Nitrogen use efficiency of cotton (Gossypium hirsutum L.) as influenced by wheat–cotton cropping systems

Wheat–cotton rotations largely increase crop yield and improve resources use efficiency, such as the radiation use efficiency. However, little information is available on the nitrogen (N) utilization and requirement of cotton under wheat–cotton rotations. This study was to determine the N uptake and use efficiency by evaluating the cotton (Gossypium hirsutum L.) N use and the soil N balances, which will help to improve N resource management in wheat–cotton rotations. Field experiments were conducted during 2011/2012 and 2012/2013 growing seasons in the Yangtze River region in China. Two cotton cultivars (Siza 3, mid-late maturity with 130 days growth duration; CCRI 50, early maturity with 110 days growth duration) were planted under four cropping systems including monoculture cotton (MC), wheat/intercropped cotton (W/IC), wheat/transplanted cotton (W/TC) and wheat/direct-seeded cotton (W/DC). The N uptake and use efficiency of cotton were quantified under different cropping systems. The results showed that wheat–cotton rotations decreased the cotton N uptake through reducing the N accumulation rate and shortening the duration of fast N accumulation phase as compared to the monoculture cotton. Compared with MC, the N uptake of IC, TC and DC were decreased by 12.0%, 20.5% and 23.4% for Siza 3, respectively, and 7.3%, 10.7% and 17.6% for CCRI 50, respectively. Wheat–cotton rotations had a lower N harvest index as a consequence of the weaker sink capacity in the cotton plant caused by the delayed fruiting and boll formation. Wheat–cotton rotations used N inefficiently relative to the monoculture cotton, showing consistently lower level of the N agronomic use efficiency (NAE), N apparent recovery efficiency (NRE), N physiological efficiency (NPE) and N partial factor productivity (NPFP), particularly for DC. Relative to the mid–late maturity cultivar of Siza 3, the early maturity cultivar of CCRI 50 had higher N use efficiency in wheat–cotton rotations. An analysis of the crop N balance suggested that the high N excess in preceding wheat (Triticum aestivum L.) in wheat–cotton rotations led to significantly higher N surpluses than the monoculture cotton. The N management for the cotton in wheat–cotton rotations should be improved by means of reducing the base fertilizer input and increasing the bloom application.     

不同模拟雨量下微集水种植对农田水肥利用效率的影响

为了探索微集水种植的增产机理及其适宜的雨量范围,通过大田模拟降雨试验,在2006－2007年研究了作物生长期间不同降雨量下微集水种植玉米对农田水肥利用效率的影响。结果表明,在230～440 mm雨量下,微集水种植玉米可提高其籽粒产量及水肥利用效率,2006年籽粒产量、农田水分利用效率（WUE）以及氮、磷和钾养分利用效率（NUEN、NUEP和NUEK）在230 mm雨量下较对照分别提高了75.4%、73.3%、56.0%、44.4%和106.8%,340 mm雨量下分别提高了36.7%、40.2%、22.8%、18.1%和35.5%,440 mm雨量下与平作相比差异不明显;2007年籽粒产量、WUE、NUEN、NUEP和NUEK在230 mm雨量下较对照分别提高了82.8%、77.4%、64.0%、52.2%和123.9%,340 mm雨量下分别提高了43.4%、43.1%、30.4%、21.8%和41.2%;440 mm雨量下籽粒产量、WUE和NUEN分别提高了11.2%、9.5%和10.1%。由此可知,在玉米全生育期降雨量230～440 mm范围内,通过微集水种植可以增加籽粒产量,提高农田水肥利用效率,尤其在雨量较低时,提高水肥利用效率及增产效果尤为明显。     

Effect of Rainfall Collecting with Ridge and Furrow on Soil Moisture and Root Growth of Corn in Semiarid Northwest China

