Effect of different crop management systems on net primary productivity and relative carbon allocation coefficients for corn (Zea mays L.)

In order to evaluate the effect of different crop management practices on corn (Zea mays L.) net primary productivity (NPP) and relative carbon allocation coefficients, a field experiment was conducted based on a completely randomized block design with four replications in the Agricultural Research Station, Ferdowsi University of Mashhad, Iran during two growing season 2008-2009 and 2009-2010. Treatments including two low input management systems based on application of cow manure and compost municipal made from house-hold waste, a medium input system and a high input system. Application of inputs and management practices were based on a basic assumption made prior to the start of the experiment. On the other words, for each of the management system the particular set of inputs were allocated. In this respect, for low input system 30 t.ha-1 cow manure or 30 t.ha-1 compost municipal made from house-hold waste, twice hand weeding were used. In medium management system, 15 t.ha-1 compost municipal made from house-hold waste, 150 kg.ha-1 urea, two seed bed operations, 1.5 l.ha-1 2, 4-D herbicide applied at five-leaf stage and one time hand weeding were used. In high input system, the inputs were two seed bed operations, 2 l.ha-1 Paraquat herbicide used after seeding and 1.5 l.ha-1 2, 4-D applied at five-leaf stage. Results showed that the effect of different crop management practices on the shoot biomass, seed weight, root biomass, total biomass, shoot biomass: root biomass (S:R), SRL and HI were significant (p≥0.01). High input management system enhanced total biomass and S:R and decreased seed weight, root biomass and SRL. The highest and the lowest total biomass observed in high input (18.3 kg.m-2.yr-1) and low input with using compost (10.3 kg.m-2.yr-1), respectively. The maximum SRL observed in low input based on cow manure application (19.8 cm.cm-3 soil) and the minimum SRL was in high input (1.3 cm.cm-3 soil). Range of relative carbon allocation coefficients to seed, shoot, root and extra-root were estimated as 0.10-0.17, 0.19-0.52, 0.23-0.39 and 0.15-0.25, respectively. Low input with cow manure application increased allocated carbon to seed, root and extra-root and decreased allocated carbon to shoot. The highest allocated carbon to root observed in low input with using manure (6.5 g C m-2.yr-1) and the lowest allocated carbon to root was in high input (2.7 g C m-2.yr-1). The maximum and the minimum NPP were obtained in low input with cow manure application (16.6 g C m-2.yr-1) and high input (8.9 g C m-2.yr-1), respectively. It seems that crop management system based on low input of cow manure application enhanced carbon allocation to below-ground biomass of corn due to improvement in soil physical, chemical and biological properties and also nutrient availability which could be regarded as an alternative to reduce CO2 production and moderate climate changes.