Impact of Cropping Systems on Soil Organic Carbon Levels and Enzyme Activity

Monocropping makes agriculture more susceptible to the adverse effects of climate change. Resilient agriculture systems that can buffer crops against various agricultural vulnerabilities is the need of the hour. In this context, a study was conducted to assess the impact of various rice based cropping systems on soil health.Aims: To study the effect of different rice based cropping systems on soil enzyme activity and organic carbon.Study Design: Randomized block design, Replications – 3.Place and Duration of Study: Integrated Farming System Research Station (IFSRS) of Kerala Agricultural University located at Karamana, Thiruvananthapuram, during kharif, rabi and summer seasons of 2019-2020.Methodology: The experiment consists of eleven cropping systems (T1 : rice - fallow - fallow, T2 : rice - rice - fallow, T3 : rice - daincha - cowpea, T4 : (rice + daincha) - rice - green gram, T5 : rice - cassava - amaranthus, T6 : rice - cassava - cowpea, T7 : rice - para grass - fodder cowpea, T8 : rice - fodder cowpea - fodder maize, T9 : rice - okra - culinary melon, T10 : rice - okra - yard long bean and T11 : rice - rice – amaranthus).Results: Soil organic carbon and enzyme activities were found highest in the cropping system (rice+daincha) – rice – green gram during kharif. During rabi, soil organic carbon and activity of urease and acid phosphatase were highest in rice- daincha- cowpea while dehydrogenase activity was highest in rice- fodder cowpea – fodder maize. During summer, rice- okra – yard long bean, rice- cassava- amaranthus and rice- cassava – cowpea recorded the highest urease, acid phosphatase and dehydrogenase activity, respectively. The organic carbon was highest for the sequence rice – okra –culinary melon. The soil organic carbon and enzyme activities were least in rice- fallow-fallow cropping sequence during all the three cropping seasons.Conclusion: Brown manuring, use of leguminous crops and cover crops in the crop sequence instead of leaving the land fallow and addition of organic sources of nutrition increase the soil organic carbon and enzymatic activity of microbes. The increase in soil organic carbon and activity of enzymes in soil owing to crop rotation of rice with arable crops relies on the crop species which are cultivated.

Growth and Yield of Grain Cowpea (Vigna unguiculata sub sp. cylindrica) in Response to Foliar Nutrition and Graded Levels of Phosphorus and Potassium

Aim: To assess the growth and yield of grain cowpea in response to varied doses of phosphorus (P) and potassium (K) supplemented with foliar application of nano diammonium phosphate (DAP) and potassium salt of active phosphorus (PSAP).Study Design: The field experiment was a factorial experiment, laid out in randomised block design with two levels of P, three levels of K and two sources of foliar nutrition, compared against a control, with three replications.Place and Duration of Study: The study was conducted at the Integrated Farming System Research Station, Karamana, Nedumcaud, Thiruvananthapuram, Kerala, India, during the period from December 2022 to February 2023.Methods: The study utilized PGCP-6 cowpea variety and adopted fertilizer recommendations as per KAU POP (Package of Practices Recommendations of the Kerala Agricultural University). The entire dose of FYM, P and K and half dose of nitrogen (N) were applied as basal dose. The remaining half dose of N was applied at 15 days after sowing (DAS). Additionally, foliar application of nano DAP and PSAP (each @ 0.4 %) was done at 20 DAS and 40 DAS.Results: The results of the study revealed that the treatment combination, p2k1f2 and p2k1f1 had comparable leaf area per plant and leaf area index (LAI) (at 60 DAS). The highest seed yield (1642 kg ha-1) was recorded with p2k1f2. Higher dose of P and K along with foliar application of nano DAP (0.4 % at 20 DAS and 40 DAS) had significant effect on the total DMP and haulm yield.Conclusion: Combined application full dose of N, half dose of P, full dose of K and foliar application of PSAP (0.4 %) at 20 DAS and 40 DAS could be recommended as the best treatment combination for yield enhancement in grain cowpea.

Assessment of Nutrient Status in the Cassava Growing Tracts of Southern Laterites (Agro Ecological Unit 8), Kerala, India

As part of the study, a survey was conducted to identify the soil fertility constraints of cassava growing tracts of AEU 8, Thiruvananthapuram, which is one of the major cassava growing regions of the State of Kerala in peninsular India. The method of sampling of the survey was random sampling wherein a random sample of size one was taken from each of 50 ha cassava area. Panchayat wise soil samples were collected (77 samples) by geo referenced soil sampling method from major cassava growing areas of the unit. The samples are analyzed for the soil fertility parameters following standard analytical procedures. Results indicated that the soil was very strongly acidic to strongly acidic, normal electrical conductivity, medium organic carbon, medium nitrogen and potassium, high phosphorus, sufficient calcium, sulphur, zinc and copper, deficient magnesium and boron.