Yield and soil system changes from conservation tillage in dryland farming: A case study from North Eastern Tanzania

Yield levels in smallholder farming systems in semi-arid sub-Saharan Africa are generally low. Water shortage in the root zone during critical crop development stages is a fundamental constraining factor. While there is ample evidence to show that conservation tillage can promote soil health, it has recently been suggested that the main benefit in semi-arid farming systems may in fact be an in situ water harvesting effect. In this paper we present the result from an on-farm conservation tillage experiment (combining ripping with mulch and manure application) that was carried out in North Eastern Tanzania from 2005 to 2008. Special attention was given to the effects of the tested treatment on the capacity of the soil to retain moisture. The tested conservation treatment only had a clear yield increasing effect during one of the six experimental seasons (maize grain yields increased by 41%, and biomass by 65%), and this was a season that received exceptional amounts of rainfall (549 mm). While the other seasons provided mixed results, there seemed to be an increasing yield gap between the conservation tillage treatment and the control towards the end of the experiment, and cumulatively the yield increased with 17%. Regarding soil system changes, small but significant effects on chemical and microbiological properties, but not on physical properties, were observed. This raises questions about the suggested water harvesting effect and its potential to contribute to stabilized yield levels under semi-arid conditions. We conclude that, at least in a shorter time perspective, the tested type of conservation tillage seems to boost productivity during already good seasons, rather than stabilize harvests during poor rainfall seasons. Highlighting the challenges involved in upgrading these farming systems, we discuss the potential contribution of conservation tillage towards improved water availability in the crop root zone in a longer term perspective.     

The effect of system innovations on water productivity in subsistence rainfed agricultural systems in semi-arid Tanzania

Rainfed subsistence farming systems in sub-Saharan Africa generally obtain low crop yields as a result of highly erratic rainfall seasons. This paper presents results of research conducted to test the effects of improvements in farming techniques for subsistence rainfed systems. The research was carried out in the Makanya catchment of northern Tanzania where rainfall of less than 600 mm a⁻¹ and spread over two agricultural seasons per year is clearly insufficient to support staple food crops under the present farming systems in the area. The research sought to prove that, with improved efficiency in tillage techniques, grain yields can improve even under the existing challenging hydro-climatic conditions. The research tested farming system innovations (SIs) at four sites located within a spatial distance of 10 km where a combination of runoff diversion (RD), on-site rain water harvesting (WH) and conservation tillage (CT) were compared against the traditional farming methods of hand-hoeing under strict rainfed conditions (Control). For RD, runoff generated from natural storms was directed into infiltration pits dug along the contour with the excavated soil deposited upward of the trenches (fanya juus). The impact of these techniques on maize yields under different SIs was investigated.The results showed that the innovations resulted in increased maize grain yields of up to 4.8 t ha⁻¹ compared against current averages of less than 1 t ha⁻¹. The average productivity of the available water over four seasons was calculated to range between 0.35 and 0.51 kg m⁻³. For the SIs that were tested, the distribution of yields within a cultivated strip showed variations with better yields obtained on the down slope side of the cultivated strip where ponding effects resulted in higher water availability for infiltration and storage. However, due to the large seasonal climate variability, statistical analysis did not show significant differences in the yields (p < 0.05) between different cultivation techniques.The study showed that there is scope to improve grain yields with the little available rainfall through the adoption of techniques which promote water availability and retention within the field. The re-partitioning of water within the field creates mitigation measures against the impact of dry spells and allows alternative cropping in addition to the traditional maize cultivated in the rainfall seasons.     

Water productivity in rainfed systems: overview of challenges and analysis of opportunities in water scarcity prone savannahs

Addressing the Millennium Development Goals on food and poverty over the coming decade puts enormous pressure on the world’s finite freshwater resources. Without water productivity (WP) gains, the additional freshwater in agriculture will amount to 5,600 km³ year⁻¹ in 2050. This is three times the current global irrigation use. This paper focuses on the underlying processes and future opportunities of WP gains in water scarcity prone and poverty stricken savannah regions of the world. The paper studies the consumptive (green) WP dynamics rainfed farming systems, and shows that the often assumed linear relationship between evapotranspiration (ET) and yield (Y) does not translate into constant WP over a wide range of yields. Similarly, crop transpiration (T) and Y show non-linearity under on-farm and low yield conditions. This non-linearity is validated against several on-farm research experiments in semi-arid rainfed farming systems. With integrated soil and water management, focusing on dry spell mitigation and soil fertility can potentially more than double on-farm yields, while simultaneously improve green (ET) WP and productive green (T) WP. Through the adoption of appropriate soil and water management in semi-arid smallholder farming systems, crop yields improve and result in improved livelihoods and WP gains.     

