Combining controlled-release urea with potassium chloride to reduce soil N/K leaching and promote growth of Italian ryegrass.

Nitrogen (N) and potassium (K) are essential nutrients for Italian ryegrass (Lolium multiflorum L.) growth. A 2-year field experiment with a split-plot design was conducted to study the effect of N fertilizer type combined with different K fertilizer rates on the soil mineral N and K availability, and growth characteristics of Italian ryegrass. The main plots were assigned to two N fertilizer types, controlled-release urea (CRU) and common urea. While low, moderate and high potassium chloride (KCl) rates (150, 300 and 450 kg ha-1, respectively) were assigned to the subplots. Compared with the common urea treatments, the CRU significantly increased the SPAD value, plant height, leaf area, and photosynthetic index of Italian ryegrass, which significantly prolonged the green stage of Italian ryegrass and prevented premature senescence. Moreover, the dry yields of the CRU increased by 4.5-12.5% in 2019 and 10.9-25.3% in 2020 compared with the urea, respectively. At the same time, compared with the KCl150 and KCl450 treatments, the KCl300 treatment resulted in better plant growth. Overall, the CRU × KCl300 maximized the soil inorganic N and different soil K forms, and reduced the soil N/K leaching. The root length, volume, surface area, average diameter, tips and branches were also improved, and there was a significant N × K interaction effect on the tips. The CRU combined with 300 kg ha-1 KCl fertilization enhanced crop growth by improving leaf photosynthesis, soil fertility, and yield and should be recommended as the best fertilizer ratio for Italian ryegrass production.

Humic Acid Extracted from Danty via Catalytic Oxidation Using H2O2/Birnessite: Characteristics and Agricultural Beneficial Effects.

Extraction optimization is very important for the quality of humic acid (HA). In this study, actived HA (HAb) was extracted from danty via catalytic oxidation using birnessite as a catalyst and H2O2 as an oxidant. Single-factor experiments and the response surface method were used to optimize the acidic functional group content of HAb. It was found that the maximum acidic functional group content of HAb can be achieved when danty-crushing time, H2O2 concentration, and birnessite dose were 105.7 min, 20, and 2%, respectively. Fourier transform infrared spectra showed that HAb had more surface functional groups than commercial HA (HAc) and HA extracted using the traditional method of the International Humic Substances Society (HAI). In addition, acidic functional group titration showed that HAb had 84.3% more acidic functional groups and 118.9% more carboxyl groups than HAI. Additionally, HAb had the greatest effect on promoting the dissolution of carbonate and bicarbonate, promoting the settlement of calcaline alkaline soil, and improving the germination rate of wheat seeds under saline and alkaline stress. This study provides a basis for the efficient extraction of active HA with rich functional groups and its application in agriculture and many other fields.

Application of mixotrophic acidophiles for the bioremediation of cadmium-contaminated soils elevates cadmium removal, soil nutrient availability, and rice growth.

A major challenge in radically alleviating the threats posed by Cd-contaminated paddy fields to human health is to reduce the Cd levels in both soils and rice grains. In this study, the microbial extraction (ME) treatment using a mixotrophic acidophilic consortium was used for the bioremediation of Cd-contaminated soils. The results showed that the ME treatment enhanced the total Cd (40%) and diethylenetriamine pentaacetic acid-soluble Cd (DTPA-Cd, 64%) removal efficiencies in contaminated soils. In addition, ME treatment decreased the levels of Cd acid-soluble and reducible fractions and thereby reduced Cd uptake in rice tissues. Microbial community analysis indicated that the indigenous soil microbial diversity and composition were not changed after the ME treatment, but the relative abundance of functional microbes associated with Cd removal was improved. Notably, soil available nutrient levels were elevated upon inoculation with mixotrophic acidophiles, resulting in an increase in rice growth and grain weight. This study provides a scientific basis for the potential application and evaluation of ME treatment in the field for remediating Cd-contaminated paddy soils.

Cadmium Speciation Distribution Responses to Soil Properties and Soil Microbes of Plow Layer and Plow Pan Soils in Cadmium-Contaminated Paddy Fields.

Cadmium (Cd) speciation ratio in arable land determines the Cd exposure risk and Cd uptake in crops. However, the driving mechanisms of Cd speciation change on the vertical scale of paddy fields remain poorly understood. In this study, the effects of plow layer and plow pan on Cd speciation distribution were investigated in a long-term Cd-contaminated rice ecosystem. The Cd accumulative effect within rice grain was enhanced with high levels of activated Cd speciation ratios in soils. Activated Cd speciation ratios were higher in plow layer soils, while stabilized Cd speciation ratios were elevated in plow pan soils. Soil physicochemical properties and soil microbes synergistically affected the Cd speciation changes in different ways between the two soil layers. Soil pH and organic elements in plow layer environment directly hindered the transformation of stabilized Cd speciation, while in plow pan environment, soil pH and organic elements indirectly decreased activated Cd speciation ratios and resulted in the accumulation of stabilized Cd speciation via regulating the predominant bacterial taxa. This study will improve our understanding of how soil environments regulate Cd speciation distributions in rice ecosystems and help to seek effective remediation methods of Cd-contaminated paddy fields to reduce the Cd accumulation in rice.

