We compiled data from 495 observations and 103 papers and carried out a meta-analysis of the responses of fine root biomass, production, decomposition, and morphology to precipitation increases and decreases. In addition, we evaluated the effects of plant life form, soil depth, and experiment duration on the responses of fine roots to precipitation changes. Our results confirmed that decreased precipitation limited fine root diameter and accelerated turnover. Increased precipitation stimulated fine root elongation and enhanced the fine root accumulation. The responses of fine roots to precipitation changes varied among plants of different life forms. Tree fine root production and decomposition and non-tree fine root diameter varied most strongly under decreased precipitation. Specific root length of non-tree fine roots was much higher than that of tree fine roots under increased precipitation. Decreased precipitation limited the growth of fine roots in 20–40 cm deep soil, whereas increased precipitation promoted the growth of fine roots in both shallow and deep soil layers. The responses of fine roots to decreased precipitation were affected by experiment duration. Results filled the gap of evaluation data on the effect of precipitation change on fine root morphology and dynamics, which are useful for better predicting the C cycle under precipitation change.

Micrometeorological methods are ideally suited for continuous measurements of N₂O fluxes, but gaps in the time series occur due to low-turbulence conditions, power failures, and adverse weather conditions. Two gap-filling methods including linear interpolation and artificial neural networks (ANN) were utilized to reconstruct missing N₂O flux data from a corn–soybean–wheat rotation and evaluate the impact on annual N₂O emissions from 2001 to 2006 at the Elora Research Station, ON, Canada. The single-year ANN method is recommended because this method captured flux variability better than the linear interpolation method (average R² of 0.41 vs. 0.34). Annual N₂O emission and annual bias resulting from linear and single-year ANN were compatible with each other when there were few and short gaps (i.e., percentage of missing values <30%). However, with longer gaps (>20 d), the bias error in annual fluxes varied between 0.082 and 0.344 kg N₂O-N ha^-1 for linear and 0.069 and 0.109 kg N₂O-N ha^-1 for single-year ANN. Hence, the single-year ANN with lower annual bias and stable approach over various years is recommended, if the appropriate driving inputs (i.e., soil temperature, soil water content, precipitation, N mineral content, and snow depth) needed for the ANN model are available.

Straw ditch-buried returning is a new straw returning mode; however, the different effect of straw ditch-buried returning and frequently used straw returning modes on soil organic carbon (SOC) sequestration is still unclear. A 2 yr field experiment was conducted and four treatments (CK: no straw returning; WR: wheat straw returning with rotary tillage; WP: wheat straw returning with plowing; WD: wheat straw ditch-buried returning) were set to assess the effects on SOC fractions and sequestration in rice–wheat rotation. Results indicated that WD had significantly higher total organic carbon than did WP and CK in wheat season. Soil dissolved organic carbon and easily oxidizable carbon contents were significantly increased by 21.3%, 24.3%, 38.6%, and 43.5% under WR than that under CK in rice and wheat seasons, respectively. Soil microbial biomass carbon (MBC) content was highest under WP in rice season, but in wheat season, WR had significantly higher MBC than WP and WD. Soil carbon pool management index was significantly higher in WR than CK, with the increase of 41.0% and 108.6%. After 2 yr rotation, WD had a significant higher SOC stock and sequestration than WP. Therefore, WD could be an available mode to increase SOC sequestration in rice–wheat rotation system.

Limited research exists on legacy effects of land application of feedlot manure on accumulation, redistribution, and leaching potential of water-extractable organic carbon (WEOC) in soil profiles. We sampled a clay loam soil at six depths (0–1.50 m) 2 yr after the last application (2014) of 17 continuous annual manure applications (since 1998). The amendment treatments were stockpiled (SM) or composted (CM) feedlot manure containing straw (ST) or wood-chip (WD) bedding at three application rates (13, 39, and 77 Mg ha^-1 dry basis). There was also an unamended control (CON) and inorganic fertilizer (IN) treatment. The soil samples were analyzed for concentrations of WEOC. The total mass or accumulation of WEOC in the soil profile was greater (P?≤?0.05) by 1.2–3.3 times for the CM-ST-77 treatment than 12 of 14 other treatments, and it was significantly greater for amended than CON or IN treatments. The total WEOC mass was 14%–20% greater for CM-ST than CM-WD, SM-ST, and SM-WD treatments, and it was 16%–22% greater for CM than SM at the 39 and 77 Mg ha^-1 rates. The 77 Mg ha^-1 rate of the four manure type-bedding treatments had the significantly greatest (by 37%–527%) concentrations of WEOC at the six depths compared with other treatments, suggesting greater redistribution and leaching potential. Significant manure effects occurred on soil WEOC 2 yr after the manure was last applied following 17 continuous applications, and it indicated an increased risk of leaching potential at the higher application rate.

