Managing grazing animals to achieve nutrient cycling and soil improvement in no-till integrated systems

Transcription

1 Nutr Cycl Agroecosyst (21) 88: DOI 1.17/s x RESEARCH ARTICLE Managing grazing animals to achieve nutrient cycling and soil improvement in no-till integrated systems Paulo César de Faccio Carvalho Ibanor Anghinoni Anibal de Moraes Edicarlos Damacena de Souza Reuben Mark Sulc Claudete Reisdorfer Lang João Paulo Cassol Flores Marília Lazzarotto Terra Lopes Jamir Luis Silva da Silva Osmar Conte Cristiane de Lima Wesp Renato Levien Renato Serena Fontaneli Cimelio Bayer Received: 23 May 29 / Accepted: 17 March 21 / Published online: 3 April 21 Ó Springer Science+Business Media B.V. 21 Abstract Crop-livestock systems are regaining their importance as an alternative to unsustainable intensive farming systems. Loss of biodiversity, nutrient pollution and habitat fragmentation are a few of many concerns recently reported with modern agriculture. Integrating crops and pastures in no-till systems can result in better environmental services, since P. C. de Faccio Carvalho (&) I. Anghinoni M. L. Terra Lopes O. Conte C. de Lima Wesp R. Levien C. Bayer Faculty of Agronomy, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 7712 Cx Postal 776, Porto Alegre, RS CEP , Brazil paulocfc@ufrgs.br conservation agriculture is improved by system diversity, paths of nutrient flux, and other processes common in nature. The presence of large herbivores can positively modify nutrient pathways and soil aggregation, increasing soil quality. Despite the low diversity involved, the integration of crops and pastures enhances nature s biomimicry and allows attainment of a higher system organization level. This paper illustrates these benefits focusing on the use of grazing animals integrated with crops under no-tillage systems characteristic of southern Brazil. Keywords Conservation agriculture Grazing intensity Mixed systems Nutrient cycling Soil quality A. de Moraes C. R. Lang Universidade Federal do Parana, Curitiba, Brazil J. P. C. Flores Virginia Polytechnic Institute & State University, Blacksburg, VA, USA E. D. de Souza Universidade Federal de Goias, Jatai, Brazil R. M. Sulc Ohio State University, Columbus, OH, USA J. L. S. da Silva Embrapa Clima Temperado, Pelotas, Brazil R. S. Fontaneli Embrapa, Centro Nacional de Pesquisa de Trigo, Passo Fundo, Brazil Introduction In the last century, particularly since the so-called green revolution, crop and livestock production systems became increasingly specialized (Entz et al. 25). Emphasis was put on technical efficiency, leading to significant effects on productivity, and farming systems were transformed into large-scale, specialized, energy-intensive farming operations (Kirschenmann 27). This specialization occurred not only in farming systems, but also in the research supporting agricultural production systems (Lemaire et al. 25).

2 26 Nutr Cycl Agroecosyst (21) 88: During this same period, mixed systems have become synonymous with extensive systems, which are concentrated in the poorer areas of the world with declining technical support because they are perceived as being the opposite of what is considered modern intensified agriculture. However, mixed systems have a huge social significance. Sixty percent of rural poor populations use mixed systems (Thomas 21). Depending on how we define mixed systems (Schiere and Kater 21), they represent 2.5 billion hectares across the globe, and are responsible for more than 5% of the meat and 9% of the milk consumed (Keulen and Schiere 24). Short-term consequences of intensification were highly positive and the world increased grain production massively. However, long-term consequences of intensified agriculture have not all been positive, and include lack of sustainability, primarily through the loss of biodiversity and pollution via inefficient nutrient management (Lemaire et al. 25). Russelle and Franzluebbers (27) presented the growing concern with specialized agricultural systems, because of increasingly negative responses from the environment that are manifested in (1) water contamination with excessive nutrients, pesticides, and pathogens; (2) decreasing groundwater levels due to high demand and competition from a variety of stakeholders, including specialized crop production; (3) rising greenhouse gas concentrations from soils depleted in organic matter; and (4) dysfunctional soils that have become degraded from excessive tillage, salt accumulation, and pesticide inputs. Thus, intensive agriculture and livestock production have recently become the center of debate because of their negative effects on the environment. Production is no longer the sole objective of farming systems. Environmental regulations are becoming a crucial aspect of production systems and trade markets in response to new requirements demanded by the general public. This recent concern over environmental quality has led to a renewed interest in crop-livestock systems, primarily because they provide opportunities for diversification of rotations, perenniality, nutrient recycling, and greater energy efficiency (Entz et al. 25). A number of studies have confirmed that integrated systems tend to be more sustainable, use less energy per unit area and have higher energy efficiency than either specialized crop or livestock systems (e.g. Vilela et al. 23; Entz et al. 25). Moreover, integrated crop-livestock systems can positively change the biophysical and socio-economic dynamics of farming systems (Keulen and Schiere 24), reestablishing sustainable rural development (Lemaire et al. 23) and promoting higher overall farm profitability (Entz et al. 25). Complex integrated arrangements can be designed according to the nature of the components, the objectives and the agricultural culture involved, as well as according to spatial scales in which the integration occurs (within-farm or area-wide scale). For the purposes of this review, we consider within farm integrated crop-livestock systems typical of southern Brazil (cash crop/grazing cattle rotations), in which not only does a rotation of components exist, but the components are specifically managed and oriented to provide synergistic benefits at the landscape level. Numerous publications have dealt with the integration of crops and livestock; however, there is almost no information about the use of grazing animals integrated with crops under no-tillage systems, which typifies agricultural production in southern Brazil. In this context, our paper aims to present some of the southern Brazilian research and experiences with integrated crop-livestock production systems. Integrated crop-livestock systems in perspective The integration of crops and livestock is not a new technology; rather, it is a re-emerging concept. Since the domestication of plants and animals, there is evidence that integrated crop-livestock systems where the most common pattern in the Neolithic age when humans first gathered into small village and farmstead groups. Crop production was probably first combined with animal husbandry 8 1 millennia ago (Russelle et al. 27). In Latin America, integrated crop-livestock systems originally were used to establish pastures in a rotational sequence beginning with a grain crop, usually rice (Oryza sativa L.), to take advantage of the increased fertility in the short term after clearing forested land (Entz et al. 25). Recently, integrated crop-livestock systems have been conceived as a means for reclaiming pastures degraded by overstocking and lack of fertility, which improves productivity through land use intensification and mitigates the

