Effect of cotton-cowpea intercropping on C and N mineralisation patterns of residue mixtures and soil. uri icon


  • C = C(E)(1 - e(-kt))
  • C = C(S)/1+e(-(t t0/k))
  • Carbon and nitrogen mineralisation potential of mixed cotton (Gossypium hirsutum L.) and cowpea (Vigna unguiculata (L.) Walp) crop residues produced under intercropping, as well as a reddish-brown soil classified by FAO as Ferralic Cambisol previously under intercrops, were studied over a 10-week incubation period under controlled conditions (25 degrees C and moisture content of 70% field capacity, 125 mm) in the laboratory. Treatments consisted of cotton residues ( 100 : 0), cowpea residues ( 0 : 100), and cotton-cowpea residues ( 50 : 50, 70 : 30, and 30 : 70). These ratios were based on yields obtained in different cotton-cowpea intercrop treatments from a field study. Cowpea residues ( 0 : 100) released the highest amount of mineral N of 36.4 mg/kg soil, and cotton residues ( 100 : 0) least, 19.2 mg/kg soil, while the other mixtures were in between. All treatments except for cowpea residues ( 0 : 100) and the 30 : 70 mixture showed immobilisation of soil N during the first 2 weeks of incubation. The trend for C mineralisation was similar to that of N, and cowpea residues ( 0 : 100) released the highest amount, 492 mg C/kg soil, while cotton residues ( 100 : 0) recorded the least, 315 mg C/kg soil. The C mineralisation patterns of cowpea residues ( 0 : 100) and 30 : 70 treatments were exponential and were well described by the equation:
  • where C(E) is exponentially mineralisable C fraction, k is the rate constant, and t is time in days. The mineralisation patterns for other treatments were sigmoidal and were well described by the equation:
  • where CS is sigmoidally mineralisable C fraction; t(0) is time in days required for complete mineralisation of CS, while k is rate constant. The amount of N released from soil previously under cotton-cowpea intercrops and sole crops was approximately one-third of the amount released when the residues were incorporated. The highest amount of N released (12.2 mg/kg soil) was from soil previously under sole cowpea, while soil from the 1 : 1 cotton-cowpea intercrop released 9.9 mg/kg soil and soil from sole cotton released 5.9 mg/kg soil. There was no significant effect ( P > 0.05) of previous crop on C mineralisation patterns of the soil. Mixtures slow down N losses and increase nutrient use efficiency of legume residues, especially in the short-term. When cotton is grown as a sole crop, starter N to offset negative effects of initial N-immobilisation at the start of season is required. A better understanding of controlling parameters of decomposition can make it possible to predict C and N mineralisation patterns in mixtures. Reduced C mineralisation in cotton-cowpea mixtures may result in more C sequestration and, hence, SOM build-up and improved sustainability in the long term in intercropping systems.

publication date

  • 2009
  • 2009