Three micro-catchment measures that are named fish-scale pits (FSPs), artificial digging (AD), and contour plowing (CP) for soil erosion prevention are widely used in the Loess Plateau. To clarify the effectiveness of these measures in intercepting runoff and reducing erosion and the mechanism of water flow movement, intermittent simulated rainfall events was carried out in the 15° slopes with FSPs, AD, CP, and control slope (CK). The results demonstrated the following. (1) For cumulative rainfall <83 mm, three measures effectively intercepted runoff and reduced sediment compared with the CK. The runoff and sediment reduction effect of three measures gradually disappeared when cumulative rainfall increased to 83, 99, and 108 mm, and the sediment generation of the three measures successively exceeded that of the CK and was more than two times higher. (2) Laminar or transition flow occurred for the CK, and the flow pattern changed from subcritical to supercritical at 101 mm of cumulative rainfall. For three measures, the flow patterns became turbulent within a short time but remained subcritical. (3) A correlation analysis showed that the soil detachment rate, hydraulic shear stress, and stream power in the micro-catchment measures can be described using linear functions, which reduced the rill erodibility and enhanced the soil’s resistance to concentrated flow erosion. This research has important guiding significance on the rational and effective implementation of micro-catchment practices to prevent severe soil erosion and increase water storage for crop production on the Loess Plateau of China.

This study aims to assess the decomposition of manure biodegraded by fly larvae and the nutrient mineralization rates to understand the efficiency of the biodegraded manures for further use as soil amendment. A litter bag experiment was carried out over 75 d in an Acrisol in Benin using poultry manure, pig manure, mixture of poultry and sheep manure, mixture of poultry and cow manure, and mixture of poultry and pig manure, biodegraded by Musca domestica larvae. Nutrients content in the manures during the different stages of decomposition was analyzed. The mono-component exponential model Y_t?=?Y₀ × e^-kt best described the manure decomposition and nutrients mineralization. The manures decomposed fast in the soil, and their nutrients were released fast in the poultry manure, the mixture of poultry and pig manure, and the mixture of poultry and cow manure. Nutrient mineralization increased in the order of P < N < K or N < P < K. Biodegradation of animal manures by fly larvae produced high-quality organic fertilizer through fast N and P release. This could aid in reducing the quantities of these elements applied as mineral fertilizer by farmers for sustaining agricultural soil productivity.

Nitrogen (N) losses from agricultural tile drainage systems are environmental and economic losses for producers. This field study quantified N losses from three reps of shallow (SD), deep/conventional (DD), and controlled drainage (CD) on farmland in Nova Scotia. Drainage systems were under corn and alfalfa–oats–clover production. Outflow water and gas samples were obtained and analyzed for nitrate and nitrous oxide. Nitrate-N loads were 5.0, 11.1, and 6.4 kg ha^-1 in 2015; 1.8, 6.7, and 2.8 kg ha^-1 in 2016; and 0.74, 1.8, and 1.6 kg ha^-1 in 2017 for SD, DD, and CD, respectively. Controlled drainage reduced NO₃^--N loading by 42.3%–58.2% when compared with the conventional/DD in 2 of 3 yr of study, whereas SD was found to reduce NO₃^--N loading by 54.9%–73.1% compared with DD in all years studied. Total NO₃^--N losses in this study were measured during the growing season (1 Apr. to 31 Oct.); the magnitude of NO₃^--N losses and treatment effects may vary if studied year-round. Nitrous oxide fluxes were variable and low in magnitude throughout the study. Cumulated N₂O losses were <1% of the applied N for all drainage types. Controlled drainage increased yields compared with SD and DD. The use of CD in the region could aid in reducing climate stresses, as well as overall NO₃^--N loads exiting drainage systems and may enhance crop yields compared with conventional systems. Future studies on dissolved N₂O losses from drainage water may provide important insight into whether dissolved N₂O losses exceed surface emissions.

