Crop-pasture Systems Research Articles

High capacity of integrated crop–pasture systems to preserve old soil carbon evaluated in a 60-year-old experiment

High capacity of integrated crop–pasture systems to preserve old soil carbon evaluated in a 60-year-old experiment

Quantifying soil organic carbon’s critical role in cereal productivity losses under annualized crop rotations

Understanding the impact of soil degradation on crop productivity is essential for decision-makers to predict agronomic, economic, and environmental outcomes of agricultural operations. Soil organic carbon (SOC) is influenced by the cropping system and affects soil health through its effect on other soil physical, chemical, and biological properties. Data from a 56-year long-term experiment in Uruguay’s Pampa region were analyzed to quantify the effects of soil degradation on wheat (Triticum aestivum L.), and barley (Hordeum vulgare) yields. A significant degree of soil degradation was generated by six rotations with variable annual crop and pasture proportions (0%, 33%, 50%, and 66% of non harvest pasture). Yield records (n = 368) and annual values of 14 explanatory variables containing soil, climatic, and management indicators were evaluated using random forest regressions. Rotation-induced SOC variation ranged from 1.2% to 2.6%, and robust relationships between SOC, soil physical, chemical, and biological properties were established. Over time, yields increased in crop pasture systems but plateaued for the annualized crop rotation (0% pasture). Yield improvements due to agronomic technology advances partly mask soil degradation effects. SOC losses lead to a reduction in yield, even when the SOC level was above 2%. Thus, no critical level of SOC could be determined. SOC interacted with climate indicators to impact yield. This analysis confirms the central role of SOC in yield outcomes beyond nutrient availability, and its potential to represent a wide range of soil functions. Our findings indicate that crop rotations with a higher percentage annual vs. perennial crops negatively impact SOC, associated soil properties, and yield potential.

Soil organic matter in physical fractions after intensification of irrigated rice-pasture rotation systems

Crop-pasture systems improve soil quality, but their intensification through the increase of the frequency of annual crops may reduce it. We evaluated the impacts of six no-till rice rotations systems on soil quality after five years in a field scale long term experiment established on a site with a 30 years old stabilized rice-pasture rotation. Rotations included: continuous rice (ContRc); rice-soybean (Rc-Sy); rice-soybean-rice-sorghum (Rc-Sy-Sg); rice-soybean-pasture (Rc-Sy-Past); and rice-pasture, with short (Rc-SPast) and long-term pastures (Rc-LPast). Cover crops were included in winter between cash crops. All rotation phases coexisted and were replicated three times in space. Soil quality indicators included: soil organic carbon and total nitrogen contents in bulk soil (TSOC and TN, respectively) and in particulate (>53 μm, POM-C and POM-N) and mineral associated soil organic matter fractions (<53 μm, MAOM-C and MAOM-N). Soil cores were collected at 0−5 cm and 5−15 cm soils depths (results presented at 0−5 and 0−15 cm depths). Additionally, soil samples were taken up to 60 cm soil depth every 15 cm for TSOC and TN. After five years, no differences were observed in TSOC (29.3 Mg C ha−1) or TN (3.16 Mg N ha−1) between rotations in the first 0−15 cm as well as for each layer and in the aggregated 0−60 cm of soil. Neither POM-C nor POM-N contents were different between treatments that had perennial pastures in the rotation. However, Rc-LPast had 18 and 19 % greater POM-C and POM-N respectively than the average of Rc-Sy and Rc-Sy-Sg, (6.06 Mg C ha−1 and 0.48 Mg N ha−1, 0−15 cm depth). Meanwhile, the POM-C represented 23.6 % of TSOC in Rc-LPast, but in rotations that replaced pastures (Rc-Sy and Rc-Sy-Sg) represented only 20 %. For soils in temperate zones, under a stable rice-pasture rotation, there are intensification alternatives which preserved TSOC in the midterm. However, the reduction in the particulate fractions observed in the rice rotations that substituted perennial pastures with other crops, suggests that TSOC may be more vulnerable to losses in the long term.

