Soil Nitrous Oxide (N\u3csub\u3e2\u3c/sub\u3eO) Emission from Integrated Soil Fertility Management in Maize (\u3ci\u3eZea mays\u3c/i\u3e L.) Cropping Systems

Integrated Soil Fertility Management (ISFM) has been recommended to address challenges of low soil fertility by incorporating locally available organic resources (ORs) together with inorganic nitrogen (N) fertilizers. Despite ISFM success in field trials, there is limited information on ORs contribution to atmospheric greenhouse gas concentrations through N2O emission. A short-term field study was conducted at two sites with different soil types; silt loam (Aludeka) and silty-clay soil (Sidada) to assess the influence of selected ORs on soil N2O emissions. The ORs treatments included; Calliandra carothyrsus (CL), farmyard manure (FYM) and maize stover (MS) with (+N) and without (-N) inorganic N fertilizer. The study also evaluated the relationship between N2O emissions and soil organic carbon, mineral N, total nitrogen, soil temperature, moisture content, soil nitrate (NO3-) and ammonium (NH4+). Relative to the control (0.19±0.1 Kg N2O-N ha-1), cumulative N2O emissions were significantly (P= 0.01) higher by 6, 9 and 13 fold under MS +N (1.05±0.8 Kg N2O-N ha-1), FYM +N (1.74±0.8 Kg N2O-N ha-1) and CL +N (2.54±1.2 Kg N2O-N ha-1), respectively at the Aludeka site. At Sidada, cumulative N2O emissions were similar across all the treatments (P = 0.149). Approximately 240% and 411% of increase in cumulative N2O emissions across treatments at Sidada and Aludeka, respectively, was related to inorganic N fertilizer application. At Aludeka, cumulative N2O emissions exhibited significant positive relationship with soil NO3-(r = 0.894, P = 0.03) and NH4+ (r = 0.817, P = 0.013), and negatively correlated with soil C: N ratio (r = -0.710, P = 0.049). While at Sidada soil properties did not exhibit significant relationship with cumulative N2O emissions. The study suggests that influence of OR on N2O emissions in maize based-cropping system vary depending on the type of soil and increases when OR are applied in combination with inorganic N fertilizers

Managing soil organic carbon in tropical agroecosystems: evidence from four long-term experiments in Kenya

In sub-Saharan Africa, maize is one of the most important staple crops, but long-term maize cropping with low external inputs has been associated with the loss of soil fertility. While adding high-quality organic resources combined with mineral fertilizer has been proposed to counteract this fertility loss, the long-term effectiveness and interactions with site properties still require more understanding. This study used repeated measurements over time to assess the effect of different quantities and qualities of organic resource addition combined with mineral nitrogen (N) on the change of soil organic carbon (SOC) contents over time (and SOC stocks in the year 2021) in four ongoing long-term experiments in Kenya. These experiments were established with identical treatments in moist to dry climates, on coarse to clayey soil textures, and have been conducted for at least 16 years. They received organic resources in quantities equivalent to 1.2 and 4 t C ha−1 yr−1 in the form of Tithonia diversifolia (high quality, fast turnover), Calliandra calothyrsus (high quality, intermediate turnover), Zea mays stover (low quality, fast turnover), sawdust (low quality, slow turnover) and local farmyard manure (variable quality, intermediate turnover). Furthermore, the addition of 240 kg N ha−1 yr−1 as mineral N fertilizer or no fertilizer was the split-plot treatment. At all four sites, a loss of SOC was predominantly observed, likely because the sites had been converted to cropland only a few decades before the start of the experiments. Across sites, the average decline of SOC content over 19 years in the 0 to 15 cm topsoil layer ranged from 42 % to 13 % of the initial SOC content for the control and the farmyard manure treatments at 4 t C ha−1 yr−1, respectively. Adding Calliandra or Tithonia at 4 t C ha−1 yr−1 limited the loss of SOC contents to about 24 % of initial SOC, while the addition of sawdust, maize stover (in three of the four sites) and sole mineral N addition showed no significant reduction of SOC loss over the control. Site-specific analyses, however, did show that at the site with the lowest initial SOC content (about 6 g kg−1), the addition of 4 t C ha−1 yr−1 farmyard manure or Calliandra with mineral N led to a gain in SOC contents. The other sites lost SOC in all treatments, albeit at site-specific rates. While subsoil SOC stocks in 2021 were little affected by organic resource additions (no difference in three of the four sites), the topsoil SOC stocks corroborated the results obtained from the SOC content measurements (0–15 cm) over time. The relative annual change of SOC contents showed a higher site specificity in farmyard manure, Calliandra and Tithonia treatments than in the control treatment, suggesting that the drivers of site specificity in SOC buildup (soil mineralogy, soil texture, climate) need to be better understood for effective targeting management of organic resources. Farmyard manure showed the highest potential for reducing SOC losses, but the necessary quantities to build SOC are often not realistic for smallholder farmers in Africa. Therefore, additional agronomic interventions such as intercropping, crop rotations or the cultivation of crops with extended root systems are necessary to maintain or increase SOC.</p

