The effects of cultivation patterns and nitrogen levels on fertility and bacterial community characteristics of surface and subsurface soil.

The cropping system affects the physicochemical property and microbial community of paddy soil. Previous research mostly focused on the study of soil 0-20 cm underground. However, there may be difference in the laws of nutrient and microorganism distribution at different depths of arable soil. In surface (0-10 cm) and subsurface (10-20 cm) soil, a comparative analysis including soil nutrients, enzymes, and bacterial diversity was carried out between the organic and conventional cultivation patterns, low and high nitrogen levels. Analysis results suggested that under the organic farming pattern, the contents of total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP), and soil organic matter (SOM) as well as alkaline phosphatase and sucrose activity increased in surface soil, but the SOM concentration and urease activity decreased in subsurface soil. A moderate reduction of nitrogen applied to soil could enhance soil enzyme activity. It was demonstrated by α diversity indices that high nitrogen levels remarkably undermined soil bacterial richness and diversity. Venn diagrams and NMDS analysis manifested great difference in bacterial communities and an apparent clustering tendency under different treatment conditions. Species composition analysis indicated that the total relative abundance of Proteobacteria, Acidobacteria, and Chloroflexi retained stable in paddy soil. LEfSe results revealed that a low nitrogen organic treatment could elevate the relative abundance of Acidobacteria in surface soil and Nitrosomonadaceae in subsurface soil, thereby tremendously optimizing the community structure. Moreover, Spearman's correlation analysis was also performed, which proved the significant correlation of diversity with enzyme activity and AN concentration. Additionally, redundancy analysis disclosed that the Acidobacteria abundance in surface soil and Proteobacteria abundance in subsurface soil exerted conspicuous influence on environmental factors and the microbial community structure. According to the findings of this study, it was believed that reasonable nitrogen application together with an organic agriculture cultivation system could effectively improve soil fertility in Gaoyou City, Jiangsu Province, China.

Effect of Digestate and Straw Combined Application on Maintaining Rice Production and Paddy Environment.

Few studies have focused on the combined application of digestate and straw and its feasibility in rice production. Therefore, we conducted a two-year field experiment, including six treatments: without nutrients and straw (Control), digestate (D), digestate + fertilizer (DF), digestate + straw (DS), digestate + fertilizer + straw (DFS) and conventional fertilizer + straw (CS), to clarify the responses of rice growth and paddy soil nutrients to different straw and fertilizer combinations. Our results showed that digestate and straw combined application (i.e., treatment DFS) increased rice yield by 2.71 t ha-1 compared with the Control, and digestate combined with straw addition could distribute more nitrogen (N) to rice grains. Our results also showed that the straw decomposition rate at 0 cm depth under DS was 5% to 102% higher than that under CS. Activities of catalase, urease, sucrase and phosphatase at maturity under DS were all higher than that under both Control and CS. In addition, soil organic matter (SOM) and total nitrogen (TN) under DS and DFS were 20~26% and 11~12% higher than that under B and DF respectively, suggesting straw addition could benefit paddy soil quality. Moreover, coupling straw and digestate would contribute to decrease the N content in soil surface water. Overall, our results demonstrated that digestate and straw combined application could maintain rice production and have potential positive paddy environmental effects.

[Effects of combined applications of pig farm slurry and chemical fertilizer on medium- and micro-element contents and quality of wheat].

Taking Yangmai 18, widely cultivated in south of Huaihe River, as experimental material, this study investigated the effects of application of 0, 30, 60, 90 and 120 m3 x hm(-2) pig farm slurry (PS) at the wintering stage combined with the application of 0, 30, 60, 90 kg x hm(-2) urea at the heading stage on medium- and micro-element contents and quality of wheat. The results showed that the Ca, Mg and Fe contents of plant firstly decreased then increased with the extension of the growth period, but the Cu, Zn and Mn contents decreased continuously through the growth period. Ca, Mg, Cu and Zn reached the highest value at every growth stage except the jointing stage when applying 120 m3 x hm(-2) PS with 90 kg x hm(-2) urea. Fe and Mn reached the highest value at every growth stage when applying 120 m3 x hm(-2) PS with 90 kg x hm(-2) urea. The contents of Ca, Mg, Cu, Zn, Fe and Mn all increased with increasing PS application across the growth period. Regarding the quality of wheat, applying 90 m3 x hm(-2) PS with 60 kg x hm(-2) urea was the best fertilization pattern. Combined applications of anaerobically treated PS with N fertilizer could increase medium- and micro-element contents and quality of wheat. Generally, it was recommended to apply 60-120 m3 x hm(-2) PS at the wintering stage and 90 kg x hm(-2) urea at the heading stage under field conditions.

