Understanding the mechanism of soil organic carbon (SOC) sequestration is of paramount importance in sustaining crop productivity and mitigating climate change.  Long-term trials were employed to investigate the responses of total SOC and its pools, i.e., mineral-associated OC (MOC), particulate OC (POC, containing Light-POC and Heavy-POC), to fertilization regimes at Yangling (25-year), Tianshui (35-year) and Pingliang (37-year) under a rain-fed cropping system in the Loess Plateau.  The fertilization regimes in each trial included three treatments, i.e., control (no nutrient input, CK), chemical fertilizers (CF), and organic manure plus chemical fertilizers (MCF).  Relative to the CK, long-term fertilization appreciably increased SOC storage by 134, 89 and 129 kg ha^–1 yr^–1 under CF, and 418, 153 and 384 kg ha^–1 yr^–1 under MCF in plough layer soils (0–20 cm), respectively, at the Yangling, Tianshui and Pingliang sites.  The MOC pools accounted for 72, 67 and 64% of the total SOC at the above three sites with sequestration rates of 76, 57 and 83 kg ha^–1 yr^–1 under CF and 238, 118 and 156 kg ha^–1 yr^–1 under MCF, respectively.  Moreover, the MOC pool displayed a saturation behavior under MCF conditions.  The POC accordingly constituted 27, 33 and 36% of SOC, of which Light-POC accounted for 11, 17 and 22% and Heavy-POC for 17, 16 and 15% of SOC, respectively.  The sequestration rates of POC were 58, 32 and 46 kg ha^–1 yr^–1 under CF, and 181, 90 and 228 kg ha^–1 yr^–1 under MCF at the three respective sites, in which Light-POC explained 59, 81 and 72% of POC under CF, and 60, 40 and 69% of POC under MCF, with Heavy-POC accounting for the balance.  Compared with CK, the application of CF alone did not affect the proportions of MOC or total POC to SOC, whereas MCF application markedly reduced the proportion of MOC and increased the POC ratio, mainly in the Light-POC pool.  The distribution of SOC among different pools was closely related to the distribution and stability of aggregates.  The present study confirmed that organic manure amendment not only sequestered more SOC but also significantly altered the composition of SOC, thus improving SOC quality, which is possibly related to the SOC saturation level.

 

Potassium (K) and magnesium (Mg) levels and their balances are two factors affecting the growth of plant.  However, the responses of different crop cultivars to K/Mg ratios are less clear.  This study was aimed at assessing the different responses of tomato (Solanum Lycopersicum L.) cultivars to the different K/Mg supply ratios.  Three tomato cultivars (Zhongza 9 (ZZ), Gailiangmaofen (MF), and Jinpengchaoguan (JP)) were grown in pots with three different K⁺/Mg²⁺ ratios (4:0, 4:1 and 8:1, represented by K/Mg_4:0, K/Mg_4:1, and K/Mg_8:1, respectively).  Compared with K/Mg_4:1 treatment, the leaf chlorophyll content, net photosynthetic rate, and total biomass of tomato seedlings under K/Mg_4:0 treatments were decreased by 69.7, 89.1, and 53.1%, respectively.  The Mg deficiency symptoms were observed when the Mg content in shoot became lower than 4 mg g^–1 DW.  Compared with K/Mg_4:1 treatment, total biomass of tomato seedlings of K/Mg_8:1 treatment was decreased by 21.6%; the shoot and root Mg contents were decreased by 10.4 and 21.8%, respectively; and Mg uptake of tomato was reduced by 34.1%.  There were significant differences in biomass and Mg uptake for the three cultivars between the different K⁺/Mg²⁺ treatments.  The Mg uptake of the three different cultivars ranked as ZZ>JP>MF under Mg deficiency and high K condition.  In conclusion, the growth and Mg uptake and allocation of tomato were influenced significantly by imbalance K and Mg supply. JP and ZZ were the cultivars with the highest efficiency in Mg uptake. 

The pellicle-forming yeast could cause the quality deterioration of wine.  In this study, a pellicle-forming strain Hmp-1 was isolated from the spoilage blackberry wine, and identified as Pichia membranifaciens based on the morphology and partial nucleotide sequence of 26S rDNA.  The effects of fermentation conditions (ethanol, sulfur dioxide, sugar, and temperature) on the growth of P. membranifaciens strain Hmp-1 and Saccharomyces cerevisiae strain FM-S-115 (a strain used for the blackberry wine fermentation) were investigated, respectively.  The results indicated that Hmp-1 had lower resistance to these factors compared to FM-S-115, and the growth of Hmp-1 was completely inhibited by 10% (v/v) or 50 mg L^–1 SO₂ during the fermentation of blackberry wine.  These results suggested that Hmp-1 could effectively be controlled by increasing ethanol or SO₂ concentration during the fermentation and storage of blackberry wine.  Furthermore, the analysis based on gas chromatography-mass spectrometry (GC-MS) showed that Hmp-1 remarkably decreased kinds of volatile compounds in blackberry wine, especially aldehydes and esters.  In addition, some poisonous compounds were detected in the blackberry wine fermented by FM-S-115 and Hmp-1.  These results suggested that Hmp-1 was a major cause leading to the quality deterioration of blackberry wine.

 

Excessive nitrogen (N) fertilization of high value horticultural crops is a common problem that not only increases the cost to farmers, but also negatively affects crop growth and the environment.  A three-year field experiment was conducted in an intensive kiwifruit orchard in Shaanxi Province, China to compare the effects of reduced N fertilization applied as urea (U), and controlled release urea (CRU) on the N nutrition of kiwi vines, fruit yield and quality, and nitrate-N accumulation in the soil profile.  The three treatments included a conventional N application rate (CF-U, 900 kg N ha^–1 yr^–1 as urea), two reduced N fertilization treatments where the amount of N fertilizer applied as U and CRU was reduced by 25% in 2013 and 2014, and by 45% in 2015.  The 25 and 45% reduced N treatments had no adverse effects on the N concentrations in leaves and pruning branches and the fruit yield and quality of kiwi vines.  However, they significantly enhanced the partial factor productivity of applied N (PFP_N) and the economic benefits, and reduced nitrate accumulation in the 0–200 cm soil profile.  The same benefits of reduced N fertilization were observed for both the U and CRU treatments, but the CRU treatment had the added benefit of decreasing the loss of nitrate through leaching.  We concluded that the current level of N fertilization in kiwi orchards is very excessive, and reducing the N fertilizer rate by 25–45% could not only guarantee fruit yield, but also reduce N accumulation and loss.