Production potential and nutrient dynamics in K-efficient cassava+ legume intercropping systems

Abstract

The research work entitled “Production potential and nutrient dynamics in K- efficient cassava + legume intercropping systems” was conducted at College of Agriculture, Vellayani during 2019-2025. The major objectives were to standardize the nutrient management practice for K efficient cassava in cassava + legume intercropping systems, to assess the biological efficiency of intercropping systems and to appraise the decomposition dynamics and nutrient mineralization of legume biomass/ residues and the changes in soil properties. The study was conducted as two experiments - i) to evaluate different nutrient management practices in cassava variety Sree Pavithra under intercropping systems and ii) to study the decomposition dynamics and nutrient release from legume biomass/ residues. The first experiment was laid out in farmer’s field at AEU 8 in randomized block design with ten treatments and three replications during the period August 2022 to May 2023. The treatments included T1 : 100 % recommended dose of fertilizers (RDF), T2 :100 % RD of N and P + 50 % K, T3 : 100 % RD of N and P + 25 % K, T4 : 100 % RD of N and P + 0 % K, T5 : 50 % RDF, T6 : 50 % RDF + PGPR Mix I liquid, T7 : 50 % RD of N and P + 25 % K, T8 : 50 % RD of N and P + 25 % K + PGPR Mix I liquid, T9 : 50 % RD of N and P + 0 % K and T10 : 50 % RD of N and P + 0 % K + PGPR Mix I liquid. In situ green manuring of cowpea was done before planting cassava and allowed to decompose for 3 weeks. The RDF adopted in cassava was 100:50:100 kg NPK ha-1. PGPR Mix I was applied at 50 mL L-1, thrice, basal, at 2 and 4 MAP. The grain legumes, cowpea (Shubra) and red gram (APK 1) were evaluated as intercrops in two separate layouts. A control treatment without fertilizer application was also maintained. The intercrops were fertilized separately as per the nutrient recommendations. Other cultural practices were followed as per the recommendations for the crops. The results indicated that nutrient management practices had significant influence on growth characters, yield and nutrient uptake in cassava. Under cowpea intercropping, yield attributes (number of tubers, mean tuber weight, tuber girth) and tuber yields (50.04 t ha-1) were higher in T10, on par with T8 and T6. These treatments also recorded higher and comparable DMP and nutrient uptake. Among quality characters, crude protein content alone recorded significant differences in response to the nutrient management practice adopted. In cowpea, higher number of pods (11.67) and pod yield per plant (13.25 g) were observed in T5 and was on par with T7 and T9. Seed yield (428.68 kg ha-1) was higher in T7, on par with T2, T5 and T9. Competitive indices (LER and LEC) worked out revealed yield advantages with intercropping in all the treatments except control. The highest CEY (52.23 t ha-1) was obtained in T8 (50 % RD N and P + 25 % K + PGPR Mix I liquid). Application of PGPR Mix I (T6, T8 and T10), influenced the organic C fractions in soil favourably. Total microbial counts enumerated in these treatments were also higher and comparable. The post harvest available status of K in soil alone varied significantly and was the highest in T6. Among the nutrient management practices adopted in cassava when intercropped with cowpea, the maximum net income (₹ 458142 ha-1) were realized in T10 (50 % RD N and P + 0 % K + PGPR Mix I liquid). In cassava + red gram intercropping, the highest number of tubers per plant (12.0), mean tuber weight (0.96 kg), tuber weight per plant (9 kg), tuber yield (44.44 t ha-1), DMP and nutrient uptake were recorded in T10, on par with T6 and T8. Crude protein content (2.96 %) in tuber was significantly higher in T6. The growth and yield of red gram were significantly affected by the nutrient management practices evaluated in cassava. The number of pods per plant (28.33) was the highest in T4. Average pod weight, pod yield per plant, number of seeds, seed yield, DMP and nutrient uptakes were higher and comparable in T2, T4, T5, T7 and T9. The LER computed recorded values > 1 in treatments T6, T8 and T10, and LEC values less than 0.25 in all treatments indicating that intercropping with red gram was not advantageous. Treatment T10 recorded the highest CEY (44.96 t ha-1). Soil organic C fractions were higher and comparable in T10, T8 and T6. The available NPK status in soil declined with intercropping, and comparatively higher contents were recorded in treatments involving PGPR application and 100 percent RDF. Microbial activity was favourably influenced by PGPR application, with higher counts in T10, T8 and T6. Economic analysis of the cassava + red gram intercropping system revealed the highest net income (₹ 329379 ha-1) in treatment T10 (50 % RD N and P + 0 % K + PGPR Mix I liquid), among the nutrient management practices studied. Experiment II was conducted as two parts - i) field experiment on the decomposition dynamics and nutrient release from legume biomass/ residues and ii) incubation study on C and N mineralization from legume biomass/ residues. The experiment for the decomposition study was laid out at farmer’s field in AEU 8 during November 2022 to December 2023, in completely randomized design adopting the standard litter bag technique with twelve treatments (leaves, stem, roots and whole plant of green manure cowpea, grain cowpea and red gram respectively) replicated thrice. Among the three legumes, decomposition was most rapid in green manure cowpea, followed by grain cowpea and red gram, and among the plant tissues, it was the slowest in red gram roots (23 fortnights), followed by grain cowpea roots (14 fortnights). The higher decay rate (1.99 g fortnight-1) recorded in grain cowpea leaves was on par with green manure cowpea leaves (1.89 g fortnight-1). Half life values were the lowest for the same treatments. Changes in the nutrient and biochemical parameters revealed decline in N, P, K, Mg, cellulose and phenol contents at the end of decomposition, whereas Ca, micronutrients (Fe, Cu, Mn, Zn) and lignin, accumulated. Nutrient release, irrespective of the plant tissues were the highest for K (93-99 %), followed by N and P, and remained the lowest for Zn. Correlation analysis revealed the significant influence of lignin, C: N ratio and N content on the decay rates. The C and N mineralisation from the biomass were ascertained in the incubation experiment for 120 days, from February to May 2023. The experimental design and treatments were same as in the decomposition study. Total C mineralized followed the order green manure cowpea > grain cowpea > red gram. Among the plant parts, leaves/

stem had higher C mineralization, and roots, the lowest. Mineralisable N contents in the early stages of decomposition were high, the ammoniacal form accounting for the major proportion, but declined as the duration of incubation increased. The NH4+ and NO3- contents analysed at fortnightly intervals revealed the mineralization to occur within 45-60 days after incubation. Considering the yield and economics, in situ green manuring of cowpea, application of 12.5 t FYM, 50 kg N, 25 kg P along with soil application of PGPR Mix I at 50 mL L-1 thrice, basal, at 2 and 4 MAP, can be recommended as the suitable nutrient management practice for K efficient cassava variety Sree Pavithra, under intercropping with the grain legume, cowpea or red gram. Grain cowpea intercropping was more advantageous than red gram, based on the competitive indices assessed in medium K soils. Decay rates and nutrient mineralization were the highest in green manure cowpea, and among the plant tissues, leaves were the most amenable to decomposition. The soil chemical and biological properties were also favourably influenced with legume residue incorporation.