3 Nutr Cycl Agroecosyst (21) 88: clearing of native vegetation, particularly in the Cerrados and Amazon regions (Landers 27; Zimmer et al. 24). In those integrated systems, grain crops established on the degraded pasture lands provide the cash flow necessary for the substantial investment in lime and fertilizer needed to correct the soil fertility status. Annuals (Sorghum bicolor L. Moench, Pennisetum glaucum (L.) R. Br.) and perennial forages (Brachiaria spp., Panicum spp.) are often used in rotation with soybean (Glycine max L.), maize (Zea mays L.), cotton (Gossypium L.), sunflower (Helianthus annuus L.) and bean (Phaseolus vulgaris L.). In southern Brazil, integrated crop-livestock systems have been adopted traditionally in irrigated rice grown in rotation with Italian ryegrass (Lolium multiflorum Lam) or native pastures (Reis and Saibro 24). In recent times integrated systems have been used as an alternative for reducing risk due to frequent summer cash crop failures and low winter grain cash crop market prices, thus providing the potential for increased profits and land use efficiency (Carvalho et al. 26). This Brazilian subtropical region has 8. million hectares annually cultivated with soybean, 3.4 million hectares with maize and around 1.1 million hectares with rice (Moraes et al. 27). Hence, soybean, maize and rice represent 29% of cultivated area in summer. In the last few years, approximately 3.5 million hectares have been cultivated with winter crops such as wheat (Triticum aestivum L.), oat (Avena sativa L.), barley (Hordeum vulgare L.), triticale (X triticosecale Witt.), and rye (Secale cereale L.). The remaining area, i.e. 9. million hectares, represents potential income lost during winter, with soils being exposed or simply seeded to cover crops. The cover crops used are primarily forage species, but they are rarely grazed. During that winter period, livestock face lack of feed and the existing pastures are under harsh conditions in general. Hence, there is still a vast area that could potentially integrate livestock grazing on winter cover crops in rotation with summer crops under no-tillage management in southern Brazil. No-tillage soil management is an alternative to the traditional rehabilitation of production systems, which have lead to high and unsustainable inputs (Kluthcouski and Stone 23). No-till technology is an environmentally friendly system offsetting most of modern agriculture s negative impacts. No-till systems are well recognized for controlling soil erosion, increasing carbon sequestration, lowering energy consumption and carbon dioxide emission, and decreasing the pollution of surface waters (Holland 24). Despite the positive aspects of no-tillage soil management, there are recent reports showing in some cases, particularly on tropical oxisols, that notillage is not sufficient for maintaining soil quality and a positive carbon balance within a succession of annual crops. Landers (27) stated that crop successions must maintain on average over 6 Mg/ha dry matter in crop residues within rotations. However, most rotations are not capable of maintaining that minimum level of crop residue on the soil. Salton (27) reported that crop rotations have had negative carbon balance, and continuous cropping is not able to increase, nor maintain, soil carbon stocks. According to Landers (27), incorporating pastures and animals in rotation with crops cultivated in no-tillage systems optimizes even more the beneficial characteristics of conservation agriculture, particularly via the capacity of pastures to sequester carbon (Salton 27), but also by increasing biodiversity, improving nutrient cycling, and reducing economic risk (Moraes et al. 27). Russelle et al. (27) stated that multiple agronomic and environmental benefits can be realized when land is converted from low diverse cropping systems to rotations that include forages. The author cited Randall et al. (1997) and Shiftlet and Darby (1985) to illustrate that introduction of perennial crops into previous annual crop systems reduces the risk of environmental damage during the cropping phase by decreasing nitrate leaching up to 96% and nearly eliminating soil erosion by water. Lemaire et al. (23) cited that pastures have analogous effects as forests and can help agricultural systems regulate environmental fluxes to achieve multiple environmental benefits through positive effects with regard to: (1) hydrological impacts and maintenance of surface and subterranean water quality; (2) carbon sequestration; (3) nitrogen flux regulation; (4) gas emission regulation (N 2 O, NH 3,CH 4 ); (5) organic matter stability and soil quality maintenance; (6) stimulation of soil biological activity; (7) immobilization and retention of pesticides and heavy metals. Concerning the integration of pastures in crop rotations in southern Brazil, Moraes et al. (22) reported several advantages, including maintenance of physical, chemical and biological soil characteristics,

