Estimation of irrigation requirements for drip-irrigated maize in a sub-humid climate

Drip-irrigation is increasingly applied in maize (Zea mays L.) production in sub-humid region. It is critical to quantify irrigation requirements during different growth stages under diverse climatic conditions. In this study, the Hybrid-Maize model was calibrated and applied in a sub-humid Heilongjiang Province in Northeast China to estimate irrigation requirements for drip-irrigated maize during different crop physiological development stages and under diverse agro-climatic conditions. Using dimensionless scales, the whole growing season of maize was divided into diverse development stages from planting to maturity. Drip-irrigation dates and irrigation amounts in each irrigation event were simulated and summarized in 30-year simulation from 1981 to 2010. The maize harvest area of Heilongjiang Province was divided into 10 agro-climatic zones based on growing degree days, arid index, and temperature seasonality. The simulated results indicated that seasonal irrigation requirements and water stress during different growth stages were highly related to initial soil water content and distribution of seasonal precipitation. In the experimental site, the average irrigation amounts and times ranged from 48 to 150 mm with initial soil water content decreasing from 100 to 20% of the maximum soil available water. Additionally, the earliest drip-irrigation event might occur during 3- to 8-leaf stage. The water stress could occur at any growth stages of maize, even in wet years with abundant total seasonal rainfall but poor distribution. And over 50% of grain yield loss could be caused by extended water stress during the kernel setting window and grain filling period. It is estimated that more than 94% of the maize harvested area in Heilongjiang Province needs to be irrigated although the yield increase varied (0 to 109%) in diverse agro-climatic zones. Consequently, at least 14% of more maize production could be achieved through drip-irrigation systems in Heilongjiang Province compared to rainfed conditions.     

畜禽产品水足迹研究进展

畜禽产品的生产过程需要消耗大量水资源,对畜禽产品进行水足迹评价能够清楚地认识其对水资源的消耗情况。目前,人们对畜禽产品的需求日益增长,水资源消耗也在持续升高,因此研究如何缓解畜禽产品生产带来的水资源压力,已成为人们必须要面对的问题。评价畜禽产品的用水量和对不同生产阶段的用水分析,将有助于生产者和消费者确定用水量最大的过程,并针对性地实施提高用水效率的战略。本文介绍了国内外畜禽产品水足迹研究现状,对比分析了不同畜禽产品水足迹评价方法,展望了畜禽产品水足迹的发展,最终提出以下降低畜禽产品水足迹的主要措施:1)减少饲料生产的水足迹;2)提高饲料转化率;3)水资源管理和提高畜禽动物生产性能;4)改变人们的消费习惯。     

Aquaponics and sustainability: The comparison of two different aquaponic techniques using the Life Cycle Assessment (LCA)

Aquaponics is generally regarded as a sustainable practice, but its environmental burdens were not yet deeply investigated. In this study, Life Cycle Assessment (LCA) was used to assess the environmental impacts of two hypothetical coupled aquaponics systems (CAPS): Raft System (RAFT) and Media-Filled Beds System (MFBS). Rainbow trout (Oncorhynchus mykiss) and lettuce (Lactuca sativa) were considered as cultivated species in both systems. The Simapro^© software V.8.0 was used for calculation. The comparison between the two virtual systems indicated the floating technique as the less impacting one. Even though energy consumption appears to be higher in the floating system, LCA results were markedly influenced by the extensive use of inert materials in MFSB. In both systems, contribution analyses underlined that the main environmental impacts are related to infrastructures, electricity and fish feed. The LCA analyses carried out in this study highlights that the choice of less impacting materials, and the optimization of management practices, should be taken as priorities in order to reduce environmental impacts of this activity.     

Efficiency of wheat straw mulching in reducing soil and water losses from three typical soils of the Loess Plateau,China

