Effect Of Soil Tillage Research Articles

Assessing the effect of soil tillage on crop growth: A meta-regression analysis on European crop yields under conservation agriculture

Many strategies exist to combat soil degradation through erosion and compaction on agricultural fields. One of these strategies is conservation agriculture (CA). Reduced or no-tillage techniques, together with crop residue management and crop rotation are the pillars of CA. The term reduced tillage covers a range of tillage practices but it never involves inverting the soil. In this way, soil disturbance is minimised and crop residues are left on the soil. Studies in many European countries have shown that CA can indeed be very effective in combating soil erosion. However, soil and water conservation do not appear as main drivers in farmers’ decisions to shift or not to CA. Economic factors tend to be more important, but there are a lot of uncertainties on this domain. Studies show that production costs are mostly reduced, mainly by reduced fuel costs. Although many European studies have investigated the effect of reduced soil tillage on crop yields, a lot of uncertainties still exist. Most of the studies only cover a small range of field experiments, in one region. We present a meta-regression analysis (47 European studies, 563 observations) that compares crop yields under conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) techniques. We analysed the possible influence on the relative yield ((RT or NT)/CT) of crop type, tillage depth, crop rotation, climate, CT yield and length of application of RT or NT. Our analysis shows that, while the introduction of conservation tillage in Europe may indeed have some negative effect on yields, these effects can be expected to be limited: the overall average reduction we found was ca. 4.5%. NT reduces crop yield on average with 8.5%. However, RT leads to a reduction in crop yields for maize and winter cereals only. By applying a linear mixed model, the importance of tillage depth and crop type as classification effects could be confirmed. Surprisingly, no-tillage did perform worse under drier climatic conditions. Negative effects such as an increased prevalence of pests and a lower quality of seed placement seem to outweigh possible gains due to increased water availability. On clay and sandy soils, however, this negative effect of no-tillage is counteracted, and all conservation tillage techniques perform better under drier climatic conditions. Another important finding is that, in cereals only rotations, relative yields under conservation tillage tend to decrease with time. Our analysis shows that conservation tillage is certainly a viable option for European agriculture from the viewpoint of agricultural productivity. Potential negative effects on agricultural productivity can be strongly reduced by applying sufficiently deep tillage and using a crop rotation including crops other than cereals.

Effect of inter-row cultivation on soil carbon dioxide emission in a peach plantation

Soil biological properties and CO2emission were compared in undisturbed grass and regularly disked rows of a peach plantation. Higher nutrient content and biological activity were found in the undisturbed, grass-covered rows. Significantly higher CO2fluxes were measured in this treatment at almost all the measurement times, in all the soil water content ranges, except the one in which the volumetric soil water content was higher than 45%. The obtained results indicated that in addition to the favourable effect of soil tillage on soil aeration, regular soil disturbance reduces soil microbial activity and soil CO2emission.

Can non-inversion tillage and straw retainment reduce N leaching in cereal-based crop rotations?

Finding ways of reducing nitrate leaching in Northern Europe has become an extremely important task, especially under the projected climate changes that are expected to exacerbate the problem. To this end, two field experiments were established under temperate coastal climate conditions to evaluate the effect of tillage, straw retainment and cropping sequences, including cover crops, on nitrate leaching. The experiments were established in autumn 2002 on a loamy sand with 92 g clay kg −1 and a sandy loam with 147 g clay kg −1. The tillage treatments were stubble cultivation to 8–10 cm or 3–4 cm, direct drilling, or ploughing to 20 cm. The hypothesis was that (i) decreasing soil tillage intensity would decrease leaching compared to ploughing, (ii) leaving straw in the field would decrease leaching compared to removing straw, and (iii) a spring/winter crop rotation with catch crops would be more efficient in reducing nitrate leaching than a winter crop rotation. Overall, we were not able to confirm the three hypotheses. The effect of soil tillage on leaching might be blurred because the studied crop rotations had a high proportion of winter crops and because catch crops were grown whenever the alternative would have been bare soil in autumn and winter. The spring/winter crop rotation with catch crops was not found to be more efficient in reducing nitrate leaching than the winter crop rotation. In contrast, in a single year the winter crop rotation showed significantly lower leaching than the spring/winter crop rotations, probably due to the spring/winter crop rotation including peas, which may be considered a high-risk crop. Our study highlights that management practices that improve biomass production throughout the year are crucial in order to tighten the nitrogen cycle and thereby reduce nitrate leaching.