4 262 Nutr Cycl Agroecosyst (21) 88: erosion control, more efficient use of natural resources and pollution control. In addition, the authors mentioned improvements in crop protection, increased animal and crop production, greater economic returns, better weed control and break in disease and insect cycles. Indeed, Costa and Rava (23) reported a 75% reduction in Rhizoctonia and Sclerotinia bean infections using rotations with perennial tropical forages. Integrated crop-livestock systems can increase biodiversity via the attributes of organic matter provided by pastures (Lemaire et al. 23). The resulting flora and fauna diversity, as well as microbial and faunal soil communities, change the soil and its physio-chemical properties (Lemaire et al. 23). The pastoral environment is particularly important to the colonization/extinction metapopulational processes of many organisms (eg. insects, mollusks) and is a forage resource for many birds and mammals, frequently being their reproduction site. For these reasons, Lemaire et al. (23) consider pastures essential for biodiversity maintenance at the landscape level, being the habitat of invertebrates that are important to carbon and nitrogen cycles. Despite the potential benefits reported for croplivestock integration, this technology can only be successful if some basic concepts are followed. According to Moraes et al. (22) some of the key principles that must be adopted include: (1) notillage, (2) crop rotation, (3) nutrient inputs, (4) improved animal and crop genetics, and (5) sound grazing management. From all those requirements, the pasture phase and related grazing management is commonly considered to be essential in defining the nature and intensity of potential relationships. Managing pastures and grazing animals in no-till integrated crop-livestock systems The potential effects of pastures in integrated croplivestock systems depends on the pasture phase model, where management options include grazing and/or harvesting, annual and/or perennial forages, grasses and/or legumes. In short, a huge number of combinations can be planned depending on crop type and objectives. Annual crop rotations typical of southern Brazil have alternative forage species defined according to the cash crop cycle. Oat is commonly used as the preceding crop to maize, because its early maturity fits well with early planting dates required for full season maize, whereas oat and/or Italian ryegrass are often used preceding soybean, which is planted later than maize. Italian ryegrass has the potential to perennate in those systems by annual reseeding (Carvalho et al. 25). With regard to legume utilization, Vicia spp. have been used with oats in rotation with maize aiming to increase soil nitrogen availability, whilst Trifolium spp. and Lotus spp. are most commonly seen in rotation with irrigated rice, because rice yield after those species can be equivalent to or even greater than rice fertilized with 9 kg/ha of nitrogen (Saibro and Silva 1999). There is some conflict over how much residue cover is needed for no-till establishment of cash crops following forage cover crops that are grazed. In the pasture phase, the aboveground biomass is consumed by the grazing animal, which is the same biomass vital to the health and functioning of the no-tillage crop production system. The positive linear relationship between residual biomass of the preceding cover crop and yield of the succeeding crop (Landers 27) in notill systems does not encompass pastures being used by grazing animals, which has been cause for debate. This technical dilemma, together with the concern that grazing animals will compact the soil, generates resistance to the adoption of grazing within no-tillage production areas in southern Brazil (Carvalho et al. 27). Probably the most common perception of farmers, who are hesitant to participate in integrated systems, is that cattle trampling has a negative effect on soil physical properties. This has proven to be a major obstacle to the adoption of the integrated system, despite studies that refute this claim (Moraes et al. 22; Flores et al. 27; Cardoso et al. 27; Souto 28). Bayer (1996) estimated that 1 12 Mg/ha of crop residue dry matter was needed in southern Brazil if the objective was to maintain or increase carbon stocks in no-tillage systems without grazing. Thus, the resulting question is how much, if any, and with what intensity, should biomass be removed by grazing animals in integrated crop-livestock production systems? There are no simple answers, in that the more biomass left for the succeeding crop, the less animal production can be expected. A schematic representation of grazing animal impacts on the success of crop-livestock integration

5 Nutr Cycl Agroecosyst (21) 88: is illustrated in Fig. 1, which is helpful in discussing overall relationships. Grazing intensity determines the mean herbage mass/sward height existing during the pasture utilization phase, which in turn affects solar energy intercepted, herbage accumulation rate and carbon sequestration by consequence. The same grazing intensity, by defining herbage allowance per animal and sward structure, affects herbage intake per animal and per unit area. Hence, the amount of nutrient cycling by the animal is defined by grazing intensity. In general, the more animals per unit area the fewer nutrients are fixed in animal products per unit of herbage ingested. In such situations, usually the amount of nutrients recycled per unit area increases, but it depends on how long forage production is negatively affected by higher grazing intensities. Ultimately, animal production is a result of the herbage consumed and converted into animal products. Therefore, the resulting aboveground biomass left after the pasture phase (residue cover) is an outcome of grazing management. Biomass residues in no-till systems, and the soil physical (aggregation, compaction), chemical (nutrient cycling, carbon stocks) and biological (microbiological activity and diversity) environment at the moment of sowing the succeeding crops, are all defined by the average grazing intensity used during pasture utilization. Thus, crop development is partially due to conditions created by grazing management. As a result, both crop and livestock productions are strongly affected by the way grazing animals are managed in those systems. As described above, grazing intensity is one of the main variables affecting the success of integrated croplivestock systems using no-tillage technology. Consequently, much effort has been invested in evaluating the impact of grazing animals in integrated systems in southern Brazil (e.g. Baggio et al. 29; Silva et al. 28; Moraes et al. 22; Cassol 23; Flores 24). In general, considering what is usually managed at the farm level, animals and the grazing processes can be manipulated essentially by two management actions: defining grazing intensity by establishing the amount of animal live weight per unit area (stocking rate) in relation to available forage; and distribution of animals within the area (continuous or rotational stocking management). Thus, to control grazing there are few variables to be effectively handled. From the above discussion, defining the grazing intensity to be used seems to be the most important management action affecting overall system productivity and sustainability (Carvalho et al. 25). Fig. 1 Schematic representation of how grazing intensity affects integrated crop-livestock systems under no-tillage soil management (adapted from Carvalho et al. 25)