Effect of Ridge Height, Row Grade, and Field Slope on Nutrient Losses in Runoff in Contour Ridge Systems under Seepage with Rainfall Condition.

Seepage plays a key role in nutrient loss and easily occurs in widely-used contour ridge systems due to the ponding process. However, the characteristics of nutrient loss and its influential factors under seepage with rainfall condition in contour ridge systems are still unclear. In this study, 23 seepage and rainfall simulation experiments are arranged in an orthogonal rotatable central composite design to investigate the role of ridge height, row grade, and field slope on Nitrate (NO3--N) and Orthophosphate (PO4+3-P) losses resulting from seepage in contour ridge systems. In total, three types of NO3--N and PO4+3-P loss were observed according to erosion processes of inter-rill-headward, inter-rill-headward-contour failure, and inter-rill-headward-contour failure-rill. Our results demonstrated that second-order polynomial regression models were obtained to predict NO3--N and PO4+3-P loss with the independent variables of ridge height, row grade, and field slope. Ridge height was the most important factor for nutrient loss, with a significantly positive effect and the greatest contribution (52.35-53.47%). The secondary factor of row grade exerted a significant and negative effect, and was with a contribution of 19.86-24.11% to nutrient loss. The interaction between ridge height and row grade revealed a significantly negative effect on NO3--N loss, whereas interactions among the three factors did not significantly affect PO4+3-P loss. Field slope only significantly affected NO3--N loss. The optimal design of a contour ridge system to control nutrient loss was obtained at ridge height of 8 cm, row grade of 2°, and field slope of 6.5°. This study provides a method to assess and model nutrient loss, and improves guidance to implement contour ridge systems in terms of nutrient loss control.

Controlled-release urea improved rice yields by providing nitrogen in synchrony with the nitrogen requirements of plants.

BACKGROUND: Excessive application of nitrogen (N) fertilizer and low nitrogen-use efficiency (NUE) are prevalent problems in rice production. Controlled-release urea (CRU) is widely adopted to increase rice yields, but the synchronicity of N release from CRU with uptake of N by plants has rarely been studied. A 2-year field experiment involving CRU and urea applications at three different N rates (240, 192 and 144 kg N ha-1 , equal to 100%, 80% and 60% of the recommended rate, respectively) was performed to compare their effects on N uptake, soil N content and rice yields. RESULTS: The successive release curves of CRU in the soil matched the corresponding N uptake curves of rice plants, and significant linear correlations were observed. Grain yield and N uptake under the CRU treatment increased by 5.25-7.88% and 7.13-17.94% than urea treatments, at the same N rate, and no obvious difference was found between CRU60% and Urea100%. CRU80% and CRU60% presented the highest NUE. The contents of ammonium-nitrogen (NH4 + -N), nitrate-nitrogen (NO3 - -N), and total N and the chlorophyll relative value - SPAD (Soil Plant Analysis Development) values - of the leaves under the CRU treatments were significantly higher than those under the urea treatments from heading to harvest. The contents of exchangeable sodium ion (Na+ ) and calcium ion (Ca2+ ) and the cation exchange capacity increased in response to CRU. CONCLUSION: CRU increased rice yields by providing N strongly in synchrony with the N requirements of the plants, and applying CRU at 192 kg N ha-1 was an effective strategy to conserve N fertilizer, increase soil N contents and enhance NUE. © 2021 Society of Chemical Industry.

Combining Organic Fertilizer With Controlled-Release Urea to Reduce Nitrogen Leaching and Promote Wheat Yields.

Soil deterioration, low nitrogen use efficiency (NUE), and environmental risks caused by excessive chemical N fertilizer use are key factors restricting sustainable agriculture. It is extremely critical to develop effective N management strategies that consider both environmental and agronomic benefits. From 2017 to 2019, a field experiment was conducted to assess the effects of combinations of organic fertilizers (OF, provided at 30, 50, and 70% of the total applied N) and controlled-release urea (CU) on the NUE, N leaching and wheat yield compared with the effects of urea and CU. The results suggested that OF released N slowly in the early stage and showed a significant residual effect, while CU released N quickly in the first 2 months. The OF substitutes with 30-50% CU increased wheat yield by 4.2-9.2%, while the 70%OF+30%CU treatment showed no significant difference relative to the urea treatment. The average maximum apparent NUE recovery (50.4%) was achieved under the 50%OF+50%CU treatment, but the partial factor productivity was not affected by the N type. As the OF application rate increased, the total carbon content increased, and the total N value decreased. The NO 3 - -N and NH 4 + -N concentrations in the OF+CU treatments were lower before the jointing stage but higher from the grain-filling to mature stages than those in the urea treatment. NO 3 - -N and NH 4 + -N were mainly concentrated in the 0-60-cm layer soil by OF substitution, and N leaching to the 60-100-cm soil layer was significantly reduced. Hence, the results suggest that the combination of 30-50% OF with CU synchronizes absorption with availability due to a period of increased N availability in soils and proved to be the best strategy for simultaneously increasing wheat production and reducing N leaching.