Effects of long-term grazed crop and pasture systems under no-till on organic matter fractions and selected quality parameters of soil in the Overberg, South Africa

There is limited soil research on semi-arid, grazed no-till crop and pasture systems. The long-term (10 years) effect of three grazed no-till dryland crop and pasture rotation systems, and perennial lucerne pasture were assessed on soil carbon (C) and nitrogen (N) stocks, soil organic matter functional pools and selected soil quality parameters in the Overberg, South Africa. The largest soil C and N stocks (0–30 cm) were found in crop–pasture systems containing wheat and medic/clover (70.2–74.9 Mg C ha−1 and 8.3–8.4 Mg N ha−1), compared with perennial lucerne pasture (63.4 Mg C ha−1 and 7.7 Mg N ha−1) or cropping-only systems (54.7–58.9 Mg C ha−1 and 6.3–6.7 Mg N ha−1). Significantly higher labile C and N (free particulate organic matter fraction) contents were observed in crop–pasture systems (1.37–1.74 g C kg−1 and 0.107–0.110 g N kg−1) than in continuous cropping systems (0.9–1.0 g C kg−1 and 0.042–0.045 g N kg−1), attributed to higher annual C and N inputs and lower extent of soil disturbance. Significant positive correlations were found between soil C and N functional pools and soil quality parameters (soil respiration, effective cation exchange capacity and aggregate stability) and wheat yields. The results show the importance of the medic/clover pasture and wheat rotations in enhancing soil quality in the Overberg region.

System impacts of introducing crop grazing into pasture-based systems: the McClymont Memorial Lecture

The present paper briefly discusses the impacts of introducing dual-purpose (DP) crops as a grazing resource into what were previously pasture-only grazing systems. The emphasis is on the high-value crops wheat and canola, since these have the greatest potential to increase profits by providing both winter grazing and a high-value grain or seed crop at harvest. A major potential impact of grazing on such crops is that the reduction in grain yield caused by grazing offsets the value of the grazing obtained. The paper shows that this is not the case and that if crop grazing is performed correctly, there will be minimal impact on grain or seed yield; yield may even be increased. ‘Correctly’ in this context refers mainly to the timely removal of livestock from the crop. Increases in grain yield after grazing arise principally from the conservation of soil water from the winter period through to the grain-ripening stage. The paper emphasises that although the digestibility and crude protein content of DP crops are high, the use of long-season bread wheats as a grazing resource requires that system managers pay greater attention to the sodium and magnesium status of the grazing livestock. This is because of the often high potassium and very low sodium concentrations of wheat forage, which leads to high potassium : sodium ratios in the rumen and reduced absorption of dietary magnesium. Supplementation with sodium and/or magnesium has significantly increased the liveweight gain of stock grazing wheat, but is contra-indicated when grazing canola. The paper also considers the interaction between the amount of grazing provided directly by the crop(s), relative to the possibly increased grazing available from the pasture component of the system, due to ‘pasture spelling’ while livestock are grazing the crop. Data are presented to show that, overall, the introduction of crop grazing into a previously pasture-based system greatly increases the total amount of grazing obtained. In addition, of the total extra grazing obtained in crop–pasture versus pasture-only systems, up to 40% has been found to come from spelled pasture. This has major implications for the management of the total system. The paper concludes by suggesting that, in the future, research on crop–pasture systems should continue, but should pay greater attention to the grazing of DP crops by cattle and particularly by breeding livestock. In addition, there is a need for much better data on the contribution of crop residues to the total grazing system, plus data on the effects of the introduction of DP crops on the wool production of the total grazing system.

The influence of land use and management on soil carbon levels for crop-pasture systems in Central New South Wales, Australia

Changes in land use and management have been proposed as a way to increase soil organic carbon (SOC) in crop and pasture systems. Some of the proposed activities to improve SOC are the introduction of pasture phases in cropping systems, stubble retention, no-till cropping, improved fertilisation, introduction of more productive pasture species and grazing management. There is also growing interest in novel farming systems, such as pasture cropping (intercropping cereal crops with established perennial pastures), which may improve SOC. However, there have been few broad scale surveys to determine whether these land management changes have an impact on commercial farms. In this study, comparisons of land use were established for mixed farming and pasture cropping systems in the slopes region (average annual rainfall: 500–650mm) and for cropping and pasture in the plains region (average annual rainfall: 300–500mm) of Central West NSW, Australia. The survey aimed to determine the difference in SOC stocks (Mg C ha−1) and the composition of three soil organic carbon fractions (particulate – POC, humus – HUM and resistant – ROC). The influences of management actions and pasture composition were also assessed across pasture and cropping land uses. Cropping systems had lower SOC stocks in the soil than pasture systems in each region, but pasture cropping was not different from perennial pasture. Generally, there were larger differences in the POC due to land use and management than the other SOC fractions. Management practices in cropping systems explained greater variability in SOC than in pastures. For cropping systems, higher amounts of P fertiliser were associated with higher SOC, POC and ROC while higher amounts of N fertiliser were associated with lower SOC, POC and ROC. For pastures, the proportion of bare ground was associated with lower SOC and POC. These associations indicate there is an opportunity to increase SOC by converting cropping land to permanent pasture, increasing the frequency of pasture phases, changing crop fertiliser regimes and reducing bare ground in pastures, but further work is needed to verify the causality behind these associations.

