Application of the Simple Biosphere Model 2 (SiB2) with Irrigation Module to a Typical Low-Hilly Red Soil Farmland and the Sensitivity Analysis of Modeled Energy Fluxes in Southern China

Land surface processes are an important part of the Earth’s mass and energy cycles. The application of a land surface process model for farmland in the low-hilly red soil region of southern China continues to draw research attention. Conventional model does not perform well in the simulation of irrigated farmland, because the influence of land surface water is not considered. In this study, an off-line version of the Simple Biosphere model 2 (SiB2) was locally parameterized in a typical farmland of the low-hilly red soil region using field observations and remote sensing data. The performance of SiB2 was then evaluated through comparison to Bowen-ratio direct measurements in a second growing period of rice in 2015 (late rice from 23 July to 31 October). The results show that SiB2 underestimated latent heat flux (LE) by 16.0% and overestimated sensible heat flux (H) by 16.7%, but net radiation flux (Rn) and soil heat flux were reasonably simulated. The single factor sensitivity analysis of Rn, H, and LE modeled in SiB2 indicated that downward shortwave radiation (DSR) and downward longwave radiation (DLR) had a significant effect on Rn simulation. In driving data, DSR, DLR and wind speed (u) were the main factors that could cause a distinct change in sensible heat flux. An irrigation module was added to the original SiB2 model to simulate the influence of irrigated paddy fields according to the sensitivity analysis results of the parameters (C1, bulk boundary-layer resistance coefficient; C2, ground to canopy air-space resistance coefficient; and Ws, volumetric water content at soil surface layer). The results indicate that application of the parameterized SiB2 with irrigation module could be better in southern Chinese farmland

Determination of comprehensive quality index for tomato and its response to different irrigation treatments

In order to investigate better irrigation scheduling with the compromise between yield and quality of greenhouse-grown tomato under limit water supply, two experiments of different irrigation treatments were conducted in the arid region of northwest China during spring to summer in 2008 (2008 season) and winter in 2008 to summer in 2009 (2008-2009 season). After measuring single quality attributes, the analysis hierarchy process (AHP) and technique for order preference by similarity to an ideal solution (TOPSIS) were used to determine the weight of single quality attributes and comprehensive quality index, respectively. The results show that the rank of comprehensive quality index had good fitness to that of single quality attributes, indicating that the comprehensive quality index was reliable. Compared to full irrigation, applying 1/3 or 2/3 of full irrigation amount at the seedling stage had slight improvement of comprehensive quality and limit water saving. Applying 1/3 or 2/3 of full irrigation amount at the fruit maturation and harvesting stage decreased the yield by 23.0-40.9%, but had the best comprehensive quality. However, applying 1/3 of full irrigation amount at the flowering and fruit development stage significantly reduced crop water consumption and had obvious improvement of comprehensive quality, but did not decrease the yield significantly and water use efficiency in the 2008 season. And applying 2/3 of full irrigation amount at the flowering and fruit development stage significantly decreased crop water consumption and slightly improved the comprehensive quality, but did not decrease the yield significantly in the 2008-2009 season. Considering the water saving amount, yield and comprehensive quality, applying 1/3 or 2/3 of full irrigation amount at the flowering and fruit development stage and no water stress in other growth stages appears to be a better irrigation scheduling with the compromise between yield and quality of greenhouse-grown tomato, which can be recommended for the spring to summer and winter to summer seasons in the arid region of northwest China.Tomato Comprehensive quality index AHP TOPSIS Greenhouse Irrigation scheduling

Effects of Nitrogen Application in Recovery Period after Different High Temperature Stress on Plant Growth of Greenhouse Tomato at Flowering and Fruiting Stages