Quantifying risk for water harvesting under semi-arid conditions: Part II. Crop yield simulation

Risk assessment of maize yield was carried out using a crop growth model combined with a deterministic runoff model and a stochastic rainfall intensity model. These were compared with empirical models of daily rainfall–runoff processes. The combination of the deterministic runoff model and the stochastic rainfall intensity model gave more flexible performance than the empirical runoff model. Scenarios of crop simulation included production techniques (water harvesting, WH, and conventional total soil tillage, CT) and initial soil water content at planting (empty, half and full). The in-field water harvesting technique used in the simulation was a no-till type of mini-catchment with basin tillage and mulching. The lower the initial soil water content at planting, the greater the yield difference between the WH and CT production techniques. With the low initial soil water content at planting, the WH production technique had up to 50% higher yield compared to the CT production technique, clearly thus demonstrating the superiority of the WH production technique. Under all the variations in agronomic practices (planting date, plant population, cultivar type) tested, the WH had a lower risk than CT under these semi-arid climatic conditions (i.e., WH increased the probability of higher crop yields).     

Evaluation of post-rainy season crops with residual soil moisture and different tillage methods in rice fallow of eastern India

In eastern India, farmers grow rice during rainy season (June-September) and land remains fallow after rice harvest in the post-rainy season (November-May) due to lack of sufficient rainfall or irrigation facilities. But in lowland areas of eastern India, sufficient carry-over residual soil moistures are available in rice fallow in the post-rainy season (November-March), which can be utilized for growing second crops in the region. During the post-rainy season when irrigation facilities are not available and rainfall is meager, effective utilization of carry-over residual soil moisture and conservation agriculture become imperative for second crop production after rice. Implementation of suitable tillage/seeding methods and other agro-techniques are thus very much important to achieve this objective. In this study four pulse crops (lathyrus, blackgram, pea, and greengram) were sown utilizing carry-over residual soil moisture and with different tillage/seeding methods viz. relay cropping (RC)/farmers’ practice, reduced tillage (only two ploughing) (RT), conventional tillage (CT) and zero tillage (ZT). Study revealed that the highest grain yields of 580, 630, 605 and 525 kg ha⁻¹ were obtained from lathyrus, blackgram, pea and green gram, respectively, with RT treatment. On the other hand, with conventional tillage, 34-44% lower yields were obtained than that of RT. Crops with reduced tillage performed better than that with zero tillage or relay cropping also. Impacts of different tillage methods on important soil physical properties like infiltration, bulk density were also studied after harvesting first crop (rice) and before growing second crops (pulses) in rice fallow. The lowest mean bulk density (1.42) was recorded in the surface soils of CT treatment while the corresponding value under ZT treatment was 1.54 Mg m⁻³.     

Representation of rainfed valley ricefields using a soil-water balance model

Soil-water conditions for ricefields located in valleys in micro-catchments are simulated using a daily soil-water balance model. The crop is primarily rainfed but there is also limited irrigation water. The simulation covers a complete year and includes features such as rainfall, irrigation releases, runoff from uplands, actual evaporation and evapotranspiration, percolation losses through the bed and bunds of the ricefield, standing water in the field and overflows from the ricefield. A specific location in Sri Lanka is selected to illustrate the approach. The impacts of different conditions are explored including alternative irrigation releases, increased losses through the bed and bunds of the ricefield and a lower overflow from the ricefield. Simulations indicate that ricefields which are towards the valley sides have an increased inflow due to runoff from adjacent uplands; this can lead to improved rice yields. However, reducing heights of the bunds to half the original value results in substantial overflows during periods of high rainfall while the number of days without submergence almost doubles. This uncomplicated model is consistent with the limited field data and information available; it provides a realistic representation of the important processes and indicates why poor crop yields often occur.     

