Excessive application of N fertilizer in pursuit of higher yields is common due to poor soil fertility and low crop productivity. However, this practice causes serious soil depletion and N loss in the traditional wheat cropping system in the Loess Plateau of China. Growing summer legumes as the green manure (GM) crop is a viable solution because of its unique ability to fix atmospheric N2. Actually, little is known about the contribution of GM N to grain and N utilization in the subsequent crop. Therefore, we conducted a four-year field experiment with four winter wheat-based rotations (summer fallow-wheat, Huai bean–wheat, soybean–wheat, and mung bean–wheat) and four nitrogen fertilizer rates applied to wheat (0, 108, 135, and 162 kg N/ha) to investigate the fate of GM nitrogen via decomposition, utilization by wheat, and contribution to grain production and nitrogen economy through GM legumes. Here we showed that GM legumes accumulated 53–76 kg N/ha per year. After decomposing for approximately one year, more than 32 kg N/ha was released from GM legumes. The amount of nitrogen released via GM decomposition that was subsequently utilized by wheat was 7–27 kg N/ha. Incorporation of GM legumes effectively replaced 13–48% (average 31%) of the applied mineral nitrogen fertilizer. Additionally, the GM approach during the fallow period reduced the risk of nitrate-N leaching to depths of 0–100 cm and 100–200 cm by 4.8 and 19.6 kg N/ha, respectively. The soil nitrogen pool was effectively improved by incorporation of GM legumes at the times of wheat sowing. Cultivation of leguminous GM during summer is a better option than bare fallow to maintain the soil nitrogen pool, and decrease the rates required for N fertilization not only in the Loess Plateau of China but also in other similar dryland regions worldwide. 相似文献
Although green manure rotation is often used to promote soil fertility and crop yield, the effects of this management practice on the nitrogen or phosphorus balance and the relationship between nutrient balance and the increase in soil nutrients have not been systematically studied.
Materials and methods
We investigated the apparent nitrogen and phosphorus balances and their associations with soil nitrogen and phosphorus increases, respectively, in a 34-year-old experimental site with various green manures and rice rotations using linear and logistic models. Cropping treatments included a rice-rice-winter fallow treatment as a control (RRW) and three green manure rotation treatments: rice-rice-ryegrass (RRR), rice-rice-oil rape (RRO), and rice-rice-Chinese milk vetch (RRC).
Results and discussion
We found that apparent nitrogen and phosphorus balances of RRR, RRO, and RRC were 164, 162, and 149 kg hm?2, which were all significantly lower than 200 kg hm?2 of RRW (P <?0.05). Moreover, the optimal fitted model of the relationship between cumulative nutrient balance and the increase in soil nutrients was different among treatments. Specifically, the correlation coefficients of cumulative nitrogen balance and soil nitrogen increase of RRR, RRO, and RRC in the linear model (0.49, 0.80, and 0.63) were all significantly lower than in the logistic model (0.81, 0.90, and 0.82). The correlation coefficients of cumulative phosphorus balance and increase in soil phosphorus of RRW in the linear model (0.81) were significantly lower than in the logistic model (0.91). Parameter analysis of the optimal fitted model revealed that RRC would increase the storage capacity of soil nitrogen and decrease the rate of soil phosphorus accumulation.
Conclusions
Our results suggested that long-term rice-rice-green manure rotation could significantly change the apparent nitrogen and phosphorus balance and their association with soil nitrogen and phosphorus content, respectively. Our study highlights the importance of green manure rotation in an agro-ecological environment and soil fertility in a double rice cropping system in red paddy soil.
Mat rush (Juncus effusus L.), used for ‘Tatami’ (a traditional Japanese mat), is a type of crop requiring a large amount of fertilizer (450–600 kg ha−1 of N). In a heavily fertilized mat rush paddy field we examined the monitoring of soil water content (θ) by using the water content reflectometer (WCR). WCR sensors with and without coating rods were prepared and tested for their performance in different solutions. In addition, these sensors for Gley Lowland Soils were also calibrated for measuring θ. The results showed that the measured water content using the uncoated WCR, increasing with the EC of the solution, was 1.6 times of that for distilled water while the output for the coated WCR became 1.04 times. The coating prevents conduction losses while it influences the sensitivity of the WCR sensor. The monitoring of θ using both coated and uncoated WCR sensors in a mat rush paddy field was conducted throughout a cropping season. For the coated sensors, water content could be determined accurately even after fertilizer applications, while with the uncoated sensors it was overestimated. Thus, it was concluded that the use of insulated WCR sensors make it possible to accurately monitor the near surface soil moisture in a heavily fertilized paddy field. 相似文献
Soil microbial habitats are altered by mulching, a common practice in urban areas during which vegetation is removed and soils covered to suppress weeds and retain moisture. Soil microorganisms drive nitrogen-cycling processes in mulched soils, because living plants no longer take up ammonium-N released during decomposition of residual organic matter. Because ammonia oxidizers carry out the first, rate-limiting step of nitrification, we compared ammonia oxidizers in experimental, unfertilized plots of mulched and vegetated soils. We hypothesized that mulched and vegetated soils would support contrasting communities of bacterial and archaeal ammonia oxidizers, as determined by quantitative PCR and primers specific for genes encoding ammonia monooxygenase subunit A (amoA). Clone libraries of archaeal amoA also were constructed to compare diversity in soil cores, duplicate blocked plots, and treatments (bark-mulched, gravel-mulched, and unmanaged old field vegetation). Gene copies from ammonia-oxidizing bacteria (AOB) ranged from 2.2 × 106 to 2.7 × 107 gene copies per gram dry soil and did not differ across treatments. In contrast, gene copies from ammonia-oxidizing archaea (AOA) ranged from 9.1 × 105 to 1.0 × 108 copies per gram dry soil, with bark-mulched soils having significantly lower abundance. Community structure of AOA in gravel-mulched soils was distinct from the other two treatments. At 97% amino acid similarity, 22 operational taxonomic units, or OTUs, were identified, with only one OTU found in all 18 clone libraries. This ubiquitous OTU-1, which was highly similar to published amoA sequences recovered from soils, comprised 55% of all 482 translated sequences. Greater variability in OTU richness was observed among cores from mulched soils than from vegetated soils. Our observations supported our hypothesis that AOA communities differ in mulched and vegetated soils, with mulched soils providing altered and variable microniches for these N cycling microorganisms. 相似文献