Fucang Zhang

Benefits of CO2 enrichment on crop plants are modified by soil water status

Three species, wheat, maize and cotton, were grown in pots and subjected to high (85–100% field capacity, ΘF), medium (65–85% ΘF) and low (45–65% ΘF) soil moisture treatments and high (700 μl l−1) and low (350 μl l−1) CO2 concentrations. Biomass production, photosynthesis, evapotranspiration and crop water use efficiency were investigated. Results showed that the daily photosynthesis rate was increased more in wheat and cotton at high [CO2] than in maize. In addition, differences were more substantial at low soil water treatment than at high soil water treatment. The daily leaf transpiration was reduced significantly in the three crops at the high CO2 concentration. The decrease at low soil water was smaller than at high soil water. Crop biomass production responses showed a pattern similar to photosynthesis, but the CO2-induced increase was more pronounced in root production than shoot production under all soil water treatments. Low soil water treatment led to more root biomass under high [CO2] than high soil water treatment. CO2 enrichment caused a higher leaf water use efficiency (WUE) of three crops and the increase was more significant in low than in high soil water treatment. Crop community WUE was also increased by CO2 enrichment, but the increase in wheat and cotton was much greater than in maize. We conclude that at least in the short-term, C3 plants such as wheat and cotton may benefit from CO2 enrichment especially under water shortage condition.

A simulation model of water dynamics in winter wheat field and its application in a semiarid region

Abstract Many models for water flow in cropped soil contain parameters such as rooting density, root permeability, and root water potential. Usually these parameters are chosen by trial-and-error method and direct measurements are difficult and impractical in some cases. This study presents a simulation model capable of analyzing water transport dynamics in a soil–plant–atmosphere continuum (SPAC). This model is developed by combining an existing mathematical model for soil water flow, a modified transpiration model taking into account of the air pressure and diurnal changes of the extinction coefficient of crop canopies, and a new simple model for root water uptake. Using data from lysimeters in a field experiment carried out on a wheat crop, we also developed two new empirical equations for the estimation of total canopy resistance and soil evaporation. We then applied the model for 2 years (1990–1991, 1991–1992) on winter wheat in a semiarid area of northwest China. Required parameters, particularly soil hydraulic and crop parameters, were determined by field and laboratory tests. Outputs from the simulation were in good agreement with the independent field measurements of seasonal changes in soil water content, canopy transpiration, surface evaporation, and root water uptake along the soil profile. In addition, this simulation agreed well with the actual measurements of seasonal crop water consumption and soil water balance among the treatments for different irrigation amounts.

Effects of alternate partial root-zone irrigation on soil microorganism and maize growth

Partial root-zone irrigation creates a dynamic heterogeneous distribution of soil moisture that may affect the numbers and activities of soil microorganisms. In this study, three irrigation methods, i.e. conventional irrigation (CI), alternate partial root-zone irrigation (APRI, alternate watering on both sides of the pot) and fixed partial root-zone irrigation (FPRI, fixed watering on one side of the pot), and three watering levels, i.e. well-watered, mild and severe water deficit, were applied on pot-grown maize. Numbers of soil microorganisms, plant height, stalk diameter, leaf area and biomass accumulation were monitored over the treatment period. A quadratic parabola relationship between the number of soil microorganisms and soil water content was found, indicating the number of soil microorganisms reached a peak at the mild soil water deficit condition, possibly due to better soil aeration. The peak number of soil microorganism was obtained when soil water content was 66, 79 and 75% of field capacity for CI, FPRI and APRI, respectively. Soil microorganisms were evenly distributed in both sides of APRI and their total numbers were always higher than those under other two irrigation methods for the same soil water content. The count of soil microorganisms in the dry root zone of FPRI was reduced by a lack of water. Maximum biomass accumulation was obtained under well watered condition but severe water deficit led to a 50% reduction in the CI treatment. Such reduction was much smaller under APRI and therefore the highest water use efficiency was obtained. Our results suggest that APRI maintained the best aeration and moisture condition in the soil and enhanced the activities of soil microorganisms, which might also have benefited the plant growth.

