The Importance of Root Dynamics in Cropping Systems Research

SUMMARY

This paper examines the nature and importance of the dynamics of crop root growth, particularly root turnover, and the application to different cropping systems. Methods now available to investigate root dynamics are summarized, and information being obtained is presented. Effects of physical, chemical, and biological factors on root dynamics are discussed. Growth of new roots and death of older roots can change the initial distribution in soil, allowing roots to exploit zones that have a more favorable nutrient or water supply. In herbaceous crops, the lifespan of roots appears to range between 16 and 36 per cent of the annual growth cycle. However, there is a paucity of data with which results can be compared. Localized enrichment of the water and nutrient supply enhances root turnover, and plants growing in soil well supplied with nutrients tend to have shorter-lived roots than those from nutrient limiting conditions. Both drought and excess water can induce premature root death, as can the resupply of water after drought. Turnover of roots contributes to carbon deposition in soil through their death and decay, as well as from the release of exudates from those roots during their lifetime. Improved understanding of root turnover is important for the development of more sustainable cropping systems. In particular, it could be used to improve the exploitation of N released from green manure as well as capturing N that has been leached below the rooting zone of staple crops. It is stressed that root turnover has more importance for plants with longer life cycles than in short season annual crops.     

Problems and Perspectives of Yam-Based Cropping Systems in Africa

SUMMARY

Yams (Dioscorea spp.) constitute an important starchy staple in sub-Saharan Africa (SSA) where food security for a growing population is a critical issue. Mixed cropping in yam based systems is the norm in the region and productivity of yams in these systems is below potential. It is concluded that there is much scope for improvement of yam based cropping systems in SSA in order to meet the needs of the region. The strategy of crop breeding to select yam varieties suitable for various cropping systems must consider a truly multidisciplinary systems approach. Further manipulation must be made to tuber dormancy to expand flexibility in field propagation in different cropping systems and improve storage and marketing. The sustainability of yam based cropping systems in SSA could improve if agronomic research was focused on strategies for improving soil fertility, weed and pest management including design of cropping systems and suitable rotations.     

The Future of Cereal Yields and Prices: Implications for Research and Policy

SUMMARY

Crop yields experienced significant increases in much of the world over the last 30 years, in large part due to investment in agricultural research, irrigation, and rural infrastructure. However, recent declines in yield growth are major causes of concern for future food security. Especially in Asia and sub-Saharan Africa the future prospects for food production are problematic. Both regions must meet strong growth in food demand–driven mainly by income growth in Asia and by population growth in sub-Saharan Africa. The production challenges in the two regions are fundamentally different: much of Asia is facing post-Green Revolution challenges of how to sustain crop yield growth following widespread adoption of modern varieties while dealing with environmental degradation in some high intensity crop production systems. Sub-Saharan Africa has yet to experience a Green Revolution, and must boost crop yield growth in the face of less favorable agroclimatic environments than in Green Revolution breadbaskets of Asia. In this paper, we review the past and possible future developments in yield growth in Asia and sub-Saharan Africa, the possible causes of the current yield growth problems and the management challenges both regions face to overcome them.     

Sterility in Wheat and Response of Field Crops to Applied Boron in the Indo-Gangetic Plains

Summary

Results of field experiments across the Indo-Gangetic Plains (IGP) region indicates that soil B deficiency induces sterility in wheat and results in poor crop yields of legumes and cereals. The deficiency of soil B and the response of crops to applied B generally increases from the northwestern to the eastern end of the IGP, this trend being influenced by the distribution of the soil parent material and the variation in the climatic conditions within the IGP. An earlier FAO study rated Nepal as the lowest of thirty countries in its soil B status and showed that a higher soil B deficiency problem exists in the eastern half of the Indian-IGP, therefore crop response to applied B is more likely in these areas. Few studies have made qualitative and quantitative assessment of sterility in wheat in the IGP and the positive response of other crops to B application also suggest B deficiency related sterility problems in these crops. Micronutrient research in the IGP often rates Zn followed by Fe and Mn deficiencies in some instances, as its major soil micronutrient deficiency problems. However, the deficiency of B perhaps is as important if not more, than Fe and Mn deficiency. The awareness of soil B deficiency is not as widespread as its occurrence in the IGP region. This article reviews and discusses the sterility problems in wheat and the response of several field crops to applied B to highlight the growing importance of soil B deficiency in the IGP.     

Survey of Rice Cropping Systems in Kampong Chhnang Province,Cambodia

Although Cambodia might have achieved self-sufficiency and an exported surplus in rice production,its rice-based farming systems are widely associated with low productivity,low farmer income and rural poverty.The study is based on a questionnaire village survey in 14 communes containing 97 villages of Kampong Chhnang Province from March to June,2011.It analyzes the prevailing rice-based cropping systems and evaluates options for their improvement.Differences in cropping systems depend on the distance from the Tonle Sap water bodies.At distances greater than 10 km,transplanted wet-season rice cropping system with low productivity of about 1.6 t/hm 2 prevails.This deficiency can be primarily attributed to soils with high coarse sand fractions and low pH (< 4.0),use of ’late’ cultivars,and exclusive use of self-propagated seeds.To improve this cropping system,commercial ’medium’ cultivars help prevent crop failure by shortening the cultivation period by one month and complementation of wet-season rice with non-rice crops should be expanded.Areas adjacent (≤ 1 km) to the water bodies become inundated for up to seven months between July until January of each year.In this area,soils contain more fine sand,silt and clay,and their pH is higher (> 4.0).Farmers predominantly cultivate dry-season recession rice between January and April.Seventy-nine percent of the area is sown directly and harvested by combines.Adoption ratio of commercial rice seeds is 59% and yields average 3.2 t/hm 2.Introduction of the second dry-season rice between April and July may double annual yields in this rice cropping system.Besides upgrading other cultivation technologies,using seeds from commercial sources will improve yield and rice quality.Along with rice,farmers grow non-rice crops at different intensities ranging from single annual crops to intensive sequences at low yields.     

