Yield and Nitrogen Use Efficiency of Sweet Potato in Response to Cover Crop and Nitrogen Management

Abstract

Core Ideas Legumes improved N supply for sweet potato grown subsequently. Mucuna aterrima supply more N to sweet potato than other cover crops. Previous legume cultivation reduces 35.2% the mineral N rate on sweet potato. Higher mineral N rate increased growth of sweet potato vines. Selected cover crops can provide N to sweet potato (Ipomoea batatas [L.] Lam) crops cultivated in succession and reduce the need for mineral N application. This study was conducted to determine the growth, leaf N concentration, N uptake, N removal, storage root yield, and N‐use efficiency of sweet potato crop in response to different cover crop sources and mineral N fertilizer rates. A field experiment was performed over 2 agricultural yr using a randomized complete block design with split‐plots and four replications. Whole plots consisted of four cover crops: One control (spontaneous weeds), two legumes (Crotalaria spectabilis and Mucuna aterrima), and one cereal (Pennisetum glaucum). Subplots consisted of four N rates (0, 50, 100, and 200 kg ha−1) applied to the sweet potato. When no N was applied, M. aterrima supplied more N to sweet potato grown in succession but had the same effect as C. spectabilis on root yield. P. glaucum and spontaneous weeds had the same effect on the N supply and performance of sweet potato. The N rates for the optimum root yield of sweet potato were 49.6 and 76.6 kg N ha−1 when grown after legume and non‐legume species. In tropical conditions, the use of legumes as cover crops reduced the need for mineral N fertilizers by up to 35.2% for sweet potato. The cultivation history of a field should be an important consideration when determining the N fertilization for sweet potato because a high N supply favored the growth of vegetative plant parts.

Impact of Nitrogen Fertilization on Tuber Yield, Sugar Composition and Nitrogen Uptake of Two Yacon (Smallanthus sonchifolius Poepp. & Endl.) Genotypes

“…With increasing fertilization level, the efficiency of tubers for accumulating DM or sugar decreased in general. This is similar to the findings of Fernandes et al who reported a decreasing N uptake efficiency under high N levels above 120 kg N ha −1 for sweet potatoes [16]. Also, Maltas et al reported decreasing N utilization and uptake efficiency with increasing N fertilizer (above 120 kg N ha −1 ) in potatoes [21].…”

“…N concentrations in the present study were noticeably higher and comparable to those of fodder beet, which ranged from 1.7 to 3.3% [20]. Similar to these are findings of N concentration in leaves of sweet potatoes, which ranged from 2.9 to 4.2%, also influenced by fertilizer [16]. RG had significantly lower N concentrations in aboveground biomass, while overall N uptake was significantly higher.…”

“…Fernandes et al reported that under high N rates, tuber yield by sweet potato were similar in all treatments. Losavio et al also reported no significant effect of N fertilization on tuber yield by Jerusalem artichoke [16,35]. This is also in accordance with Maltas et al, who reported increasing tuber yields of potatoes with increasing N fertilization, but no significant differences in the higher N rates of about 120 kg N ha −1 under comparable climatic conditions [21].…”

“…In general, a reaction similar to that of Jerusalem artichoke or potato would have been expected, where higher amounts of N fertilizer delayed maturity [51,53]. This would lead to a decrease in DM content, as well as a decrease in carbohydrates [16,21]. Furthermore, a difference in sugar composition would be expected.…”

“…The expected N requirement of yacon reported in the literature ranges from 24 to 98 kg N ha −1 [6,[13][14][15]. These values are below the N requirement of sweet potatoes and potatoes, which require up to 200 kg N ha −1 [12,16], while simultaneously having lower yield potentials per ha. In order to determine yacons' need for N fertilization, it is critically important to measure the N uptake of different plant parts, and thus to determine complete N removal.…”