Cassava-maize intercropping systems in southern Nigeria: radiation use efficiency, soil moisture dynamics, and yields of component crops

Open Access Article; Published online: 30 Apr 2022Efficient utilization of incident solar radiation and rainwater conservation in rain-fed smallholder cropping systems require the development and adoption of cropping systems with high resource use efficiency. Due to the popularity of cassava-maize intercropping and the food security and economic importance of both crops in Nigeria, we investigated options to improve interception of photosynthetically active radiation (IPAR), radiation use efficiency (RUE), soil moisture retention, and yields of cassava and maize in cassava-maize intercropping systems in 8 on-farm researcher-managed multi-location trials between 2017 and 2019 in different agro-ecologies of southern Nigeria. Treatments were a combination of (1) maize planting density (low density at 20,000 maize plants ha-1 versus high density at 40,000 maize plants ha-1, intercropped with 12,500 cassava plants ha-1); (2) fertilizer application and management targeting either the maize crop (90 kg N, 20 kg P and 37 kg K ha-1) or the cassava crop (75 kg N, 20 kg P and 90 kg K ha-1), compared with control without fertilizer application. Cassava and maize development parameters were highest in the maize fertilizer regime, resulting in the highest IPAR at high maize density. The combined intercrop biomass yield was highest at high maize density in the maize fertilizer regime. Without fertilizer application, RUE was highest at low maize density. However, the application of the maize fertilizer regime at high maize density resulted in the highest RUE, soil moisture content, and maize grain yield. Cassava storage root yield was higher in the cassava fertilizer regime than in the maize fertilizer regime. We conclude that improved IPAR, RUE, soil moisture retention, and grain yield on nutrient-limited soils of southern Nigeria, or in similar environments, can be achieved by intercropping 40,000 maize plants ha-1 with 12,500 cassava plants ha-1 and managing the system with the maize fertilizer regime. However, for higher cassava storage root yield, the system should be managed with the cassava fertilizer regime

Developing recommendations for increased productivity in cassava-maize intercropping systems in southern Nigeria

Open Access Article; Published online: 31 Aug 2021Cassava-maize intercropping is a common practice among smallholder farmers in Southern Nigeria. It provides food security and early access to income from the maize component. However, yields of both crops are commonly low in farmers’ fields. Multi-locational trials were conducted in Southern Nigeria in 2016 and 2017 to investigate options to increase productivity and profitability through increased cassava and maize plant densities and fertilizer application. Trials with 4 and 6 treatments in 2016 and 2017, respectively were established on 126 farmers’ fields over two seasons with a set of different designs, including combinations of two levels of crop density and three levels of fertilizer rates. The maize crop was tested at low density (LM) with 20,000 plants ha−1 versus high density (HM) with 40,000 plants ha−1. For cassava, low density (LC) had had 10,000 plants ha−1 versus the high density (HC) with 12,500 plants ha−1.; The fertilizer application followed a regime favouring either the maize crop (FM: 90 kg N, 20 kg P and 37 kg K ha−1) or the cassava crop (FC: 75 kg N, 20 kg P and 90 kg K ha−1), next to control without fertilizer application (F0). Higher maize density (HM) increased marketable maize cob yield by 14 % (3700 cobs ha−1) in the first cycle and by 8% (2100 cobs ha−1) in the second cycle, relative to the LM treatment. Across both cropping cycles, fertilizer application increased cob yield by 15 % (5000 cobs ha−1) and 19 % (6700 cobs ha−1) in the FC and FM regime, respectively. Cassava storage root yield increased by 16 % (4 Mg ha−1) due to increased cassava plant density, and by 14 % (4 Mg ha−1) due to fertilizer application (i.e., with both fertilizer regimes) but only in the first cropping cycle. In the second cycle, increased maize plant density (HM) reduced cassava storage root yield by 7% (1.5 Mg ha−1) relative to the LM treatment. However, the negative effect of high maize density on storage root yield was counteracted by fertilizer application. Fresh storage root yield increased by 8% (2 Mg ha−1) in both fertilizer regimes compared to the control without fertilizer application. Responses to fertilizer by cassava and maize varied between fields. Positive responses tended to decline with increasing yields in the control treatment. The average value-to-cost ratio (VCR) of fertilizer use for the FM regime was 3.6 and higher than for the FC regime (VCR = 1.6), resulting from higher maize yields when FM than when FC was applied. Revenue generated by maize constituted 84–91% of the total revenue of the cropping system. The highest profits were achieved with the FM regime when both cassava and maize were grown at high density. However, fertilizer application was not always advisable as 34 % of farmers did not realize a profit. For higher yields and profitability, fertilizer recommendations should be targeted to responsive fields based on soil fertility knowledge

