Analysis of competition and phosphorus response in maize/soybean and maize/rice intercrops in relation to soil phosphorus availability in different environments

Field experiments were conducted at University of Hawaii in three environments to evaluate the productivity of intercrops, leaf properties, and root dry matter in relation to soil P. Intercrops of maize with soybean or rice were established at ten levels of soil P and evaluated against sole crop checks for grain yield, dry matter, P uptake and efficiency.; The response of grain and total dry matter yield to P ({dollar}partial{dollar}Y/{dollar}partial{dollar}P) was proportional to the inverse of P level for both maize and soybean in each environments. The presence of soybean with maize had little effect on the performance of intercrop maize, however soybean yields were significantly reduced. Grain and dry matter yield of sole crop soybean increased with increased P availability whereas intercrop soybean yield decreased. The magnitude of the increase or decrease (slope) depended on environment and the sign of the slope changed by intercropping. Higher maize yields across environments and P levels were associated with reduced growth of intercrop soybean.; Intercrop advantage, as measured by the Land Equivalent Ratio, and the competitiveness of soybean decreased as P availability increased. The increased competitiveness of intercrop maize at high P levels was correlated with a reduction in yield of intercrop soybean. The advantage due to intercropping was maximum under low soil P availability under a wide range of environmental conditions.; Growth of intercrop maize was no different than the sole crop for their leaf properties and P uptake, but was profoundly affected by environment and P availability in the soil. Soybean leaf properties, leaf tissue P concentration and P uptake were affected by environment, P level and intercrop system and their interactions.; Phosphorus use efficiency, measured as the grain yield or dry matter per unit of P uptake, decreased with increased P availability. Taken together, the intercrops extracted more P than sole crop maize. P use efficiency was reduced by intercropping.; Total root biomass in the surface layer of the intercrops was higher than in the sole crops, with the difference changing according to P levels and year.; The increased productivity of intercrops was associated with increased P uptake. In low-input subsistence agriculture, accelerated P mining--the faster removal of limited soil P--may cause the intercrop systems to be less sustainable.