Wangsheng Gao

Recharge and groundwater use in the North China Plain for six irrigated crops for an eleven year period.

Water tables are dropping by approximately one meter annually throughout the North China Plain mainly due to water withdrawals for irrigating winter wheat year after year. In order to examine whether the drawdown can be reduced we calculate the net water use for an 11 year field experiment from 2003 to 2013 where six irrigated crops (winter wheat, summer maize, cotton, peanuts, sweet potato, ryegrass) were grown in different crop rotations in the North China Plain. As part of this experiment moisture contents were measured each at 20 cm intervals in the top 1.8 m. Recharge and net water use were calculated based on these moisture measurement. Results showed that winter wheat and ryegrass had the least recharge with an average of 27 mm/year and 39 mm/year, respectively; cotton had the most recharge with an average of 211 mm/year) followed by peanuts with 118 mm/year, sweet potato with 76 mm/year, and summer maize with 44 mm/year. Recharge depended on the amount of irrigation water pumped from the aquifer and was therefore a poor indicator of future groundwater decline. Instead net water use (recharge minus irrigation) was found to be a good indicator for the decline of the water table. The smallest amount of net (ground water) used was cotton with an average of 14 mm/year, followed by peanut with 32 mm/year, summer maize with 71 mm/year, sweet potato with 74 mm/year. Winter wheat and ryegrass had the greatest net water use with the average of 198 mm/year and 111 mm/year, respectively. Our calculations showed that any single crop would use less water than the prevalent winter wheat summer maize rotation. This growing one crop instead of two will reduce the decline of groundwater and in some rain rich years increase the ground water level, but will result in less income for the farmers.

Effects of Subsoiling on Soil Moisture Under No-Tillage for Two Years

Abstract In order to improve the water use efficiency under conservation tillage, the effects of subsoiling on soil moisture under no-tillage were studied. An experiment of 40 cm subsoiling in a field kept under no-tillage for 2 years was operated from 2005 to 2006. Based on the data of the soil moisture and crop yield, the physical basis of subsoiling for water conservation and yield increase was analyzed. The results showed that the soil water storage under subsoiling, from the soil surface to a depth of 100 cm was more than that under no-tillage for the growth season. In the 0–100 cm soil depth, the soil moisture in 50–100 cm depth under subsoiling was more compared with no-tillage, which increased when its drought and decreased when its rainy with the increase in soil depth. Compared with no-tillage, subsoiling could reduce the water consumption of oats in the 0–50 cm depth and increase the water consumption in the 50–100 cm depth. Also, subsoiling increased the yield by 18.29% and the water use efficiency by 16.8% in a two-year average. The effects of subsoiling on water conservation and yield increase were affected by precipitation, and a well-proportioned rainfall was better to increase yield and water use efficiency. Meanwhile, subsoiling decreased bulk density, which increased with the available precipitation. Subsoiling under no-tillage is the effective rotation tillage to contain more soil moisture and improve water use efficiency in ecotone of North China.

Review of Current Status and Research Approaches to Nitrogen Pollution in Farmlands

In this paper, the history, current status, and research approaches to nitrogen pollution were reviewed using systems analysis and deductions. The seriousness of N pollution world-wide was highlighted and recommendations were made to address the situation. A new hypothesis based on phytoremediation, which means the use of plants to directly or indirectly degrade or remove contaminats from soil and water, was proposed.

Subsoiling and Ridge Tillage Alleviate the High Temperature Stress in Spring Maize in the North China Plain

Abstract High temperature stress (HTS) on spring maize ( Zea mays L.) during the filling stage is the key factor that limits the yield increase in the North China Plain (NCP). Subsoiling (SS) and ridge tillage (R) were introduced to enhance the ability of spring maize to resist HTS during the filling stage. The field experiments were conducted during the 2011 and 2012 maize growing seasons at Wuqiao County, Hebei Province, China. Compared with rotary tillage (RT), the net photosynthetic rate, stomatal conductance, transpiration rate, and chlorophyll relative content (SPAD) of maize leaves was increased by 40.0, 42.6, 12.8, and 29.7% under SS, and increased by 20.4, 20.0, 5.4, and 14.2% under R, repectively. However, the treatments reduce the intercellular CO 2 concentration under HTS. The SS and R treatments increased the relative water content (RWC) by 11.9 and 6.2%, and the water use efficiency (WUE) by 24.3 and 14.3%, respectively, compared with RT. The SS treatment increased the root length density and soil moisture in the 0-80 cm soil profile, whereas the R treatment increased the root length density and soil moisture in the 0-40 cm soil profile compared with the RT treatment. Compared with 2011, the number of days with temperatures ⩾33°C was more 2 d and the mean day temperature was higher 0.9°C than that in 2012, whereas the plant yield decreased by 2.5, 8.5 and 10.9%, the net photosynthetic rate reduced by 7.5, 10.5 and 18.0%, the RWC reduced by 3.9, 5.6 and 6.2%, and the WUE at leaf level reduced by 1.8, 5.2 and 13.1% in the SS, R and RT treatments, respectively. Both the root length density and the soil moisture also decreased at different levels. The yield, photosynthetic rate, plant water status, root length density, and soil moisture under the SS and R treatments declined less than that under the RT treatment. The results indicated that SS and R can enhance the HTS resistance of spring maize during the filling stage, and led to higher yield by directly improving soil moisture and root growth and indirectly improving plant water status, photosynthesis and grain filling. The study can provide a theoretical basis for improving yield of maize by adjusting soil tillage in the NCP.