Effects of shallow water table on capillary contribution, evapotranspiration, and crop coefficient of maize and winter wheat in a semi-arid region

A lysimeter experiment was conducted during 19866—96 to study the impacts of groundwater tables on the capillary contribution, evapotranspiration, and crop coefficient of maize and winter wheat grown in a semi-arid region in loess loam soils. The depth of groundwater table was set to 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, and 2.50 m, respectively. The results showed that the rate of capillary contribution from groundwater to crop root-zone was influenced mainly by the depth of the water tables. The daily variation in capillary contribution was not the same as pan evaporation; the peak was delayed when the water table was >0.8 m, and the time of delay increased with the depth of water table. The crop evapotranspiration was decreased with increasing groundwater table in the early growth period and harvest period. The maximum evapotranspiration occurred at 1.2 m groundwater table in the other periods. Values of crop coefficients (K c ) were estimated based on the measured evapotranspiration (ET) and reference crop ET computed by the modified Penman method. The estimated K c was significantly different from the values computed and used in the region in the absence of groundwater table effects, and it varied markedly with groundwater tables. Relationships between the crop coefficient and the depth of groundwater table were developed using mean crop coefficients derived from multi-year data. It was found that linear model was better for the period Octobermp;mdash;February in the winter wheat growing season and June in the summer maize growing season. The polynomial model was suitable for the period March;mdahs;June in the winter wheat growing season and from July to October in the summer maize growing season.

Alternate Application of Osmotic and Nitrogen Stresses to Partial Root System: Effects on Root Growth and Nitrogen Use Efficiency

ABSTRACT Effects of alternately applying osmotic and nitrogen (N) stresses to partial root zone were studied on maize seedlings. The maize seedlings were grown in Hoaglands nutrient solution with the roots divided equally into two containers. Half of the root system was subjected to an osmotic stress (W) using PEG 6000 added in the solution at −0.2 MPa and/or nitrogen stress (N) with the N-free Hoaglands solution. After 6 days, four of such treatments, C (control), W, N, and WN were shifted to the other halves of the root systems. Results showed that when compared to the control, total root dry weight and the root/shoot ratio increased markedly for all the stress treatments. There were no statistically significant differences in shoot biomass and N accumulation of the whole plant among all the treatments. Nitrogen use efficiency for the N and WN was significantly enhanced when compared to the C and W treatments, and the shoot N concentrations were less for N and WN than for C and W. The root vitality of the non-treated halves under the W, N, or WN treatments increased by 21.1–65.6% when compared to the other halves of the same root system or by 19.7–68.9% when compared to the control roots. Such a compensation of root function was evident during our days 1, 3, and 5 observations. After each alternation, rates of biomass accumulation of all previously stressed half root systems were significantly higher than the other halves or the controls. Our results suggested that significant compensation mechanisms of growth and functions in the root system occurred both when N and osmotic stresses were localized in part of the root system and during the subsequent recovery from either of such stresses.

Optimization of Controlled Water and Nitrogen Fertigation on Greenhouse Culture of Capsicum annuum

This study investigated the effects of different combinations of irrigation and nitrogen levels on the growth of greenhouse sweet peppers, assessing yield, quality, water use efficiency (WUE), and partial factor productivity from applied N (PFPN). By using controlled drip irrigation, the optimal conditions for efficient, large-scale, high-yield, and high quality production of sweet peppers in Northwest China were determined. Using the local conventional irrigation and nitrogen regime as a control (105% ET0, N: 300 kg·hm−2), three alternative irrigation levels were also tested, at 90%, 75%, and 60% ET0. These were combined with nitrogen levels at 100%, as the control, and 75%, 50%, and 25%, resulting in 16 combination treatments. The results show that different supplies of water and nitrogen nutrition had a significant impact on the growth, yield, WUE, PFPN, and quality of fruit. The treatments of W0.90N0.75, W0.90N0.50, W0.75N0.75, and W0.75N0.50 can better maintain the “source-sink” relationship of peppers. They increased the economic yield, WUE, and PFPN. A principal component analysis was performed to evaluate indicators of fruit quality, revealing that the treatment of W0.75N0.50 resulted in the best fruit quality. For greenhouse sweet peppers produced in Northwest China, the combination of W0.90N0.75 resulted in the highest economic yield of 34.85 kg·hm−2. The combination of W0.75N0.75 had the highest WUE of 16.50 kg·m−3. The W0.75N0.50 combination treatment had the highest fruit quality score. For sustainable ecological development and in view of limited water resources in the area, we recommend the W0.75N0.50 combination treatment, since it could obtain the optimal fruit quality, while its economic yield and WUE were 9% and 4% less than the maximum, respectively. This study provides a theoretical basis for the optimal management of water and nitrogen during production of greenhouse sweet peppers in Northwest China.