Effect of mulch type and NPK (17-17-17) rates on soil nutrient content, growth and yield of cabbage (Brassica oleracea var. capitata) in volcanic highland region of Rwanda

Abstract

Soil fertility decline, due to soil loss by erosion, nutrient mining and sub optimal fertilizer use, is the major constraint in cabbage production in the volcanic highland region of Rwanda. The objective of the study was to assess the effect of mulch type and NPK (17-17-17) fertilizer rates on growth, nutrient uptake, yield of cabbage (Brassica oleracea var. capitata) and soil nutrient content in the volcanic highland region of Rwanda. Field experiments were conducted in two cropping seasons; September 2016 to January 2017 and December 2016 to March 2017 at the experimental farm of the College of Agriculture, Busogo sector, in the northern-west region of Rwanda. A “3×4” factorial experiment in a Randomized Complete Block Design (RCBD) with three replications was used. Factors were three mulching treatments; black plastic, wheat straw and an un-mulched control and four rates of NPK (17-17-17) fertilizer; 0kgha-1, 60kgha-1, 120kgha-1 and 180kgha-1. Soil samples were collected twice; before transplanting and after harvesting. Cabbage growth parameters were measured at early and late stage. Dry matter accumulation and nutrient uptake (N, P, and K) were analyzed at cabbage heading. Head weight and diameter were recorded at commercial maturity. The data obtained was subjected to ANOVA using SAS version 9.3 software and mean separation was done using LSD at 95% confidence level. Main effect of wheat straw mulch significantly increased cabbage height (32.79cm), interactions of wheat straw mulch and fertilizer rate of 120kgha-1 significantly increased stem diameter (23.46cm), while interactions of black plastic mulch and fertilizer at rate of 120kgha-1 significantly increased head diameter (26.80cm) and yield (4850.44g per plant). Main effects of fertilizer at rate of 60kgha-1 and 120kgha-1 respectively increased K (88.76kgha-1) and P (41.66kgha-1) uptake in cabbage leaves while interactions of black plastic mulch and fertilizer application at rate of 120kgha-1 significantly increased N uptake (58.52kgha-1). There was higher soil moisture under black plastic mulch (33.83%) and fertilizer application at 180kgha-1 (36.08%). Interactions of black plastic mulch and fertilizer application at rate of 180kgha-1 and 120kgha-1 significantly increased soil P (158.12ppm) and K (0.37cmolckg-1) availability respectively and interaction of wheat straw mulch and 120kgha-1 significantly increased soil total N (0.43%). The recommended combination was wheat straw mulch with 120kgha-1 for increased soil moisture content and nutrient availability, uptake and cabbage growth and yields in volcanic highlands of Rwanda.