High temperatures have become a severe factor limiting growth and yield for tomatoes (Lycopersicon esculentum Mill.) due to unfavorable, above-optimum temperatures. Temperature and nitrogen application were the main regulatory factors in tomato plant cultivation. This research was undertaken to evaluate the effects of nitrogen application and high temperature on tomato morphology, dry matter accumulation and distribution, root vitality and nitrogen content of the above ground. Tomato variety “Jinfen No. 1” was planted and exposed to 4 day/night temperature levels (25 °C/15 °C as control CKT; 30 °C/20 °C, lightly high-temperature LHT; 35 °C/25 °C, moderate high-temperature MHT; 40 °C/30 °C, severe high temperature SHT) for 7 days after five nitrogen supply levels (N1–N5: 0, 1.3, 1.95, 2.6 and 3.75 g/plant, respectively; 2.6 g/plant is the recommended nitrogen-application rate, as control CKTN4). Within conditions, there was an extremely significant difference (p p < 0.01) between high temperatures and nitrogen supply levels, except for plant height sampling on the 1st day in the recovery period. Dry matter accumulation decreased, and the accumulation rate slowed down. Dry matter accumulation under low nitrogen treatment was higher than in high nitrogen treatment. The proportion of dry matter in leaves decreased, the proportion of dry matter in stems increased and the difference in dry matter accumulation and proportion of dry matter between different nitrogen treatments decreased. Under LHT, the root activity of the tomato was increased under all nitrogen levels, while under MHT and SHT, high nitrogen and low nitrogen supply significantly inhibited root activity. Lightly high-temperature stress can increase root activity, and LHTN4 can increase by 5.15% compared with CKTN4. Appropriate nitrogen application can alleviate the damage caused by high-temperature stress on tomato plants and enhance the resistance of tomato plants, while excessive nitrogen application will aggravate the damage degree of tomato plants. In this study, the optimal nitrogen application rates under CKT-SHT treatment were 2.6, 2.6, 1.95 and 1.3 g/plant, respectively

Role of Hydraulic Signal and ABA in Decrease of Leaf Stomatal and Mesophyll Conductance in Soil Drought-Stressed Tomato

Drought reduces leaf stomatal conductance (gs) and mesophyll conductance (gm). Both hydraulic signals and chemical signals (mainly abscisic acid, ABA) are involved in regulating gs. However, it remains unclear what role the endogenous ABA plays in gm under decreasing soil moisture. In this study, the responses of gs and gm to ABA were investigated under progressive soil drying conditions and their impacts on net photosynthesis (An) and intrinsic water use efficiency (WUEi) were also analyzed. Experimental tomato plants were cultivated in pots in an environment-controlled greenhouse. Reductions of gs and gm induced a 68–78% decline of An under drought conditions. While soil water potential (Ψsoil) was over −1.01 MPa, gs reduced as leaf water potential (Ψleaf) decreased, but ABA and gm kept unchanged, which indicating gs was more sensitive to drought than gm. During Ψsoil reduction from −1.01 to −1.44 MPa, Ψleaf still kept decreasing, and both gs and gm decreased concurrently following to the sustained increases of ABA content in shoot sap. The gm was positively correlated to gs during a drying process. Compared to gs or gm, WUEi was strongly correlated with gm/gs. WUEi improved within Ψsoil range between −0.83 and −1.15 MPa. In summary, gs showed a higher sensitivity to drought than gm. Under moderate and severe drought at Ψsoil ≤ −1.01 MPa, furthermore from hydraulic signals, ABA was also involved in this co-ordination reductions of gs and gm and thereby regulated An and WUEi

Partitioning of available energy in canopy and soil surface in croplands with different irrigation methods

Available energy partitioning in the canopy and at the soil surface under the control of biophysical environment critically influences agricultural water resources management and the regional climate. Drip irrigation technology has been extensively promoted in arid regions and is gradually replacing conventional border irrigation technology, which alters the soil surface hydrothermal conditions and influences the available energy partitioning both in canopy and at the soil surface through biophysical processes. The water-saving effect of drip irrigation has been well studied previously, however, its biophysical controls of available energy partitioning in canopy and soil surface remain insufficiently understood. In this study, we made continuous comparative measurements in two maize fields with border irrigation and drip irrigation during the growing seasons in the period 2014–2018 by simultaneously using eddy covariance systems, sap flow gauges and micro-lysimeters. We found that drip irrigation increased transpiration by 10% and reduced soil evaporation by 40% during the partial canopy period, and these values decreased to 1% and 26%, respectively as the crop developed to complete canopy cover period. However, drip irrigation increased sensible heat fluxes both in canopy and soil surface by 93% and 46%, respectively during the partial canopy period, and by 10% and 231%, respectively during the complete canopy period. The soil moisture drives the discrepancy of available energy partitioning in both canopy and soil surface between two fields. Slow-release effect of the drip irrigation in replacing warm air in soil pores enhanced thermal convection in soil surface, small irrigation volume and small moisture area decreased evaporation loss, and frequent irrigation and sufficient soil moisture induced stable energy interaction between canopy and soil surface, therefore enhancing more sensible heat directed to canopy and soil surface in drip irrigated field. The results enhanced understanding of ecohydrology processes in agroecosystems and provided valuable information for agricultural water resource management

Assessing suitability of major meteorological factors for facility agriculture in mainland China