Combining management based indices with environmental parameters to explain regional variation in soil carbon under dryland cropping in South Australia

Identifying drivers of variation in soil organic carbon (OC) at a regional scale is often hampered by a lack of historical management information. Focusing on red-brown-earth soils (Chromosol) under dryland agriculture in the Mid-North and Eyre Peninsula of South Australia, our aims were 2-fold: (i) to provide a baseline of soil OC stocks (0.3 m) and OC fractions (mid-infrared predictions of particulate, humus, and resistant OC in 0.1 m samples) in cropping and crop-pasture systems; and (ii) to evaluate whether the inclusion of management-based indices could assist in explaining regional-level variation in OC stocks and fractions. Soil OC stocks in both regions varied ~20 Mg ha–1, with higher OC stocks in the Mid-North (38 Mg ha–1) than the Eyre Peninsula (29.1 Mg ha–1). The humus OC fraction was the dominant fraction, while the particulate OC was the most variable. Environmental variables only partially explained soil OC variability, with vapour pressure deficit (VPD) offering the greatest potential and likely acting as an integrator of temperature and moisture on plant growth and decomposition processes. Differences between broad-scale cropping and crop–pasture systems were limited. In the Mid-North, variability in soil OC stocks and fractions was high, and could not be explained by environmental or management variables. Higher soil OC concentrations (0.1 m) in the Eyre Peninsula cropping than crop–pasture soils were largely accounted for in the particulate OC fraction and are therefore unlikely to represent a long-term stable OC pool. Use of the management data in index format added some explanatory power to the variability in OC stocks over the main environmental variables (VPD, slope) within the Eyre Peninsula cropping soils only. In the wider context, the management data were useful in interpreting differences between regional findings and highlighted difficulties in using uninformed, broad-scale management categories.

Influence of rates of reactive phosphate rock and sulphur on potentially available phosphorous in organically managed soils in the south-eastern near-Mediterranean cropping region of Australia

Reactive phosphate rock (RPR) is the only phosphorous (P) fertiliser allowed for organically managed, broad-acre crop-pasture systems in southern Australia. However, soils are usually deficient in P, and the soils, climate, and plant species grown, do not promote extensive dissolution of RPR so the fertiliser is poorly effective for crop and pasture production. Biological oxidation of elemental sulphur (S) mixed and applied with RPR may sufficiently increase dissolution of P from RPR to improve its effectiveness as a P fertiliser. However, this needs to be confirmed in field studies in the region. Rates of RPR and S required to optimise dissolution of RPR are not known for the soils, environments, and agricultural systems used. Both pot and field studies showed that mixing RPR and S, and incorporating the mix into soil (top 10 cm for field studies), significantly increased Olsen P and soil solution P, even in strongly acidic soils (pHCa < 4.6). In general, Olsen P increased linearly with the applied rate of P up to 42–70 kg P ha−1 and the rate of change in Olsen P per unit of applied P increased with the applied rate of S up to 400 kg S ha−1. This interaction suggested that the effectiveness of RPR + S may be compromised by segregation of RPR and S. In addition, there was evidence that S application may not necessarily create a more acidic soil environment necessary for enhanced dissolution of RPR.

Banco de sementes no solo em sistemas de cultivo lavoura-pastagem

O objetivo deste trabalho foi avaliar o efeito de sistemas de cultivo, do preparo do solo e dos níveis de adubação sobre o banco de sementes, em solos de áreas submetidas a: três sistemas de cultivo - lavoura contínua (L), lavoura-pastagem-lavoura (LPL) e pastagem-lavoura-pastagem (PLP); dois sistemas de preparo do solo - convencional (C) e semeadura direta (D); dois níveis de adubação - manutenção (1) e corretiva gradual (2); e uma área de pastagem contínua, com preparo convencional e adubação corretiva gradual. No sistema de cultivo lavoura-pastagem, a densidade de sementes, excluindo-se as áreas de cultivo de LPLC1 e de LPLC2, foi menor do que nas lavouras contínuas e maior do que na pastagem contínua. Nas áreas de lavoura, o banco de sementes foi menor em áreas com semeadura direta do que com preparo convencional do solo, mas nas áreas de PLP, com adubação corretiva gradual, não houve diferença entre os sistemas de preparo do solo. A adubação causou redução na densidade de sementes apenas nas áreas de cultivo de LPLC e PLPC. A adoção de sistemas de cultivo lavoura-pastagem com semeadura direta pode auxiliar no manejo de plantas daninhas em áreas de lavoura de grãos.