Características químicas de um Latossolo sob diferentes sistemas de preparo e adubação orgânica

O não-revolvimento do solo e a incorporação dos resíduos culturais e fertilizantes alteram a disponibilidade e distribuição dos nutrientes no perfil. O objetivo deste estudo foi avaliar as alterações químicas devido aos sistemas de preparo do solo e à natureza das fontes de fertilizantes. O trabalho foi desenvolvido em Latossolo Vermelho distroférrico, no município de Chapecó (SC), no período de 1998 a 2002. O delineamento experimental utilizado foi de blocos ao acaso com parcelas subdivididas e quatro repetições. Nas parcelas foram avaliados dois sistemas de preparo do solo: convencional (SPC) e plantio direto (SPD) e nas subparcelas três fontes de fertilizantes: nitrato de amônio (NA), esterco de aves (EA) e esterco de suínos (ES), aplicados na dose de 120 kg ha-1 de N. Após o quarto cultivo de milho, foram coletadas amostras de solo em quatro profundidades (0-10, 10-20, 30-40 e 50-60 cm). Observou-se que a adubação orgânica proporcionou aumentos nos teores de P, K, Ca, Mg, Zn e Cu, principalmente na camada de 0-10 cm em SPD. A mobilização periódica do solo acarretou melhor distribuição dos nutrientes na camada arável, reduzindo a formação de gradiente no perfil do solo. A utilização de EA acarretou aumento nos valores de pH do solo, enquanto o NA causou redução com conseqüente aumento dos teores de Al trocável.

Temperatura do solo em função do preparo do solo e do manejo da cobertura de inverno

Com o objetivo de avaliar o efeito do preparo do solo e do manejo da cobertura de inverno (consórcio aveia-preta + nabo forrageiro) sobre a temperatura do solo, realizou-se um experimento em um Nitossolo em Botucatu-SP no outono/inverno de 2000. Utilizou-se um delineamento em blocos casualizados em esquema fatorial 3 x 3 (três preparos e três manejos). O preparo do solo constou de: preparo convencional, preparo conservacionista com escarificação e plantio direto, e o manejo da cobertura: consórcio dessecado, rolado e triturado. Foram avaliados a temperatura do solo (termopares) a 5 cm de profundidade, de hora em hora, aos 7, 14, 30, 45 e 60 dias após a emergência das plantas do consórcio; o teor de água do solo na profundidade de 10 cm, nas mesmas épocas; e a cobertura do solo (massa seca e índice de cobertura), imediatamente após aplicação dos tratamentos. O sistema plantio direto apresentou temperaturas do solo menores que as do preparo convencional, até o 14º dia após emergência (DAE) das plantas. A partir do 30° DAE das plantas, a temperatura não foi mais influenciada pelos tratamentos, devido à cobertura do consórcio e ocorrência de boa disponibilidade de água no solo. Os manejos da cobertura com rolo-faca, triturador e herbicida não influenciaram a temperatura do solo. A temperatura do solo não interferiu no crescimento e desenvolvimento das culturas de cobertura.

Effect of soil tillage and weed control methods on weed biomass and yield of lentil (Lens culinaris Medic.)

The study was carried out in dryfarming areas in Ankara, Turkey, over 2 years (2001 – 2002 and 2002 – 2003). The objective was to determine different soil tillage and weed control methods on weed biomass and yield components, yield of lentil (Lens culinaris). This study compared the effects of two tillage systems (shallow minimum tillage and traditional tillage) and three weed control methods (weedy check, hand weeding and herbicide) on weed biomass, growth characteristics, seed yield and some yield components of lentil. Significant differences were found among weed control methods for weed biomass and yield parameters of lentil. Tillage systems had no significant effect on weed biomass or yield of lentil. The highest yield and lowest weed biomass was found in the hand-weeded treatment compared to the other weed control methods. Results of this research indicate that weeds are a main constraint for lentil growing under dryland conditions. Grain yield of lentil was reduced more than 60% due to uncontrolled weeds.