Agricultural ecosystems are one of the largest global contributors to nitrate (NO₃^-) contamination of surface- and groundwater through fertilizer application. Improved fertilizer practices are needed to manage crop nutrient supply in corn (Zea mays L.) while minimizing impacts to clean water reserves. The goal of this study was to compare current nitrogen (N) fertilizer practices (urea at planting) with “packages” of improved management practices (a combination of right timing and product) that farmers potentially use. We conducted measurements in a continuous corn system from November 2015 to May 2017 at a large field scale (four 4 ha plots). Nitrate concentration was measured below the root zone and drainage estimated using a soil water budget approach in which evapotranspiration was measured using the eddy covariance method. The objective was to compare NO₃^--N leaching from fields receiving urea vs. urea + combination of nitrification and urease inhibitors (NUI) fertilizer applications at planting, urea–ammonium nitrate (UAN) vs. UAN + NUI applied at sidedress, and a combination of these practices: urea + NUI at planting vs. UAN at sidedress. Drainage was only significant in the non-growing season. Neither fertilizer products applied with NUI at planting or sidedress proved to significantly reduce NO₃^--N leaching. The combination of delaying fertilization to sidedress and applying UAN significantly reduced the soil water NO₃^--N concentration compared with urea + NUI at planting (mean of 5.2 vs. 6.7 mg L^-1) but only in 2015–2016. Based on these results, applying UAN at sidedress is recommended, although additional study years are needed to confirm those results.

Phosphorus (P) fertilizers are added to improve the soil P fertility, but the rate of P release can greatly influence its availability. Organic acids are effective in the release of inorganic P (P_i), but the contribution of each P_i fraction is not well understood. This study reported the transformation rate of P and solubility of P_i fractions induced by organic acids. Path analysis was utilized to explore the direct and indirect effects of P_i fractions on the amount of total P_i (TP_i) solubilized. Results showed that the P release was initially rapid, followed by a slower release that lasted up to 2160 h, and the Elovich equation was the best-fitted kinetic equation to estimate the transformation rate of available P. The amount of TP_i-solubilized by oxalic and citric acids tended to increase with increasing organic acid concentrations. Oxalic acid exhibited a lower TP_i-solubility capability than citric acid when the organic acid concentration was ≤1 mmol L^-1, whereas citric acid was higher at ≥1.5 mmol L^-1. The Al-P-solubilized had the highest content of studied fractions, and path analysis revealed that the Al-P-solubilized exhibited a significant direct effect on TP_i-solubilized. Thus, Al-P is a potential P source in black soil.

Limited research exists on short-term legacy effects of land application of different feedlot manures on barley (Hordeum vulgare L.) yield and soil macronutrient (NO₃-N, PO₄-P, K, and SO₄-S) supply. In a study conducted in southern Alberta, feedlot manures with straw (ST) or wood-chip (WD) bedding were either stockpiled or composted and applied annually to a clay loam soil at 13, 39, and 77 Mg ha^-1 dry wt. for 17 yr. Control treatments without any amendments or with inorganic fertilizer were included. In the second and third year (2016–2017) after discontinuing manure applications in 2014, barley silage yield and soil nutrient supply measured in situ with plant root simulator (PRS^®) probes were determined. No significant (P > 0.05) treatment effects occurred on barley yield. Significant treatment effects occurred on soil nutrient supply, but these depended on date and interaction with other treatment factors. Manure rate generally increased soil nutrient supply. Soil NO₃-N and PO₄-P supply were 40%–59% lower for composted manure with ST than the other three manure type-bedding treatments, and they were 26%–53% greater for stockpiled than composted manure. This indicated variable manure type effects at different dates. At the two highest rates, soil K supply was 60%–106% greater for ST than WD bedding, and the reverse trend occurred where SO₄-S supply was 40%–174% greater for WD than ST bedding. Overall, short-term legacy effects of feedlot manure type and bedding were more persistent on soil macronutrient supply than barley silage yield.