6 264 Nutr Cycl Agroecosyst (21) 88: In general, farming systems use high grazing pressures and stocking rates are set higher than pasture carrying capacity, which negatively affects both pasture and crops in the rotation. Consequences can include steers with low carcass quality at slaughter (Aguinaga et al. 26), lack of residue cover for the crop grown in succession (Cassol 23), higher weed populations (Lunardi et al. 28) and lower water holding capacity of the soil (Conte et al. 27). The impact of grazing pressure on animal performance during the pasture phase is illustrated by a steer fattening/soybean integrated system using an oat? Italian ryegrass pasture mixture (Fig. 2). The average stocking rates were around 4.4, 3.3, 2., and 1.1 steers/ha for pasture grazing heights of 1, 2, 3 and 4 cm, respectively. Daily animal gain was similar for the 2, 3 and 4 cm pasture height treatments; however, the optimal animal performance was considered to occur at 3 cm (1.12 kg/steer/day) because it resulted in the best carcass quality (Aguinaga et al. 26). There was a linear decline in animal performance per area with increasing pasture height, resulting from declining stocking rates on those high nutritive value pastures. In this experiment, individual animal gain varied little, thus animal gain per unit area was correlated directly with stocking rate. Results showed negative effects of higher grazing intensities on soybean yield only in the first year, when the system was not yet stable (Fig. 3). By the second year of integration, the system started to behave according to expected pasture/crop succession relationships, and soybean yield became less affected by grazing intensity, despite the fact that biomass residue cover at the time of soybean sowing varied from around 1.5 to 6 Mg/ha (Carvalho et al. 25). These results indicate that the yield of successive crops in no-tillage systems is less dependent on Soyben grain yield (kg/ha) Pasture height (cm) Fig. 3 Soybean grain yield grown after cover crop pastures that were grazed at different intensities (defined by sward height). Data are 6-year yields from Cassol (23), Flores (24), Flores et al. (27), Rocha (27), Lopes (28) and Conte (unpublished data) (a) Animal daily gain (kg) (b) residue cover when the preceding cover is grazed by animals than when it is grown as a cover crop only. These results have been confirmed by many similar experiments conducted in southern Brazil (e.g. Vieira 24), the hypothesis being that the nature of nutrient cycling occurring in those systems has a greater overall positive effect that overcomes any negative effects associated with a reduction in residue cover (discussed in more detail later). With regard to grazing methods, continuous and rotational stocking are the most common used in croplivestock systems in southern Brazil. The continuous stocking method is usual on large farms while rotational stocking is used mainly on small dairy farms. Although the method of grazing is a matter of debate, there is scientific consensus that both methods are similar when optimum grazing intensities are used (Briske et al. 28). However, little information is available regarding the impact of grazing method on performance of crop-livestock systems under no- 1,2 6 1,1 1,,9 y = -,7x 2 +,48x +,4853 R² =, ,8,7, Pasture height (cm) Animal gain (kg live wt./ha) y = -11,72x + 648,4 R² =, Pasture height (cm) Fig. 2 Steer performance [liveweight gain per animal (a) and per unit area (b)] during the pasture phase of a crop-livestock system. Data are 8-year averages, calculated from Cassol (23), Aguinaga et al. (26), Rocha (27), Bravo et al. (27), Lopes et al. (28) and Wesp (unpublished data)