连作对糜子抽穗后光合特性和干物质积累的影响

【目的】探究连作对糜子生长发育及籽粒产量形成的影响,明确导致糜子连作障碍的生理机制,为糜子高产高效栽培提供理论依据。【方法】以"内糜5号"为试验材料,设置糜子连作和芸豆与糜子轮作(对照)2个处理,分别于抽穗期、开花期、灌浆前期、灌浆后期、成熟期,测定连作、轮作下糜子旗叶光合特性、叶绿素含量、植株主茎绿叶面积和地上部干物质量,并于成熟期测定产量及其构成因素等指标。【结果】(1)连作显著降低了糜子旗叶净光合速率、叶绿素总含量、叶绿素b含量及植株主茎绿叶面积,在抽穗期和开花期影响尤为显著;(2)连作导致糜子抽穗后植株衰老进程加快,籽粒灌浆被迫提前终止,使植株干物质积累量减少、籽粒产量下降。【结论】连作糜子植株早衰和功能叶片光合性能下降是导致籽粒产量下降的主要原因,因此在栽培中应注重合理的轮作倒茬。     

不同栽培措施对连作马铃薯土壤真菌、真菌 性病害和产量的影响

通过连续3 a 利用不同栽培措施克服马铃薯连作障碍的定位试验,结果 表明,2009～2011 年
深翻处理的耕层土 壤真菌数量与连作相比降低29.59%～51.63%,菌剂处 理降低10.41%～71.96%,微肥处
理对改善土壤真菌数量效果不明显。深翻处理的马铃薯早疫病发病率比 连作降低10.00 个百分点到35.00
个百分点,菌剂处 理降低11.67 个百分点到38.33 个百分点,微肥处 理降低11.66 个百分点到26.67 个百分点;
深翻处理的马铃薯早疫病病情指数比 连作低20.34%～75.51%,菌剂处 理降低23.83%～64.50%,微肥处 理
降低20.34%～52.26%,并且差异达到显著或极显著水平。 深翻处理的马铃薯晚疫病发病 率比连作低15.00
个百分点到37.50 个百分点,菌 剂处理降低7.50 个百分点到36.67 个百分点,微 肥处理降低15.00 个百
分点到25.83 个百分点;深翻处理的马铃薯晚疫病病情指 数比连作低57.03%～80.44%,菌 剂处理降低
24.69%～66.67%,微 肥处理降低27.12%～50.76%,并且差异达到显著或极显著水平。深翻处理的马铃薯
比连作增产21.20%～29.99%,微肥处理 比连作增产6.14%～20.49%,菌剂处理比连作增产1.29%～13.42%,
并且差异达到显著或极显著水平。     

Effects of long‐term fertilization on the weed growth and community composition in a double‐rice ecosystem during the fallow period

The vegetation cover during the non‐cropping season could have important implications for the maintenance and recovery of soil fertility, as well as for biodiversity conservation in croplands. In this study, five fertilization regimes (control: non‐fertilization; N: inorganic N fertilization; P: inorganic P fertilization; NPK: balanced fertilization with inorganic N, P and K; NPKM: balanced NPK plus farmyard manure) were conducted from 1981 in a double‐rice (Oryza sativa L.)‐cropping system in subtropical China. The effects of long‐term fertilization were investigated on the weed growth, diversity and community structure during the fallow period. The results showed that, relative to the control, both inorganic fertilization alone (N, P and NPK) and NPKM in the rice‐growing season significantly increased the weed density and biomass during the fallow period in the paddy field. There was no significant difference in the weed species richness (the number of species) among the treatments. Compared with the control, fertilization tended to reduce the weed diversity (Shannon's H′) and evenness (Shannon's E), especially in the N treatment. Long‐term fertilization resulted in a significant shift in weed community's composition during the fallow period. The weed community's structure was affected by soil nutrients in the order P > N > K.     

A Method for Baiting Corticium rolfsii and of Estimating the Sclerotial Population in Soil

Abstract

The use of tissue blocks of Xanthosoma sagittifolim for baiting Corticium rolfsii from soil is described. The baiting technique has been found efficient for gross estimation of the viable sclerotial content of air-dried soil. The results obtained by this method compare well with those determined by the sieving technique of Rodriguez-Kabana et al.     

Relative Efficiency of Zinc Sulfate and Zinc Oxide–Coated Urea in Rice–Wheat Cropping System

Abstract

Rice–wheat cropping system covers about 24 million hectares in China, India, Pakistan, Nepal, and Bangladesh, and zinc deficiency is widespread in rice–wheat belts of all these five countries. The current practice of applying zinc sulfate heptahydrate (ZnSO₄ · 7H₂O) to soil is problematic because of the poor quality of the nutrients available in the market to the farmers. Zinc (Zn)–coated urea is therefore being manufactured to guarantee a good‐quality Zn source. This article reports the results from a field study conducted to study the relative efficiency of zinc sulfate and zinc oxide (ZnO)–coated ureas in rice–wheat cropping system. The highest grain yield of rice–wheat cropping system was obtained with 2.0% coating of urea. Zinc sulfate was also a better coating material than ZnO. Partial factor productivity, agronomic efficiency, apparent recovery, and physiological efficiency of applied Zn decreased as the level of Zn coating was increased.