Effect of soil tillage, crop rotation and nitrogen application rates on bread-baking quality of spring wheat (Triticum aestivum L.) in the Swartland wheat producing area of South Africa

Spring wheat (Triticum aestivum L.) is produced in the wheat producing areas of the Western Cape Province, Republic of South Africa, primarily for bread-baking purposes. Milling and baking characteristics are therefore of utmost importance. In a long-term tillage and crop rotation experiment in the Swartland, it was found that during the 2000 growing season, flour yield was increased by conventional tillage but hectolitre mass did not respond to tillage during the same season or on average for the period 1992–1998. Although grain protein content and ultimately loaf volume were also higher with conventional tillage when compared to no-tillage, the latter resulted in the highest grain protein yield owing to slightly higher grain yield obtained with no-tillage. The inclusion of a legume crop (lupin) and canola in rotation with wheat had little effect on either milling or baking characteristics, possibly owing to the fact that legumes were only planted once in a four-year cycle. Increased N-fertiliser rates (140 kg N ha−1) resulted in reduced hectolitre mass, but higher grain protein when compared to low N rates of 60 kg N ha−1. This study once more illustrated the complexity of the bread-baking process and the need for good management practices in order to obtain both high yield and good bread-baking quality under Mediterranean climatic conditions.

Evolution of weed beet ( Beta vulgaris L.) seed bank: Quantification of seed survival, dormancy, germination and pre-emergence growth

Weed beet is an important weed of sugar beet crops. Weed and cropped beets can cross easily and the management of weed beet is therefore crucial in the case of the advent of GM sugar beet, especially herbicide-tolerant cultivars, in order to ensure the co-existence of GM and non-GM crops and to avoid the appearance of herbicide-resistant weed beet. The inability of weed beet to compete in most other crops of the rotation makes the seed bank evolution a crucial stage of the life-cycle because in the rotation, sugar beet is at the most cultivated only every 3 years. The present study used seed burial experiments and laboratory analyses to characterise each step of the evolution of the weed beet seed bank and the external factors that could modify seed persistence in the soil. A monthly seed mortality of 10% was observed between October and December, while mortality was nil during the other seasons. Equations were then developed to describe the observed seasonal variations in seed survival. Seed dormancy also varied with season: the proportion of non-dormant seeds increased during winter (appearance of secondary dormancy) and decreased during the remaining seasons (loss of dormancy). In addition, the germinating seeds decreased with seed age and seed depth, while the presence of light stimulated germination. These observations were also translated into equations. Last, the pre-emergence hypocotyl growth and its variability were studied according to seed age, but no significant effect was observed. The results confirm the importance of the effects of cropping system on the evolution of the weed seed bank, especially the effect of soil tillage, which determines the date and conditions of seed burial, seed excavation and germination stimulation.

Effects of soil tillage on the yield and quality of tobacco in Croatia

The effect of soil tillage on the yield and quality of flue-cured tobacco was studied from 1998 to 2001 at the Experimental Station of the Tobacco Institute Zagreb in Croatia. The trial soil was a Luvisol with an acid reaction and a low content of colloids and organic matter. There were three treatments in the experiment: 1. autumn ploughing, 2. spring ploughing, and 3. autumn ploughing + chisel ploughing in spring. The treatments were arranged in random blocks with four replications. Soil ploughed in both autumn and spring gave higher yields of flue-cured tobacco in comparison with autumn ploughing alone. Soil ploughed only in autumn became compacted due to settling during the winter and spring because of the unstable structure and unfavourable texture.

