Nitrogen Dynamics in Tropical Soils Treated with Liquid and Granular Urea Fertilizers

The mineralization of urea fertilizer mostly regulates the nitrogen dynamics in the soil. A laboratory-scale study was conducted to compare the nitrogen dynamics in two tropical soil series incubated with either liquid urea (LU) or granular urea (GU) at 0, 300, 400 or 500 mg/kg of soil. The soils samples used in the experiment were the Bungor and Selangor soil series which have a sandy clay loam and clay texture, respectively. The NH4+-N, NO3−-N concentration in the soils were measured for four weeks to determine the urea-N mineralization while ten pore volumes of water were used for the NH4+-N and NO3−-N leaching loss. At the same application rate, higher NH4+-N and NO3−-N concentrations were recorded in the LU applied soils throughout the incubation period in case of N mineralization. Urea-N recovery was higher in GU than LU treated soils in the first two weeks while no urea-N was present in both GU and LU treated soils after the third week of incubation. The leaching of N (NH4+-N and NO3−-N) was higher in GU treated soils than that of LU and leaching was increased with increased application rate in both LU and GU in both soils. The NH4+-N and NO3−-N concentrations were higher in the Selangor soil whereas the total N leaching loss was higher in Bungor soil. The results suggest that the LU was a better N fertilizer source than GU for rapid mineralization, quicker N availability and lower N leaching loss.

Understanding nitrogen transport in the unsaturated zone with fluctuations in groundwater depth

Fluctuations in groundwater depth play an important role and are often overlooked when considering the transport of nitrogen in the unsaturated zone. To evaluate directly the variation of nitrogen transport due to fluctuations in groundwater depth, the prediction model of groundwater depth and nitrogen transport were combined and applied by least squares support vector machine and Hydrus-1D in the western irrigation area of Jilin in China. The calibration and testing results showed the prediction models were reliable. Considering different groundwater depth, the concentration of nitrogen was affected significantly with a groundwater depth of 3.42–1.71 m, while it was not affected with groundwater depth of 5.48–6.47 m. The total leaching loss of nitrogen gradually increased with the continuous decrease of groundwater depth. Furthermore, the limited groundwater depth of 1.7 m was found to reduce the risk of nitrogen pollution. This paper systematically analyzes the relationship between groundwater depth and nitrogen transport to form appropriate agriculture strategies.

Is organic farming environmentally more friendly?

<p>Reviews and meta-analyses generally support the perception that organic farming systems are more environmentally friendly than conventional farming systems. Organic agriculture results in more soil organic matter and higher microbiological activity, thus, providing better water holding capabilities, decreased both runoff and concentration of nitrate in soil, leading to fewer risks of nitrate leaching loss from the soil to water bodies. However, environmental quality parameters can differ between organic plant and animal production farms, moreover, they can be higher calculated per unit product.</p><p>We used the ARMOSA process-based crop model (Valkama et al., 2020) to evaluate contribution of plant and animal organic farming to soil organic carbon (SOC) sequestration and N leaching loss reduction compare to conventional systems in South Savo (Finland). Since organic systems often produce about 30% less yields compared to conventional systems, we calculated SOC changes per total gross energy in harvested yields. For model inputs we used daily meteorological data, statistical annual crop yields, statistical data for sales of nitrogen fertilizers in the region during the last 20 years (1999-2018). Five-year crop rotations were simulated on loamy sand soil (C 3.5 %, C/N ratio 17, pH 6.2). On plant production farms, rotations consisted of cereals (with addition of pea in organic), oilseed rape and grass. Conventional crops were fertilized with mineral fertilizer, and residues were removed (PC-R) or retained (PC+R). Organic crops were fertilized with green manure only (PO<sub>g</sub>+R) or also with commercial organic fertilizer (PO<sub>f</sub>+R). On animal production farms, conventional (AC-R) and organic (AO-R) rotations consisted of 2 years of cereals and 3 years of grass, sown with clover in organic system. Conventional animal system was fertilized with mineral fertilizer and slurry, while organic system with slurry only, and residues were removed in both systems.</p><p>Simulations showed that both conventional plant production systems (PC-R and PC+R) led to SOC decline of 650 kg ha<sup>-1</sup>yr<sup>-1</sup> at 0-30 cm soil depth. Organic systems showed either less SOC decline (120 kg ha<sup>-1</sup>yr<sup>-1</sup>) as in PO<sub>g</sub>+R, or slight SOC increase (55 kg ha<sup>-1</sup>yr<sup>-1</sup>) as in PO<sub>f</sub>+R. In contrast, organic animal production system did not differ from conventional system in terms of SOC change, showing a slight decreasing trend of about 150 kg ha<sup>-1</sup>yr<sup>-1</sup>. Estimates of SOC per gross energy in harvested yields showed the highest value (1.3 kg GJ<sup>-1</sup>) for organic plant production fertilized with commercial organic fertilizer (PO<sub>f</sub>+R), while the lowest value (-18 and -13 kg GJ<sup>-1</sup>) for conventional plant production systems (PC-R and PC+R, respectively). In contrast, the estimates did not differ much between organic (-2.2 kg GJ<sup>-1</sup>) and conventional (-1.8 kg GJ<sup>-1</sup>) animal production systems. Simulated N leaching loss varied between 6 and 9 kg ha<sup>-1</sup> yr<sup>-1</sup> for all systems, except for organic plant rotation with green manure (PO<sub>g</sub>+R), which N leaching loss was only 3 kg ha<sup>-1</sup> yr<sup>-1</sup>. </p><p>The modelling results suggest that organic plant production farms can be more environmentally friendly per unit area as well as per unit product compared to conventional farms, while organic animal production farms seem to cause similar environmental impact as conventional farms.</p>

