Full substitution of chemical fertilizer by organic manure decreases soil N2 O emissions driven by ammonia oxidizers and gross nitrogen transformations.

Replacing synthetic fertilizer by organic manure has been shown to reduce emissions of nitrous oxide (N2 O), but the specific roles of ammonia oxidizing microorganisms and gross nitrogen (N) transformation in regulating N2 O remain unclear. Here, we examined the effect of completely replacing chemical fertilizer with organic manure on N2 O emissions, ammonia oxidizers, gross N transformation rates using a 13-year field manipulation experiment. Our results showed that organic manure reduced cumulative N2 O emissions by 16.3%-210.3% compared to chemical fertilizer. The abundance of ammonia oxidizing bacteria (AOB) was significantly lower in organic manure compared with chemical fertilizer during three growth stages of maize. Organic manure also significantly decreased AOB alpha diversity and changed their community structure. However, organic manure substitution increased the abundance of ammonia oxidizing archaea and the alpha diversity of comammox Nitrospira compared to chemical fertilizer. Interestingly, organic manure decreased organic N mineralization by 23.2%-32.9%, and autotrophic nitrification rate by 10.5%-45.4%, when compared with chemical fertilizer. This study also found a positive correlation between AOB abundance, organic N mineralization and gross autotrophic nitrification rate with N2 O emission, and their contribution to N2 O emission was supported by random forest analysis. Our study highlights the key roles of ammonia oxidizers and N transformation rates in predicting cropland N2 O.

Mixed cropping with duck co-culture: an agroecological system to improve grain quality and farm profitability.

BACKGROUND: Previous studies found that mixed cropping combined with duck co-culture (MCDC) system could improve the efficiency of grain production and positively affect soil nutrient contents. However, the effects on grain quality, and profitable income have not been evaluated yet. In this study, a field experiment with four combinations of different rice varieties and ducks was conducted during both the early and late rice growing seasons. RESULTS: The field survey demonstrated that MCDC system significantly decreased the grain appearance of chalky rice rate and the chalkiness degree with an average of 56.82%, and 54.28%, respectively. Leaf SPAD value, photosynthetic rate, and aboveground dry weight were all improved in the MCDC and mixed-cropping systems, relative to the mono-cropping system. The net income obtained from the mono-cropping, mixed cropping (no ducks), and MCDC (with ducks) systems (from grain and ducks' meat) was 581.2 USD ha-1 yr-1 , 1001.8 USD ha-1 yr-1 , and 5242.1 USD ha-1 yr-1 in both growing seasons, respectively. CONCLUSION: Planting genetically diverse rice varieties and co-culture with ducks increased rice growth rates, productivity and grain quality. The MCDC system would provide more ecological and economic benefits compared with the conventional mono-cropping system. © 2022 Society of Chemical Industry.

Water mimosa (Neptunia oleracea Lour.) can fix and transfer nitrogen to rice in their intercropping system.

BACKGROUND: Cereal-legume intercropping systems are an environmentally friendly practice in sustainable agriculture. However, research on the interspecific interaction of nitrogen (N) between rice and aquatic legumes has rarely been undertaken. To address this issue, a pot experiment was conducted to investigate N utilization and the N interaction between rice and water mimosa (Neptunia oleracea Lour.) in an intercropping system. The root barrier patterns consisted of solid barrier (SB), mesh barrier (MB), and no barrier (NB) treatments. The N fertilizer application rates were low, medium, and high N rates. RESULTS: The results showed that the NB treatment better facilitated rice growth compared with the MB and SB treatments. And the nitrate N content and urease activity of rice rhizospheric soil in the NB treatment were the highest of the three separated patterns. The ammonium N content in water mimosa rhizospheric soil and N2 fixation of water mimosa ranked as NB > MB > SB. CONCLUSIONS: The amount of N fixation by water mimosa was 4.38-13.64 mg/pot, and the N transfer from water mimosa to rice was 3.97-9.54 mg/pot. This can promote the growth of rice and reduce the application of N fertilizer. We suggest that the rice-water mimosa intercropping system is a sustainable ecological farming approach and can be applied in the field to facilitate rice production. © 2021 Society of Chemical Industry.

Mix-cropping of rice and water mimosa (Neptunia oleracea Lour.) increases rice photosynthetic efficiency, yield, grain quality and soil available nutrients.

BACKGROUND: Cereal cultivation with legumes plays an important role in improving biodiversity and productivity. However, there are limited references concerning rice/legume mix-cropping in paddy fields. An aquatic leguminous plant, water mimosa (Neptunia oleracea Lour.), was introduced and a related field experiment of two seasons (early and late seasons in 2019) was carried out to explore the effects of rice/water mimosa mix-cropping on rice growth, yield, grain quality and soil nutrients in the present study. Three treatments - rice monocropping, rice/water mimosa intercropping and mix-cropping - were employed in this study. RESULTS: Results showed that rice grew better with greater height, tiller number, chlorophyll content, actual photosynthetic efficiency [Y(II)], maximum photochemical efficiency (Fv /Fm ) and photochemical quenching coefficient (qP) in the intercropping and mix-cropping treatments. In addition, the intercropping and mix-cropping treatments increased nutrient uptake of nitrogen (N) by11.89-24.42%, phosphorous (P) by 17.75-36.61% and potassium (K) by 19.22-47.44%, and rice yield by 19.9% and 21.8%. Conversely, the non-photochemical quenching coefficient (NPQ), chalkiness degree and chalky rate of rice were lower in the intercropping and mix-cropping treatments relative to those in the monocropping treatments. Notably, soil alkali-hydrolysable N (AN), available P (AP) and K (AK) contents were the highest in the mix-cropping treatments among the three cropping systems. CONCLUSION: We suggest that rice/water mimosa mix-cropping is an environmentally friendly agroecological system with a higher output and can be extended for green rice production and largely applied in the paddy field. © 2021 Society of Chemical Industry.

Effects of the integration of mixed-cropping and rice-duck co-culture on rice yield and soil nutrients in southern China.

BACKGROUND: Biodiversity-based agricultural systems can improve production efficiency and sustainability, with fewer negative environmental impacts and lower use of external inputs. Mixed-cropping and rice-duck co-culture have been shown to produce ecological benefits and to have positive effects on paddy soil. However, the effects of a combination of mixed cropping with different rice cultivars and duck co-culture on soil nutrients availability and grain yields have not been evaluated. A paddy field experiment was carried out over two rice growing seasons to test these effects. RESULTS: Several combinations of rice cultivars, when integrated with duck co-culture, significantly increased the soil organic matter and total nitrogen contents during the rice growing seasons, as compared to mono-cropping systems. In mixed-cropping combined with duck co-culture (MCDC) systems, the soil alkali-hydrolyzable nitrogen content ranged from 4.33% to 17.86% higher than that in mono-cropping systems. Similar increases were found for soil available phosphorus (8.71-15.91%) and soil available potassium (8.65-39.43%) contents. Furthermore, MCDC produced higher grain yields and harvest indexes for both study seasons. CONCLUSION: The integration of MCDC systems had positive effects on soil nutrient contents of paddy fields, which could, in turn, lead to yield enhancements, as well as additional income for farmers in the form of organic duck meat. © 2019 Society of Chemical Industry.