Organic wastes from bioenergy and ecological sanitation as a soil fertility improver: a field experiment in a tropical Andosol

Abstract

Abstract. Andosols require the regular application of phosphorus (P) to sustain crop productivity. On an Andosol in NW Tanzania, we studied the short-term effects of amending standard compost, biogas slurry and CaSa compost (containing biochar and sanitized human excreta) on (i) the soil's physico-chemical properties, on (ii) biomass growth and crop productivity, and on (iii) the plants' nutrient status. The practice-oriented experiment design included the intercropping of seven locally grown crop species planted on 9 m2 plots with five repetitions arranged as a Latin rectangle. Differences in plant growth (biomass production and crop yield, e.g., of Zea mays) and crop nutrition (total C, N, P, K, Ca, Mg, Zn, etc.) were related to pH, CEC (cation exchange capacity), total C and the availability of nutrients (N, P, K, etc.) and water (water retention characteristics, bulk density, etc.) in the soil. None of the amendments had any significant effect on soil water availability, so the observed variations in crop yield and plant nutrition are attributed to nutrient availability. Applying CaSa compost increased the soil pH from 5.3 to 5.9 and the level of available P from 0.5 to 4.4 mg per kg. Compared to the control, adding biogas slurry, standard compost and CaSa compost increased the aboveground biomass of Zea mays by, respectively, 140, 154 and 211 %. The grain yields of maize on soil treated with biogas slurry, standard compost and CaSa compost were, respectively, 2.63, 3.18 and 4.40 t ha−1, compared to only 1.10 t ha−1 on unamended plots. All treatments enhanced crop productivity and increased the uptake of nutrients into the maize grains. The CaSa compost was most effective in mitigating P deficiency and soil acidification. We conclude that all treatments are viable as a substitute for synthetic fertilizers. Nevertheless, further steps are required to integrate the tested soil amendments into farm-scale nutrient management and to balance the additions and removals of nutrients, so that the cycle can be closed.

Recycling Improves Soil Fertility Management in Smallholdings in Tanzania

“…In addition, [93] found that application rates of >25 kg·P·ha −1 ·season −1 over the course of four seasons were capable of replenishing levels of P in a P deficient soil in Western Kenya. In contrast, the application of 40 or 70 kg·P·ha −1 in the form of biogas slurry or standard compost, respectively, was not sufficient to increase extractable soil P, as demonstrated in a short-term field trial on the local Andosol [61]. Adding about 140 kg·P·ha −1 with CaSa-compost, however, significantly increased levels of available P in the soil after the experiment, and thus, immediately contributed to mitigating P deficiency [17].…”

“…In prior studies focusing on a household level, we already introduced [39], demonstrated [61], and analyzed, in detail, the recycling potentials of an intersectional resource management for the example of smallholdings in Karagwe, TZ [41]. In the present work focusing on a farm level, we systematically compare specific approaches to recover residues as resources for IPNM, such as biogas slurry, urine, or co-composted human faeces, and biochar.…”

“…(In addition, unusual rainfall patterns indicate the approaching effects of climate change, and increasingly threaten the predominantly rain-fed agriculture in Karagwe). Andosols, the predominant soil type in Karagwe [61], typically suffer from P deficiency [17], as P retention potential is relatively high [63]. Crop productivity and sustainable land use therefore requires constant replenishment of P. Unbalanced inputs of N with organic and/or mineral fertilizers and uptake of N by crops often contribute to the problem [64,65].…”

“…This treatment is, therefore, adequate to maintain, or even improve, soil pH in accordance with [82], who recommends a triennial application of 1250-2250 kg·CaO·ha −1 . Empirically, an immediate rise of soil pH within one cropping season was only possible with CaSa-compost, not with standard compost or biogas slurry, and at an application rate of about 2000 kg·CaO·ha −1 [61].…”

Comparative study of soil physical characteristics of Jaipur district, Rajasthan

“…Conserving the soil feature can deliver economic gain in more competent use of nutrients and insecticides, growth in yield, enhancements in quality of water and air (USDA-ERS, 1997). The application of organic matter to the soils providing nutrients to the plants and playing a key role in the soil's water holding capacity, its porosity and water infiltration rate (Krause et al, 2016;Yazdanpanah et al, 2016). The properties of dry soil along with its type have a great importance in agriculture (Ahire et al, 2013).…”