[Hyperspectral remote sensing diagnosis models of rice plant nitrogen nutritional status].

The correlations of rice plant nitrogen content with raw hyperspectral reflectance, first derivative hyperspectral reflectance, and hyperspectral characteristic parameters were analyzed, and the hyperspectral remote sensing diagnosis models of rice plant nitrogen nutritional status with these remote sensing parameters as independent variables were constructed and validated. The results indicated that the nitrogen content in rice plant organs had a variation trend of stem < sheath < spike < leaf. The spectral reflectance at visible light bands was leaf < spike < sheath < stem, but that at near-infrared bands was in adverse. The linear and exponential models with the raw hyperspectral reflectance at 796.7 nm and the first derivative hyperspectral reflectance at 738.4 nm as independent variables could better diagnose rice plant nitrogen nutritional status, with the decisive coefficients (R2) being 0.7996 and 0.8606, respectively; while the model with vegetation index (SDr - SDb) / (SDr + SDb) as independent variable, i. e., y = 365.871 + 639.323 ((SDr - SDb) / (SDr + SDb)), was most fit rice plant nitrogen content, with R2 = 0.8755, RMSE = 0.2372 and relative error = 11.36%, being able to quantitatively diagnose the nitrogen nutritional status of rice.

[Dynamic model of rice tiller in FACE].

With Japonica cultivar Wuxiangjing 14 as test material, a free-air CO2 enrichment (FACE) experiment was conducted at Anzhen and Wuxi of Jiangsu Province in 2001 to approximately 2003. The target CO2 concentration of FACE plots was 570 micromol x mol(-1), 200 micromol x mol(-1) higher than that of ambient air. Three levels of N were supplied as LN (150 kg x hm(-2)), MN (250 kg x hm(-2)) and HN (350 kg x hm(-2)). The effects of FACE treatment on the dynamics of rice tiller was studied, and the simulation model was established as Tt = ((A1/1 + e(a1-b1t)) - (A2/1 + e(a2-b2t)) + C) x ((B1/(1 + e(a3-b3t) - (B2/1 + e(a4-b4t))+D) Where Tt was the numbers of rice tiller in t days after transplanting; A1 and A2 were the maximal tillers of production and death under ambient air, respectively; B1 and B2 were the maximal potential tillers of production and death under FACE, respectively; C was the coefficient of CO2 concentration; D was the initial tillers after transplanting; and a1, a2, a3, a4, b1, b2, b3 and b4 were the control coefficients of the model. The dynamics of tiller numbers with the days after transplanting was described, and the model fitted well under ambient air and FACE conditions. Through testing with different year experimental data, the maximum and minimum RMSE was forecasted as 44.27 and 13.96 ind x m(-2), respectively, suggesting that the model was accurate and applicable.

[Dry matter accumulation and allocation models of rice in FACE].

A fertilization experiment with 150 kg N x hm(-2), 250 kg N xhm(-2) and 350 kg N x hm(-2) was conducted on the free-air CO2 enrichment (FACE) platform at Wuxi of Jiangsu Province in 2001-2003, aimed to build a simulation model of dry matter accumulation and allocation of rice in FACE. Physiological development time and CO2 concentration were selected as the driving factor and the main affecting factor, respectively, and nitrogen application rate was introduced as the factor adjusting the dry matter accumulation and allocation in green leaf, stem and panicle. The results showed that with the increase of atmospheric CO2 concentration, the dry matter accumulation in above-ground part of rice increased remarkably, but the allocation index dropped in green leaf, changed little in panicle, while increased in stem at early stage and equaled to the CK at last. The model was tested with different experimental data, and the results indicated that the model had high fitting degree and preferable applicability and predictability.