Mulching the soil surface with a layer of plant residue is considered an effective method of conserving water and soil because it increases water infiltration into the soil, reduces surface runoff and the soil erosion, and reduces flow velocity and the sediment carrying capacity of overland flow. However, application of plant residues increases operational costs and so optimal levels of mulch in order to prevent soil and/or water losses should be used according to the soil type and rainfall and slope conditions. In this study, the effect of wheat straw mulch rate on the total runoff and total soil losses from 60-mm simulated rainstorms was assessed for two intensive rainfalls (90 and 180 mm h⁻¹) on three slope gradients typical conditions on the Loess Plateau of China and elsewhere. For short slopes (1 m), the optimal mulch rate to save water for a silt loam and a loam soil was 0.4 kg m⁻². However, for a clay loam soil the mulch rate of 0.4 kg m⁻² would be optimal only under the 90 mm h⁻¹ rainfall; 0.8 kg m⁻² was required for the 180 mm h⁻¹. In order to save soil, a mulch rate of 0.2 kg m⁻² on the silt loam slopes prevented 60%–80% of the soil losses. For the loam soil, mulch at the rate of 0.4 kg m⁻² was essential in most cases in order to reduce soil losses substantially. For the clay loam, 0.4 kg m⁻² may be optimal under the 90 mm h⁻¹ rain, but 0.8 kg m⁻² may be required for the 180 mm h⁻¹ rainstorm. These optimal values would also need to be considered alongside other factors since the mulch may have value if used elsewhere. Hence doubling the optimal mulch rate for the silt loam soil from 0.2 kg m⁻² or the clay loam soil under 90 mm h⁻¹ rainfall from 0.4 kg m⁻² in order to achieve a further 10% reduction in soil loss needs to be assessed in that context. Therefore, Optimal mulch rate can be an effective approach to virtually reduce costs or to maximize the area that can be treated. Meantime, soil conservationist should be aware that levels of mulch for short slopes might not be suitable for long slopes.     

Bioavailability of dissolved organic carbon across a hillslope chronosequence in the Kuparuk River region,Alaska

Dissolved organic matter (DOM) represents an important component of carbon and nutrient cycling in arctic ecosystems. In northern Alaska, DOM production and microbial activity differ among landscapes with varied glaciation histories with lower rates on younger landscapes. In addition, within the region, soil DOM concentrations vary at the scale of hillslope toposequences, with higher concentrations in upslope than streamside positions. However, it is unknown whether variation in DOM production quality among and within landscapes linked to patterns in DOM quality. To answer this question, we conducted a study of DOM biodegradability within and among hillslopes of different landscape age. We examined rates of DOM decomposition and several indices of the quality of water-extracted DOM collected from soils in the summer. A variety of methods indicated that DOM quality generally was consistent across hillslope positions and among landscape ages. For example, DOM fluorescence index, an index of quality for chromophoric DOM, did not vary significantly across all hillslope positions or landscape ages. There were no significant differences among landscape ages or hillslope positions in DOM specific UV absorbance, in rates of DOM mineralization, or in DOM decomposition, indicating that DOM quality was consistent regardless of its source or position along hillslope flow paths. This suggests that despite many potential sources of variation within and among arctic hillslopes linked to differences in vegetation, hydrology, microclimate, and microbial activity, there is little variation in growing-season soil DOM quality. Microbial processing of DOM within arctic hillslopes may lead to a convergence in growing season DOM quality resulting in little spatial variation. Approximately 10–20% of the growing season DOM is labile in tundra soils, slightly higher that the proportion that is labile in arctic rivers during the summer.     

Evaluation of optical sensor measurements of canopy reflectance and of leaf flavonols and chlorophyll contents to assess crop nitrogen status of muskmelon

Nitrogen losses from intensive vegetal production systems are commonly associated with contamination of water bodies. Sustainable and optimal economic N management requires correct and timely on-farm assessment of crop N status to detect N deficiency or excess. Optical sensors are promising tools for the assessment of crop N status throughout a crop or at critical times. We evaluated optical sensor measurement of canopy reflectance and of leaf flavonols and chlorophyll contents to assess crop N status weekly throughout a muskmelon crop. The Crop Circle ACS 470 was used for reflectance measurement, the SPAD 502 for leaf chlorophyll, and the DUALEX 4 Scientific for leaf chlorophyll and flavonols. Four indices of canopy reflectance (NDVI, GNDVI, RVI, GVI), leaf flavonols and chlorophyll contents and the nitrogen balance index (NBI), the ratio of chlorophyll to flavonols contents, were linearly related to crop N content and to crop Nitrogen Nutrition Index (NNI) throughout most of the crop. NBI most accurately predicted crop N status; in five consecutive weekly measurements, R² values were 0.80–0.95. For NDVI during the same period, R² values were 0.76–0.87 in the first three measurements but R² values in the last two measurements were 0.39–0.45. Similar relationships were found with the three other reflectance indices. Generally, the relationships with NNI were equal to or slightly better than those with crop N content. These optical sensor measurements provided (i) estimation of crop N content in the range 1.5–4.5%, and (ii) an assessment of whether crop N content was sufficient or excessive for optimal crop growth for NNI ranges of 0.8–2.0. Composite equations that integrated the relationships between successive measurements with the optical sensors and crop N content or NNI for periods of ≥2 weeks (often 2–3 weeks) were derived for most indices/parameters. Overall, these results demonstrated the potential for the use of these optical sensor measurements for on-farm monitoring of crop N status in muskmelon.     

