اثرات مدیریت کود سبز کوتاه مدت و خاکورزی بر عملکرد ذرت و کیفیت خاک در اندی سول

Andisols are very important land resources supporting high human population density. Maize (Zea mays L.) production on Andisols located in the Purhepecha Region of central Mexico is representative of the highlands conditions of Mexico and Latin America. Farmers struggle with low crop yield and low soil nutrient availability. A 2-year field study was conducted to evaluate the effects of green manures either tilled into the soil (CT) or cut and left on the surface as a mulch (ZT), on maize yield and soil quality. Green manure treatments were: vetch (Vicia sativa L.), oat (Avena sativa L.) and none. No extra N was added to maize. Green manure and tillage had a significant effect on maize grain yield, N uptake and P uptake with CT vetch performing better than ZT oat. Soil organic C and total N were significantly higher under ZT than under CT management. Soils with vetch had higher P concentration. Soil under ZT oat had the highest infiltration rate and penetration resistance compared with other treatments. There appears to be a trade off between soil productivity and intrinsic soil physical properties among soil treatments.

Andisols occur in populated and important agricultural areas all over the world (Shoji et al., 1993). These soils are characterized by high amount of organic matter; very low rate of N and P mineralization; high P adsorption levels and fragile physical properties when converted to agriculture and mechanical tillage. Agricultural practices such as CT and inappropriate fertilization are causing gradual deterioration of Andisols in the Purhepecha Region of the Mexican highlands (Santos-Ladín, 1986). In this region, 2.4–3.0 Mg ha−1 of conventionally tilled soils are lost every year due to erosion (Tiscareño et al., 1999) with depletion of macronutrients, from the agricultural fields. Farmers need to add increasing amounts of N as chemical fertilizer to maintain maize yields (Astier et al., 2000). Green manuring is the process of turning a crop into the soil, whether originally intended or not, irrespective of its state of maturity, for the purpose of affecting some agronomic improvement (Mac Rae and Mehuys, 1985). Green manures are known to increase soil N and P availability for the following crop and at the same time, contribute to the conservation of soil organic matter and soil biological, physical and chemical properties (Mac Rae and Mehuys, 1985 and Mc Vay et al., 1989). Acton and Gregorich (1995) defined soil quality as the condition of a soil to maintain plant growth without soil degradation or environmental damage. Soil quality evaluation frameworks must be sensitive to the specific time and spatial scale of the study (Astier et al., 2002). The objective of this study was to evaluate transitional effects over 2 years on soil productivity and soil quality resulting from green manure species and tillage management. For that purpose, the best (most sensitive) indicators were selected.

Growth of a cereal (oat) and a legume (vetch) as green manure in this Andisol generally improved maize productivity and soil physico-chemical indicators. Vetch cover crop produced higher maize yield than oat cover crop. Higher N and P uptake was observed with either green manure than without. However, maize grown with vetch had significantly higher N and P uptake than with oat. Vetch substantially increased soil P availability. Oat had positive effects on water infiltration and mechanical resistance indicators. Therefore, to avoid negatively affecting maize productivity, which is related with food self-sufficiency in rural communities of this Mexican region, incorporation of oat as a green manure must be complemented with a source of organic or inorganic N. This study also showed that tillage had an effect on SOC and STN concentration but green manure did not. Soil under ZT had higher SOC and STN concentration than under CT. Soil physical properties, such as softness and infiltration rate also had higher values under ZT than under CT. There appears to be a trade off between maize productivity and soil properties, at least in the short-time transition to ZT. Soil under VsCT produced highest maize yield, whereas soil under AsZT had highest soil physical indicators. It is important to emphasize that more than 2 years would be required to show the real long-term benefits of conservation management.