A plastic‐covered ridge and furrow farming of rainfall collecting (RC) system were designed to increase water availability to corn for improving and stabilizing agricultural production in the semiarid Loess region of northwest China. This system comprised two elements: the ridge mulched by plastic film that acts as a rainfall harvesting zone and the furrow as a planting zone. To adopt this system for large‐scale use in the semiarid region and bring it into full play, it is necessary to test the appropriate rainfall range for RC farming. A field study (using corn as an indicator crop) combined with rainfall simulation was conducted to determine the effect of RC on soil moisture, root characteristic parameters and the yield of corn under three different rainfall levels (230, 340 and 440 mm) during the growing seasons of 2006 and 2007. The results indicated that with the rainfalls ranging within 230–440 mm, the soil moisture at 0–100 cm depth for RC system in furrows was significantly higher (P < 0.05) than that of conventional flat (CF for control) practice. At 100–200 cm soil depth, there was no significant difference (P > 0.05) between soil moisture in the RC₂₃₀ plots and in the CF₂₃₀ plots during the corn growing seasons, while the soil moisture both in the RC₃₄₀ and RC₄₄₀ plots were significantly higher (P < 0.05) than those in the CF₃₄₀ and CF₄₄₀ plots. The root length, root surface area, root volume and root dry weight for RC₂₃₀ and RC₃₄₀ plots all significantly increased (P < 0.05) compared with CF₂₃₀ and CF₃₄₀ plots, but these root characteristic parameters at 440 mm rainfall slightly decreased compared with those of CF practice. Compared with the CF_230–440 pattern, the increasing amplitude of grain yield under the RC_230–440 pattern diminished with the rainfall increase and there was no obvious yield‐incrementing effect (P > 0.05) between two patterns at 440 mm rainfall in 2006. In comparison with these two farming practices, the RC system not only improved soil moisture of dry farmland, but also promoted the development of corn root systems when the rainfall ranged between 230 and 440 mm. Thus, it could be concluded that the optimal upper rainfall limit for the RC system is below 440 mm in the experiment. For corn, the adoption of the RC practice in the 230–440 mm rainfall area will make the system more effective during the whole growth period and offer a sound opportunity for sustainable farming in semiarid areas.     

Attainable yield achieved for plastic film-mulched maize in response to nitrogen deficit

Nitrogen (N) stress limits the yields of maize (Zea mays L.) that have been plastic film-mulched in northwest China. Using the tested Hybrid-Maize simulation model, which was combined with field experiments using four levels of N fertilisers (0, 100, 250 and 400 kg N ha⁻¹), we aimed to understand the variability of the attainable yield in response to N stress under plastic film mulching. We show that the application of N250 or N400 results in 100% simulated potential LAI, which is, thus, close to 100% of the simulated potential of both biomass and grain yield. However, N stress treatments significantly decreased the biomass and grain yields, achieving only 40–50% of the simulated potential (N0 treatment) and 70–80% of the simulated potential (N100 treatment). Growth dynamic measurements showed that N stress significantly decreased the LAI, delaying the source capacity growth (canopies) around the silking stage and resulting in lower final kernel numbers. The lower LAI resulted in decreased dry matter accumulation and allocation during the reproductive stage; this decrease led to a decrease in the kernel growth rate and in the grain filling duration, which resulted in a significantly lower kernel weight. This knowledge could be helpful for the optimisation of N management to close the yield gaps of dryland maize in semi-arid monsoon climate regions.     

Crop water deficit estimation and irrigation scheduling in western Jilin province,Northeast China

Jilin province is one of the main dryland grain production areas in China. Recently, limited supplemental irrigation, using groundwater in the semi-arid western area of the province, has developed rapidly to improve the low grain productivity caused by rainfall variability. Research was conducted to estimate the actual crop water requirements and identify the timing and magnitude of water deficits of the main crops such as corn (Zea mays L.), soybean (Glycine max L.) and sorghum (Sorghum bicolor L.). Using the guidelines for computing crop water requirements in FAO Irrigation and Drainage paper 56 and historical rainfall distributions, the crop water requirements, ETc and the crop water deficits of corn, soybean and sorghum were calculated. Based on the water deficit analysis, a recommended average supplemental irrigation schedule was developed. Crop production was compared to full irrigation and to a rainfed control in a field experiment.On average, compared to the rainfed control, the full irrigation and the average supplemental irrigation treatments of corn, increased yields 49.0 and 43.9%, respectively; soybean yields of those treatments increased by 41.0 and 34.7%, and sorghum yields of those treatments increased by 55.5 and 46.3%. A supplemental irrigation schedule can be used in the semi-arid western Jilin province to improve crop yields.     