动力圆盘耙高效清理作物残茬的应用综述（摘选）

作物残茬处理是水土保持和土地生产力管理的一个重要方面;同时,为了提高作物产量,保持适当的土壤质地和结构也尤为重要。耕作方式在土壤保护和管理过程中起着至关重要的作用。过度耕作会导致水土流失、土壤板结和土壤结构恶化,从而降低其生产力。因此目前的耕作方式正在向少免耕方向转变。另一方面,以农业为支柱产业的发展中国家,如孟加拉国、柬埔寨、印度、菲律宾和泰国等,仍然以露天焚烧的方式处理作物秸秆。在从传统耕作方式向保护性耕作转型的背景下,农民正在寻找适当的机具来处理作物残茬,而动力圆盘耙作为一种通用型机具能适应多种土壤和操作条件,在保护性耕作中发挥着重要的作用。该文综述了各种田间耕作机械的优点、工作质量和相关问题,并证实动力圆盘耙在农田废弃物处理中的有效性。      

黑土区坡耕地水土保持耕作措施对土壤理化性状的影响

为探寻黑土区坡耕地不同水土保持耕作措施对土壤理化性状的影响机理,开展了田间小区试验。设置横坡耕作（TP）、垄向区田（RF）、深松（SF）、横坡耕作+垄向区田（TP-R）、横坡耕作+深松（TP-S）、垄向区田+深松（RF-S）3种水土保持耕作措施及3种组合耕作措施,并以常规顺坡耕作（CK）为对照,分析了土壤孔隙度、土壤机械组成、水稳性土壤团聚体稳定性、土壤养分含量等指标,并采用TOPSIS模型对不同水土保持耕作措施进行了综合评价,筛选了土壤稳定性强且蓄水保肥效果良好的水土保持耕作措施。结果表明：在玉米的全生育期内,深松、垄向区田、横坡耕作均能提高土壤体积含水率。TP-S处理体积含水率最大,0~40cm土层平均体积含水率较CK处理增加29.47%;RF-S处理平均孔隙度最大,TP-S处理次之,平均孔隙度较CK处理分别增大10.68%、9.25%;TP-S处理能够显著提高土壤稳定性,其中平均质量直径（MWD）、几何平均直径（GMD）和大团聚体含量（R0.25）较CK处理分别增加12.30%、19.57%、13.97%;TP-S处理能够改善土壤机械组成,TP-S处理粗砂粒、粉粒、黏粒含量较CK处理增加15.40%、26.89%、1.90%,细砂粒含量较CK处理降低31.56%;TP-S处理IN（无机态氮）、AP（有效磷）、AK（速效钾）含量最高,较CK处理IN、AP、AK含量分别增加42.81%~55.32%、39.69%~40.68%、20.41%~25.45%。由TOPSIS模型综合评价结果可知,TP-S处理贴合度最高,土壤结构更稳定,且蓄水保肥效果更好,为适宜该地区的水土保持耕作措施。     

A review of rainwater harvesting

This article reviews recent literature on rainwater harvesting and its potential application for crop production. Some 170 articles published between 1970 and 1980 were found, all of them revealing an awareness of the increasing need for rainwater harvesting and a recognition of its potential.A definition of rainwater harvesting is presented on the basis of three characteristics common to it: arid to semi-arid climate, local water, and small-scale operation. The following elements are considered:runoff inducement — vegetation management, surface treatment, chemical treatment;runoff collection — Micro-Catchment Water Harvesting (MCWH) and Runoff Farming Water Harvesting (RFWH);storage and conservation.Design aspects of MCWH are reviewed: MC size, ratio of contributing area to collecting area, and layout. MCWH is especially suitable to non-irrigated areas. The Kinematic Wave Equation and Dynamic Equations have been used in modelling MCWH.RFWH can be useful in improving irrigation water availability in surface reservoirs. For modelling RFWH, the Unit Hydrograph Method is suitable. More research is required to determine the potential of runoff farming without surface reservoirs.     

辽阳市保护性耕作技术推广现状及对策

保护性耕作作为一种现代耕作技术,在建立节约型农业与可持续型农业方面有着重要的作用。为此,综合分析了辽阳市近年来实施保护性耕作技术取得的成就,总结出适合辽阳市的3种保护性耕作技术模式以及存在的一些主要问题,提出了做好保护性耕作研究、示范和推广工作的建议。     

保护性耕作对土壤理化性质和作物产量的影响

应用定位田间试验的方法，研究了不同耕作方式和秸秆还田方式对作物产量和土壤理化性质的影响。研究结果表明，传统翻耕的土壤容重大于进行保护性耕作的土壤容重；随着免耕年限的增加，土壤团聚体不断增大，进行5年保护性耕作的土壤团聚体比进行2年、3年保护性耕作的土壤团聚体有明显增加：进行免耕秸秆覆盖处理的土壤养分除碱解氮外．有机质、全氮、全钾、全磷及速效磷、速效钾均高于免耕无秸秆覆盖和传统翻耕的土壤：在施肥量相同的情况下。进行保护性耕作处理的小麦和水稻产量均比传统翻耕高，其中以半量秸秆还田免耕增产幅度最高，分别达小麦14．45％，水稻6．47％。     

