INTERCROPPING AND LEAF HARVEST MANAGEMENT FOR IMPROVED LEAF YIELDS IN TWO TRADITIONAL VEGETABLES: PUMPKIN (Cucurbita maxima L.) AND MUSTARD RAPE (Brassica juncea Czern.) IN ZIMBABWE.

Abstract

Studies were carried out to establish ideal component combinations and relative populations, relative planting dates, leaf harvest practices and the effects of nitrogen in intercrops involving food crops (maize and groundnut) and traditional vegetables (pumpkin and mustard rape). The studies were conducted on-farm in Chinyika Resettlement Area and on-station in Harare at the University Farm (UZF) in the 2002/2003 and 2003/2004 rainy seasons.

In maize intercrops, pumpkin and mustard rape were each planted at 11.7, 23.4 and 35.3 % of the maize population. In groundnut intercropping, pumpkin was planted at 0.46, 0.92 and 1.84 %, whilst mustard rape was planted at 4.15, 8.29 and 12.44 % of the groundnut population. The vegetables were planted simultaneously and within the same row as maize or within the groundnut interrow space. A second planting of mustard rape was implemented at 10 weeks after emergence (WAE) of maize or groundnut at one site in Harare.

Generally, maize grain yield was not affected by intercrop populations at all sites in both the 2002/3 and 2003/4 seasons. In addition, it was not affected by 5 to15-day leaf harvest intervals and 1 to 6-leaf harvest intensities of the vegetable component. However, groundnut seed yield was significantly (p ¡Ü 0.05) reduced by 17-45 % due to intercropping with pumpkin except in the 2003/4 season at UZF. Similarly, growth of the two traditional vegetables was significantly (p < 0.05) reduced under both food crops as reflected by reduced leaf size, number of leaves per plant and growth duration in both the 2002/3 and 2003/4 seasons. However, increasing pumpkin intercrop populations reduced weed density and weed biomass in both maize and groundnut, whilst mustard rape intercropping had no weed suppression effects.

Both leaf harvest intervals of five, 10 and 15 days and intensities of two, four and six leaves per growing tip had no effects on pumpkin dry leaf yields in both the 2002/3 and 2003/4 seasons, though harvesting four leaves per growing tip at 5-day intervals increased dry leaf yields by 153 % of the control (12-day leaf harvest interval). Five-day leaf harvest intervals and three-leaf intensities in mustard rape reduced leaf size, duration and plant height, but had higher dry leaf yields compared to the control. Mustard rape growth parameters and leaf yields were less responsive to 1, 2 and 3-leaf harvest intensities and 5, 10 and 15-day intervals in maize-11.7 % mustard rape intercropping than in pure mustard rape stands.

Mustard rape dry leaf yields were also increased by increasing nitrogen side dress level from 0 to 103.5 kg N ha-1. Likewise, leaf nitrate and nitrogen increased significantly (p < 0.001) with increases in nitrogen side dress. Leaf nitrate content was higher in mustard rape leaves harvested in the morning (0.54 %) compared to those harvested at sunset (0.46 %) at 5 WAE. There was increase in level of bitterness detected in mustard rape taste and improvement of appearance after cooking with increases in nitrogen side dress level from 0 to 34.5 kg N ha-1.

All intercrops for both pumpkin and mustard rape had intercropping advantages over sole cropping as revealed by land equivalent ratio (LER) values greater than unity. Higher LER values were recorded on-farm, where there were fruit yields.

Conclusions of the study are that mustard rape should ideally be intercropped with groundnut and pumpkin with maize, to minimize suppression of component crops. Secondly, leaf yields of mustard rape can be increased through simultaneous planting compared to staggered planting at 10 WAE of the main crops and higher intercrop populations (35.3 % in maize). More severe harvesting in both vegetables also increases leaf yields in pure stands. Thirdly, apart from high leaf yields, high pumpkin intercrop populations of up to 35.3 % of maize also have an advantage of effective suppression of weeds without any maize yield penalty to the farmer. Fourthly, mustard rape leaf yields can also be increased through increasing nitrogen side dress levels, with slightly perceptible effects on taste if the range is between 0 and 103.5 kg N ha-1.