Determination of the Best Controlled-Release Potassium Chloride and Fulvic Acid Rates for an Optimum Cotton Yield and Soil Available Potassium.

Potassium and fulvic acid (FA) fertilizer applications are two important measures for improving cotton growth. However, there are few studies on the application interactive effects of controlled-release potassium chloride (CRK) in combination with FA on cotton production. To explore the effects of CRK combined with FA on cotton, field experiments were conducted in 2018 and 2019 using a split-plot design. The main plots were assigned to two types of potassium fertilizer - controlled-release potassium chloride (CRK) and potassium sulfate (KS) - while low, moderate, and high FA application rates (90, 180, and 270 kg ha-1) were assigned to the subplots. The cotton yield, fiber quality, net profit, soil available potassium concentration, potassium use efficiency, and leaf photosynthesis were markedly affected by potassium fertilizer and FA. The cotton boll number and boll weight in the 2 years and the yield in 2019 were all affected by the interaction between potassium fertilizer and FA. Compared to the other potassium treatments, the CRK × FA180 treatment increased the seed yield and net profit by 4.29-14.92% and 13.72-62.30%, respectively, over the 2 years. The potassium agronomy efficiency and potassium recovery efficiency (KRE) of the CRK × FA180 treatment were also improved by 6.25-30.77% and 3.82-12.78% compared to those of the other potassium treatments. Overall, the FA180 treatment resulted in better cotton growth than that in the FA90 and FA270 treatments. The release period of CRK in the field during the growth period of cotton was longer than that detected by 25°C static water extraction, which increased the soil available potassium content and met the potassium demands over the whole cotton growth period. Therefore, the application of CRK in combination with 180 kg ha-1 FA is the best choice for cotton fertilization.

Effects of controlled-release urea combined with fulvic acid on soil inorganic nitrogen, leaf senescence and yield of cotton.

A split-plot field experiment was conducted in 2018-2019 to study the effects of nitrogen fertilizer types and fulvic acid (FA) rates on soil nitrogen and cotton growth. The nitrogen fertilizers included controlled-release urea (CRU) and urea, which were applied combined with three FA rates (90, 180 and 270 kg ha-1). The main plot was the nitrogen fertilizer type, and the subplot was the FA rate. The results showed that the lint yield of the FA180 treatment was 5.2-8.6% higher than the FA90 and FA270 treatments. Moreover, moderate FA application markedly improved the cotton leaf SPAD value (chlorophyll relative value), photosynthesis and chlorophyll fluorescence parameters compared with low and high FA rates. Replacing urea with CRU significantly increased the soil inorganic nitrogen and nitrogen use efficiency and also improved cotton fiber quality parameters. Meanwhile, the boll weight and seed yield of the CRU treatments were 1.5-8.4% and 3.3-19.1% higher, respectively, than the urea treatments. The interaction between nitrogen type and FA rate had a positive effect on cotton growth. Thus, the application of CRU combined with 180 kg ha-1 FA on cotton can not only improve the fiber quality and delay leaf senescence but also increase the yield and economic benefit.

Cumulative release characteristics of controlled-release nitrogen and potassium fertilizers and their effects on soil fertility, and cotton growth.

To investigate the interacting effects of polymer coated urea (PCU) and polymer coated potassium chloride (PCPC) on cotton growth, an experiment was conducted with containerized plants in 2014 and 2015. There were two kinds of nitrogen fertilizer, PCU and urea, which were combined with PCPC at three application rates (40, 80 and 120 kg ha-1). The kinds of nitrogen fertilizer formed the main plot, while individual rates of PCPC were the subplots. The results suggested N and K release patterns for PCU and PCPC in the soil were closely matched to the N and K requirements by cotton. Soil inorganic nitrogen contents significantly increased by using PCU instead of urea, and the same trend was observed with soil available potassium contents, which also had increased rates. Meanwhile, the number of bolls and lint yields of cotton in the PCU treatments were 4.9-35.3% and 2.9-40.7% higher than from urea treatments. Lint yields also increased by 9.1-12.7% with PCPC80 and PCPC120 treatments compared with PCPC40 treatment at the same nitrogen type. Hence, application of PCU combined with 80 kg ha-1 of PCPC fertilizer on cotton increased the yields and fertilizer use efficiencies in addition to improving fiber quality and delaying leaf senescence.