Comparison of Soil health and evaluation of agricultural amendments for the improvement of soils in relation to food security

Abstract

Soil is the fundamental resource not only for crops but also for all living beings. However, to achieve successful and sustainable production, and favorable environment the soil needs to be healthy. Selected parameters of soil health in Bangladesh within the recent past times viz. 1970s, 2000s and 2020s have been studied. Soils were collected from the upazilas of 16 districts of eight divisions within the period of 2018 to 2020 based on the review of secondary data of 1970s and 2000s. The first field experiment was conducted at Moddhom Majigach, Cumilla, Bangladesh during February to June, 2018 with T. Boro rice varieties of BRRI Dhan 28, BRRI Dhan 58 and BRRI Dhan 60 following completely randomized block design with locally available agricultural organic materials, such as, rice Hull (RH), rice Straw (RS) and Vermicompost (V) at the rates of 0, 4 and 8 t ha-1 of each organic fertilizers under the 2 levels of soil moisture, such as 80 and >100% and the soil temperatures were maintained (by applying hot water) at 26 to 28 and 30°C (i.e. soil temperature elevation of ST 2°C and ST 4°C) during late tillering to panicle initiation stages of rice. Another two experiments in the site of Bauphal in Patuakhali district were also conducted following completely randomized block design with the self-made organic composts, such as, Rice Hull Compost (RHC), Rice Straw Compost (RSC), Sawdust Compost (SDC) and Vermicompost (V) at the rates of 0, 2, 4 and 8 t ha-1 of each organic composts at Aman (August to December, 2018) and Boro (February to June, 2019) seasons, respectively. Rice variety BR 25 was selected as the test crop at Aman season and BR 3, BRRI Dhan 28, BRRI Dhan 47, BRRI Dhan 60, BRRI Dhan 61 and Guti Swarna were used as the test crops at Boro season for these experiments. Changes in soil pH values were not so pronounced among the studied districts, except for the soils in Barishal, Patuakhali and Faridpur districts. In Barishal and Patuakhali districts, the mean values of the soil pHs were decreased in 2020 than those of obtained in 1970s and 2000s. Where as in Faridpur district, the soil pHs were increased within this time. Soil organic matter contents of the studied 16 districts were mostly increased at the Golden Jubilee of Bangladesh as compared to 2000s and 1970s. But the pronounced decrements in the CEC of soils were recorded in Barishal, Khulna and Patuakhali districts. In Pabna and Rajshahi districts, the CEC of the soils were increased as compared to 2000s but attenuate as to 1970s. Application of rice hull, rice straw and vermicompost under two levels of moistures and temperatures in Cumilla experiment were found to be effective on the yield performance, nutrition and grain quality of rice as well as for the improvement of soil health parameters. The raise of soil temperature exerted better responses on grain yield compared to moisture treatments and the effects were more distinct with BRRI Dhan 60 (15% more with moisture; 20% with temp.) compared to BRRI Dhan 28 (6% moisture; 2% Temp.) and BRRI Dhan 58 (4% moisture; 7% temp.). However, BRRI Dhan 58 was found to be increased 12% more grain yield compared to BRRI Dhan 28 and 14% more than BRRI Dhan 60, regardless of the treatments. Maximum contents of protein in the rice grains were obtained by the T6 (V, 8 t ha-1) under 4°C raise of soil temperature and the values were 12.3% for BRRI Dhan 28, 12.9% for BRRI Dhan 58 and 12.1% for BRRI Dhan 60 followed by 11.4, 11.6 and 11.8%, respectively where rice straw was applied at 8 t ha-1. The effects of different types of fertilizers for the increase of protein contents are in the order of V > RS > RH, regardless of soil moistures and raise of soil temperatures. Significant (p ≤ 0.05) positive influences of the applied amendments on the pH were determined at post-harvest soils for the studied conditions of soils. Post harvested soils pH ranged from 5.4-5.8 at M80, 5.7-6.2 at M>100, 5.5-5.9 at ST26, 5.6-6.0 at ST26-28 and 5.7-6.3 at ST26-30 treatments. The increment of organic matter content due to the treatments were more pronounced by the application of RH, RS and V at ST26-30> ST26-28> M>100 conditions. The highest organic matter content was determined at T6 (V8) treatment under the field condition followed by RS and RH with the lower dosage of these treatments. The applied amendments with variable soil moisture and temperature levels showed a significant positive effect in increasing CEC values in the post-harvest soils. The highest CEC value (21.99 c mol kg-1) was recorded in T6 treatment under ST26-30. But, the highest increase over control (IOC: 44.25 %) for CEC was calculated at the same treatment (T6) at M>100 level followed by ST26-30 > ST26 > ST26-28 > M80 conditions, respectively. The emission of CO2 was found to be increased significantly (p ≥ 0.05) by the treatments during 40 and 80 days after transplantation (DAT) of rice. The maximum amount (53 mg/m2/h) of CO2 emission was recorded by the T2 (RS8) treatment, where the rise of soil temperature was 4°C, followed by the same treatment at the temperature