Deficit irrigations during soybean reproductive stages and CROPGRO-soybean simulations under semi-arid climatic conditions

This study was carried out to determine the effect of water stress on five different generative stages of soybeans and to evaluate the CROPGRO-soybean model under semi-arid climatic conditions. The study was conducted at the Faculty of Agricultural Engineering, Harran University research field in 2003 and 2004 growing seasons. Plants received full irrigation during vegetative stages, after which it was cut off at different reproductive stages (treatments): R_1-2, beginning of flowering and full bloom; R₃, beginning of pod; R₄, full pod; R₅, beginning of seed; and R₆, full seed. The control treatment was full irrigation throughout. Observed yields ranged from 1955 (R₆) to 3684 kg ha⁻¹ (control) in 2003, and from 1867 (R₆) to 3952 kg ha⁻¹ (control) in 2004, respectively. Generally, in both of the years any water stress imposed on soybeans in three different generative stages (R₃, R₅, and R₆) resulted in substantial yield reduction compared with full irrigation; yield reduction was greatest at the R₆ stage. Biomass and 1000 seed weight also showed significant difference. Overall, CROPGRO-soybean simulated parameters from all treatments were higher compared with observed ones. Although simulated yield results were close to measured ones, they could not track observed yield patterns. Generally, the CROPGRO-soybean simulation model failed to satisfactorily mimic observed soybean yield, biomass, and 1000 seed weight and therefore it is suggested not to be used for similar scenarios and climatic conditions.     

半干旱区中耕深松对土壤水分和作物产量的影响

为了提高半干旱区旱作农田对天然降雨的利用率,打破犁底层,增加雨水入渗,达到蓄水保墒、提高作物产量的目的,2008~2009年在朝阳半干旱区对旱地玉米和大豆进行中耕深松试验。研究表明,深松能打破犁底层,降低表层土壤容重和根系穿透阻力,提高土壤孔隙度。与对照相比,深松可以增加土壤含水量并可以提高水分入渗深度,深松区土壤水分入渗深度可达80 cm左右,未深松区土壤水分入渗深度只有40 cm左右。深松使玉米根干重增加幅度为3.6%~6.1%,使大豆根干重增加15.1%,并使大豆主根系入土深度增加3 cm,玉米增产幅度1.9%~11.3%,在干旱年份增产效果明显,大豆增产19.47%。     

耕作措施对温带半干旱地区土壤温室气体(CO2、CH4、N2O)通量的影响

通过设置在甘肃省定西市李家堡镇的不同耕作措施试验, 利用CO₂分析仪、静态箱-气相色谱法对双序列轮作次序下春小麦地、豌豆地生育期内CO₂、CH₄和N₂O通量进行了测定。试验结果表明: 4种耕作措施下春小麦地和豌豆地在生育期内均表现为CO₂源、N₂O源和CH₄汇的功能。传统耕作不覆盖、免耕不覆盖、免耕秸秆覆盖和传统耕作结合秸秆还田下, 春小麦生育期内平均土壤CO₂通量(μmol·m^-2·s^-1)分别为0.203 6、0.221 2、0.241 8、0.224 9, CH₄通量(mg·m^-2·h^-1)分别为-0.041 6、-0.078 0、-0.081 8、-0.053 7, N₂O通量(mg·m^-2·h^-1)分别为0.089 1、0.069 2、0.046 1、0.065 6; 豌豆生育期内平均土壤CO₂通量(μmol·m^-2·s^-1)分别为0.273 6、0.261 6、0.218 1、0.236 0, CH₄通量(mg·m^-2·h^-1)分别为-0.055 0、-0.073 7、-0.066 2、-0.054 5, N₂O通量(mg·m^-2·h^-1)分别为0.123 4、0.084 7、0.080 6、0.035 0。少免耕及小麦秸秆覆盖有利于减少土壤CO₂排放通量, 免耕不覆盖、免耕秸秆覆盖及传统耕作结合秸秆还田均能不同程度地增加CH₄吸收通量、减少N₂O排放通量。综合来看, 免耕不覆盖、免耕秸秆覆盖和传统耕作结合秸秆还田3种保护性耕作措施有助于减少土壤温室气体的排放量。春小麦地CO₂通量随着土壤温度、土壤含水量的逐渐升高而增大; CH₄吸收通量随着土壤含水量的逐渐升高而增大, 而随着土壤温度的逐渐升高而减小。豌豆地CO₂通量的变化与土壤含水量存在极显著正相关关系; 而春小麦地N₂O通量则与平均土壤温度呈显著正相关, 豌豆地则为极显著正相关。     

Assessment of the relationship between soil properties,Striga hermonthica infestation and the on-farm yields of maize in the dry Savannas of Nigeria

