Effect of different organic manures combined with chemical fertilizer on nitrogen use efficiency and soil fertility

Objectives There are obvious differences in composition and properties among different organic manures. The objectives of this study were to discuss the effect of different organic manures combined with chemical fertilizer on nitrogen use efficiency and soil nutrients and provide a theoretical basis for efficiently using different organic manures by optimizing fertilization techniques.

Methods Eighteen fertilizer treatments included in this field experiment were: one chemical fertilizer treatment (farmer’s N rate, N 225 kg/hm² per season); twelve treatments of organic manures (chicken manure, pig manure and cow manure) with chemical fertilizers (ratios of manure N in the total N input were 25%, 50%, 75% and 100%); four double farmer’s rate treatments of three manures(chicken manure, pig manure and cow manure) and chemical fertilizer applied singly; one without any fertilizer treatment. The effects of different fertilization systems on nitrogen uptake, nitrogen use efficiency and soil fertility of crops were studied and discussed.

Results Under farmer’s N rate (225 kg/hm²), applying chicken manure or pig manure alone had similar nitrogen harvest index (NHI) and physiological efficiency (NPE) as treatments applying chemical fertilizer alone, NHI and NPE values of treatments applying cattle manure were 79.06% kg/kg and 64.42 kg/kg. Compared with famer’s N rate, the double rate of chicken manure, pig manure or chemical fertilizer decreased crops’ NHI and NPE significantly, while the double rate of cattle manure did not decrease crops’ NHI and NPE. The difference among various ratios of chicken manure and chemical fertilizer, pig manure and chemical fertilizer, cattle manure and chemical fertilizer was not significant. Under farmer’s N rate (225 kg/hm²), applying chicken manure or pig manure alone had similar partial factor productivity (PFP) and recovery efficiency (NRE) as treatments applying chemical fertilizer alone. PFP average and NRE average of treatments applying chicken and pig manure were 39.66 kg/kg and 41.85% respectively, however, PFP and NRE of treatment applying cattle manure were 29.1 kg/kg and 15.6%. Compared with famer’s N rate, the double rate of cattle manure, chicken manure, pig manure or chemical fertilizer decreased crops’ PFP and NRE by average of 49.1% and 23.2%, respectively. Moreover, all treatments combining cattle manure, chicken manure or pig manure with chemical fertilizer also had similar PFP and NRE as treatments applying chemical fertilizer alone. Applying organic manure alone or combining organic manure with chemical fertilizer could not increase soil total N content. High level of P and K content in organic manure resulted in more soil available K and P than treatments applying chemical fertilizer alone. Available P of treatments receiving chicken or pig manure was 5.82 or 7.06 times that of treatment receiving chemical fertilizer alone.

Conclusions Under the recommended fertilization rate, chicken manure or pig manure should not be applied or combined with a small amount of nitrogen fertilizer, and cow manure with about 75% nitrogen fertilizer could achieve the same nitrogen use efficiency as chemical fertilizer, while improving soil fertility. In actual production, the proportion of manure and chemical fertilizer should be adjusted according to the characteristics of manure, so as to realize the scientific utilization of manure.