In China, more than two-thirds of protected cultivation occurs in low-tech facilities with limited ability to withstand adverse weather conditions. However, the specific meteorological factors that hinder facility agriculture production in various locations remain unclear. Here, we evaluated temperature and sunlight for assessing facility agriculture suitability in mainland China across different transplanting dates and ENSO phases (El Niño, La Niña, and Neutral) and to determine the optimal transplanting window. This aids in reducing climatic risks, and enhancing adaptation to changing climates. The results showed that growth cycles starting from March to June provide suitable temperature and sunlight, making them ideal transplanting window for many parts of northern China. However, both El Niño and La Niña significantly increased the high-temperature days and shortened the optimal transplanting window. For growth cycles starting from July to the following January, low temperatures are the primary factor limiting facility agriculture production in northern and western China. In southern China, sparse sunlight is the primary limiting factor year-round, and El Niño exacerbates this, particularly for growth cycles starting from September to November. This combined assessment of major meteorological factors, transplanting dates, ENSO phases, and regions, can assist decision-makers and growers in adapting to the changing climate and minimizing production risks

Effect of Irrigation Regimes and Soil Texture on the Potassium Utilization Efficiency of Rice

Understanding the effects of irrigation regime and soil texture on potassium-use efficiency (KUE) of rice (Oryza sativa. L) is essential for improving rice productivity. In this regard, experiments were conducted from July to October in 2016 and 2017 by using a randomized complete block design in a factorial arrangement with four replications. The rice plants were grown in three soils, with clay contents of 40%, 50%, and 60%, which were marked as S (40%), S (50%), and S (60%), respectively. For each soil type, irrigation regimes, namely, R (F, S100%), R (F, S90%), and R (F, S70%), were established by setting the lower limit of irrigation to 100%, 90%, and 70% of saturated soil water content, respectively, and the upper limit of irrigation with 30 mm of flooding water above the soil surface for all irrigation regimes. Results showed that the responses of the roots and shoots and the potassium accumulation (KA) and KUE of rice were significantly affected by the water regime and soil texture. In the same irrigation regime, increasing the soil clay content improved the K utilization of rice. Under the same soil type, R (F, S100%) was the optimal water management practice for growing rice. The R (F, S100%) S (60%) treatment presented the highest KUE, which was 56.4% in 2016 and 68.1% in 2017. The R (F, S70%) S (40%) treatment showed the lowest KUE, which was 13.8% in 2016 and 14.9% in 2017. These results enrich knowledge regarding the relationship among soil, water, and rice, and provide valuable insights on the effect of irrigation regime and soil texture on the KA and KUE of rice

Inter-comparison of the Penman-Monteith type model in modeling the evapotranspiration and its components in an orchard plantation of Southwest China

Crop evapotranspiration (ET) along with its components (canopy transpiration (T) and soil evaporation (E)) estimates are crucial for agroecosystem hydrological process research and developing agricultural water-saving strategies. An inter-comparison of the Penman-Monteith type model, including Penman-Monteith (PM), Shuttleworth-Wallace (S-W), Two-Patch (T-P) and topography- and vegetation-based surface energy partitioning algorithm (TVET), Clumping (CL) and developed Two patch-Two layer (T-T) model was conducted to estimate ET and its components in a kiwifruit orchard. Results showed that all models can well capture the pattern of eddy covariance-based hourly ET (ETEC), with a slope of 0.82–1.10, R2 of 0.78–0.83, and RMSE of 0.039–0.049 mm 0.5 h–1, and yield relatively reliable estimates validated by sap flow-based hourly T, with a slope of 0.93–1.16, R2 of 0.72–0.79, and RMSE 0.017–0.026 mm 0.5 h–1. All the P-M type models agreed well with the daily ETEC, with a slope of 0.88–1.21, R2 of 0.82–0.86, and RMSE of 0.55–0.88 mm d–1, respectively. S-W overestimated actual ET due to overestimation in both T and E, T-P and TVET models overestimated T but underestimated actual E as they ignored the soil contribution under the canopy. T-T model outperformed other models in daily ET, T, and E estimates, with R2 of 0.86, 0.73 and 0.73, and RMSE of 0.56, 0.39 and 0.46 mm d–1, respectively. The output ET and T of the different P-M type models were most sensitive to canopy resistance (rsc), while E is most sensitive to aerodynamic resistance between substrate and crop canopy. Net radiation was the most crucial meteorological factor affecting ET, T and E, as it directly participated in the energy balance calculation. The output T was sensitive to air temperature since it affected rsc, while E was relatively sensitive to soil water content since it greatly changed soil surface resistance

Evapotranspiration partitioning based on underlying conductance in a complex tree-grass orchard ecosystem in the humid area of southern China

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