Responses of microbial function, biomass and heterotrophic respiration, and organic carbon in fir plantation soil to successive nitrogen and phosphorus fertilization.

Carbon dioxide (CO2) emissions from forest ecosystems originate largely from soil respiration, and microbial heterotrophic respiration plays a critical role in determining organic carbon (C) stock. This study investigated the impacts of successive nitrogen (N) and phosphorus (P) fertilization after 9 years on soil organic C stock; CO2 emission; and microbial biomass, community, and function in a Chinese fir plantation. The annual fertilization rates were (1) CK, control without N or P fertilization; (2) N50, 50 kg N ha-1; (3) N100, 100 kg N ha-1; (4) P50, 50 kg P ha-1; (5) N50P50, 50 kg N ha-1 + 50 kg P ha-1; and (6) N100P50, 100 kg N ha-1 + 50 kg P ha-1. The N100P50 treatment had the highest cumulative soil CO2 emissions, but the CK treatment had the lowest cumulative soil CO2 emissions among all treatments. The declines of soil organic C (SOC) after successive 9-year fertilization were in the order of 100 kg N ha-1 year-1 > 50 kg N ha-1 year-1 > CK. Compared to the CK treatment, successive N fertilization significantly changed soil microbial communities at different application rates and increased the relative gene abundances of glycoside hydrolases, glycosyl transferases, carbohydrate-binding modules, and polysaccharide lyases at 100 kg N ha-1 year-1. Relative to P fertilization alone (50 kg P ha-1 year-1), combined N and P fertilization significantly altered the soil microbial community structure and favored more active soil microbial metabolism. Microbial community and metabolism changes caused by N fertilization could have enhanced CO2 emission from heterotrophic respiration and eventually led to the decrease in organic C stock in the forest plantation soil. KEY POINTS: • N fertilization, alone or with P, favored more active microbial metabolism genes. • 100 kg N ha-1 fertilization significantly changed microbial community and function. • N fertilization led to a "domino effect" on the decrease of soil C stock.

Long-term continuous cropping affects ecoenzymatic stoichiometry of microbial nutrient acquisition: a case study from a Chinese Mollisol.

BACKGROUND: Soil- and plant-produced extracellular enzymes drive nutrient cycling in soils and are assumed to regulate supply and demand for carbon (C) and nutrients within the soil. Thus, agriculture management decisions that alter the balance of plant and supplemental nutrients should directly alter extracellular enzyme activities (EEAs), and EEA stoichiometry in predictable ways. We used a 12-year experiment that varyied three major continuous grain crops (wheat, soybean, and maize), each crossed with mineral fertilizer (WCF, SCF and MCF, respectively) or not fertilized (WC, SC and MC, respectively, as controls). In response, we measured the phospholipid fatty acids (PLFAs), EEAs and their stoichiometry to examine the changes to soil microbial nutrient demand under the continuous cropping of crops, which differed with respect to the input of plant litter and fertilizer. RESULTS: Fertilizer generally decreased soil microbial biomass and enzyme activity compared to non-fertilized soil. According to enzyme stoichiometry, microbial nutrient demand was generally C- and phosphorus (P)-limited, but not nitrogen (N)-limited. However, the degree of microbial resource limitation differed among the three crops. The enzymatic C:N ratio was significantly lower by 13.3% and 26.8%, whereas the enzymatic N:P ratio was significantly higher by 9.9% and 42.4%, in MCF than in WCF and SCF, respectively. The abundances of arbuscular mycorrhizal fungi and aerobic PLFAs were significantly higher in MCF than in WCF and SCF. CONCLUSION: These findings are crucial for characterizing enzymatic activities and their stoichiometries that drive microbial metabolism with respect to understanding soil nutrient cycles and environmental conditions and optimizing practices of agricultural management. © 2021 Society of Chemical Industry.

Growth, gas exchanges and production of beet CV. katrina under organo-mineral fertilization / Crescimento, trocas gasosas e produção da beterraba CV. Katrina sob adubação organomineral

The beet culture has great economic and food importance in the world, especially with respect to energy generation. In Brazil the culture is still little studied, lacking studies in all stages of production of culture, mainly in the management of fertilization. This study aimed to evaluate the effect of organo-mineral fertilization on growth, gas exchanges and production of beet, cv. Katrina. The experiment was conducted under field conditions in the municipality of Pombal-PB, Brazil, from September to December 2015, in a randomized block design. The treatments were arranged in a 4 x 2 factorial scheme and corresponded to four periods of fermentation of the biofertilizer (10, 20, 30 and 40 days) applied in soils with and without mineral fertilization, with four replicates and 18 plants evaluated per plot. Plants were conducted for 70 days after transplanting, in 15-cm-high, 1-m-wide beds. During this period, plant growth, gas exchanges and production components were evaluated. The application of mineral biofertilizer fermented for 20 to 30 days, associated with mineral fertilization with 36 g m-2 of P2O5, 18.0 g m-2 of K2O and 14 g m-2 of N at planting, promoted better performance of growth, gas exchanges and production of beet plants. In the soil without mineral fertilization, it is recommended to use the longest biofertilizer fermentation periods, 30 to 40 days, for beet cultivation.

A cultura da beterraba tem grande importância econômica e alimentar no mundo, especialmente no que diz respeito à geração de energia. No Brasil, a cultura ainda é pouco estudada, faltando estudos em todos os estágios de produção da cultura, principalmente no manejo da adubação. Objetivou-se no presente trabalho, avaliar a adubação organomineral no crescimento, trocas gasosas e produção da beterraba cv. Katrina. O experimento foi conduzido em condições de campo, no município de Pombal, PB, no período de setembro a dezembro de 2015. O delineamento experimental utilizado foi o de blocos ao acaso, com tratamentos arranjados em esquema fatorial 4 x 2, relativos a quatro períodos de fermentação do biofertilizante (10, 20, 30 e 40 dias) aplicados em solos com e sem adubação mineral, com quatro repetições e 18 plantas úteis por parcela. As plantas foram conduzidas durante 70 dias após o transplantio, em canteiros de 15 cm de altura, com 1 m de largura. Durante esse período, avaliou-se o crescimento, trocas gasosas e os componentes de produção. A adubação com biofertilizante mineral fermentado no período entre 20 e 30 dias associado à adubação mineral com 36 g m-2 de P2O5, 18,0 g m-2 de K2O e 14 g m-2 de N no plantio, proporcionou melhor desempenho no crescimento, trocas gasosas e produção da beterraba. No solo sem adubação mineral, recomenda-se a utilização dos maiores períodos de fermentação do biofertilizante, 30 a 40 dias, para o cultivo da beterraba.