Graphical abstract

Microbial nitrogen (N) immobilization, which typically results in soil N retention but based on the balance of gross N immobilization over gross N production, affects the fate of the anthropogenic reactive N. However, global patterns and drivers of soil gross immobilization of ammonium (INH4) and nitrate (INO3) are still only tentatively known. Here, we provide a comprehensive analysis considering gross N production rates, soil properties, and climate and their interactions for a deeper understanding of the patterns and drivers of INH4 and INO3. By compiling and analyzing 1966 observations from 274 15N‐labelled studies, we found a global average of INH4 and INO3 of 7.41 ± 0.72 and 2.03 ± 0.30 mg N kg−1 day−1 with a ratio of INO3 to INH4 (INO3:INH4) of 0.79 ± 0.11. Soil INH4 and INO3 increased with increasing soil gross N mineralization (GNM) and nitrification (GN), microbial biomass, organic carbon, and total N and decreasing soil bulk density. Our analysis revealed that GNM and GN were the main stimulators for INH4 and INO3, respectively. The structural equation modeling showed that higher soil microbial biomass, total N, pH, and precipitation stimulate INH4 and INO3 through enhancing GNM and GN. However, higher temperature and soil bulk density suppress INH4 and INO3 by reducing microbial biomass and total N. Soil INH4 varied with terrestrial ecosystems, being greater in grasslands and forests, which have higher rates of GNM, than in croplands. The highest INO3:INH4 was observed in croplands, which had higher rates of GN. The global average of GN to INH4 was 2.86 ± 0.31, manifesting a high potential risk of N loss. We highlight that anthropogenic activities that influence soil properties and gross N production rates likely interact with future climate changes and land uses to affect soil N immobilization and, eventually, the fate of the anthropogenic reactive N.

Effects of application of different rates of urea, biofertilizer, (Rhizobium radiobacter sp.) as salt tolerant PGPR strain and compost on barley (Hordeum valgare L. cv. Giza 126) were studied on a saline-sodic sandy loam soil at Gelbana village, Northern Sinai Governorate, Egypt during the two successive winter seasons of 2011/2012 and 2012/2013. The studied treatments were No, control (non fertilized), N1, mineral-N (119 kg N ha-1), N2, mineral-N (179 kg N ha-1), equivalent 0 , 50 and 75% from recommended rate for barley, biofertilizer (Bio), biofertilizer (Bio) + N1, biofertilizer (Bio)+ N2, compost, compost + N1 and compost + N2. The results could be summarized as follow: available N, P, K, Fe, Mn and Zn concentrations were significantly increased due to the above mentioned treatments. On the other hand, the electrical conductivity (EC dSm-1) and soil pH values decreased due to these treatments. The applied urea, compost and biofertilizer as well as their combinations significantly, increased straw and grain yields as well as N, P, K, Fe, Mn and Zn contents in straw and grains, grain weight spike-1 and 1000-grain weight in the two growing seasons, except grains spike-1 which did not reach the level of significantly in the first season. The highest values of nitrogen use efficiency (NUE), nitrogen agronomic efficiency (NAE) and apparent nitrogen recovery (ANR) were obtained due to the treatment Biofertilizer + N1 (119 kg N ha-1). The higher rate of N fertilization i.e.,179 kg N ha-1 combined with compost was of superior effect on improving soil chemical properties and increasing barley production, protein content and nutrient uptake as compared to the other treatments. This was found to be true for straw and grains. Thus, it is suggested to use a combination of organic and inorganic fertilizers to achieve the highest yield without negative effect on grain quality.

Studying the effect of applying gypsum and sulphur to counteract the soil salinity hazardous on vegetative growth, yield and quality of rice plants (Oriza sativa L.,cv. Sakha 101) grown on a Saline-Sodic soil at (Sahl El-Tina, Village 4, Gilbana, North Sinai governorate) irrigated with low water quality of El-Salam canal was the main objective of the current study. To fulfill this objective two field experiments were carried out during the two successive seasons of 2011 and 2012. Gypsum was applied at a rate of 10.7 Mg ha-1 while sulphur was added as either elemental sulphur at a rate of 4.8 Mg ha-1 or sulphuric acid at a rate of 1190 L ha-1. The obtained results could be summarized as follows: The highest values of rice yield and its attributes as well as nutrient contents and uptake values were obtained due to treating the investigated soil with sulphuric acid. Also, the effect of treatments showed a descending increase in the order of, sulphuric acid > sulphur > gypsum > control. The treatment of sulphuric acid was superior to the other treatments. Highest proline (21.3 µmol g-1) value was recorded due to the treatment of gypsum.

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