Effect of soil tillage, crop rotation and nitrogen application rates on plant-N content of spring wheat (Triticum aestivum L.) in the Swartland wheat-producing area of the Republic of South Africa

Studies on nitrogen content in spring wheat were conducted during the 2000 and 2001 growing seasons as part of a long-term tillage and crop rotation trial. Four tillage methods were used, namely conventional tillage (CT), tine tillage (TT), minimum tillage (MT) and no-tillage (NT). Crop rotation systems used were continuous wheat (WW) and wheat/lupine/wheat/canola (WLWC). Three rates of nitrogen fertiliser (60, 100 and 140 kg. N ha-1) were applied as sub-plots. Wheat plants were sampled at tillering stage (S1), stem elongation (S2), flag leaf (S3) (2000 growing season only) and anthesis (S4). In general nitrogen content (% of plant component) decreased as the plant reached maturity. Nitrogen content expressed as g plant-1 and kg ha-1 was affected by tillage method in both growing seasons, but the response depended on the amount of precipitation during the growing season. During the low rainfall year, highest N contents were found in the NT treatment. In contrast to this, CT resulted in the highest N content during high rainfall years. Significant differences in total nitrogen content in the plant (g plant-1) due to crop rotation were observed only at the tillering and flag leaf stages. At both stages, plants from the wheat/lupine/wheat/canola system resulted in significantly higher values than those from the monoculture (wheat/wheat) plots. A non-linear increase in the N content of the wheat crop with an increase in the N-application rate from 60 to 140 kg N ha-1 indicated a decrease in N-use efficiency at higher application rates during both years.

Effect of soil tillage, crop rotation and nitrogen application rates on soil mineral-N levels in the Swartland wheat producing area of South Africa

Studies on nitrogen (N) levels in soil were conducted from 1997 to 2000 in a long-term tillage and crop rotation trial, which started in 1976. Three tillage methods namely conventional tillage (CT), tine tillage (TT), and notillage (NT) were compared. Crop rotation systems used were continuous wheat (WW) and wheat/lupin/wheat/canola (WLWC). Three rates of N-fertilisers (60, 100 and 140 kg N ha−1) were applied. All treatments received 60 kg N ha−1 at planting, while the 100 and 140 kg N ha−1 treatments received additional top-dressings of 40 kg N ha−1 at tillering and stem elongation stages respectively. Soil samplings were done at 14-day intervals, starting immediately before planting and continued till harvesting each year. Samplings at planting were done before N-fertiliser was applied and therefore regarded as pre-planting (Pp). The effect of tillage methods on mineral-N was variable and inconsistent among the soil samplings and years. During the four-year-period of this study, higher values of total mineral-N were found with conventional tillage at the pre-planting (Pp) samplings. Crop rotation did not significantly influence total mineral-N, which may be explained by the cultivation of a legume crop (lupins) once every four years only. In general the application of N-fertiliser resulted as expected in an initial increase in the mineral-N content of the soil. However, this was soon followed by a rapid decline as crops start to utilise the added nitrogen, resulting in values of less than 10 mg kg−1 soil during the grain filling stages with application rates of 60 and 100 kg N ha−1. These values may be regarded as deficient for grain yields of 4000 to 5000 kg ha−1.

Effect of soil tillage, crop rotation and nitrogen application rates on grain yield of spring wheat (Triticum aestivum L.) in the Swartland wheat producing area of the Republic of South Africa

Studies on spring wheat yield components were conducted during the 2000 and 2001 growing seasons only, while grain yield responses to tillage, crop rotation and N rates during these years were compared to the mean yield for the years 1992, 1994, 1996 and 1998 at Langgewens Experimental Farm in the Western Cape as part of a long-term tillage and crop rotation trial. Four tillage methods, namely conventional tillage (CT), tine tillage (TT), minimum tillage (MT), and no-tillage (NT) were compared. Crop rotation systems used were continuous wheat (WW) and wheat/lupin/wheat/canola (WLWC). Three rates of N fertilisers (60, 100 and 140 kg N ha−1) were applied. Tillage methods had a significant effect on the number of spikes m−2, spikelets per spike and number of kernels per spike in both the 2000 and 2001 growing seasons. Thousand kernel mass was not significantly affected by different tillage methods in both seasons. Mean grain yield for the years 1992, 1994, 1996 and 1998 did not differ significantly as a result of different tillage methods, but differences due to tillage methods were found in both the 2000 and 2001 growing seasons. Crop rotation had no significant effect on the mentioned yield components. Significantly higher mean yield for the years 1992, 1994, 1996 and 1998 were produced when wheat was rotated with lupins and canola (WLWC) compared to monoculture wheat (WW). Application of different rates of N had no significant effect on the number of spikes m−2, number of spikelets per spike and 1000-kernel mass in both growing seasons. While higher rates of N increased the number of kernels per spike in 2001 growing season, no significant differences were observed between different N rates in the dry season (2000) and the results even indicated a decrease in yield with increasing N rates in 2000. Higher grain yields were obtained by application of higher rates of N fertiliser during the wet season 2001, but significant tillage × crop rotation and tillage × nitrogen interaction for the mean grain yield during the 1992–1998 period indicated that yield responses to tillage were related to soil conditions.

