Crop Productivity And Soil Fertility As Affected By Continuous Intercropping In An Orthic Anthrosol

Intercropping is widely practised in agriculture because of its significant overyielding and nutrition acquisition advantages. Under this conditions whether soil fertility sustained or improved became a hot spot, which is well-known. However, there are few published studies about continuous intercropping on long-term changes in soil fertility. Therefore, we conducted two field experiments about the effects of intercropping systems and P application rates on soil fertility in Baiyun village, Wuwei City, Gansu Provience in northwest China. The first long-term field experiment was carried out in2003, the treatments included three intercropping systems (wheat (Triticum aestivum L. cv. Yongliang No.4)/maize(Zea mays L. cv. Zhengdan No.958), faba bean (Vicia faba L. cv. Lincan No.5)/maize and wheat/faba bean continuous and rotational intercroppings), four rotational systems (wheat-maize, wheat-faba bean, faba bean-maize and wheat-faba bean-maize), monoculture systems (monocropping maize, wheat and faba bean). The second long-term field experiment was conducted in2009which was a split-plot design, with different rates of P fertilizer (0,40and80kg P/ha) as main plot and four intercroppings (maize(Zea mays L. cv. Zhengdan No.958)/faba bean (Viciafaba L. cv. Lincan No.5)),(maize/soybean(Glycine max L.cv. Wuke No.2)),(maize/chickpea (Cicer arietinum L. cv. Longying No.1)) and (maize/turnip (Brassica campestris L.cv. Gannan No.4)) and five monocultures (maize, faba bean, soybean, chickpea and turnip) as sub-plot. We measured crop yields, above ground nutrient uptake and soil fertility in the9th (2011) and10th (2012) for the first experiment and in the3th (2011) and4th (2012) for the second experiment, respectively. Soil fertility properties included physical (soil saturation infiltration, soil particle composition, soil compaction and soil water stable aggregates concentration), chemical (soil organic matter, total N, Olsen P, available K, cation exchangeable capacity and pH) and biological properties (soil urease, acid phosphatase, nitrate reductase and sucrase activities). The main results were as follows:(1) Continuous intercropping still were overyielding and had nutrient acquisition advantage. In the first field experiment, averaged over wheat and maize, faba bean and maize, and wheat and faba bean crop combinations, crop productivity was enhanced by5.2-29.5%and2.9-12.8%in continuous intercropping; and increased by14.1-33.3%and11.6-16.2%in rotational intercropping in comparison with corresponding monoculture and rotation cropping systems over two years, respectively. N acquisition by above ground parts in continuous intercropping was increased by0-15.4%and4.4-9.8%, and in rotational intercropping by8.4-22.1%,12.7-16.1%compared to corresponding monoculture and rotational crops, respectively. P acquisition in continuous intercropping was enhanced by0-14.4%and0-10.5%, and rotational intercropping by3.7-17.4%and7.3-13.1%compared to the weighted means of monoculture and rotational crops, respectively. The percentages of K acquisition were raised by0-14.3%,0-20.4%in continuous intercropping,6.1-21.7%and2.3-28.3%in rotational intercropping, respectively.In the second field experiment, averaged over three P application rates, faba bean/maize, soybean/maize, chickpea/maize and turnip/maize intercroppings were overyielded by14.5-19.6%,19.3-38.2%,20.7-24.3%and24.8-38.6%, respectively, compared to corresponding monocultures across two years. N acquisition by above ground parts in intercropping was enhanced by19.2-20.7%,2.2-27.5%,24.8-26.5%and29.4-39.7%; P acquisition was raised by16.3-27.3%,2.4-30.6%,28.1-35.1%and36.9-40.7%; K acquisition was increased by21.5-31.9%,9.7-52.9%,31.5-38.1%and43.1-49.2%compared with corresponding monocultures across two years, respectively.(2) Intercropping improved soil physical properties. In the9lh (2011) years after crops harvest, soil concentration of water stable aggregates with greater than2mm in soil grown faba bean/maize intercropping were175%and105%higher for continuously intercropping,75%and65%higher for rotational intercropping than corresponding monocultre and rotation crops, respectively. In the10th (2012) years, soil concentration of water stable aggregates with greater than2mm in soil grown wheat/maize intercropping were188%and130%higher for monoculture and rotation crops, respectively. Soil concentration of water stable aggregates with greater than2mm in soil grown wheat/maize intercropping were138%and174%higher for rotational intercropping, respectively. Soil concentration of water stable aggregates with greater than2mm in soil grown faba bean/maize intercropping were474%and450%,135%and125%greater for continuous and rotational intercropping, respectively. In2011, soil concentration of2-0.25mm water stable aggregates in soil grown monoculture and rotation were36.9%and44%,16.2%and22.1%higher for continuous or rotational intercropping, respectively. In2012, soil concentration of2-0.25mm water stable aggregates were no differences among monoculture or rotational and intercropping, but rotational was greater than faba bean/wheat intercroppings. Soil concentration of0.25-0.106mm and smaller than0.106mm water stable aggregates were not affected by intercropping. Intercropping were not influenced on soil bulk density, texture and compaction. Soil infiltration were altered by continuous intercropping in2011and rotation in2012(with an exception of wheat with maize combination) in the long-term experiments.In the second field experiment, averaged over three P rates, soil infiltration were increased by91-131%,31.1-39.4%and9.6-25.6%in faba bean/maize, soybean/maize and turnip/maize intercropping, compared to corresponding monocultures across two years. Soil water stable aggregates with greater than2mm for faba bean/maize, soybean/maize, chickpea/maize and turnip/maize intercropping were improved by12.2-17.4%,0-46.7%,19.6-39.2%and0-34.6%compared with corresponding monocultures over two years. There were no significant differences in2-0.25mm,0.25-0.106mm, smaller than0.106mm soil aggregates, soil texture and compaction between intercropping and monoculture. Thus, soil physical properties were maintained or improved by intercropping.(3) Generally, soil chemical properties were sustained by intercropping. In the first experiment, Soil organic matter, total N, Olsen P, available K and cation exchangeable capacity were not as affected by intercropping (with an exception of soil pH in wheat/maize and faba bean/maize intercropping in2011and cation exchangeable capacity in2012). In the second experiment, averaged over P rates, soil OM were stable with an exception of chickpea/maize intercropping in2011and turnip/maize intercropping both two years. Interestly, there were no responses of soil total N to P application under both intercropping and monoculture (with an exception of faba bean/maize intercropping at80kg ha-1in2011); soil Olsen P was reduced by intercropping in2012; soil available K significantly decreased by intercropping in both years; soil cation exchangeable capacity and pH demonstrated a declined trends in2012. Soil Olsen P reduced by intercropping, which can be alleviated by P added.(4) Intercropping maintained soil biological properties. In the first experiment, soil urease activity in wheat/maize intercropping in2011and wheat/faba bean intercropping in2012were greater than corresponding monoculture and rotation, but soil acid phosphatase, nitrate reductase and sucrase activities were stable. In the second experiment, in the majority of cases soil enzymes activities did not differed across all the cropping systems at different P application rates compared to monocrops with the exception of soil acid phosphatase activity which was higher in intercropping than in the corresponding monocrops in both years, indicating that intercropping enhanced utilization of organic P in soil via altered soil acid phosphatase.(5) The greenhouse experiment demonstrated that soil water stable aggregates>2mm,2-0.25mm and0.25-0.106mm were significantly correlated with crop productivity. The path coefficients were-0.14,0.21and0.42, respectively, and were significantly in0.25-0.106mm. The determination coefficient (R2) is0.40indicated soil physical properties which explain40%the variation of productivity.