A study was conducted in Kano and Bauchi States in the dry Savanna of northern Nigeria to determine Striga incidence and infestation and relate these to soil fertility status and yield of maize. A three-stage sampling technique was used to select communities and fields in targeted Local Government Areas in the two States. The soils in the two States were generally of low fertility, characterized by low levels of total N, organic C, available P and exchangeable bases. In Kano State, Striga incidence ranged from 0 to 100%. One hundred percent of the maize fields sampled in Bauchi State had Striga. In general, Striga population was more than twice higher in Bauchi State [3.1 plants m⁻²] than in Kano State [1.4 plants m⁻²]. There were differences in Striga population and severity of attacks between the States and between communities within States. In Kano State, the Striga population was negatively related to latitude, total N, and exchangeable K and was positively related to sand and silt. In Bauchi State, Striga was negatively related to clay, exchangeable K, and Ca, and was positively related to pH and latitude. In both states, the Striga population was negatively correlated with maize grain yield. Up to 75% of the variations in maize grain yield in Kano State could be explained by Striga population and soil organic C. Management of Striga usually requires several measures, however, improving the levels of soil fertility should be the central component of any integrated Striga management approach.     

Evaluation of soil water storage efficiency for rainfall harvesting on hillslope micro-basins built using time domain reflectometry measurements

Micro-basins are slope management structures built out of earth and stones on hillslopes around cultivated trees (e.g., olive trees) for the harvesting of rainfall and runoff water, and for the rehabilitation of land degraded by water erosion.In this study, the results of an experimental survey for the comparison of soil water content for both inside and outside the micro-basins are analyzed. Measurements are taken after some rainfall events from January to December 2003 in a hilly region of Central Tunisia. The time domain reflectometry technique is used to measure soil moisture in 15 sets of soil profiles (inside and outside) at three different depths. Four different soils are evaluated, i.e., Cambisols, Kastanozems, Arenosols, and Calcisols.The data analysis shows a significant improvement on the water stock obtained by this type of management. The differences in water storage with respect to soil type, depths, and tillage are evident, but strongly connected to farm management. For optimal management conditions an important increase of average water stock is observed; however, for bad or no farm management the amelioration is zero or is even deteriorating the state of vegetation.     

Forage production,quality and water-use-efficiency of four warm-season annual crops at three sowing times in the Loess Plateau region of China

Increasing demand for livestock products is driving development of livestock systems worldwide. That requires improved and new forage production options. The Loess Plateau region in central-northern China is an important area for livestock production, as it supports11% and 19% of the country’s cattle and sheep, respectively (China statistical yearbook 2014). The rain-fed semi-arid environment of the Loess Plateau means that maximizing the water-use-efficiency (WUE) of forage production is vital to guarantee enough fodder supply the livestock demand. A three-year field experiment in north-west Loess Plateau compared forage production, water use and water-use-efficiency as well as crude protein (CP) content of forage maize, Sudan grass, foxtail millet and Japanese millet sown at three sowing dates according to the opening rain during 2011–2013. On average, forage maize produced the highest biomass (12.1 t ha⁻¹) and had the highest WUE (43.4 kg DM ha⁻¹ mm⁻¹). This was followed by Sudan grass (7.8 t ha⁻¹; 26.5 kg DM ha⁻¹ mm⁻¹), Japanese millet (6.7 t ha⁻¹; 26.2 kg DM ha⁻¹ mm⁻¹) and foxtail millet (6.7 t ha⁻¹; 24.6 kg DM ha⁻¹ mm⁻¹). Optimizing sowing date played an important role in maximizing forage production and WUE of all tested forages. Compared to the earliest sowing date, a delay of two weeks reduced forage production by 17% in maize, 35% in foxtail millet, and 16% in Japanese millet. A delay of four to six weeks reduced biomass yield by 58% in maize, 57% in foxtail millet, and 56% in Japanese millet. Late sowing also greatly reduced WUE of forage maize and foxtail millet by 33% and 42%, respectively, when compared to early sowing. The middle sowing date maximized forage production and WUE of Sudan grass in two of the three growing seasons, which was 20% and 38% higher than the early and late sowing, respectively. Late sowing in all forages reduced crop water use by 42–57 mm compared to the early sowing. Among four test crops, CP of Sudan grass (7.9%) and forage maize (7.7%) was higher than foxtail millet (6.8%) and Japanese millet (6.7%). Compared with early sowing, CP_f in late sowing significantly increased in Sudan grass and decreased in Japanese millet, in contrast, no evident sowing date effect was found in forage maize and foxtail millet. This study showed that all four warm-season annual grasses had high forage production potential, forage maize was the most reliable and efficient option. Forage maize and the millets could easily be integrated into existing cropping systems and provide opportunities as both grain and forage-producing crop to provide added flexibility for farmers.     