rise of 2°C at 80 DAT. The emissions of CO2 decreased with the higher moisture level but increased with time and the increments were most pronounced with the raises of soil temperatures. The order of emissions of CO2 from the applied organic amendments is as RS > RH > V, regardless of time, temperature and moisture levels. The emissions of CH4 were decreased significantly (p ≥ 0.05) with time and rises of soil temperatures but increased significantly with the higher moisture level. Though the elevation of soil temperature of 4°C decreased CH4 emission distinctly but the applied fertilizers were found to have significant (p ≥ 0.05) positive effects on CH4 emissions and the effects were more pronounced at 40 DAT. The maximum amount of CH4 emission (44 mg/m2/h) was obtained by the T2 (RS8) treatment having the higher level of moisture at 40 DAT. Growth and yields of rice, and selected soil health indicators under the experiments in Patuakhali district during Aman and Boro seasons of Bangladesh were found to be increased by the application of rice hull compost (RHC), rice straw compost (RSC), sawdust compost (SDC) and vermicompost (V). The highest yield (6.8 t ha-1) was recorded in V8 treatment followed by RSC8 (6.6 t ha-1), SDC8 (5.7 t ha-1), RHC8 (5.4 t ha-1), V4 and RSC4 (5.2 t ha-1) treatments, respectively under field condition during Aman season. But in Boro season, the yields of different varieties of rice were increased from 4.5 to 6.5 for BRRI Dhan 28, 4.3 to 6.0 for BRRI Dhan 47, 4.7 to 7.8 for BRRI Dhan 60, 4.5 to 6.3 for BRRI Dhan 61, 4.4 to 6.2 for BR 3 and 4.5 to 6.4 t ha-1 for Guti Swarna by the treatments. These effects of organic fertilizers were more pronounced with their higher doses. The results revealed that the maximum contents of protein among the rice varieties were obtained by the T12 (V @ 8 t ha-1) treatment and the values were 11.2% for the BRRI Dhan 60 followed by 10.3, 10.2, 10.1 and 9.9% by BR 3, BRRI Dhan 47 and Guti Swarna, BRRI Dhan 28 and BRRI Dhan 61, respectively. The higher rates of applied fertilizers were found to be significant (p ≤ 0.05) in increasing protein content of rice grain and the effects were more distinct with the BRRI Dhan 60. In Aman season, the pH values of post harvested soils were increased from 5.1 to 6.6 and the maximum pH (6.6) was determined by the T12 (V8) treatment. The soil organic matter (SOM) contents were found to be increased significantly (p ≥ 0.05) by the applied treatments and the effects were distinct with the V treatments followed by RSC. Soil organic matter contents increased by 117, 63, 76 and 68%, respectively with the application of V, RHC, RSC and SDC regardless of the rates of the treatment. The CEC of the studied soils followed the similar trends as those of soil organic matter contents. The highest CEC value was determined in the T12 (V8) treatment which received the highest rate of vermicompost. The lowest value was recorded in the control plot. Rest of the treatments also exhibited significant positive responses on the CEC of soils but the effects were not so pronounced within the doses of the treatments. In Boro season, similar trends of effects of the applied amendments on soils health parameters at post-harvest were observed like as Aman season. The pH values were increased from 5.3 to 6.9 for V, 5.3 to 6.6 for RHC, 5.3 to 6.2 for RSC and 5.3 to 6.6 for SDC and the contents of soil organic matter were found to be increased significantly (p ≥ 0.05) by the applied organic fertilizers and the increments were distinct with the V treatments followed by RSC. The higher doses of these treatments exerted prominent effects on the SOM and the maximum content of SOM was recorded in the T6 (RSC8) treatment followed by the T12 (V8) > T9 (SDC8) > T3 (RHC8) in the post-harvest soils. The application of different organic compost significantly (p ≤ 0.05) increased the CEC of the post-harvest soils under rice grown in Boro season. The highest CEC value was determined in the T12 (V8) treatment which received the highest rate of vermicompost. The applied agricultural amendments exerted expected results for the improvement of soil health under rice production in different climatic conditions. The responses of the applied organic materials were found to be the best at the elevation of soil temperature of 4 and 2°C followed by soil moisture treatments, which suggests that soil temperature and moisture are important factor for the management of organic materials in the soils. Vermicompost asserted the best response not only on the rice production but also improved soil health parameters also in both Cumilla and Patuakhali soils. The findings also suggest that the substantial research is still essential to work out the cost-benefit analysis and sustainable use of such agricultural organic materials as ameliorating agents for the production of rice under different climatic conditions. The potentials of the amending materials for the improvement of soil health and their adaption by farmers under variable climates, crop response and socio-economic considerations should also be kept in mind for further practices and for these, the government should come forward to help the targeted people.