Soil quality index and nutrient balance in rice-rice cropping system under long-term fertilizer experiment

Abstract

Long-term experiments provide the best possible platform for studying the changes in soil properties and processes, identifying emerging trends in nutrient imbalances and deficiencies and help to formulate future strategies for maintaining soil health and quality. The present study entitled “Soil quality index and nutrient balance in rice-rice cropping system under Long Term Fertilizer Experiment” was undertaken at RARS, Pattambi and College of Agriculture, Vellanikkara. The objectives were set out to estimate soil quality index and NPK balance in rice-rice cropping system as affected by nutrient management practices under Long Term Fertilizer Experiment. The Long Term Fertilizer Experiment (LTFE) in rice-rice cropping system maintained (since 1997) at RARS Pattambi has been laid out in RBD consists of 12 treatments viz.,T1 : 50 per cent NPK, T2 : 100 per cent NPK, T3 : 150 per cent NPK, T4 : 100 per cent NPK + 600 kg ha -1 CaCO3 , T5 : 100 per cent NPK, T6 : 100 per cent NP, T7 : 100 per cent N, T8 : 100 per cent NPK + Farm Yard Manure (FYM) @ 5 t ha -1 , T9 : 50 per cent NPK + FYM @ 5 t ha -1 , T10 : 100 per cent NPK + in situ growing of Sesbania aculeata, T11 : 50 per cent NPK + in situ growing of Sesbania aculeata and T12 : Absolute control (No fertilizer or manures). The soil samples from 0-15 cm depth were collected from the different treatments of LTFE after the harvest of Virippu crop, 2020 and were analysed for various physical, chemical and biological properties. Principal Component Analysis (PCA) was performed to arrive at the Minimum Data Set (MDS) and Soil Quality Index (SQI) was formulated for different nutrient management practices. Integrated nutrient management with FYM and in situ green manuring with daincha recorded higher grain and straw yields of rice. The increase in fertilizer load into the soil resulted in increase in yields while the omission of primary nutrients resulted as decline in yields. Integrated Nutrient Management practice (INM) of application of FYM along with 100 percent NPK had lower bulk density (1.17 Mg m-3 ) and higher water holding capacity (43.65 %), higher levels of available nutrients and enzyme activities in the soil. However, dehydrogenase activity did not follow the same trend as that of microbial biomass carbon in treatments wherein fertilizers alone were applied indicating the chances of shift in the microbial populations as a result of the long term application of nutrient management practices. Principal Component Analysis (PCA) was performed for 28 soil attributes to develop the MDS and SQI was formulated using non linear scoring method. The MDS included bulk density, porosity, soil pH, permanganate oxidizable carbon, available N, total N, available sulphur, microbial biomass carbon, acid phosphatase and aryl sulfatase activities. The SQI ranged from 1.82 to 3.01. The SQI declined in the order of: T8> T10 >T9> T11> T4> T3> T2= T1> T5> T6 >T7> T12. The highest SQI was observed in T8 where 100 per cent NPK and FYM were applied. When the dosage of fertilizers was increased from 50% to 100% NPK on integration with FYM, the SQI increased. The soil quality index of the INM treatments (55.50 to 62.11%) and lime incorporation (52.98%) were categorized under medium category as per the computed Relative SQI (RSQI) values. The virippu crop (2020) under LTFE maintained at RARS Pattambi was monitored and various inputs and outputs regarding primary nutrients were assessed for balance predictions using NUTMON toolbox. The NUTMON toolbox includes five inflows, viz., mineral fertilizers (IN1), manure (IN2), atmospheric deposition (IN3), biological N fixation (IN4), and sedimentation (IN5), and five outflows, viz., harvested product (OUT1), crop residues (OUT2), leaching (OUT3), gaseous losses (OUT4), and erosion (OUT5). Nutrient flows like fertilizers, manures, crop residues and harvested outputs were monitored and measured during the experiment. Other flows like nitrogen fixation, leaching, and erosion were estimated by means of regression models from the data related to climate and crop parameters. Available NPK content of soils, rice grain, straw, stubbles, weeds and all inputs were analysed and stored in background database. The data were fed into the data processing module of the NUTMON toolbox to arrive at the partial and total balance of N, P and K in the experimental soil. The total balance of N, P and K were found to decline in order of: T3>T7>T8>T6>T5>T2>T4>T10>T9>T1>T11>T12 for N, T3>T8>T6>T10>T2>T5>T4>T9>T1>T11>T12>T7 for P and T3>T2>T5>T8>T9>T10>T4>T11>T1>T12>T7>T6 for K Summarizing the results, integrated nutrient management with FYM and in situ green manuring with daincha recorded higher yield and available nutrients in the soil. The incorporation inorganic fertilizers with FYM, daincha and lime maintain the soil quality index in the long run while, SQI was poor in control, imbalanced nutrition as well as in treatments where only fertilizers were incorporated. The balance sheet of P establishes the need for maintenance dose of P fertilizers in rice-rice cropping system. The negative balance of N and K indicate the need for supplementing the nitrogen pool and the possibility of mining of K on long term intensive cropping, respectively. Further study should be focused on monitoring the soil quality index at regular intervals and analyzing the effect of nutrient management practices on microbial diversity in rhizosphere and phyllosphere.