Soil Nitrous Oxide Emissions Under Maize-Legume Intercropping System in the North China Plain

Many studies have focused on various agricultural management measures to reduce agricultural nitrous oxide (N2O) emission. However, few studies have investigated soil N2O emissions in intercropping systems in the North China Plain. Thus, we conducted a field experiment to compare N2O emissions under monoculture and maize-legume intercropping systems. In 2010, five treatments, including monocultured maize (M), maize-peanut (MP), maize-alfalfa (MA), maize-soybean (MS), and maize-sweet clover (MSC) intercropping were designed to investigate this issue using the static chamber technique. In 2011, M, MP, and MS remained, and monocultured peanuts (P) and soybean (S) were added to the trial. The results showed that total production of N2O from different treatments ranged from (0.87±0.12) to (1.17±0.11) kg ha−1 in 2010, while those ranged from (3.35±0.30) to (9.10±2.09) kg ha−1 in 2011. MA and MSC had no significant effect on soil N2O production compared to that of M (P<0.05). Cumulative N2O emissions from MP in 2010 were significantly lower than those from M, but the result was the opposite in 2011 (P<0.05). MS significantly reduced soil N2O emissions by 25.55 and 48.84% in 2010 and 2011, respectively (P<0.05). Soil N2O emissions were significantly correlated with soil water content, soil temperature, nitrification potential, soil NH4+, and soil NO3− content (R2=0.160-0.764, P<0.01). A stepwise linear regression analysis indicated that soil N2O release was mainly controlled by the interaction between soil moisture and soil NO3− content (R2=0.828, P<0.001). These results indicate that MS had a coincident effect on soil N2O flux and significantly reduced soil N2O production compared to that of M over two growing seasons.

Aggregate stability and associated C and N in a silty loam soil as affected by organic material inputs

Abstract To make recycling utilization of organic materials produced in various agricultural systems, five kinds of organic materials were applied in a field test, including crop straw (CS), biogas residue (BR), mushroom residue (MR), wine residue (WR), pig manure (PM), with a mineral fertilizer (CF) and a no-fertilizer (CK) treatment as a control. Our objectives were: i) to quantify the effects of organic materials on soil C and N accumulation; ii) to evaluate the effects of organic materials on soil aggregate stability, along with the total organic carbon (TOC), and N in different aggregate fractions; and iii) to assess the relationships among the organic material components, soil C and N, and C, N in aggregate fractions. The trial was conducted in Wuqiao County, Hebei Province, China. The organic materials were incorporated at an equal rate of C, and combined with a mineral fertilizer in amounts of 150 kg N ha −1 , 26 kg P ha −1 and 124 kg K ha −1 respectively during each crop season of a wheat-maize rotation system. The inputted C quantity of each organic material treatment was equivalent to the total amount of C contained in the crop straw harvested in CS treatement in the previous season. TOC, N, water-stable aggregates, and aggregate-associated TOC and N were investigated. The results showed that organic material incorporation increased soil aggregation and stabilization. On average, the soil macroaggregate proportion increased by 14%, the microaggregate proportion increased by 3%, and mean-weight diameter (MWD) increased by 20%. TOC content followed the order of PM>WR>MR>BR>CS>CK>CF; N content followed the order WR>PM>MR>BR>CS>CF>CK. No significant correlation was found between TOC, N, and the quality of organic material. Soil silt and clay particles contained the largest part of TOC, whereas the small macroaggregate fraction was the most sensitive to organic materials. Our results indicate that PM and WR exerted better effects on soil C and N accumulation, followed by MR and BR, suggesting that organic materials from ex situ farmland could promote soil quality more as compared to straw returned in situ.

