IMPROVING MAIZE PRODUCTIVITY AND SOIL ORGANIC CARBON SEQUESTRATION THROUGH BIOGAS SLURRY AND POULTRY MANURE UNDER DIFFERENT TILLAGE SYSTEMS

Abstract

The integrated use of slurry from a biogas digester (bioslurry), poultry manure and chemical fertilizer has potential to replace sole application of nitrogen as chemical fertilizer and improve maize productivity in a sustainable way. Field studies were designed using a randomized complete block design with a split plot arrangement during 2012-13. The trials included three tillage systems (minimum, conventional and deep tillage) with combinations of the different sources of nitrogen (bioslurry, poultry manure and chemical fertilizer), applying 100, 50 and 25% of the recommended nitrogen application to improve maize productivity. The results showed that deep tillage treatment with the recommended nitrogen application rate of the chemical fertilizer alone produced maximum plant height, stem diameter, cob length, cob diameter and number of grain rows per cob. However, deep tillage treatment with the recommended nitrogen application rate applied as 50% chemical fertilizer, 25% poultry manure and 25% bioslurry produced maximum 1000 grain weight, biological yield, grain yield and N uptake in maize grains as compared to other treatments. The maximum fertilizer N recovery efficiency in maize grains and value to cost ratio were observed in treatment where recommended nitrogen application rate applied as 50% chemical fertilizer, 25% poultry manure and 25% bioslurry. The potential of bioslurry and poultry manure to improve soil organic carbon (SOC) sequestration and soil fertility under different tillage systems were also studied in the silt loam soils of Haripur, Pakistan. The results showed that tillage systems, nitrogen treatments and their interaction significantly increased SOC stocks, total porosity, soil total nitrogen, available phosphorus, potassium and significantly decreased bulk density. The maximum soil total nitrogen was recorded in the deep tillage system with 100% nitrogen applied as poultry manure. The maximum soil available phosphorus and potassium were observed in the deep tillage system with 100% nitrogen applied as bioslurry. The maximum SOC stocks were observed in minimum tillage with 100% nitrogen applied as bioslurry. These experimental measurements were used to evaluate a dynamic simulation model of soil organic matter turnover, RothC, which was then used to estimate future carbon sequestration. The correlation between experimental and simulated values was highly significant and the root mean square error was within experimental error, suggesting that RothC is providing an acceptable representation of the changes in soil carbon that are occurring in this experiment. The uncertainty in simulations was less than 3%. Simulations using future weather scenarios suggest that addition of the recommended rate of nitrogen in 8.4 t ha-1 y-1 bioslurry increases soil carbon sequestration over 100 years (2012-2112) by 24.9±0.7 t ha-1 compared to the control where no organic waste was applied. This sequesters 7.5±0.2 t ha-1 more carbon than if the same amount of nitrogen is applied as poultry manure, requiring an application rate of 7.5 t ha-1 y-1. If the same amounts of bioslurry and poultry manure are applied, carbon sequestration is still significantly greater for bioslurry than for poultry manure (4.5±0.2 t ha-1). Losses of carbon with climate change were highest under climate scenario B2 (environmental protection with regionalisation) and B1 (environmental protection with globalisation), followed by A1B (economic growth with globalisation), with minimum losses from A2 (economic growth with regionalisation). These predicted losses are likely to be more than compensated for by application of organic fertilizers at the rates needed to supply sufficient nitrogen to the crops. The findings can be concluded that the integrated use of bioslurry and poultry manure with a reduced rate of chemical fertilizer application improved maize productivity, soil carbon sequestration and reduced the cost of chemical fertilizers.