Effects of Malic Acid and Sucrose on the Fermentation Parameters, CNCPS Nitrogen Fractions, and Bacterial Community of Moringa oleifera Leaves Silage

The present study investigated the effects of malic acid, sucrose, and their mixture on the fermentation parameters, Cornell Net Carbohydrate and Protein System (CNCPS) nitrogen fractions, and bacterial community of Moringa oleifera leaves (MOL) silages. The trial was divided into four treatments and labeled as CON (control group) and MLA, SUC, and MIX (respectively denoting the addition of 1% malic acid, 1% sucrose, and 1% malic acid + 1% sucrose to the fresh weight basis). The silage packages were opened on the 2nd, 5th, 10th, 20th, and 40th days of ensiling for subsequent determination. Malic acid and sucrose increased the lactic acid content (p < 0.05) and pH value, and the acetic acid contents of MLA and MIX were lower than those in CON (p < 0.05). Compared with sucrose, malic acid had a better capacity to preserve nutrients and inhibit proteolysis, and thus exerted better effects on the CNCPS nitrogen fractions. The results of 16S rRNA showed that the dominant phyla were Firmicutes and Proteobacteria and that the dominant genera were Lactobacillus and Weissella. With the application of silage additives and the processing of fermentation, there was a remarkable change in the composition and function of the bacterial community. The variation of the fermentation parameters and CNCPS nitrogen fractions in the MOL silages caused by malic acid and sucrose might be attributed to the dynamic and dramatic changes of the bacterial community.

Nitrogen Fractions in Soil Fertilized with Waste Organic Materials

The aim of the study was to determine the effect of sewage sludge and composts produced from sewage sludge and municipal waste on the content of various forms of nitrogen in soil. The field experiment was carried out in 2004–2015. It included three crop rotations of the following plants: potato, spring barley, winter oilseed rape and winter wheat. The experiment consisted of the following treatments: control (without fertilization), NPK, manure (FYM), compost from municipal sewage sludge and straw (CSSS), composted sewage sludge (CSS), dried and granulated sewage sludge (DGSS), “Dano” compost produced from unsorted municipal waste (CUMW) and compost from municipal green waste (CMGW). Manure, composts and sewage sludge were applied once (10 t ha−1 of d.m.) or twice (5 t ha−1 of d.m.) in a crop rotation. It was significantly shown that the highest N-total content was in the soil fertilized with CUMW (compost produced from unsorted municipal waste). The soil fertilized with manure (FYM) contained the highest quantity of N-min. The prevalent pool of nitrogen (82.65–86.52%) consisted of N compounds not undergoing acid hydrolysis, and their smallest share was determined in the soil fertilized with NPK alone.

Response of nitrogen fractions in the rhizosphere and bulk soil to organic mulching in an urban forest plantation

Nitrogen is an essential component in forest ecosystem nutrient cycling. Nitrogen fractions, such as dissolved nitrogen, ammonium, nitrate, and microbial biomass nitrogen, are sensitive indicators of soil nitrogen pools which affect soil fertility and nutrient cycling. However, the responses of nitrogen fractions in forest soils to organic mulching are less well understood. The rhizosphere is an important micro-region that must be considered to better understand element cycling between plants and the soil. A field investigation was carried out on the effect of mulching soil in a 15-year-old Ligustrum lucidum urban plantation. Changes in total nitrogen and nitrogen fractions in rhizosphere and bulk soil in the topsoil (upper 20 cm) and in the subsoil (20–40 cm) were evaluated following different levels of mulching, in addition to nitrogen contents in fine roots, leaves, and organic mulch. The relationships between nitrogen fractions and other measured variables were analysed. Organic mulching had no significant effect on most nitrogen fractions except for the rhizosphere microbial biomass nitrogen (MBN), and the thinnest (5 cm) mulching layer showed greater effects than other treatments. Rhizosphere MBN was more sensitive to mulching compared to bulk soil, and was more affected by soil environmental changes. Season and soil depth had more pronounced effects on nitrogen fractions than mulching. Total nitrogen and dissolved nitrogen were correlated to soil phosphorus, whereas other nitrogen fractions were strongly affected by soil physical properties (temperature, water content, bulk density). Mulching also decreased leaf nitrogen content, which was more related to soil nitrogen fractions (except for MBN) than nitrogen contents in either fine roots or organic mulch. Frequent applications of small quantities of organic mulch contribute to nitrogen transformation and utilization in urban forests.