RESUMO
Currently, there is no doubt that Azolla can compensate for the nitrogen requirements of rice in different agroecological zones. Compared to synthetic N-fertilizers, Azolla has various positive impacts on lowland rice production, including improving soil fertility, minimizing weeds, increasing soil organic carbon, improving microbial biomass, and thus nutrient cycling and enhancing rice growth and yield. However, Azolla has not been accepted globally by rice farmers for field use and so far, farmers are relying on increasing rates of synthetic N fertilizers instead of taking advantage of Azolla which will improve long-term soil fertility and health. This systematic literature review and scientific evidence could help policymakers, scientists and researchers to understand the benefits, limitations, and innovative ways of utilizing Azolla as a cost-effective and eco-friendly amendment in rice production. The paper uses Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) method to review the hidden potential of Azolla as a biofertilizer in paddy and summarizes its benefits and problems by collecting information from different sources and presenting under different subheadings such as critical factors affecting Azolla growth and nitrogen fixation, nitrogen fixation of Anabaena Azollae and their contribution in soil health, release and availability of Azolla-N to rice, amounts and time of Azolla inoculation, influence of Azolla on ammonia volatilization, contribution of Azolla to yield and yield components of rice, and impact of Azolla on weed emergence in rice cropping system. Literature indicated that the use of Azolla as green manure incorporated before rice transplanting or grown together with rice and left until a few days of harvest alone or in combinations with other synthetic fertilizers in the lowland rice production saved the nitrogen requirement of rice up to 60 kg N ha-1, it enhances the availability of nutrients, improves physiochemical properties of soils, minimizes soil salinity, reduces the soil pH, and minimize weed germination. However, it was observed that incorporating Azolla as green manure is labor-intensive, and maintaining the Azolla inocula and phosphorous requirement are major restrictions for farmers. Therefore, understanding mechanism of spore production, educating farmers on cheaper alternative ways of Azolla application, and testing different species of Azolla over different agroecological zones will help in maintaining Azolla biomass and applying it at low cost for further environmental conservation.
RESUMO
The effort to increase the sustainable supply of food and fibre is challenged by the potential for increased greenhouse gas (GHG) emissions from farming systems with intensified production systems. This study aimed at quantifying soil N2O emissions from smallholder organic and conventional cotton production practices in a semi-arid area, Meatu, Northern Tanzania. Field experiments were conducted to quantify N2O emissions under (i) current practices with organic (3 Mg ha-1 farmyard manure (FYM)) and conventional (30 kg mineral N ha-1) cultivation; (ii) a high input practice with organic (5 Mg ha-1 FYM) and conventional (60 kg mineral N ha-1) cultivation; and (iii) an integrated practice with organic (3 Mg FYM + legume intercropping) and conventional (30 kg N + 3 Mg ha-1 FYM) cultivation. In both organic and conventional farming, control treatments with no fertilizer application were included. The study was performed over two growing seasons, where season 1 was rather wet and season 2 was rather dry. Static chambers were used for in-situ measurement of N2O emission from soil. The current organic and conventional cotton farming practices did not differ (P > 0.05) in cumulative area-scaled and yield-scaled N2O emissions. High input conventional cotton showed higher area scaled N2O emissions than organic cotton during the wetter season, but not during the drier season. The inorganic fertilizer + FYM combination did not differ (P > 0.05) in area- and yield-scaled N2O emissions from conventional practice. Intercropping cotton and legumes did not affect (P > 0.05) N2O emission compared to 3 Mg FYM ha-1. The emission factors for both conventional and organic systems were generally above 1% in the dry season 2, but below 1% in the wetter season 1. The use of organic and inorganic fertilizers at rates up to 60 kg N ha-1, FYM-inorganic fertilizer combination, and cotton-legume intercropping increased yields, while N2O emissions stayed low, in particular with use of mineral fertilizers.
RESUMO
A field study was carried out to evaluate the effects of tillage practices on soil physical properties in Mwala district, Eastern Kenya, during the long rains (LR) and short rains (SR) of 2012/13. The treatments were disc ploughing (DP), disc ploughing and harrowing (DPH), ox-ploughing (OX), subsoiling-ripping (SSR), hand hoeing with tied ridges (HTR), hand hoeing only (H). These were investigated under three cropping systems of sole maize, sole bean, and maize-bean intercrop in a split-plot design with four replications. Soil physical properties were monitored at different weeks after planting (WAP) throughout the growing seasons. A four-season average shows that soil moisture content was significantly (P < 0.05) higher in OX > SSR > DPH > H > HTR > DP with values ranging from 13.1 to 14.1%. Soil surface roughness and crust strength varied significantly (P < 0.05) over time within the growing seasons, between the tillage practices, and across the different seasons with values ranging from 26 to 66% and 1.21 to 1.31 MPa, respectively. Tillage practices and cropping systems did not significantly affect bulk density, porosity, or K sat values. It is apparent that long term tillage experiment (>4 seasons) would be required to detect changes in soil physical properties as a result of the soil management practices.
