Agricultural and Food Security Challenges for the IGAD Region

Conference Paper No.

Nitrogen forms in three Kenyan soils Andosols, Lucidols and Ferralsols

The nitrogen cycle in soil is an integral part of the overall cycle of N in nature. The primary source of N is the atmosphere where the strongly bonded gas molecule N is predominately gas (78.08%). Total N content in soils ranges from 0.02% in the subsoil and more than 2.5% in peats; ploughed layers of most cultivated soils contain between 0.06 and 0.5%. The amount present in each case is, however determined by climate, type of vegetation, topography, parent material and activities of man. Over 95% of TN in surface soils is organically bound while the portion of non-exchangeable N is high in subsurface soil. Knowledge concerning the nature of organic N in soils is based on studies involving identification and estimation of N forms released by treatment with hot acids. Organic N forms were determined in three soils by acid hydrolysis. The total hydrolysable organic N for the 0-15 and 15-30 cm layers were 57.2 and 59.3% for Gituamba andosols; 56.9 and 61.9 for Kitale ferralsols; 39.0 and 42.1% for Katumani luvisols, respectively. Amide N ranged from 11.6 to 21.4% of total N; Hexosamine from 5.2 to 10.1% and Amino acid N from 26.2 to 37.1 %. Amino acid N therefore formed the highest portion followed by Amide N of the hydrolysable organic N

Heightening sorghum nitrogen uptake while maintaining optimal soil nutrient levels through mineral fertiliser application

Improving nutrient management of soils is important in subsistence farming systems in the tropics due to declining soil fertility resulting from continuous cropping coupled with inadequate nutrient replenishment. Balancing nutrient inputs with crop removal is crucial in reducing the build-up of nutrients and minimises nutrient losses through different pathways, thus reducing the cost of production. This study aimed at evaluating the effect of N and P fertiliser on sorghum N uptake at Kampi ya Mawe (KYM) in Makueni County and Katumani (KAT) in Machakos County, Kenya. Two factors (nitrogen and phosphorus) each at two levels (0 and 75 kg ha-1) were evaluated, resulting in four treatments, each replicated thrice. At KYM, N content in sorghum tissues increased by 24.2% in comparison with the control following application of N at 75 kg ha-1. At KAT, plots amended with N and P at 75 kg ha-1 resulted in the highest N content in sorghum tissues at the three sorghum development stages assessed. At the seedling stage, an increase of 18.8% was observed. Sole N application led to an increase in N content in sorghum tissues of 17.6% at the seedling stage. A positive linear relationship between NO3-N and N content in sorghum tissues was also observed. The study showed that soil N uptake was higher in the early growth stages of sorghum. The results of this study are essential to farmers and extension officers as a guide to ensure timely fertiliser application to ensure optimum utilisation of nutrients during crop growth

In situ nitrogen mineralization and nutrient release by soil amended with black soldier fly frass fertilizer

Black soldier fly frass fertilizer (BSFFF) is effective on crop performance, but information on nitrogen mineralization and nutrient release capacity of soils amended with BSFFF is lacking. This study utilized field incubation experiments to investigate the ammonification, nitrification, microbial populations, and quantities of nutrients released by soils amended with BSFFF and commercial organic fertilizer (SAFI) for a period equivalent to two maize cropping seasons. The paper provides a detailed breakdown and analysis of results. BSFFF has a high potential to supply adequate nutrients for optimal crop production. Higher population of soil bacteria and fungi underline its potential for improving biological soil fertility.Norwegian Agency for Development CooperationNetherlands Organization for Scientific ResearchWOTRO Science for Global Development (NWO-WOTRO)Rockefeller Foundatio

Evolving dynamics of insect frass fertilizer for sustainable nematode management and potato production

