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.

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.