Nutrient and heavy metal concentration and distribution in corn, soybean and wheat as affected by different tillage systems in the Argentine Pampas

Different tillage techniques affect the root absorption of macronutrients and trace elements. Our objective was to study the effect of conventional and zero tillage on the concentration of macro- and micronutrients and specially heavy metals and their distribution in soybean, wheat and maize plants in a area located far from contamination sources. The study was performed in a field experiment initiated in 1979 at the Agricultural Experimental Station located at Pergamino (Buenos Aires province, Argentina). The soil is a Pergamino Series Typic Argiudoll. The crops were wheat–soybean/corn in continuous sequence, in plots subjected to no tillage and conventional tillage. The experiment was a randomized block design, with four replications of each tillage treatment. Fertilizers were applied annually, averaging 90 kg N/ha/yr and 18 kg P/ha/yr. Wheat, corn and soybean were sampled in 1997 and separated into roots, aboveground material and grains. The three crops were analyzed for nitrogen (N), phosphorus (P), sulfur (S), potassium (K), boron (B), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), molybdenum (Mo), nickel (Ni) and zinc (Zn). Macronutrient concentration was higher in grains than in roots (i.e. N in corn: grains, 11.5 g kg −1; roots, 6.9 g kg −1). Micronutrients and heavy metals concentration were higher, with the exceptions of Mo and Cd, in roots than grains (i.e. Zn in soybean: grains, 44.85 mg kg −1; roots, 64.73 mg kg −1 or Cr in wheat: grains, 1.77 mg kg −1; roots, 19.70 mg kg −1). The effects of tillage were limited for nutrient concentrations, but significant for heavy metals. Soybean appeared to be more sensitive than cereals to the apparent effect of soil tillage. Compared with early published data of soils at the same location, there was only a significant relationship between Zn concentration in soils and its accumulation in plant roots.

Efeitos do preparo do solo, plantio direto e de rotações de culturas sobre o rendimento e a economicidade do feijoeiro irrigado

O objetivo deste trabalho foi identificar os efeitos de sistemas de preparo do solo e de rotações de culturas sobre o rendimento de grãos e economicidade da cultura do feijoeiro (Phaseolus vulgaris L.) irrigado pelo sistema pivô central. O trabalho foi conduzido durante seis anos consecutivos, na Embrapa-Centro Nacional de Pesquisa de Arroz e Feijão, localizado no Município de Santo Antônio de Goiás, GO, em Latossolo Vermelho-Escuro, de textura argilosa. O experimento consistiu de um fatorial 4 x 6, em delineamento inteiramente casualizado, com parcelas subdivididas. Os sistemas de preparo do solo foram: P1 arado de aiveca (novembro-dezembro) alternado com grade aradora (maio-junho); P2 arado de aiveca contínuo; P3 grade aradora contínua; P4 plantio direto; e as rotações de culturas: R1 arroz-feijão; R2 milho-feijão; R3 soja-trigo, R4 soja-trigo-soja-feijão-arroz-feijão; R5 arroz consorciado com calopogônio-feijão; e R6 milho-feijão-milho-feijão-arroz -feijão. As rotações R1, R2, R3 e R5 foram anuais, e as R4 e R6, trienais. Neste trabalho analisaram-se somente as rotações que continham feijão. O arroz, o milho e a soja foram semeados em novembro-dezembro (verão), e o feijão e o trigo, em maio-junho (inverno). Houve efeito do preparo do solo e das rotações de cultura sobre o rendimento de grãos do feijoeiro. A cultura produziu mais quando se utilizou no preparo do solo a combinação de arado de aiveca, nos cultivos de verão, e grade aradora nos de inverno. Os rendimentos do feijoeiro foram maiores quando a cultura foi implantada bienalmente na mesma área, nas rotações com arroz/calopogônio e arroz, e menores, nas rotações com milho. O feijoeiro irrigado, com relação ao preparo do solo e rotações de culturas, foi economicamente viável, propiciando taxas de retorno que variaram de 67% a 97%.