C-NMR analysis of decomposing litter and fine roots in the semi-arid Mulga Lands of southern Queensland

Plant litter and fine roots are important carbon (C) inputs to soil and a direct source of CO₂ to the atmosphere. Solid-state carbon-13 nuclear magnetic resonance (¹³C-NMR) spectroscopy was used to investigate the nature of C changes during decomposition of plant litter and fine roots of mulga (Acacia aneura F. Muell. Ex. Benth.), wheat (Triticum aestivum L.), lucerne (Medicago sativa) and buffel grass (Cenchrus ciliaris) over an 18-month period. Alkyl C was closely associated with total N concentrations in all litter materials during decay and as alkyl C increased so did total N, indicating an increase in refractory biomacromolecules. Mulga phyllodes had the greatest alkyl C concentration of all litter and fine root materials, and also exhibited the NMR peaks assigned to tannins that may slow or hinder decomposition rates and nitrification. Mulga litter and fine roots decomposed slower than all other litter materials and the soil under mulga had the highest soil C concentration, indicating slower CO₂ release. The alkyl C-to-O-alkyl C ratio is generally used as an index of the extent of decomposition, but is not useful for the decay of woody components. Of all the NMR ratios studied that may indicate the extent of decomposition, the carbohydrate C-to-methoxyl C ratio proved to have the strongest and most consistent relationship with decay time, fraction of mass remaining and total C, even though increases in alkyl C were observed with decreases in carbohydrate C.     

Medium-term gully headcut retreat rates in Southeast Spain determined from aerial photographs and ground measurements

This paper deals with gully retreat rates at different time scales, whereby the short-term time scale may span a time interval of 1–5 years, the medium-term time scale a time interval of 5–50 years, and the long-term time scale a time interval of more than 50 years. An analysis of high-altitude aerial photographs in combination with ground measurements allowed us to quantify volumetric gully-head retreat rates for 12 permanent gullies in Southeast Spain (Guadalentin and Guadix study areas) over a 40–43 year time interval (medium-term time scale). This resulted in an average retreat rate (V_e) of 17.4 m³ year⁻¹. A power relationship between drainage-basin area (A) and medium-term volumetric gully-head retreat rate, V_e=0.069A^0.380 (R²=0.51, n=21), was found by combining the gully-head retreat rates obtained in this study with those obtained by a dendrochronological method. The exponent (b) and the coefficient of determination (R²) of the power relationships V_e=aA^b increases from the short-term to the long-term time scale, expressing the increasing importance of drainage-basin area in gully development with time. Considerable differences between gully-head retreat rates measured at the short and medium-term time scales at individual gullies showed the importance of land-use changes and unsuccessful management practices on gully-head retreat, and the episodic nature of gully-head retreat when piping and tension cracking are involved. Higher gully-head retreat rates are obtained at the medium-term time scale compared to the short-term time scale but the differences are not significantly different at α=10%. The medium-term methods tend to measure proportionally more high gully retreat rates, but less extreme values compared to the short-term method. This is explained by a more equal distribution of extreme rainfall events both in space and time at a longer-term time scale, and hence a higher probability of measuring the average effect of both small and extreme rainfall events at each gully.     

Problems and prospects in the utilization of animal traction in semi-arid west Africa: evidence from Niger

The use of animal draft power for soil tillage has long been a major theme of agricultural development programmes in semi-arid West Africa. The rationale for animal traction utilization ranges from increasing agricultural productivity and income to relieving the drudgery in farm work. Yet, its adoption remains low and localized. Previous research has identified the conditions which favour the adoption of animal traction, but evidence on the potential benefits realizable from its use is mixed. The issue of how to improve the adoption and profitable utilization of animal traction in semi-arid West Africa remains an important topic given that mechanization of agriculture is inevitable. This paper uses data collected from villages in two different agroclimatic zones of Niger to demonstrate the regional variability of potential gains from animal traction. Production functions were estimated to determine the impact of animal traction use on area cultivated, labour input and aggregate yield. Multi-year partial budget streams were also estimated to evaluate the profitability of animal traction at each location. The results show that the use of animal traction did not have any significant impact on area cultivated, but increased the yields of sorghum (Sorghum bicolor (L.) Moench) and maize (Zea mays L.) by 12–15%. It increased labour input by 15 man-hha⁻¹ (man hours per hectare) in the dry agroclimatic zone, but reduced it by 50 man-h ha⁻¹ in the wet zone. Rates of return on animal traction investment ranged from −4 to 18% in the dry zone and from 14 to 58% in the wet zone. These results suggest that the impact of animal traction on agricultural production varies by region and depends on a broad set of agroecological and economic conditions. The absence of these conditions in marginal areas strictly limits potential utilization and profitability. On efficiency grounds, it is recommended that animal traction should be promoted only in areas where the climate, soil and economic conditions permit its intensive and profitable utilization.