7 Nutr Cycl Agroecosyst (21) 88: tillage management. This issue will be exemplified using a small holder integrated crop-livestock system model based on a lamb fattening operation using Italian ryegrass for winter pasture in rotation with maize or soybean in summer (Fig. 4). Continuous stocking allows greater individual animal selectivity and individual animal intake, and thus continuous stocking with high allowance (C 5.) results in higher animal daily gains (Carvalho et al. 27). However, gain per unit area was higher with rotational stocking at lower forage allowance (R 2.5), a result of a higher stocking rate (1,54, 1,238, 99, and 854 kg LWG/ha in R2.5, C2.5, R5., and C5., respectively). While the animal performance response to grazing intensity and method followed the expected classical patterns, the impact of grazing treatments on the succeeding crop was unusual. Grazing intensity clearly affected soybean yield more than the grazing method. The higher the forage allowance, the more biomass residue cover was left after the pasture phase for the succeeding grain crop phase, resulting in higher soybean yield in the first year, similar to results presented earlier (Fig. 3). However, with maize the effect of grazing intensity and method is less evident, although maize yield tended to be slightly higher with high forage allowance with continuous stocking (C5.). No evidence was found of grazing method effects and it is noteworthy that the non-grazed treatments yielded similarly or even less than the grazed treatments (Carvalho et al. 27). Pizzolo (25) reported the response of soil mineral nitrogen pool to those grazing regimes. Extractable nitrogen ( 9 cm soil depth) at the end of the pasture phase was higher in the continuous stocking managed at higher grazing intensities (179 ± 12.5, 14 ± 3.5, 99 ± 1.1 and ±.1 kg/ha of nitrogen, respectively for C2.5, R2.5, C5. and R5.). Increased stocking rate increases the excretal returns, accelerating nitrogen cycling rates and increasing soil nitrogen in mineral forms (NH 4? -N). Throughout the soybean rotation, soil mineral nitrogen remained high (1 kg/ ha N), reaching a peak of more than 5 kg/ha of nitrogen after harvest, with the adsorbed NH 4? -N form (a) Animal daily gain (g) (b) Animal gain (kg/ha) C 2.5 C 5. R 2.5 R 5. Grazing management C 2.5 C 5. R 2.5 R 5. Grazing management (c) Soybean grain yield (kg/ha) C 2.5 C 5. R 2.5 R 5. NG Grazing management (d) Maize grain yield (kg/ha) C 2.5 C 5. R 2.5 R 5. NG Grazing management Fig. 4 Effect of grazing intensity and method on animal (a, b) and crop performance (c, d) in a small holder crop-livestock system model. C and R refer to continuous or rotational stocking methods, NG refer to non grazing, while 2.5 and 5. refer to multiplier factor that the forage allowance exceeded potential intake of the animals (data from animal performance are 4-year averages, soybean and maize from 1 year rotation, Carvalho et al. 27)

8 266 Nutr Cycl Agroecosyst (21) 88: predominating over the mobile NO 3 - -N. Pizzolo (25) concluded that soil nitrogen conservation could be accomplished in a management scheme including leniently grazed pasture followed by a high N-demand crop such as maize. Indeed, Fig. 4d illustrates the potential behavior of such a system. Lenient grazing intensities had significantly lower extractable mineral nitrogen, associated with increased levels of slow-release nitrogen in the soil organic matter. Leaving sufficient plant residues on the field favored immobilization and soil moisture, thereby providing healthy conditions for microbial biomass growth and ensuring long-term soil N reserves (Pizzolo 25). A crop with high nitrogen demand, such as maize, usually yields better after a pasture phase that is moderately grazed (Lustosa 1998; Assmann et al. 23). In general, southern Brazilian studies have shown that winter grazing does not compromise performance of succeeding crops and may even increase yield provided animal stocking and grazing are managed appropriately (Moraes et al. 23). Data from systems where the pasture phase operation includes beef backgrounding and/or fattening, lamb fattening and dairy cattle integrated with production of soybean, maize and bean demonstrate that moderate grazing is not deleterious to the succeeding crop (Lustosa 1998; Bona Filho 22; Flores et al. 27; Souto 28; Lopes et al. 28). When compared with cover cropping options, which aim only to produce biomass for residue cover in no-till systems, the utilization of cover crops for grazing should be considered because it increases profits and improves soil quality. Nutrient cycling and soil properties Calculations of nutrient fluxes in farm production systems can furnish basic information about sustainability of those systems. Evaluations of nutrient cycling and balance are more complex in integrated crop-livestock systems under no-tillage and few have been conducted in the Brazilian subtropical region. It is expected, in such systems, that the capacity of pastures for carbon sequestration and nutrient cycling is related to its management for a specific climatic zone. For example, in situations with overstocking of animals, a lower amount of aboveground residues left on the soil surface results in lower stocks of carbon input to the soil, and of other nutrients such as nitrogen, phosphorus and potassium, with a resultant decline in soil quality. It is important to consider long term studies when evaluating nutrient cycling, because addition or loss of organic matter and energy in the soil over time will modify the functioning of the soil system and the fertility status. Considering the soil as an open system in non-equilibrium, and based on its dissipative structures and auto-organization processes, emergent properties can result from order level changes mediated by fluxes of matter and energy, which are important for the regulation of soil functions and quality, as well as for the sustainability of farm production systems (Mielniczuk et al. 23). A long-term crop-livestock experiment in southern Brazil: soil carbon and nitrogen The research was conducted for 7 years in a Rhodic Hapludox (Oxisol). The previous cropping system was a soybean/oat rotation without grazing. The experimental design was a completely randomized block with three replicates. Total and particulate carbon and nitrogen stocks increased with time in an integrated crop-livestock system under no-tillage (Fig. 5). The integrated system consisted of a summer crop of soybean grain in rotation with an oat/italian ryegrass winter cover crop continuously grazed at different intensities (1, 2, 3 and 4 cm pasture height) by yearling beef steers. The rates of total carbon (1.16 Mg ha -1 year -1 ) and nitrogen (.12 Mg ha -1 year -1 ) stocks increase are considered high (Corazza et al. 1999) even for subtropical conditions. It would be expected that an increase would occur only in the particulate fractions, which are most affected by management practices, but not for total content in a relatively short time (6 years). Moderate grazing intensities (annual temperate pastures managed at 2 and 4 cm sward height) promoted an increase in all carbon and nitrogen stocks (total and particulate) in a similar fashion as occurred in the no-grazing control treatment (Fig. 6). However, in the highest grazing intensity (1 cm sward height), losses of carbon and nitrogen were observed after the third year of the experiment.