Estimativa da adubação nitrogenada para o milho em sistemas de manejo e culturas de cobertura do solo

O uso de fertilização mineral e de leguminosas são as principais alternativas para fornecimento, em larga escala, de nitrogênio (N) a culturas exigentes deste nutriente. Os riscos de poluição ambiental decorrentes da adubação nitrogenada podem ser elevados; portanto, em uma agricultura sustentável, torna-se necessário aprimorar a recomendação desta adubação. Este trabalho objetivou desenvolver uma estimativa da necessidade de adubação nitrogenada que considere o sistema de preparo e o uso de culturas de cobertura. Utilizou-se um experimento de longa duração, localizado na Depressão Central do Rio Grande do Sul, em Argissolo Vermelho Distrófico típico. O delineamento foi o de blocos casualizados com parcelas subsubdivididas e três repetições. As parcelas principais foram três sistemas de preparo: convencional, reduzido e direto; as subparcelas foram três sistemas de cultura: aveia/milho, ervilhaca/milho e aveia + ervilhaca/milho + caupi; as subsubparcelas foram: solo descoberto/milho, cultura de cobertura/milho, cultura de cobertura/milho + 90 kg ha-1 de N, cultura de cobertura/milho + 180 kg ha-1 de N. Com base nos resultados obtidos neste experimento, foi desenvolvida uma equação que considera o efeito do preparo do solo sobre a mineralização do N total do solo e a contribuição da cultura de cobertura na disponibilidade de N, como uma conseqüência da quantidade de N acumulada na fitomassa e a relação C/N. A partir desta equação, foi possível estimar a quantidade de N a ser adicionada pela adubação mineral, visando alcançar um rendimento projetado. Embora avaliada com uma base limitada de dados, a equação desenvolvida para estimar a recomendação de adubação nitrogenada apresentou satisfatória concordância com os dados experimentais.

Influence of cropping system on sharp eyespot in winter wheat

Wheat was assessed for sharp eyespot in three field trials using factorial designs which investigated preceding crops and soil tillage effects (inversion vs non-inversion), soil structure (compacted vs non-compacted) and wheat management techniques (sowing date and density, nitrogen fertiliser rate and form, removal or burial of cereal straw). A previous host vs non-host crop increased sharp eyespot. The effect of soil tillage depended on crop succession: if the previous crop was a host, soil inversion vs non-inversion decreased disease by burying infectious host crop residues; if the previous crop was a non-host itself preceded by a host, soil inversion vs non-inversion increased disease by carrying infectious material back to the soil surface. Uncompacted vs compacted soil increased sharp eyespot, but only at early stages. Early sowing always increased disease. High plant density (giving rise to low tillering) increased early and decreased late disease levels. A high vs low nitrogen rate and a low vs high ammonium content of the fertiliser slightly increased sharp eyespot. Removal or burial of straw did not affect disease. A hierarchy of the factors was established: crop succession and soil tillage were dominant factors; among the wheat management practices, only sowing date and plant density had important effects.

Influence of soil tillage on net N‐mineralization under sugar beet

AbstractThe shift from conventional to reduced soil tillage may affect physical and chemical soil properties and thereby net N‐mineralization. The aim of this study was to quantify the effect of soil tillage on net N‐mineralization at different depths. For this purpose the mineralization rate in the 0–10, 10–20, and 20–30 cm soil layer of conventionally and reduced tilled, N unfertilized plots under sugar beet was estimated with a field incubation method in 1993 and 1994. This method was compared to a balance method which takes into account N uptake of the crop and mineral N in the soil (0–90 cm).The mineralization rate in 1993 and 1994 was determined by the increase of soil temperature in spring and the change of water content in summer. Although the amount of cumulated mineralized N did not differ. soil tillage affected the mineralization rate in the three soil layers depending on the distribution of organic matter. In the reduced tilled soil the mineralization rate in the upper soil layer (0–10 cm) was higher than in conventionally tilled soil, whereas in the layer 10–20 cm depth the mineralization rate of the conventional treatment exceeded that of the reduced tilled treatment. These differences in mineralization rate between conventional and reduced tillage were more distinct in 1994 than in 1993. Since the amount of N mineralized during the season and the period of highest N‐mineralization rate in the arable soil layer did not differ due to soil tillage the necessity of an increased N‐fertilization in reduced tillage systems cannot be concluded from these results. This is supported by results of the white sugar yield, which showed no interaction between tillage and N fertilization. Results of the field incubation method differed considerably from those of the balance method. This is primarily due to lacking parameters in the N balance.