Mitigating Groundwater Depletion in North China Plain with Cropping System that Alternate Deep and Shallow Rooted Crops

In the North China Plain, groundwater tables have been dropping at unsustainable rates of 1 m per year due to irrigation of a double cropping system of winter wheat and summer maize. To reverse the trend, we examined whether alternative crop rotations could save water. Moisture contents were measured weekly at 20 cm intervals in the top 180 cm of soil as part of a 12-year field experiment with four crop rotations: sweet potato→ cotton→ sweet potato→ winter wheat-summer maize (SpCSpWS, 4-year cycle); peanuts → winter wheat-summer maize (PWS, 2-year cycle); ryegrass–cotton→ peanuts→ winter wheat-summer maize (RCPWS, 3-year cycle); and winter wheat-summer maize (WS, each year). We found that, compared to WS, the SpCSpWS annual evapotranspiration was 28% lower, PWS was 19% lower and RCPWS was 14% lower. The yield per unit of water evaporated improved for wheat within any alternative rotation compared to WS, increasing up to 19%. Average soil moisture contents at the sowing date of wheat in the SpCSpWS, PWS, and RCPWS rotations were 7, 4, and 10% higher than WS, respectively. The advantage of alternative rotations was that a deep rooted crop of winter wheat reaching down to 180 cm followed shallow rooted crops (sweet potato and peanut drawing soil moisture from 0 to 120 cm). They benefited from the sequencing and vertical complementarity of soil moisture extraction. Thus, replacing the traditional crop rotation with cropping system that involves rotating with annual shallow rooted crops is promising for reducing groundwater depletion in the North China Plain.

Carbon footprints of grain-, forage-, and energy-based cropping systems in the North China plain

PurposeLow carbon footprint agriculture has received increasing attention in the effect of reducing greenhouse gas emissions and mitigating climate change. However, little is known about how crop diversification may affect the system productivity and the carbon footprint.MethodsIn this study, we analyzed the carbon footprints of four cropping systems: winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) (WM, grain crop pattern, 1-year cycle); ryegrass (Lolium perenne L.)–sweet sorghum (Sorghum bicolor (L.) Moench) (RS, forage crop pattern, 1-year cycle); ryegrass–sweet sorghum → winter wheat–summer maize (RSWM, grain plus forage crop pattern, 2-year cycle); and switchgrass (Panicum virgatum L.) perennial cropping (SG, energy crop pattern) that have been evaluated in a long-term (2009–2015) field experiment in the North China Plain (NCP). Carbon footprints were expressed using three metrics: CFa (per unit area), CFb (per kg of biomass), and CFe (per unit of economic output).Results and discussionThe results showed that switchgrass as a perennial herbaceous crop with one cut per year had the lowest annual carbon footprint at three metrics. The WM cropping system had the highest annual CFa, CFb, and CFe values which were 1.73, 2.23, and 1.78 times higher, respectively, than those of the RSWM cropping system. The RS cropping system had the lower annual CFa, CFb, and CFe values, which accounted for 20.9, 3.4, and 2.9%, respectively, of the WM cropping system. The four cropping systems had annual carbon footprints at per unit area, per kilogram of biomass and per unit of economic output ranked from lowest to highest of SG < RS < RSWM < WM.ConclusionsWe conclude that appropriately designed, diversified cropping systems that include grain, forage, and bioenergy crops can effectively reduce the carbon footprint while maintaining or even increasing the systems productivity in the North China Plain.

Effects of Drip Irrigation Patterns on Wheat Yield and Water Use Efficiency in Heilonggang Region

A field experiment with different drip irrigation patterns was conducted in Heilonggang region,Hebei Province,China in the 2010–2011 and 2011–2012 winter wheat growing seasons to develop suitable drip irrigation schedule in this region.The yields and water use efficiencies(WUE) of wheat in different drip irrigation treatments with flood irrigation as control were compared under total water supplies of 225,180,150,and 120 mm,respectively.Under the condition of 225 mm irrigation,drip irrigation and irrigation frequency(1–3 times) had no significant difference in effect on yield and WUE.Drip irrigation resulted in 45–105 mm reduction of irrigation amount as compared to the control,with no significant yield loss,and a significant increase of WUE.Correlation analysis indicated that the contribution of yield components showed a sequence of spike number1000-grain weightgrain number per spike.These results showed that drip irrigation technique should have potentials of water saving and yield stability in wheat production of the experimental region.