9 Nutr Cycl Agroecosyst (21) 88: Fig. 5 Carbon (a) and nitrogen (b) stocks in the total (COT e NT) and particulate (C-MOP and N-MOP) fractions of the organic matter in the 2 cm soil layer over time under no-tillage (Souza 28) Fig. 6 Carbon (a) and nitrogen (b) stocks in the total (COT and NT) and particulate (C-POM and N-MOP) fractions of the organic matter after 6 years (27) in the 2 cm soil layer, as affected by grazing intensity under no-tillage. Treatments A long-term crop-livestock experiment in southern Brazil: phosphorus fractions and availability In the same experiment previously described, total phosphorus content was high at the beginning of the experiment (Fig. 7a), reaching 88 mg kg -1 in the 2 cm soil layer. Such high values, even for a highly weathered basalt oxisol, resulted from phosphate fertilizer applications that exceeded the amount of phosphorus exported in soybean grain and beef steers. Phosphorus forms (inorganic and organic Fig. 7a) and fractions (labile, moderately labile and low labile Fig. 7b) increased in a similar fashion in the grazed and no-grazing treatments over the 6 years of the experiment, with phosphorus being accumulated primarily in the inorganic, moderately labile fraction. While the inorganic form was accumulated to the 2 cm soil depth, the organic form was accumulated only to 1 cm deep (data not shown). However, negative effects of grazing were observed in the more were grazed sward heights of 1 cm (G-1), 2 cm (G-2), 3 cm (G-3) and 4 cm (G-4 cm), and no-grazing (NG) control (Souza 28) labile (resin and bicarbonate Fig. 8) phosphorus fraction, primarily in the 1 cm soil depth layer (Table 1). A long-term crop-livestock experiment in southern Brazil: potassium balance and cycling Available potassium content, exception made for G-1 treatment, was initially high in the experimental area, above the critical level for high CEC soils (9 mg kg -1 CQFS RS/SC, 24) and was maintained over the 7 years of the experiment (Fig. 9). While there were no significant differences (P [.5) among grazing treatments for available soil potassium content, a contrasting behavior among the treatments was clear: in the no-grazing (NG) treatment there was a trend for potassium content to increase, but in all grazing treatments, especially in the G-1, there was a trend for available potassium content to decrease over

10 268 Nutr Cycl Agroecosyst (21) 88: Fig. 7 Distribution of soil phosphorus forms over time (a) and after 6 years of different grazing intensities (b) in the 2 cm soil layer, under no-tillage. Treatments were grazed sward heights of 1 cm (G-1), 2 cm (G-2), 3 cm (G-3) and 4 cm (G-4 cm), and no-grazing (NG) control (Souza 28) Table 1 Phosphorus availability (resin paper method) in soil layers after 6 years of different grazing intensities (G-1; G-2; G-3 and G-4 cm) and no-grazing (NG) under no-tillage (Souza 28) Grazing intensity Soil layer (cm) 1 (mg kg -1 ) 1 2 (mg kg -1 ) 2 (mg kg -1 ) Fig. 8 Labile soil phosphorus (resin paper? NaHCO 3 extractors, Hedley et al. 1982) evolution in the 2 cm soil layer affected by grazing intensity (G-1; G-2; G-3 and G-4 cm) and no-grazing (NG) under no-tillage (Souza 28) time. Declines in available soil potassium in integrated crop-livestock systems have been observed under subtropical conditions (Fontaneli et al. 2), characterizing a negative balance in the soil, which is related to losses, primarily as animal wastes (Wilkinson and Lowrey 1973). A potassium gradient developed in the soil profile, with levels being higher near the soil surface after pasture than after the soybean phase of the rotation (Fig. 1). In the no-grazing area, despite having less cycled potassium (Fig. 11), levels of this nutrient were higher in the soil profile than in the grazed areas, especially in those more intensively grazed, which probably was due to losses in the system under grazing. Amounts of accumulated potassium in different pools (soybean, pastures and animals) in one cycle of the crop-livestock system were high (Fig. 11). In fact, they were higher than crop demand because, as pointed out by Mielniczuk (25), more than 8% of K in plant residues is released within 3 days. G-1 33 b 11 a 22 a G-2 46 a 8 a 27 a G-4 43 a 12 a 28 a NG 46 a 9 a 27 a K available, mg dm May/1 16 n.s. May/8 n.s. 14 n.s G-1 G-2 G-4 NG Grazing intensity Fig. 9 Available potassium (Mehlich 1) in the 2 cm soil layer over time as affected by grazing intensity (G-1; G-2; G-3 and G-4 cm) and no-grazing (NG) under no-tillage (Ferreira 29) A lower amount of cycled K (21 kg ha -1 ) was detected in the no-grazing area, in contrast with the most intensively grazed area (G-1, with 327 kg ha -1 ). The observed values are comparable with those found by Rossato (24), in a corn/wheat/black oat (Avena strigosa) system in a subtropical environment. n.s.