Potato production faces major challenges from inadequate soil fertility, and nematode infestation, yet synthetic fertilizers and nematicides are costly and harmful to the environment. This study explored the potential of chitin-fortified black soldier fly-composted organic fertilizer (BSFCOF) as a multipurpose organic fertilizer amendment for enhancing potato yield and suppressing potato cyst nematodes (PCN). The BSFCOF was applied at a rate equivalent to 150 kg N ha-1 and fortified with chitin from black soldier fly pupal exuviae at inclusion rates equivalent to 0.5, 1, 2, 3, 4 and 5% chitin. Data were collected on potato growth characteristics, PCN population densities, and soil chemical properties for two growing cycles. Results showed that chitin fortified BSFCOF significantly improved potato growth parameters, chlorophyll concentration, marketable tuber yield and number of marketable tubers. The marketable tuber yield achieved using chitin-fortified BSFCOF was 70 – 362%, and 69 – 238% higher than the values achieved using unfertilized soil during the first and second growing cycles, respectively. Soil amendment with chitin-fortified BSFCOF significantly reduced the number of cysts per 200 g soil-1, number of eggs and J2 per cyst-1, eggs g-1 soil and reproduction rate by 32 – 87%, 9 – 92%, 31– 98% and 31 – 98%, respectively. The PCN suppression increased with chitin inclusion rates. There were significantly higher values for soil pH, ammonium nitrogen, nitrate nitrogen, available phosphorus, calcium, magnesium, potassium, and cation exchange capacity in soil amended with BSFCOF compared to unamended soil. This study demonstrates that BSFCOF fortified with 5% chitin is an effective soil enhancer with multiple benefits, including improved soil fertility, potato performance, and effective management of potato cyst nematodes

Biochar and gypsum amendment of agro-industrial waste for enhanced black soldier fly larval biomass and quality frass fertilizer.

Black soldier fly (BSF) (Hermetia illucens L.) is one of the most efficient bio-waste recyclers. Although, waste substrate amendments with biochar or gypsum during composting process are known to enhance nutrient retention, their impact on agro-industrial waste have not been documented. Hence, this study focuses on a comparative effect of agro-industrial waste amended with biochar and gypsum on BSF larval performance, waste degradation, and nitrogen (N) and potassium retention in frass fertilizer. Brewery spent grain was amended with biochar or gypsum at 0, 5, 10, 15 and 20% to determine the most effective rates of inclusion. Amending feedstock with 20% biochar significantly increased wet (89%) and dried (86%) larval yields than the control (unamended feedstock). However, amendment with 15% gypsum caused decrease in wet (34%) and dried (30%) larval yields but conserved the highest amount of N in frass. Furthermore, the inclusion of 20% biochar recorded the highest frass fertilizer yield and gave a 21% increase in N retention in frass fertilizer, while biomass conversion rate was increased by 195% compared to the control. Feedstock amendment with 5% biochar had the highest waste degradation efficiency. Potassium content in frass fertilizer was also significantly enhanced with biochar amendment. At maturity, frass compost with more than 10% inclusion rate of biochar had the highest cabbage seed germination indices (>100%). The findings of this study revealed that initial composting of biochar amended feedstocks using BSF larvae can significantly shorten compost maturity time to 5 weeks with enhanced nutrient recycling compared to the conventional composting methods

Nitrogen fertilizer replacement value of black soldier fly frass fertilizer and synchrony of nitrogen mineralization for maize production

Though, the use of black soldier fly frass fertilizer (BSFFF) is promoted globally, information on nitrogen (N) fertilizer replacement value (NRFV) and synchrony of N mineralization for crop production remains largely unknown. Comparative studies between BSFFF and commercial organic fertilizer (SAFI) were undertaken under field conditions to determine synchrony of N release for maize uptake. The BSFFF, SAFI and urea fertilizers were applied at the rates of 0, 30, 60 and 100 kg N ha-1. Yield data from urea treated plots were used to determine the NFRV of both organic inputs. Results showed that maize from BSFFF treated plots had higher N uptake than SAFI treated plots. High N immobilization was observed throughout the active growth stages of maize in soil amended with BSFFF while soil treated with SAFI achieved net N release at the silking stage. Up to 3 times higher negative N fluxes were observed in SAFI amended soils compared to BSFFF treated plots at tasseling stage. The BSFFF applied at 30 and 60 kg N ha-1 achieved significantly higher NFRV than all SAFI treatments. Our findings revealed that BSFFF is a promising and sustainable alternative to SAFI and/or Urea for enhanced maize production