农业耕作措施减沙的能量分析

从径流能量入手,在室内人工降雨试验的基础上,分析了坡面耕作措施对径流能量的削减作用。耕作措施可有效减少坡面产流、产沙,其径流能量消减率可达26.84%～51.58%,在径流能量传递过程中,3种耕作措施能量传递均小于对照,其中等高耕作对径流能量消减率最大,减沙作用与径流能量消减之间呈对数关系,耕作措施对径流能量的消减作用受雨强和坡度的影响,随雨强和坡度增大,消减作用减弱。     

Rainfall retention probabilities computed for different cropping-tillage systems

Rainfall and runoff event data from several different cropping and tillage systems on three field-sized watersheds in the Southern Piedmont of the U.S.A. are used to estimate empirical probability distributions of the USDA Soil Conservation Service runoff curve number. Long-term rainfall records from a nearby gauge are also employed to obtain probabilities for rainfall event occurrence and depth. These probability distributions of runoff curve number and rainfall occurrence and depth are incorporated in a recursive computer procedure to compute estimated probability distributions of annual rainfall retention for the different cropping-tillage systems. Comparison of these estimated rainfall retention probability distributions shows a reduction in the risk for low rainfall retention with the installation of conservation tillage systems.     

Effects of conservation tillage practices on winter wheat water-use efficiency and crop yield on the Loess Plateau,China

In the semi-humid to arid loess plateau areas of North China, water is the limiting factor for rain-fed crop yields. Conservation tillage has been proposed to improve soil and water conservation in these areas. From 1999 to 2005, we conducted a field experiment on winter wheat (Triticum aestivum L.) to investigate the effects of conservation tillage on soil water conservation, crop yield, and water-use efficiency. The field experiment was conducted using reduced tillage (RT), no tillage with mulching (NT), subsoil tillage with mulching (ST), and conventional tillage (CT). NT and ST improved water conversation, with the average soil water storage in 0–200 cm soil depth over the six years increased 25.24 mm at the end of summer fallow periods, whereas RT soil water storage decreased 12 mm, compared to CT. At wheat planting times, the available soil water on NT and ST plots was significantly higher than those using CT and RT. The winter wheat yields were also significantly affected by the tillage methods. The average winter wheat yields over 6 years on NT or ST plots were significantly higher than that in CT or RT plots. CT and RT yields did not vary significantly between them. In each study year, NT and ST water-use efficiency (WUE) was higher than that of CT and RT. In the dry growing seasons of 1999–2000, 2004–2005 and the low-rainfall fallow season of 2002, the WUE of NT and ST was significantly higher than that of CT and RT, but did not vary significantly in the other years. For all years, CT and RT showed no WUE advantage. In relation to CT, the economic benefit of RT, NT, and ST increased 62, 1754, and 1467 yuan ha⁻¹, respectively, and the output/input ratio of conservation tillage was higher than that of CT. The overall results showed that NT and ST are the optimum tillage systems for increasing water storage and wheat yields, enhancing WUE and saving energy on the Loess Plateau.     

机械化保护性耕作与行走式节水补灌技术的集成研究

针对我国北方干旱和半干旱地区因春旱引起的播种难出苗以及因土壤缺墒造成的诸多耕作问题,讨论了机械化保护性耕作技术和行走式节水补灌两项抗旱耕作适用技术的内容、特点及其发展历程;并对两项技术的共同性和互补性进行了分析;建议在研究、开发、试验、示范、推广和运用中集成配套,对两项抗旱耕作技术现有适用机械的主要结合点(免耕施肥坐水播种联合作业机)做进一步的研究,提高其通用性与精准性,以彰显免耕施肥坐水播种联合作业工艺的优势,达到干旱地区抗旱节水与增产节支的目的.     

北票市保护性耕作技术推广研究

保护性耕作是旱作农业区节水抗旱、保护环境、节本增效的重要措施。概述北票市农业机械化发展现状,介绍保护性耕作技术在北票市的推广应用情况、实施效果与推广经验,为推动北票市保护性耕作技术进一步应用提供参考。     

保护性耕作现状及发展趋势

在分析美国、加拿大、巴西、澳大利亚、欧洲等国家、地区和我国保护性耕作技术现状的基础上,阐明了保护性耕作是旱地农业发展的一条重要途径,并针对我国实际情况,提出了相关的建议.     

