Breeding crops for reduced-tillage management in the intensive, rice–wheat systems of South Asia

The importance of reduced tillage in sustainable agriculture is well recognized. Reduced-tillage practices (which may or may not involve retention of crop residues) and their effects differ from those of conventional tillage in several ways: soil physical properties; shifts in host–weed competition; soil moisture availability (especially when sowing deeply or under stubble); and the emergence of pathogen populations that survive on crop residues. There may be a need for genotypes suited to special forms of mechanization (e.g. direct seeding into residues) and to agronomic conditions such as allelopathy, as well as specific issues relating to problem soils. This article examines issues and breeding targets for researchers who seek to improve crops for reduced-tillage systems. Most of the examples used pertain to wheat, but we also refer to other crops. Our primary claim is that new breeding initiatives are needed to introgress favourable traits into wheat and other crops in areas where reduced or zero-tillage is being adopted. Key traits include faster emergence, faster decomposition, and the ability to germinate when deep seeded (so that crops compete with weeds and use available moisture more efficiently). Enhancement of resistance to new pathogens and insect pests surviving on crop residues must also be given attention. In addition to focusing on new traits, breeders need to assess germplasm and breeding populations under reduced tillage. Farmer participatory approaches can also enhance the effectiveness of cultivar development and selection in environments where farmers’ links with technology providers are weak. Finally, modern breeding tools may also play a substantial role in future efforts to develop adapted crop genotypes for reduced tillage.     

马铃薯免耕稻草覆盖栽培技术研究

[目的]探讨马铃薯免耕稻草覆盖栽培技术的可行性。[方法]从马铃薯生育期、经济性状、产量、品质及经济效益等方面对马铃薯免耕稻草覆盖栽培技术进行分析。[结果]与常规地膜覆盖相比,免耕稻草覆盖的马铃薯产量约高2．9％,但纯收入约低16％。[结论]该马铃薯免耕稻草覆盖栽培技术需经技术改良,降低成本后再进行推广和应用。     

The implications of land preparation, crop establishment method and weed management on rice yield variation in the rice-wheat system in the Indo-Gangetic plains

The implications of adopting alternative seeding methods for rice and wheat establishment were examined at three geographically separate sites in the rice-wheat system of the Indo-Gangetic plains, across northern India. Rice yields in cultivated plots, established by either wet or dry seeding methods, were evaluated in comparison to yields from zero-tillage plots and under conventional transplanting methods. In the same trials, the effects of crop establishment methods in wheat were assessed both on wheat yields and rice yields. Rice crop establishment methods markedly influenced the emerging weed flora and attainable yields were measured in relation to intensity of weed management. Over four years, average rice grain yields in the absence of weed competition were greatest (6.56 t ha⁻¹) under wet seeding (sowing pre-germinated rice seed on puddled soil), and similar to those from transplanted rice (6.17 t ha⁻¹) into puddled soil, and dry seeded rice after dry soil tillage (6.15 t ha⁻¹). Lowest yields were observed from dry seeded rice sown without tillage (5.44 t ha⁻¹). Rice yield losses due to uncontrolled weed growth were least in transplanted rice (12%) but otherwise large (c. 85%) where rice had been sown to dry cultivated fields or to puddled soil, rising to 98% in dry seeded rice sown without soil tillage. Weed competition reduced multiple rice yield components, and weed biomass in wet seeded rice was six-fold greater that in rice transplanted into puddled soil and twice as much again in dry seeded rice sown either after dry tillage or without tillage. Wheat grain yields were significantly higher from crops sown into tilled soil (3.89 t ha⁻¹) than those sown without tillage (3.51 t ha⁻¹), and also were elevated (5% on average) where the soil had been dry cultivated in preparation for the previous rice crops rather than puddled. The method of wheat cultivation did not influence rice yield. Soil infiltration rates in the wheat season were least where the land had been puddled for rice (1.52 mm h⁻¹), and greater where the soil had been dry-tilled (2.63 mm h⁻¹) and greatest after zero-tillage (3.54 mm h⁻¹).These studies demonstrated at research managed sites across a wide geographic area, and on farmers’ fields, that yields of dry seeded rice sown after dry cultivation of soil were broadly comparable with those of transplanted rice, providing weed competition was absent. These results support the proposition that direct seeding of rice could provide an alternative to the conventional practice of transplanting, and help address rising costs and threats to sustainability in the rice-wheat rotation. Further, analysis of patterns of long-term rainfall data indicated that farmers reliant on monsoon rainfall could prepare fields for dry direct seeded rice some 30 days before they could prepare fields for either transplanting or seeding with pre-germinated seed. Dry, direct seeding of rice contributes a valuable component of an adaptive strategy to address monsoonal variability that also may advance the time of wheat establishment and yield. Whilst the results illustrate the robustness, feasibility and significant potential of direct seeded rice, they also highlight the critical nature of effective weed control in successful implementation of direct seeding systems for rice.     

