RESUMO
A better understanding of the fate and transport of fertilizer nitrogen (N) is critical to maximize crop yields and minimize negative environmental impacts. Plastic film mulching is widely used in drylands to increase soil water use efficiency and crop yields, but the effects on fertilizer N use efficiency need to be evaluated. A field experiment with 15N-urea (260 kg N ha-1) was conducted to determine the fate and transport of fertilizer N in a ridge-furrow system with plastic film mulched ridge (Plastic), compared with a flat system without mulching (Open). In the Plastic, the 15N-urea was applied to the ridge only (Plastic-Ridge), or to the furrow only (Plastic-Furrow). Maize grain yield and net economic benefit for Plastic were significantly higher (by 9.7 and 8.5%, respectively) than those for Open. Total plant 15N uptake was 72.5% greater in Plastic compared with Open, and 15N was allocated mostly to the grain. Losses of the applied urea-N were 54.5% lower in Plastic and much more residual 15N was recovered in 0-120 cm soil compared with Open (42.7 and 26.8% of applied 15N, respectively). Lateral N movements from furrow to ridge and from ridge to furrow were observed and attributed to lateral movement of soil water due to microtopography of ridges and furrows and uneven soil water and heat conditions under mulching and plant water uptake. The ridges were the main N fertilizer source for plant uptake (96.5 and 3.5% of total N uptake in Plastic from ridge and furrow, respectively) and the furrow was the main source of N losses (78.6 and 21.4% of total N losses in Plastic from furrow and ridge, respectively). Gas emissions, especially ammonia volatilization was probably the main N loss in furrow. Thus, appropriately localized N application - into the ridges, and management strategies should be designed for Plastic to maximize N use efficiency by crops, decrease N gas losses and maintain sustainable agricultural systems in drylands.
RESUMO
In order to increase crop yield in semi-arid and arid areas, plastic film mulching (PFM) is widely used in Northwestern China. To date, many studies have addressed the effects of PFM on soil physical and biochemical properties in rain-fed agriculture in Northwestern China, but the findings of different studies are often contradictory. Therefore, a comprehensive review of the impacts of PFM on soil water content, soil nutrients and food production is needed. We compiled the results of 1278 observations to evaluate the overall effects of PFM on soil water content, the distribution of nitrate and soil organic carbon, and crop yield in rain-fed agriculture in Northwestern China. Our results showed that PFM increased soil moisture and nitrate concentration in topsoils (0-20â¯cm) by 12.9% and 28.2%, respectively, but slightly decreased (1.8%) soil organic carbon (SOC) content in the 0-10â¯cm soil layer. PFM significantly increased grain yields by 43.1%, with greatest effect in spring maize (79.4%). When related to cumulative precipitation during the crop growing season, yield increase from PFM was greatest (72.8%) at 200-300â¯mm, which was attributed to the large increase for spring maize and potato, implying that crop zoning would be beneficial for PFM in this region. When related to N application rate, crop yields benefited most from PFM (80.2%) at 200-300â¯kg/ha. A cost-benefit analysis indicated that PFM increased economic return by an average of 29.5%, with the best improvement for spring maize (71.1%) and no increase for spring wheat. In conclusion, PFM can significantly increase crop yield and economic return (especially for spring maize) in rain-fed agriculture areas of Northwestern China. Crop zoning is recommended for PFM to achieve the largest economic benefit. However, full account needs to be taken of the environmental impacts relating to N loss, SOC depletion and film pollution to evaluate the sustainability of PFM systems and further research is required to quantify and mitigate these impacts.