Effect of Organic Fertilizers on Nitrate Accumulation in Vegetables and Mineral Nitrogen in Tropical Soils of Morogoro, Tanzania

Abstract

Nitrogen (N) nutrition is a key factor for vegetable growth and yield. However, different rates of nitrogen fertilization may trigger different responses to vegetables. A survey was conducted to investigate the effect of soil fertility management practices on nitrate concentration in vegetables. The survey results were used to plan experiments on the effect of chicken and cattle manures on nitrate levels in Chinese cabbage (Brassica rapa) and amaranthus (Amaranthus cruentus) grown in Tanzania and the patterns of mineral nitrogen in soils under open field conditions. Chicken or cattle manure at 200, 300 kg N ha −1 and 170 250 kg N ha −1 for Chinese cabbage and amaranthus respectively, and control were compared in a randomized complete block design. We observed a higher nitrate content in fertilized Chinese cabbage at day 30 than at day 44 after sowing, ranging from 3243 to 4993 mg kg −1 fresh matter regardless of the N source and rates. Only application of manures at high levels (250 kg N ha −1 ) induced significantly (p < 0.05) higher nitrate contents in amaranthus at day 28 after sowing, although there was a clear indication of nitrate accumulation even at 170 kg N ha −1 application. Soil NH 4 + -N + NO 3 − -N in both Chinese cabbage and amaranthus plots were increased with increasing N application rates and differences between control and amended soils were significant (p < 0.01). There was a positive relationship between NO 3 − concentration in vegetables and NO 3 − -N in the rooted top soil layer (0-15 cm). However, higher NH 4 + concentrations depressed NO 3 − build up in crops and a significant negative relationship between soil (NH 4 + -N)/(NO 3 − -N) ratio and crop NO 3 − content was found. It is concluded that low manure application rates result in similar yields to high rates but reduces nitrate accumulation in vegetables and excess mineral nitrogen in soils.

Yield, Quality, and Nutrient Concentrations of Strawberry (Fragaria ×ananassa Duch. cv. ‘Sonata’) Grown with Different Organic Fertilizer Strategies

“…High pH and High NH 4 /NO 3 Ratio. In accordance with previous investigations, 26,27 the pH dw from plants supplied with organic fertilizers was higher than for plants receiving inorganic fertilizers. The higher root zone pH could be responsible for the lower fruit yield in the organic treatments because it influences root growth and nutrient solubility/availability and uptake.…”

An Ecological and Economical Assessment of Integrated Amaranth (Amaranthus hybridus) and Nile Tilapia (Oreochromis niloticus) Farming in Dar es Salaam, Tanzania

“…The overall amaranth yields in this study were slightly higher than those reported from a study by Baitilwake et al [45], who investigated the impact of different fertilization regimes on amaranth and spinach yield in Morogoro. The yields from the present study were also two times higher than those reported from a study by Mulandana et al [46] in South Africa.…”

“…Manure applications were done a week before to allow for proper mineralization [57]. Sowing was done by mixing 10 g of amaranth seeds with 1 kg of sand to obtain uniform stands, and then broadcasted at a rate of 1 g of seeds per m 2 [45,58]. The first harvest was done 21 days after sowing, to remove mature leaves for sale and give space for young plants to grow to maturity.…”

Fish polyculture system integrated with vegetable farming improves yield and economic benefits of small-scale farmers

“…This integration has the potential to improve production and economics for small‐scale farmers because B . rapa chinensis is a common crop on rural farms in Tanzania (Baitilwake, De Bolle, Salomez, Mrema & De Neve ) and a preferred vegetable by producers and consumers because it is easy to cultivate, with a short growing period (Kalisz, Kostrzewa, Sękara, Grabowska & Cebula ), has a unique flavour, health benefits (Pant, Radovich, Hue & Miyasaka ), an attractive appearance (Thosaikham, Jitmanee, Sittipout, Maneetong, Chantiratikul & Chantiratikul ) and high market demand worldwide (Cartea, Francisco, Soengas & Velasco ). Furthermore, B .…”

“…One form of such integration is that involving African sharptooth catfish, Clarias gariepinus and Nile tilapia, Oreochromis niloticus polyculture integrated with Chinese cabbage Brassica rapa chinensis. This integration has the potential to improve production and economics for small-scale farmers because B. rapa chinensis is a common crop on rural farms in Tanzania (Baitilwake, De Bolle, Salomez, Mrema & De Neve 2012) and a preferred vegetable by producers and consumers because it is easy to cultivate, with a short growing period (Kalisz, Kostrzewa, Se z kara, Grabowska & Cebula 2012), has a unique flavour, health benefits (Pant, Radovich, Hue & Miyasaka 2012), an attractive appearance (Thosaikham, Jitmanee, Sittipout, Maneetong, Chantiratikul & Chantiratikul 2014) and high market demand worldwide (Cartea, Francisco, Soengas & Velasco 2010). Furthermore, B. rapa chinensis responds well to moist fertile soil and can be produced annually in the tropics under full sun conditions and it is one of the most productive leaf vegetables grown with an average edible leaf yield of 3577 g m À2 (Idris, Ali, Gayah, Hassan & Abidin 2011;Kalisz 2011;Wong, Tseng, Hsu, Lur, Mo, Huang, Hsu, Lee & Liu 2014).…”