作物复种的免耕直播栽培研究进展

综述了国内外水稻、油菜等作物复种的免耕直播栽培技术的发展,免耕稻田土壤的物理化学特性及生物特征,免耕直播栽培对作物生长发育及产量的影响,以及适合于我国水稻-油菜复种的免耕直播栽培的技术。指出作物免耕直播与翻耕移栽具有同样的产量潜力,省工、节本、增效的效益显著,是我国作物低成本、高效益栽培的主要途径之一。     

Conservation agriculture and smallholder farming in Africa: The heretics’ view

Conservation agriculture is claimed to be a panacea for the problems of poor agricultural productivity and soil degradation in sub-Saharan Africa (SSA). It is actively promoted by international research and development organisations, with such strong advocacy that critical debate is stifled. Claims for the potential of CA in Africa are based on widespread adoption in the Americas, where the effects of tillage were replaced by heavy dependence on herbicides and fertilizers. CA is said to increase yields, to reduce labour requirements, improve soil fertility and reduce erosion. Yet empirical evidence is not clear and consistent on many of these points nor is it always clear which of the principles of CA contribute to the desired effects. Although cases can be found where such claims are supported there are equally convincing scientific reports that contradict these claims. Concerns include decreased yields often observed with CA, increased labour requirements when herbicides are not used, an important gender shift of the labour burden to women and a lack of mulch due to poor productivity and due to the priority given to feeding of livestock with crop residues. Despite the publicity claiming widespread adoption of CA, the available evidence suggests virtually no uptake of CA in most SSA countries, with only small groups of adopters in South Africa, Ghana and Zambia. We conclude that there is an urgent need for critical assessment under which ecological and socio-economic conditions CA is best suited for smallholder farming in SSA. Critical constraints to adoption appear to be competing uses for crop residues, increased labour demand for weeding, and lack of access to, and use of external inputs.     

A research agenda to explore the role of conservation agriculture in African smallholder farming systems

Controversy surrounds the promotion of conservation agriculture (CA) in smallholder farming systems in sub-Saharan Africa. The introduction of CA is a profound change in farm management. Benefits in reduced erosion and stabilized crop production may be obtained, but technical performance at field level is but one of the determinants of adoption. For various reasons, all of the CA principles are not always fully implemented by farmers and results not as favourable as expected. As with other approaches to increasing agricultural productivity, the production constraints, farmers’ objectives, and the expected benefits and costs of implementing CA are important aspects that influence adoption. At farm and village levels, trade-offs in the allocation of resources become important in determining how CA may fit into a given farming system. At a regional level, factors such as the market conditions, interactions among stakeholders and other institutional and political dimensions become important. At each level, opportunities or difficulties emerge that enhance or impede development, adaptation and adoption of CA. The ex-ante identification of situations for where CA (and which form of CA) is appropriate demands research from a multi-stakeholder, multi-level, and interdisciplinary perspective. Recommendations are made where research is required to address key knowledge gaps.     

稻田免耕稻草覆盖马铃薯光合特性的研究

[目的]探索稻田免耕马铃薯高产的生理机制。[方法]采用随机区组设计,设马铃薯免耕栽培和传统翻耕栽培2个处理,在马铃薯块茎增长期间,测定供试叶片的光合速率、胞间CO2浓度、气孔导度和蒸腾速率。[结果]一天中稻田免耕马铃薯的净光合速率、气孔导度、蒸腾速率、水分利用效率都高于翻耕处理,而胞间CO2浓度低于翻耕处理。免耕马铃薯平均每穴的产量为490 g,翻耕的为230 g,两者的差异达到极显著水平。同时,免耕的大、中薯个数及产量也明显高于翻耕处理。[结论]该研究从光合特性方面揭示了稻田免耕马铃薯增产的机理,为生产实践提供了科学依据。     

Soil quality effects of tillage and residue under rice–wheat cropping on a Vertisol in India

Soil quality in rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping systems is governed primarily by the tillage practices used to fulfill the contrasting soil physical and hydrological requirements of the two crops. The objective of this study was to develop a soil quality index (SQI) based on bulk density (BD), penetration resistance (PR), water stable aggregates (WSA) and soil organic matter (OM) to evaluate this important cropping system on a Vertisol in India. Regression analysis between crop yield and SQI values for various tillage and crop residue management treatments indicated SQI values of 0.84–0.92, 0.88–0.93 and 0.86–0.92 were optimum for rice, wheat and the combined system (rice + wheat), respectively. The maximum yields for rice and wheat were 5806 and 1825 kg ha⁻¹ occurred at SQI values of 0.85 and 0.99, respectively. Using zero tillage (ZT) for wheat had a positive effect on soil quality regardless of the treatments used for rice. Regression analyses to predict sustainability of the various tillage and crop residue treatments showed that as puddling intensity for rice increased, sustainability without returning crop residues decreased from 6 to 1 years. When residue was returned, the time for sustainable productivity increased from 6 to 15 years for direct seeded rice, 5 to 11 years with low-intensity puddling (P₁) and 1 to 8 years for high-intensity (P₂) puddling. For sustainability and productivity, the best practice for this or similar Vertisols in India would be direct seeding of rice with conventional tillage and residues returned.     

免耕技术研究进展

免耕是适合中国国情的实用技术,对中国农业可持续发展作用甚大。在此,阐述了免耕定义、原理、作用及免耕的历史与发展,归纳了免耕对土壤水分、温度、土壤物理、土壤化学、土壤生物学和作物生长发育及最终产量、经济效益方面等的影响：免耕由于减少了土壤蒸发,有利于提高水分利用效率,促进作物生长;但免耕降低土壤温度,特别是春季,不利于作物的生长,同时,免耕土壤结构、土壤微生物数量与活性相对稳定有利于提高养分利用效率和作物生长。在产量和效益方面,免耕有利于提高产量,更有利于提高效益。     

免耕对水稻生长和产量的影响

2005～2006年,对双免耕(早晚季免耕)、单免耕(晚季免耕)以及常规耕作的水稻进行了连续2 a 4季的生长和产量比较试验.结果表明:免耕与常规耕作在水稻生育期、经济性状和产量等方面无显著性差异.免耕栽培具有减轻劳动强度和缓解双抢期间季节紧、劳力缺等优势,且每季可节本增收229.5～627.0元/hm2.水稻免耕具有较好的推广前景,其中单免耕最值得推广.