Study On Phosphorus Uptake And Utilization Of Maize In Maize-soybean And Maize-sweet Potato Relay Strip Intercropping Systems

Intercropping, an important agricultural system for meeting local food demands and ensuring food security in China can enhance crop yield and also increase utilization of resources due to below-ground root interactions between intercropped species. Maize-based intercropping, especially with legumes, can result in overyielding of the whole cropping system and lead to efficient utilization of soil phosphorus (P). A field experiment with different P application amount including 0,35,70,105,140 kg ha-1 and a root barrier pot experiement with no barrier and plastic barrier were conducted in 2012 and 2013 to study the effects of P nutrition on P accumulation and use efficiency of maize in maize-soybean and maize-sweet potato relay strip intercropping systems along with their interspecific promotion and mechanism. A pot experiment with and without barrier was conducted to find the interspecific interactions, when root was separated by plastic barrier, there were not any interspecific interactions but only P fertilizer effect, when root was not separated, there exsited interspecific interactions and P fertilizer effects at the same time. The main results were as follows:1. Effects of interspecific interactions and P application rates on maize yield in maize-soybean and maize-sweet potato relay strip intercropping systemsThere were significant yield advantages of the maize-soybean intercropping and the maize-sweet potato intercropping in the year 2012 and 2013. Maize yield was highly influenced by intercropping and P application. Yield advantages of intercropping were mainly the results of interspecific interactions and different P application rates. The grain yields of maize were inceased by intercropping regardless of P application. In the maize-soybean intercropping and the maize-sweet potato intercropping, grain yields of maize were generally increased by interspecific interactions with an increasing of 16.84% and 7.17% respectively under P70 treatment,22.67% and 12.60% under Po treatment. Yield increase in intercropped maize was highly dependent on interspecific interactions when without any P supply.Increasing application of P fertilizer could help increase maize yield within limits, indicating that yield advantage of intercropping was also affected by P supply. In maize-soybean, maize yield presented a higher increasing with the increasing of P fertilizer compared with maize-sweet potato intercropping. The suitable P application rate and potential of yield in maize-soybean and maize-sweet potato intercropping were different. In the year 2012, maize yields of both intercropping systems reached a maximum with P application rate at 105 kg ha-1, including 7200.345 kg ha-1 for maize-soybean and 7141.661 kg ha-1 for maize-sweet potato. In 2013, two crop strips exchanged, maize yield reached a maximum with P application rate at 70 and 105 kg ha-1 respectively with yield being 6894.879 kg ha-1 and 6789.549 kg ha-1, maize yield increased by 11.06% and 9.54% compared with Po treatment. The average maize yield under maize-soybean was higher than that under maize-sweet potato regardless of P fertilizer. Maize intercropped with soybean could reduce P fertilizer input and get high yield compared with maize intercropped with sweet potato. The findings indicated that kernels per ear and 1000-kernel weight played an important role in the overyielding of maize and resulting in a yield difference between different intercropping systems.2. Effects of interspecific interactions and P application rates on P accumulation and distribution and use efficiency of maize in maize-soybean and maize-sweet potato relay strip intercropping systemsInterspecific interactions increased P accumulation and distribution of stems, leaves and grains in maize-soybean and maize-sweet potao intercropping systems. And the facilitation was stronger in maize-soybean compared with maize-sweet potato. P accumulation in maize increased when growing without root barrier with an increase of 14.67% and 5.17 (P0), and 17.05% and 5.62%(P70) respectively in maize-soybean and maize-sweet potato intercropping. Interspecific interactions increased P uptake significantly when maize intercropped with soybean. P distribution in grians increased with an increase of 7.8% (P0) and 9.7% (P70) due to interspecific promotion. In the year 2013 after strip rotation, preceding crop affected P accumulation differently with or without P application. Interspecific interactions also increased P use efficiency (PUE) by an average of 7.81%. P use efficiency was significantly higher in maize-soybean than that in maize-sweet potato. When without root barrier, P production efficiency (PPE) increased by 7.00%.P accumulation and distribution in stems, leaves and grains were higher with P application rate at 105 kg ha-1 in 2012. Planting patterns and P application rate had a significant interaction. In the year 2013, accumulation of P reached the top with P application rate at 70 and 140 kg ha-1 respectively in maize-soybean and maize-sweet potato intercropping. Increasing application of P fertilizer help enhance P accumulation and distribution and PUE. P accumulation of maize-soybean was significantly higher than that of maize-sweet potato when P application was less than 70 kg P2O5 ha-1. PPE increased with the increasing of P application. PUE, PPE, PHI decreased significantly when application of P more than a certain amount.3. Effects of interspecific interactions and P application rates on soil nutrition and enzyme activity in maize-soybean and maize-sweet potato relay strip intercropping systemsThere existed interspecific interactions in increasing soil available P concentration, decreasing soil pH to a certain extent. Soil available P concentration was significantly higher when root was not seperated. In maize-soybean intercropping, interspecific interactions decreased pH significantly, weakened with P supply. However, interspecific interaction affected soil pH of maize-sweet potato insignificantly whether applying P fertilizr or not. Total nitrogen concentration and ammonium nitrogen in maize-soybean were significantly higher than that in maize-sweet potao with an increasing of 32.26% and 37.73% respectively. Organic matter in maize-soybean intercropping remained a relatively high level with same application rate of P fertilizer. Concentration of total potassium and soil organic appeared insignificant between different intercropping treatments during each growing stage. Ways of root barriers and P application affected acid phosphatase activity significantly. Interspecific interactions increased acid phosphatase activity significantly by 14.02% and 6.84% respectively. Effects of different preceding crops on acid phosphatase activity were different.Soil available increased with the increasing of P fertilizer at each growing stage, and reached the top with P application rate at 140 kg ha-1. Soil available P concentration increased mostly with the increasing of P fertilizer when P application rate was 0 to 70 kg ha-1. Increasing application of P fertilizer increased available P insignificantly when P application amount was more than 70 kg ha-1. Total nitrogen, nitrate nitrogen and organic matter concentration increased with the increase of P fertilizer, and then declined when P application amount was more than 105 kg ha-1 Inorganic nitrogen and organic matter kept a relatively high level with P application rate at 70 to 105 kg ha-1. P fertilizer affected acid phosphatase activity significantly. For maize-soybean and maize-sweet potao intercropping, acid phosphatase activity and urease activity reached a maxium with P application rate at 105 kg ha-1, and the followed by 140 kg ha-1. Enzyme activity in maize-sweet potato appeared a relatively low level compared with maize-soybean intercropping.4. Interspecific interactions in maize-soybean and maize-sweet potato relay strip intercropping systems in increasing P accumulation and use efficiencyAggressiveness and nutrition competition ratio illustrate the mechanism of maize P absorption with or without a root partition of two relay intercropping systems. Similar trend was found in 2012 and 2013. There existed a similar interspecific interaction of two intercropping systems, including maize showed stronger competitive ability compared with soybean or sweet potato (Acs>0), and decreased after application of P fertilizer. This indicated that maize was the advantage intercrops and soybean or sweet potato in a disadvantage position. Application of P can alleviate interspecific competition. As for P nutrition competition, different competitiveness of intercrops was revealed, including a stronger competitive ability for maize compared to soybean or sweet potato (NCRcs>1). Acs value and NCRcs value were higher in maize/soybean as compared to maize/sweet potato, indicated that advantage of maize grain yield was mainly due to the relatively stronger interspecific and nutrition competition and the characteristic of soybean such as nitrogen fixation may also play an important role.In conclusion, there existed interspecific facilitation of two intercropping systems, including maize intercropped with soybean showed a more significant interspecific facilitation compared maize intercropped with sweet potato. Application of P fertilizer with 70-105 kg ha-1 in maize-soybean intercropping and 105-140 kg ha-1 in maize-sweet potato intercropping could meet the demand of P fertilizer.