Shoot growth potential drives N uptake in maize plants and correlates with root growth in the soil

Variation in nitrogen (N) acquisition ability is known to exist among maize genotypes. Field experiments were conducted and the N-efficient maize inbred line 478 and the N-inefficient line Wu312 were employed to illustrate whether the amount of N taken up in maize plants with different N acquisition ability was determined by the shoot growth potential or by the root size. To meet the accelerated growth of the shoot from the jointing stage to the grain-filling stage, the net N gain in whole plants of both genotypes increased dramatically and accounted for 77% and 74% of the total N increment in 478 and Wu312, respectively. Similarly, the 4th to 8th nodal root whorls were initiated predominantly between 35 and 76 d after sowing, which accounted for about 90% of the total root length on 93 d after sowing. The whole plant N content of the N-efficient 478 was significantly higher than that of the N-inefficient Wu312. 478 had also longer root length, including axial and lateral roots, of the embryonic roots and each whorl of shoot-borne roots, and greater root length density (RLD) than Wu312. In spite of the smaller root size, Wu312 had higher shoot N concentration than 478 during the whole growth period, implying that N was not limited for shoot growth in Wu312. It was concluded that maize root growth, especially initiation and development of the shoot-borne roots, as well as the amount of N taken up were coordinated with shoot growth and demand for nutrients. Although a large root system and high RLD in the soil profile were beneficial for efficient N acquisition, amount of N taken up by the two maize genotypes in the presence of sufficient N supply was determined by the shoot growth potential, and not by the root size.     

我国旱区作物根域微集水种植技术研究进展及展望

概述了我国旱作区作物根域微集水种植技术的增产机理与效果,在总结现有研究基础上,指出了目前根域微集水种植技术研究中存在的若干问题,并提出针对该技术的完善与深化应加强其影响作物生产力机制及水肥耦合机理方面的研究,科学评价在不同雨量区根域微集水种植的应用效果和水保效应,同时应进一步规范根域微集水种植技术的相关技术标准和操作规程。作者认为该技术在深化试验研究与广泛示范的基础上,在旱农区有十分广阔的应用前景,是提高旱区降水资源化效率及作物增产的重要技术途径。     

黄土高原地区紫花苜蓿不同叶位光合日变化特征研究

为了解紫花苜蓿(Medicago sativa L.)冠层同化能力的差异及影响因子,为其品种改良和田间管理提供依据,用LI-6400型便携式光合测定仪于2006年观测了不同叶位叶片光合作用日变化特征。结果表明:现蕾期苜蓿不同叶位叶片的净光合速率(Pn)、蒸腾速率(Tr)日变化均呈现"三峰"曲线,有明显的光合"午休"现象;不同叶位之间Pn存在极显著差异(P<0.01),高低表现为上位叶>中位叶>下位叶;且胞间CO₂浓度(Ci)存在显著差异(P<0.05),表现为下叶位>中位叶>上位叶,气孔限制值(Ls)与Ci表现出相反趋势,即上位叶>中位叶>下位叶,Tr差异不显著;根据Pn、Ci、Ls的变化方向,苜蓿上、中、下叶位光合速率的下降在光合有效辐射(PAR)达到全天最大值之前受气孔因素限制,之后受非气孔因素限制;苜蓿叶片的光合速率具有分层的特点:上层强光区为高光合速率层,下层弱光区为低光合速率维持层,中层为中光区,光合速率介于上层与下层之间。