11 Nutr Cycl Agroecosyst (21) 88: Higher values for cycled potassium in grazed areas are expected due to higher accumulated biomass and potassium content (Ferreira 29). K available, mg dm (a) A long-term crop-livestock experiment in southern Brazil: soil properties and quality indicators 5 1 After soybean Microbial biomass and activity Microbial biomass and basal respiration were stimulated with increasing grazing intensity (Table 2). According to Cattelan and Vidor (199), microbial biomass increases with accumulation of organic residues in the soil. In this research, besides the increase of animal wastes, there was also a higher pasture root mass at the end of the pasture phase with increasing grazing intensity (Souza 28). The C-MB/TOC comprised only 2 4% of TOC (Gama-Rodrigues 1999). However, this is a very dynamic fraction with significant variations without affecting such labile pool of the soil organic matter, which is essential for nutrient cycling and for the dynamics of other soil organic matter fractions. Metabolic quotient (qco 2 ) measurements are important in detecting stressful environmental conditions; however, they were not affected by grazing. Non significant effects may also be related to the small portion (15 3%) of the microbial biomass being catabolically active (Mac Donald 1986), since the rest of the microorganisms remain in latent or inactive forms (Moreira and Siqueira 26). Microbial diversity Integrated crop-livestock systems which use no-tillage and are managed under different grazing intensities can maintain similar levels of microbiological quality as those under no-tillage cash/cover crop production only. The capacity of carbon substrate utilization by soil microorganisms, as expressed by Shannon diversity index, based on the capacity of carbon substrate utilization by soil microorganisms, was not affected (P [.5) by grazing treatments. Despite that, the numerically lower Shannon index found for the no grazing control (6.52) and highest grazing intensity (6.93) treatment, may indicate that moderate grazing intensity stimulates microbial diversity. Pastures being grazed, especially Italian ryegrass, promote exudation Soil depth, cm 15 F test Treat. (p>,5; LSD= 8) Depth (p<,5; LSD= 63) Treat.x Depth (p>,5; LSD= 139) (b) 1 After grazing (c) F test Treat. (p>,5; LSD= 66) Depth (p<,5; LSD= 66) Treat.x Depth (p>,5; LSD= 147) After soybean F test Treat. (p<,5; LSD= 59) Depth (p<,5; LSD= 59) Treat.x Depth (p>,5; LSD= 131) G-1 G-2 G-3 G-4 NG Fig. 1 Available potassium (Mehlich 1) in the soil profile under different grazing intensities (G-1; G-2; G-3 and G-4 cm) and no grazing (NG) in May 27 (a), November 27 (b), and May 28 (c) (Ferreira 29). Treat. treatment, MSD minimum significant difference by Tukey (P \.5) of organic compounds by roots (Tisdall and Oades 1982), serving as energy sources for microorganisms. This positive effect on microbial activity would occur only up to the point where grazing intensity becomes great enough to cause soil compaction and a consequent decline in macroporosity and oxygen supply, as

12 27 Nutr Cycl Agroecosyst (21) 88: K cycling, kg ha a ab Soybean shoot 26/7 (n.s.) Soybean grain 26/7 (n.s.) Herbage mass (*) Mulch (n.s.) Animal carcass (n.s.) Animal wastes (n.s.) 237 b b b aggregation than non grazed or intensively grazed treatments (Table 3). The beneficial grazing effects on soil aggregation were observed in the 2 cm layer, but especially in the 5 1 cm soil layer, and increased with time the animals were kept on pasture. In general, grazing at 2 cm sward height promoted the best soil aggregation, by a higher proportion of larger size ([2 mm) or weighted mean values of water soluble aggregates. Such an effect agrees with the literature (Haynes and Beare 1996) relating improvements in aggregate stability to crop residues, soil organic matter, and greater soil microbial activity, all of which contribute to increases in the production of various binding agents for soil aggregation. G-1 G-2 G-3 G-4 NG Grazing intensity Carbon management index Fig. 11 Potassium cycled in different pools of pasture, soybean and animal (carcass and wastes) under different grazing intensities (G-1; G-2; G-3 and G-4 cm) and nograzing (NG) under no-tillage (Ferreira 29). * and NS indicate significant and not significant by F test (P \.5), respectively. Means with same letter within each pool are not significantly different, by Tukey test (P [.5) may have occurred in the G-1 treatment (Flores et al. 27). It is important emphasize the spatial variability of grazed systems that would require future studies involving more intensive sampling to avoid missing biologically meaningful differences that fail to be statistically significant. Soil aggregation Crop-livestock systems at moderate grazing intensities (2 and 4 cm sward height) promoted better soil The carbon management index (CMI) is an indicator of the quality of soil management, which allows evaluation of the process of gain or loss of soil quality: high CMI values indicate high soil quality (Blair et al. 1995). In pastures grazed at 2 and 4 cm, CMI was similar to the reference (1, for nograzing) (Table 4), indicating those areas maintained high lability of the organic matter. The most intensive grazing (1 cm) treatment had significantly lower CMI (65), indicating degradation in the quality of the soil organic matter. Low CMI values (around 56) were found by Diekow et al. (25) for soil under fallow and black oat/corn without nitrogen addition as compared to a native pasture soil (reference = 1). The CMI is a widely used indicator to characterize soil and cultural management system effects on soil properties and quality. Table 2 Microbial biomass, basal respiration and metabolic quotient (qco 2 ), and microbial biomass/total organic carbon ratios (C-MB/TOC) in a soil under a no-tillage crop-livestock integration system with different grazing intensities (G-1; G-2; and G-4 cm) and a no-grazing (NG) control (Souza et al. 28) Microbial attributes G-1 a G-2 a G-4 a NG b Microbial biomass (mg C kg -1 of soil) 648 a 574 b 515 c 465 d Basal respiration (daily mg C-CO 2 kg -1 of soil) 8.1 a 7.6 b 7.4 b 6.3 c Metabolic quotient (mg CO 2 /mg C day -1 ) ns C-MB/TOC (%) 1.98 a 1.82 a 1.51 b 1.47 b Mean values followed by the same letter on the line are not different by Duncan test (P \.5) a Pasture sward height b No-grazing area

