Effects of Integrated Soil Fertility Management on Soil Microbial Biomass, Nitrogen Mineralization, Phosphorus Dynamics, and Maize Productivity in Humic Nitisols of Kenya

Abstract

Nitrogen and phosphorus are the two most important macronutrients, often limiting crop production. Their responses to diverse integrated soil fertility technologies are still poorly understood in acidic Nitisols. A randomized complete block design was laid out in an acidic Nitisols at Kangutu Primary School in Chuka subcounty to investigate the effects of selected integrated soil fertility management technologies on; 1) soil microbial biomass carbon, nitrogen, and phosphorus, 2) nitrogen mineralization, partial factor productivity, and apparent recovery, 3) soil phosphorus fractions, degrees of saturation, maximum sorption, legacy and phosphorus use efficiency, and 4) maize productivity. The study used the Agricultural Production Systems sIMulator Model (APSIM) to simulate nitrogen mineralization under the technologies. Integrating: conventional tillage + maize residue + goat manure + Dolichos lablab intercrop; minimum tillage + maize residue + Tithonia diversifolia + goat manure; and minimum tillage + maize residue + goat manure + Dolichos lablab intercrop recorded the highest increase in microbial carbon, nitrogen, and phosphorus by 78%, 48%, and 41%, respectively. Nitrogen mineralization under the technologies was significantly (p < 0.0001) variable in certain sampling dates. Conventional tillage + maize residue + goat manure + Dolichos lablab intercrop had 5.11 and 52.80 kg N ha-1 significantly higher apparent nitrogen recovery and partial factor productivity, respectively. Similarly, minimum tillage + maize residue + goat manure + Dolichos lablab intercrop greatly increased apparent nitrogen recovery by 5.75 relative to control. Generally, APSIM poorly simulated nitrate and ammonia nitrogen based on the lowest root means square error and the highest d-index. Resin phosphorus, sodium bicarbonate-extractable inorganic phosphorus, and maximum phosphorus sorption increased by 182, 76, and 52 mg P kg-1 under minimum tillage + maize residue + inorganic fertilizer + goat manure. Sodium hydroxide-extractable inorganic phosphorus and maximum phosphorus sorption significantly increased by 216 mg P kg-1 and 49 mg P kg-1 under conventional tillage + maize residue + inorganic fertilizer + goat manure. The same technology had the highest phosphorus partial factor productivity of 0.093 and 0.140 kg biomass kg-1 P and phosphorus agronomic efficiency of 0.080 and 0.073 kg biomass kg-1 P during the short and long rains cropping seasons. The findings of this study underpin the importance of integrated soil fertility management technologies in managing soil nitrogen and phosphorus in a maize-based cropping system. The study, therefore, recommends integrated technologies as alternatives or complementary to the sole use of inorganic fertilizers. It also recommends minimal use of model default (inbuilt) values for improved APSIM performance in N mineralization estimation.