Influence of low soil nitrogen and phosphorus on gluten polymeric and monomeric protein distribution in two high quality spring wheat cultivars

The effect of low levels of nitrogen, phosphorus and a combination of the two on the distribution of polymeric and monomeric proteins in two high quality spring bread wheat cultivars was investigated for two consecutive seasons. Size exclusion-high performance liquid chromatography (SE-HPLC) was used to determine the quantity and relationships of monomeric and polymeric proteins, and their relationship with flour protein content (FPC) and SDS sedimentation volume (SDSS). The low nitrogen and combined low nitrogen and low phosphorus treatments had a much larger effect on the protein fractions than the low phosphorus treatment alone. The SDS-soluble large monomeric protein fraction and the percentage SDS-insoluble monomeric proteins, were significantly increased under low nitrogen and a combination of low nitrogen and low phosphorus treatments. The percentage SDS-insoluble large and total polymeric proteins was significantly reduced under low nitrogen and a combination of low nitrogen and phosphorus treatments. The SDS-soluble and -insoluble small polymeric proteins were significantly increased under both low nitrogen and a combination of low nitrogen and low phosphorus treatments. The low nitrogen treatment consistently caused the lowest FPC and SDSS values. Under low nitrogen conditions, there was a significant positive correlation between the SDS-soluble gliadins and SDSS, and FPC.     

Modeling the water and nitrogen transports in a soil–paddy–atmosphere system using HYDRUS-1D and lysimeter experiment

Efficient water and fertilizer use is of paramount importance both in rain-fed and irrigated rice cultivation systems to tread off between the crop water demand during the dry spell and the fertilizer leaching. This lysimeter study on paddy in a lateritic sandy loam soil of the eastern India, to simulate the water and solute transports using the HYDRUS-1D model, reveals that this model could very well simulate the soil depth-specific variations of water pressure heads and nitrogen (N) concentrations with the efficiency of >86 and 89%, respectively. The change in the level of water ponding depth did not have a significant effect on the time to peak and the temporal variability of N concentration in the bottom soil layer. The lysimeter-scale water balance analysis indicated that the average deep percolation loss and crop water use were 35.01 ± 2.03 and 39.74 ± 1.49% of the total water applied during the crop growth period, respectively. Similarly, the amount of N stored in the plant and lost through soil storage, deep percolation, and other losses (mineralization, denitrification, and gaseous N loss to the atmosphere through plant leaves) were 1.60 ± 0.16, 0.17 ± 0.04, 12.00 ± 0.48, and 86.23 ± 0.41% of the total applied nitrogen, respectively. The simulation results reveal that a constant ponding depth of 3 cm could be maintained in paddy fields to reduce the N leaching loss to 7.5 kgN/ha.     

Rate of leaf production in response to soil water deficits in field pea

Plant leaf area is critical for predicting the amount of radiation intercepted by a crop, and thereby, for estimating dry matter production. Under soil water deficit conditions, plant leaf expansion is reduced as a result of both a reduction in the rate of leaf production (RLP) and in the rate of individual leaf expansion. Quantifying the effect of soil water deficits on plant leaf expansion depends in part on predicting its effects on the timing of leaf production. The effect of soil water deficits on RLP was examined for three pea cultivars in greenhouse and field experiments. The level of soil water deficit was characterized as the fraction of transpirable soil water (FTSW). A quantitative function between RLP and FTSW was established in greenhouse experiments and was tested in independent pot and field experiments. A good consistency in this relationship across a diversity of experimental conditions and cultivars was shown. The logistic function obtained represents an effective way to simulate the effects of soil water deficits on RLP, especially as FTSW could be estimated from a soil water balance. RLP was reduced only for FTSW<0.2, and consequently, RLP was less sensitive to soil water deficits than transpiration and leaf expansion. Soil water deficit induced a slight rise in canopy temperature due to stomatal closure. However, this rise in temperature for FTSW<0.4 cannot account for maintaining RLP compared to the drop of transpiration and of leaf expansion rates observed for FTSW between 0.4 and 0.2. RLP can be considered independent of soil water content if FTSW>0.2. In the field, such level of soil water deficit inducing a decrease of RLP occurs generally only after the end of leaf production during the last reproductive stages of pea crop. Thus, except in situations of extreme soil water deficit and on shallow soils, leaf production depends solely on air temperature.