Tillage effect on root rot severity, growth and yield of beans

The effect of soil tillage on plant growth, yield and root rot severity of beans was investigated in field plots with and without root rot infestation in 1992 and 1993. There was a significant reduction in root rot severity, and an increase in plant dry weight and yield in the root-rot-infested soils with deep tillage in both years. Deep tillage also significantly increased plant dry weight and yield in the non-root-rot soils in a dry year. The resistant cultivar (A300) had significantly less root rot damage than the susceptible cultivar (Harowood) in both root rot and non-root rot infested soils. Significant differences in plant dry weight and yield in relation to cultivars were not detected. Therefore, deep tillage can reduce soil compaction and increase yield of beans and reduce root rot severity. Key words:Phaseolus vulgaris L., deep tillage, fusarium root rot, rhizoctonia root rot, yield

Influência do preparo do solo e da natureza do fertilizante nitrogenado na cultura do milho

Foi instalado um ensaio de campo, em solo Podzólico Vermelho-Escuro latossólico (PELa), para avaliar a influência do preparo do solo e a natureza da fonte do fertilizante nitrogenado, para adubação em cobertura, na cultura do milho. Os tipos de preparo do solo avaliados foram o convencional e o plantio direto. Em relação às fontes de nitrogênio, foram utilizadas: uma sólida, o sulfato de amônio (20%N), e outra fluida, o uran (32%N), aplicados à superfície do solo sem incorporação. A absorção de nitrogênio (mg/planta) foi determinada nas folhas, colmos, panículas e espigas, aos 53 e 67 dias após a emergência das plântulas. Na colheita, após a maturidade fisiológica, foi determinada a quantidade de nitrogênio acumulado e exportado, bem como a produção de grãos e alguns de seus componentes. O tipo de preparo do solo não apresentou influência na produção no primeiro ano de sua implantação. Entretanto, o plantio direto permitiu o aproveitamento do nitrogênio, mesmo quando se verificou redução na disponibilidade da água, estimada, através do balanço hídrico.

Tillage and agricultural sustainability

Agricultural sustainability implies an increasing trend in per capita productivity to meet the present needs without jeopardizing the future potential. Soil tillage, soil surface management to alleviate soil-related constraints to crop production, is a basic and an important input with short- and long-term effects on sustainability. An important effect of soil tillage on sustainability is through its impact on the environment e.g. soil degradation, water quality, emission of greenhouse gases from soil-related processes, etc. The need to attain agricultural sustainability is particularly urgent in several tropical eco-regions and soils of low-carrying capacity in the tropics. Soil tillage influences atricultural sustainability through its effects on soil processes, soil properties, and crop growth. However, there is no one blueprint of a universally applicable sustainable tillage system. Appropriate tillage systems are soil- and crop-specific and their adaptation is governed by both biophysical and socio-economic factors. In addition to increasing crop yields, tillage methods must also facilitate soil and water conservation, improve root system development, maintain a favorable level of soil organic matter content, and reverse degradative in the soil's life-support processes. Important components or sub-systems of conservation-effective tillage systems include mulch farming, no-till or reduced tillage systems, use of cover crops and planted fallows, agroforestry, raised beds or ridge-tillage, and soil inversion or deep plowing. The ecological limits for the applicability of these components or sub-systems differ widely. The efforts of a multi-disciplinary team (comprising soil scientists, agricultural engineers, agronomists, economists and social scientists) are needed to develop site-specific tillage methods to achieve both short- and long-term goals of agricultural sustainability.