Integrating Plantain (Plantago lanceolata L.) and Italian Ryegrass (Lolium multiflorum Lam.) into New Zealand Grazing Dairy System: The Effect on Farm Productivity, Profitability, and Nitrogen Losses

A two-year farm system study was conducted at Canterbury, New Zealand to evaluate the effects on farm productivity, profitability, and nitrogen (N) losses of integrating plantain (Plantago lanceolate L.) and Italian ryegrass (Lolium multiflorum Lam.) into a ryegrass and white clover (RGWC)-based dairy system. Three farm systems were compared: (1) a lower input RGWC-based system (LIRG) with stocking rate of 3.5 cow/ha, annual N fertiliser rate of 150 kg/ha, and imported feed level of <1.2 t DM/cow/year; (2) a lower input ryegrass + plantain-based system (LIRG + PL) with a stocking rate of 3.5 cow/ha, annual N fertiliser rate of 150 kg/ha, and imported feed level of <1.2 t DM/cow/year; and (3) a higher input RGWC-based system (HIRG) with a stocking rate of 5.0 cow/ha, annual N fertiliser rate of 300 kg/ha, and imported feed level of >1.2 t DM/cow/year. Cows in the LIRG + PL system grazed a diverse mix of Italian ryegrass, perennial ryegrass, white clover, and plantain (60% of farmlet area), and a mixed sward of plantain–white clover (40% of farmlet area). The average annual herbage harvested was similar between LIRG + PL and LIRG (11.7 t DM/ha), but greater in HIRG (12.7 t DM/ha) with the increased N fertiliser rate. During the calving to dry-off period, the average imported supplement feed per ha was higher in HIRG (8.0 t DM) compared with LIRG (3.2 t DM) and LIRG + PL (3.7 t DM). Average milk solid production (MS; fat + protein) was similar in LIRG + PL (1640 kg/ha) and LIRG (1622 kg/ha), but greater in HIRG (2130 kg/ha). Estimated profitability (NZD/ha) at milk price of NZD 6.5/kg MS was 10% greater for HIRG than LIRG + PL and LIRG, and similar (<1.5% numerical difference) between LIRG + PL and LIRG. The average estimated annual N leaching loss from the LIRG and LIRG + PL was 31% and 56% less than the loss from the HIRG. These large reductions in N leaching loss were achieved without a large decrease in profitability (i.e., LIRG and LIRG + PL compared to HIRG). In addition, the estimated reduction in N losses from the LIRG + PL system compared to LIRG suggests that an Italian ryegrass + plantain-based dairy system is a viable strategy to reduce the environmental footprint while maintaining farm profitability. However, the environmental benefits of plantain and Italian ryegrass estimated in this study require further confirmation through direct measurements at full farm level.

Assessing the Effects of Nitrification Inhibitor DMPP on Acidification and Inorganic N Leaching Loss from Tea (Camellia sinensis L.) Cultivated Soils with Increasing Urea–N Rates

The effects of nitrification inhibitor in tea gardens with different urea–N rates have rarely been assessed. For eight months, a glasshouse experiment was conducted to investigate the effects of a nitrification inhibitor (3, 4–dimethylpyrazole phosphate, DMPP) on the changes of soil pH and inorganic N loss. Urea (0, 300, 500, and 800 kg N ha−1) with or without DMPP (1% of urea–N applied) were added to pots that hosted six plants that were three years old. Next, three leaching events were conducted with 600 mL of water after 7, 35, and 71 days of intervention while soil samples were collected to determine pH and inorganic N. Averaged across sampling dates, urea–N application at an increasing rate reduced soil pH with the lowest values at 800 kg urea–N ha−1. Adding DMPP increased soil pH up to a rate of 500 kg ha−1. Irrespective of the addition of DMPP, gradient urea–N application increased the leaching loss of inorganic N. On overage, DMPP increased soil pH and decreased leaching losses of total inorganic N, suggesting a higher soil N retention. Therefore, we believe that this increase in soil pH is associated with a relatively lower proton release from the reduced nitrification in the DMPP–receiving pots. This nitrification reduction also contributed to the N loss reduction (NO3−–N). Altogether, our results suggest that DMPP can reduce N leaching loss while maintaining the pH of tea–cultivated soils. Therefore, DMPP application has a significant potential for the sustainable N management of tea gardens.