Nitrification and urease inhibitors mitigate global warming potential and ammonia volatilization from urea in rice-wheat system in India: A field to lab experiment

The efficacy of alternative nitrogenous fertilizers for mitigating greenhouse gas and ammonia emissions from a rice-wheat cropping system in northern India was addressed in a laboratory incubation experiment using soil from a 10-year residue management field experiment (crop residue removal, CRR, vs. incorporation, CRI). Neem coated urea (NCU), standard urea (U), urea ammonium sulfate (UAS), and two alternative fertilizers, urea + urease inhibitor NBPT (UUI) and urea + urease inhibitor NBPT + nitrification inhibitor DMPSA (UUINI) were compared to non-fertilized controls for four weeks in incubation under anaerobic condition. Effects of fertilizers on global warming potential (GWP) and ammonia volatilization were dependent on residue treatment. Relative to standard urea, NCU reduced GWP by 11 % in CRI but not significantly in CRR; conversely, UAS reduced GWP by 12 % in CRR but not significantly in CRI. UUI and UUINI reduced GWP in both residue treatments and were more effective in CRI (21 % and 26 %) than CRR (15 % and 14 %). Relative to standard urea, NCU increased ammonia volatilization by 8 % in CRI but not significantly in CRR. Ammonia volatilization was reduced most strongly by UUI (40 % in CRI and 37 % in CRR); it was reduced 28-29 % by UUINI and 12-15 % by UAS. Overall, the urease inhibitor, alone and in combination with the nitrification inhibitor, was more effective in mitigating greenhouse gas and ammonia emissions than NCU. However, these products need to be tested in field settings to validate findings from the controlled laboratory experiment.

Relay cropping of wheat (Triticum aestivum L.) in cotton (Gossypium hirsutum L.) improves the profitability of cotton-wheat cropping system in Punjab, Pakistan

Delayed sowing of wheat (Triticum aestivum L.) in cotton-based system reduces the productivity and profitability of the cotton-wheat cropping system. In this scenario, relay cropping of wheat in standing cotton might be a viable option to ensure the timely wheat sowing with simultaneous improvement in wheat yields and system profitability. This 2-year study (2012-2013 and 2013-2014) aimed to evaluate the influence of sowing dates and relay cropping combined with different management techniques of cotton sticks on the wheat yield, soil physical properties, and the profitability of the cotton-wheat system. The experiment consisted of five treatments viz. (S1) sowing of wheat at the 7th of November by conventional tillage (two disc harrows + one rotavator + two plankings) after the removal of cotton sticks, (S2) sowing of wheat at the 7th of November by conventional tillage (two disc harrows + two plankings) after the incorporation of cotton sticks in the field with a rotavator, (S3) sowing of wheat at the 7th of November as relay crop in standing cotton with broadcast method, (S4) sowing of wheat at the 15th of December by conventional tillage (two disc harrows + one rotavator + two plankings) after the removal of cotton sticks, and (S5) sowing of wheat at the 15th of December by conventional tillage (two disc harrows + two plankings) after the incorporation of cotton sticks in the field with a rotavator. The highest seed cotton yield was observed in the S5 treatment which was statistically similar with the S3 and S4 treatments; seed cotton yield in the S1 and S2 treatments has been the lowest in both years of experimentation. However, the S2 treatment produced substantially higher root length, biological yield, and grain yield of wheat than the other treatments. The lower soil bulk density at 0-10-cm depth was recorded in the S2 treatment which was statistically similar with the S5 treatment during both years of experimentation. The volumetric water contents, net benefit, and benefit-cost ratio were the highest in the S3 treatment during both years of experimentation. Thus, relay cropping of wheat in standing cotton might be a viable option to improve the soil physical environment and profitability of the cotton-wheat cropping system.

Effects of residue incorporation and plant growth on soil labile organic carbon and microbial function and community composition under two soil moisture levels

This study investigates the effects of residue incorporation coupled with plant growth and soil moisture level on wheat biomasses, soil nutrients, labile organic carbon (LOC), microbial metabolic profiles, and community composition. Four management practices were used in a 180-day pot experiment: (1) control (CON), (2) maize (Zea mays L.) residue incorporation without plants (MR), (3) wheat (Triticum aestivum L.) plants without maize residue (WP), and (4) maize residue incorporation with wheat plants (MRWPs). Each management practice included soil moisture at both 40 and 80% of field capacity. At wheat harvest, soil nutrient contents in the WP and MRWP treatments were significantly lower than in the CON and MR treatments. In comparison with the CON treatment, MR, WP, and MRWP treatments resulted in 35, 23, and 67% increases in dissolved organic carbon content; 17, 12, and 34% increases in hot-water extractable organic carbon content; and 78, 50, and 150% increases in microbial biomass carbon content. Furthermore, microbial utilizations of carboxylic acids and polymer carbon sources in the MR, WP, and MRWP treatments were 261 and 88%, 239 and 105%, and 300 and 126% higher than in the CON treatment. The MR and CON treatments had similar phospholipid fatty acid (PLFA) content but the WP and MRWP treatments had significantly increased gram-negative content and changes to community composition compared with the CON and MR treatments. The wheat biomass, LOC, and PLFA contents significantly increased with greater soil moisture. Overall, these results suggest an additive effect of residue incorporation and plant growth on LOC contents, primarily due to the changes in microbial utilization of carbon sources and community composition.