Fixação biológica de nitrogênio por plantas de trevo (Trifolium spp) em sistema de integração lavoura-pecuária no Sul do Brasil

Este trabalho foi realizado com o objetivo de avaliar o efeito da inclusão de plantas de trevo (Trifolium spp) sob pastejo em sistema de integração lavoura-pecuária sobre a quantidade de N fixada, a produtividade, os componentes de rendimento da cultura de milho e os teores de nitrato no solo. O delineamento utilizado foi de blocos ao acaso, com três repetições, em que as parcelas foram constituídas dos resíduos de espécie forrageira (trevo e aveia) e as subparcelas, das quatro doses de N em cobertura (0; 60; 120; e 240 kg/ha). Durante o período de cultivo do milho (2004/2005), as parcelas contendo resíduo de trevo apresentaram maiores de teores de N-nitrato na profundidade de 0-5 cm em comparação àquelas cultivadas anteriormente com aveia, indicando que a cultura de milho encontraria praticamente todo o suprimento de nitrogênio, em decorrência do cultivo anterior de trevos pastejados. Não foram observados indícios de lixiviação de nitratos provocados pelos resíduos de leguminosas até a camada de 20 cm de profundidade do solo. No segundo ano de experimento, plantas de trevo pastejadas contribuíram, no mínimo, com suprimento de N de 90 kg/ha, como resultado da fixação biológica para a cultura de milho. No entanto, plantas de milho cultivadas sobre resíduos de aveia apresentaram máxima produtividade de grãos com aplicação de 180 kg/ha de N.

Acidification problems of duplex soils used for crop-pasture rotations

The acidification of duplex soils used for crop-pasture rotations has been reported widely in Australia in the winter dominant rainfall regions. At some locations induced soil acidity limits crop and pasture yield. The rate of soil acidification is affected by soil properties, agricultural management and rainfall. Rates of acid addition of 0.6-6 kmol H+/ha.year have been measured from long term crop pasture rotation experiments; these rates are comparable with values reported from pastoral studies in higher rainfall areas. Components of both the carbon and nitrogen cycles contribute to this acid addition, with loss of nitrate nitrogen below the rooting depth of these predominantly annual plant systems likely to be the main cause of acidification. Lime application has been recommended as a means of correcting acidification and improving crop and pasture yield. There is little information on the longevity of any beneficial effects of lime, the movement of lime in the soil and re-acidification of the soil in crop-pasture systems. A long term experimental site with rotation, deep tillage and lime treatments has been soil sampled throughout a 9-year period for changes in soil pH and aluminium. Soil pH decreased with increasing time after lime application. At lower lime rates (0.5-1.0 t/ha) there was no difference in pH or exchangeable A1 after 9 years, compared with the unlimed soil. At the higher lime rates there was downward movement of the neutralising effect of lime with time, as well as acidification of the soil. However, the yield responses obtained with all of the lime rates were maintained 9 years after 1 application of lime, even though the soil was strongly acid according to the measures used. Strategies for countering soil acidificaton may require an initial application of lime if acidity factors are restricting yield. Management systems which increase the permeability of the B horizon of duplex soils and which promote plant growth and a deep root system are essential for countering acidity in a croppasture rotation.

Productivity of grazed Makarikari grass-lucerne, Rhodes grass-lucerne and lucerne pastures in the northern wheat belt of Australia

Three Makarikari grasses (Panicum coloratum var. makarikariense) viz. 0.4634, cv. Pollock and cv. Bambatsi and Rhodes grass (Chloris gayana) cv. Pioneer, each grown with lucerne (Medicago sativa) cv. Hunter River, and sward lucerne were compared for productivity and stability in a rotational grazing system at three stocking rates (22.2, 14.8 and 7 . 4 Merino wethers/ha for grasslucerne pastures; 14.8, 11.1 and 7.4/ha for lucerne swards) on a cracking clay soil on the Darling Downs, Queensland over four years. There were no differences between the Makarikari grass cvv. Pollock and Bambatsi pastures. However, each produced more dry matter and animal liveweight, and persisted better, than Rhodes grass pasture during dry conditions that occurred during the first two years. Rhodes grass nevertheless recovered during two subsequent wet summers. During those two dry years, wool production from sward lucerne was equal to that of the grass-lucerne pastures at both 14.8 and 7.4 animals/ha. Animal liveweight from lucerne was greater than from grass-lucerne pastures at 7.4 animals/ha only. Wide variation, both between and within seasons, was measured in the quantity of feed produced by pastures in this study. This is discussed in relation to the concept of stocking rate of pasture grown on limited areas of grain farms in the northern wheat belt, and to the provision of a continuing feed supply in integrated crop-pasture systems.