yields (Chivenge et al 2009) and field SOM stabilization (Gentile et al 2008b), establishes novel and integrated conclusions on the benefits of ISFM. These previous studies looked at a variety of organic residue qualities, but this paper focuses on the comparison of high versus low quality residues in order to elucidate general principles.…”

“…N fertilizer was applied at rates of 0 or 120 kg N ha −1 season −1 in a split application 4 and 8 weeks after planting, and maize was grown consecutively each growing season. Details of the full treatment structure and trial management have been previously reported (Chivenge et al 2009;). Mean quality parameters for the residues applied in the field are listed in Table 1.…”

“…Mean quality parameters for the residues applied in the field are listed in Table 1. Crop yield was measured each growing season from 2002 to 2006 to determine the interactive effects of combining inputs on crop production (Chivenge et al 2009). Additionally, short-term N dynamics were assessed during the 2007 long rains growing season in the 1.2 C ha −1 residue plots ).…”

Small Scale Farmers’ Indigenous Agricultural Adaptation Options in the Face of Declining or Stagnant Crop Yields in the Fako and Meme Divisions of Cameroon

“…The second on-the-farm option involves investments in agroforestry and mixed farming. Trees can increase above ground biomass, provide litter and enhance soil organic content as well as enhance soil organic carbon and nitrogen which are very vital for crop yields [37]. Globally, about 1.2 billion people are using agroforestry methods in their farms [38].…”