Long-term evidence for ecological intensification as a pathway to sustainable agriculture

Ecological intensification (EI) could help return agriculture into a ‘safe operating space’ for humanity. Using a novel application of meta-analysis to data from 30 long-term experiments from Europe and Africa (comprising 25,565 yield records), we investigated how field-scale EI practices interact with each other, and with N fertilizer and tillage, in their effects on long-term crop yields. Here we confirmed that EI practices (specifically, increasing crop diversity and adding fertility crops and organic matter) have generally positive effects on the yield of staple crops. However, we show that EI practices have a largely substitutive interaction with N fertilizer, so that EI practices substantially increase yield at low N fertilizer doses but have minimal or no effect on yield at high N fertilizer doses. EI practices had comparable effects across different tillage intensities, and reducing tillage did not strongly affect yields

Soil Nitrous Oxide (N2O) Emission from Integrated Soil Fertility Management in Maize (Zea mays L.) Cropping Systems

Integrated Soil Fertility Management (ISFM) has been recommended to address challenges of low soil fertility by incorporating locally available organic resources (ORs) together with inorganic nitrogen (N) fertilizers. Despite ISFM success in field trials, there is limited information on ORs contribution to atmospheric greenhouse gas concentrations through N2O emission. A short-term field study was conducted at two sites with different soil types; silt loam (Aludeka) and silty-clay soil (Sidada) to assess the influence of selected ORs on soil N2O emissions. The ORs treatments included; Calliandra carothyrsus (CL), farmyard manure (FYM) and maize stover (MS) with (+N) and without (-N) inorganic N fertilizer. The study also evaluated the relationship between N2O emissions and soil organic carbon, mineral N, total nitrogen, soil temperature, moisture content, soil nitrate (NO3-) and ammonium (NH4+). Relative to the control (0.19�0.1 Kg N2O-N ha-1), cumulative N2O emissions were significantly (P= 0.01) higher by 6, 9 and 13 fold under MS +N (1.05�0.8 Kg N2O-N ha-1), FYM +N (1.74�0.8 Kg N2O-N ha-1) and CL +N (2.54�1.2 Kg N2O-N ha-1), respectively at the Aludeka site. At Sidada, cumulative N2O emissions were similar across all the treatments (P = 0.149). Approximately 240% and 411% of increase in cumulative N2O emissions across treatments at Sidada and Aludeka, respectively, was related to inorganic N fertilizer application. At Aludeka, cumulative N2O emissions exhibited significant positive relationship with soil NO3-(r = 0.894, P = 0.03) and NH4+ (r = 0.817, P = 0.013), and negatively correlated with soil C: N ratio (r = -0.710, P = 0.049). While at Sidada soil properties did not exhibit significant relationship with cumulative N2O emissions. The study suggests that influence of OR on N2O emissions in maize based-cropping system vary depending on the type of soil and increases when OR are applied in combination with inorganic N fertilizers

Mitigating N2O emissions from soil: From patching leaks to transformative action

Further progress in understanding and mitigating N2O emissions from soil lies within transdisciplinary research that reaches across spatial scales and takes an ambitious look into the future