AGRONOMIC AND ENVIRONMENTAL EFFECTS OF SHIFTHING INTEGRATED CROPPING-LIVESTOCK SYSTEMS
4. SYNTHESIS OF RESULTS AND CONCLUSIONS
Three years of experimental data demonstrated that shifting cultivation from ICLS to CC after a long term period of change (25 years) showed either stable or higher yields under CC than the ICLS system. Wheat yields under CC were not primarily the result of the decreasing availability of N, but of declining NUE and RE, which in turn could have been caused by decreasing biological activity in the soil. Based on conceptions about NUE, we attempted to obtain insight into changes in the soil N supply and the differences between wheat response to N inputs grown under CC and ICLS systems. We also evaluated the potential environmental issues related to NUE. We suggest that although yields were lowest under the ICLS rotation, such a system had higher NUE and RE, which were mainly the result of the decreasing availability of N and other nutrients as a consequence of increasing biological activity by nutrient (and maybe C) sequestration. In this sense we have documented that sequestration into
the stable C pool could be improved by adding supplementary nutrients, and that nutrient availability (N, phosphorus and sulphur) is critical to improve net humification efficiency and thus sequester C into the more stable pool of SOM.
Results from N response experiments suggested that NUE proved to be more related with RE or uptake efficiency than IE or utilization efficiency. The value of NUE in wheat grown under ICLS was high because RE tends to be high as well, whereas IE was low. However, under CC systems NUE and RE were lower than ICLS, but IE was higher. Such results indicate that under ICLS plant uptake of the applied fertiliser N was maximized and thus losses from the soil plant system diminished. However, to some extent under the ICLS rotation conditions (higher biological activity, less soil compaction, water storage capacity, etc.) were promoted, so that N applied was conserved in the cropping system as a whole. This was reflected also in 15N recovery of the soil, which was similar in either of the N application times (planting and tillering), and then if a high amount of N was captured, there would be less potential for losses.
In conclusion, systems that combine a nutrient (and C) sequestering phase (pasture phase) with a SOM decomposition phase (cropping phase), would overall achieve a better performance (increasing soil fertility and crop productivity), provided such a system included balanced plant nutrition on space and time. This system of land management is currently a potential tool to contribute to atmospheric carbon dioxide remediation and mitigation of climate change.
REFERENCES
[1] GARCÍA-PRÉCHAC, F., et al., Intensificación agrícola: Oportunidades y amenazas para un país productivo y natural, CSIC, Colección Artículo 2, Montevideo (2010) 126 pp.
[2] MALLARINO, A., et al., Legume species and proportion effects on symbiotic dinitrogen fixation in legume –grass mixtures, Agron. J. 82 (1990) 785–789.
[3] CHRISTOPHER, S., LAL, R., Nitrogen limitation on carbon sequestration in North America cropland soils, Crit. Rev. Plant Sciences 26 (2007) 45–64.
[4] DÍAZ ROSELLÓ, R.1992. Evolución de la materia orgánica en rotaciones de cultivos, Revista INIA 1 (1992)103–110.
[5] GARCÍA-PRÉCHAC, F., et al., Integrating no-till into crop–pasture rotations in Uruguay, Soil Till. Res. 77 (2004) 1–13.
[6] ERNST, O., SIRI-PRIETO, G., Impact of perennial pasture and tillage systems on carbon input and soil quality indicators, Soil Till. Res. 105 (2009) 260–268.
[7] SALVAGIOTTI, F., et al., Nitrogen uptake, fixation and response to fertiliser N in soybeans: A review, Field Crops Res. 108 (2008) 1–13.
[8] URQUIAGA, S., et al., Nitrogen dynamics in soybean-based crop rotations under conventional and zero tillage in Brazil, In: Management Practices for Improving Sustainable Crop Production in Tropical Acid Soils. IAEA-TECDOC, Vienna (2006) 13–46.
[9] ERNST, O., Efecto de una leguminosa invernal como cultivo de cobertura sobre rendimiento en grano y respuesta a nitrógeno de maíz sembrado sin laboreo, Agrociencia 10 (2006) 25–35.
[10] STUDDERT, G., 2006. Rotaciones de cultivos en el sudeste de la provincia de Buenos Aires (Argentina): una herramienta para el manejo de la dinámica del nitrógeno y del carbono en el suelo, Tesis de Doctor Ingeniero Agrónomo, Universitat de Lleida, España (2006)
[11] MAZZILLI, S., et al., Priming of soil organic carbon decomposition induced by corn compared to soybean crops, Soil Biol. Biochem. 75 (2014) 273–281.
[12] CANO, J., et al., Balance aparente de fósforo en rotaciones agrícolas del litoral oeste del Uruguay Informaciones Agronómicas INPOFOS Cono Sur. Acassuso, Buenos Aires, Argentina 32 (2006) 8–11.
[13] KIRKEGAARD, J., et al., Break crop benefits in temperate wheat production, Field Crops Res. 107 (2008) 185–195.
[14] ERNST, O., et al., Balance aparente de N, P y K en función de la intensidad de uso del suelo por la agricultura, Cangüe Nº 32, Nota técnica (2012).
[15] CREWS, T., PEOPLES, M., Legume versus fertiliser sources of nitrogen: ecological tradeoffs and human needs, Agric. Ecosyst. Environ. 102 (2004) 279–297.
[16] HARDARSON, G., et al., Guidelines on Nitrogen Management in Agricultural Systems, IAEA-TCS-29, Vienna (2008).
[17] BRENTRUP, F., PALLIERE, C., Nitrogen use efficiency as an agro-environmental indicator, OECD Workshop on Agri-Environmental Indicators, Leysin, Switzerland (2010).
[18] SHEARER, G, KOHL, D., N2 fixation in field setting: Estimations based on natural 15N abundance. Review, Aust. J. Plant. Physiol. 13 (1986) 699–756.
[19] HAUCK, R, BREMNER, J.M., Use of tracers for soil and fertiliser nitrogen research, Adv. Agron. 28 (1976) 219–266
[20] UNKOVICH, M.J., et al., Prospects and problems of simple linear models for estimating symbiotic N2 fixation by crop and pasture legumes, Plant Soil 329 (2010) 75–89.
[21] WALTER, D., et al., Sulfur affects root growth and improves nitrogen recovery and internal efficiency in wheat, J. Plant Nutr. 40 (2017) 1231–1242.
[22] PEOPLES, M.B, et al., The potential environmental benefits and risks derived from legumes in rotations, Agron. Monograph 52 (2009) 349–385.
[23] ERNST, O., et al., Depressed attainable wheat yields under continuous annual no-till agriculture suggest declining soil productivity, Field Crops Res. 186 (2016) 107–116.
[24] FONTAINE, S.C., et al., Fungi mediate long term sequestration of carbon and nitrogen in soil through their priming effect, Soil Biol. Biochem. 43 (2011) 86–96.
[25] ERNST, O., et al., Shifting crop-pasture rotations to no-till annual cropping reduces soil quality and wheat yield, Field Crops Res. 217 (2018) 180–187.