13 Nutr Cycl Agroecosyst (21) 88: Table 3 Water stable aggregate mean values in different soil layers under a no-till crop-livestock integrated system with different grazing intensities (G-1; G-2 and G-4 cm) and a no-grazing (NG) control (Souza 28) Soil layer (cm) Final comments Grazing intensity sward height (cm) G-1 (mm) G-2 (mm) G-4 (mm) NG (mm) Mean Mean of three evaluations along pasture cycle in 27 The presence of grazing animals in grain cropped areas under no-tillage soil management with cover crops affects the system properties. Such effects can be positive or negative, depending on grazing management. The soil is the central component of the processes that indicates the direction (? or -) of such modifications. The catalyzing component is the animal, which recycles the vegetative material and modifies the dynamics of nutrient cycling when compared with systems where winter cover crops are grown solely for production of plant residues for soil cover. When grazing livestock were integrated into a cash crop rotation, and when this was done using moderate, controlled grazing intensities, soil aggregation was significantly improved, as well as the soil microbial activity. Positive impacts were also observed in the chemical attributes of associated Table 4 Carbon stock index (CSI), lability (L), lability index (LI) and carbon management index (CMI) in the 2 cm soil layer in a no-till crop-livestock integration system under different grazing intensities (G-1; G-2 and G-4 cm) and nograzing (NG) after seven grazing/crop cycles (Souza 28) Grazing intensity CSI L LI CMI G b.12 b.733 b 65 b G a.131 a 1.72 a 17 a G a.146 a 1.45 a 1 a No grazing a.14 a 1 a a Reference: CMI = 1. Mean values followed by the same letter in the column are not different by Tukey test (P \.5). G-1, G-2 and G-4 represent grazed sward heights of 1, 2 and 4 cm, respectively variables, such as total and particulate organic carbon and nitrogen, phosphorus availability and potassium cycling and balance. Some soil properties, primarily the physical ones, can be negatively impacted. Despite this, crop productivity is not necessarily reduced by the presence of grazing animals during the previous winter cover crop cycle. In the final analysis, we conclude that summer grain production integrated with animal production on cover crops during the winter season in a subtropical environment is in essence an additional harvest gathered from the same area, which increases soil quality and the efficiency of land use. Acknowledgments The authors are grateful to CNPq, FAPERGS, Fundação AGRISUS, MAPA and Agropecuária Cerro Coroado for funds, Caterina Batello and Eric Kueneman from FAO Crop and Grassland Service for their support to disseminate information in conservation agriculture, and Gilles Lemaire for being responsible for a new research generation in southern Brazil. References Aguinaga AAQ, Carvalho PCF, Anghinoni I et al (26) Produção de novilhos superprecoces em pastagem de aveia e azevém submetida a diferentes alturas de manejo. Rev Bras Zoot 35: Assmann TS, Ronzelli P, Moraes A et al (23) Rendimento de milho em área de integração lavoura-pecuária sob o sistema plantio direto, em presença e ausência de trevo branco, pastejo e nitrogênio. Rev Bras Ciên Solo 27: Baggio C, Carvalho PCF, Silva JLS et al (29) Padrões de deslocamento e captura de forragem por novilhos em pastagem de azevém anual e aveia-preta manejada sob diferentes alturas em sistema de integração lavoura-pecuária. Rev Bras Zoot 38: Bayer C (1996) Dinâmica da matéria orgânica em sistemas de manejo de solos. Thesis, Universidade Federal do Rio Grande do Sul Blair GJ, Lefroy RDB, Lisle L (1995) Soil carbon fractions based on their degree of oxidation, and the development of a carbon management index, for agricultural systems. Aust J Agric Res 46: Bona Filho A (22) Integração lavoura x pecuária com a cultura do feijoeiro e pastagem de inverno, em presença e ausência de trevo branco, pastejo e nitrogênio. Thesis, Universidade Federal do Paraná Bravo ES, Carvalho PCF, Macari S et al (27) Produção de novilho super-precoce em sistema de integração lavourapecuária submetido a diferentes alturas de pastejo. Paper presented at the international symposium on integrated crop-livestock systems. Curitiba, August 27 Briske DD, Derner JD, Brown JR et al (28) Rotational grazing on rangelands: reconciliation of perception and experimental evidence. Rangel Ecol Manage 61:3 17

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