Quantifying rainfall-runoff relationships on the Dera Calcic Fluvic Regosol ecotope in Ethiopia

Droughts, resulting in low crop yields, are common in the semi-arid areas of Ethiopia and adversely influence the well-being of many people. The objective of this study was to assess the benefit that in-field rainwater harvesting (IRWH) would have, compared to conventional tillage, on maize yields on a semi-arid ecotope at Dera situated on the eastern part of the Rift Valley. Rainfall-runoff measurements were made during 2003 and 2004 on 2 m × 2 m plots provided with a runoff measuring system and replicated three times for each treatment. There were two treatments: conventional tillage (CT) and no-till (NT), the latter with a flat surface that promotes runoff and therefore IRWH. Rainfall intensity was measured at 1 min intervals with an automatic tipping bucket instrument, and runoff was measured after each rain event. Measured runoff as a function of rainfall intensity and duration from half the rainfall-runoff events was used to determine the critical parameters of a appropriate runoff model. The calibrated model was found to be capable of predicting runoff in a satisfactory way.Rainfall-runoff measurements were made during the rain seasons in 2003 and 2004 during which there were 25 rain events with >9 mm of rain. There was no statistical difference between the runoff on the two treatments. The measured runoff (R) for the two rain seasons, expressed as a fraction of the rainfall during the measuring period (P), i.e. R/P, gave values of 0.46 and 0.39 for the NT and CT treatments, respectively.Results from 7 years of field experiments with IRWH at Glen in South Africa were used to estimate the yield benefit of NT for Dera compared to CT. The results were 696 and 494 kg ha⁻¹ for 2003 and 2004, respectively. Based on the estimated average long-term maize yield of 2000 kg ha⁻¹ at Dera, this was an estimated yield increase ranging from 25% to 35%.     

Impact of modified tillage on runoff and nutrient loads from potato fields in Prince Edward Island

Potato production accounts for ∼24% of the cultivated land-use in Prince Edward Island, Canada. The island often experiences prolonged dry periods interspersed with excessive rainfall events throughout the growing season. Thus, water retention is important for maximum crop production while sediment and nutrient loading to surface water systems are also concerns. Therefore, agronomic practices that reduce the environmental impact of potato production are being sought. Basin tillage (BT) is a potential option in which small dams are created in the furrows (row middles), resulting in basins that enhance infiltration, reduce runoff, minimize contaminant loads, and increase yields.This on-farm study compared BT against two types of ‘conventional’ hilling treatments with replicated plots on four field sites over two growing seasons. Field sites had sandy loam soils with topography slopes ranging from 3% to 5%. Within each field, nine 25 m long and 3.66 m wide (4 rows) plots were established, including three plots of each hilling treatment (CT = conventional tillage; RS = row shaper tillage; BT = basin tillage). Runoff volume, nutrient (phosphate, ammonium, nitrate) and suspended solids loads were measured using collection barrels on the down slope end of each furrow.Basin tillage had 78% and 75% less runoff than CT and RS, respectively (P < 0.05). Runoff differences between BT and CT were significant at all sites while runoff differences between BT and RS were significant at three of four sites. Reductions for each parameter (on a mass basis) averaged across all sites were: sediment 89%, nitrate 45%, ammonium 38%, and phosphate 15%; although, treatment effect was not significant for some mass loads in some fields. No significant effect on marketable potato yield was observed at any site; soil water was not limiting in either growing season. Overall, basin tillage was effective at reducing runoff and nutrient losses without affecting yield and appears to be an effective tool for decreasing environmental risks.     

Effect of nozzle type on runoff and yield of corn and sorghum under center pivot sprinkler systems

Summary Corn (Zea mays L.) and grain sorghum (Sorghum bicolor L.) production were compared under impact and spray nozzled center pivot sprinkler systems. The crops were grown under two pairs of sprinkler systems located approximately 110 km apart. One system of each pair was equipped with high pressure (379 or 414 kPa) impact sprinkler heads and the other system was equipped with low pressure (172 or 207 kPa) spray nozzles. Half of each circle was planted to corn and half was planted to sorghum. Additionally, four tillage treatments were included in the experimental design (conventional tillage, conventional tillage + deep ripping, conventional tillage + diking, and minimum tillage). The evaporative losses from the high pressure system with impact sprinkler heads were not significantly different from the low pressure system with spray nozzles. The minimum tillage and deep ripped treatments reduced runoff while diking eliminated it. The two nozzle types did not produce significantly different grain sorghum yields; however, corn yielded significantly more under the high pressure system with impact sprinkler heads than under the low pressure system with spray nozzles. The different tillage treatments did not influence yields of either crop significantly.Contribution of the Texas Agricultural Experiment Station. Paper No. 19198