For the upland rice farmers, the standard sowing time was mostly set to mid-January, with one group sowing three weeks later (Table 4). Supa India was set as the conventional variety. Application of Di Ammonium Phosphate (DAP) combined with Urea or just DAP was established as the conventional soil fertility management practice. For the improved S. asiatica management strategy in the uplands, NERICA-1, -4 and -10 were selected. During Participatory Variety Selection (PVS) conducted in the same location in the previous years, these short-duration varieties had shown to be more S. asiatica resistant than the short- duration NERICA variety tested in the sowing-date trials (NERICA-14). One group decided to postpone sowing with four weeks, whereas another group postponed sowing with 10 days as a means to minimize the risk of S. asiatica infection. The third group did not dare to postpone sowing any later than the conventional practice, while the fourth group advanced sowing with one week, compared to the conventional sowing date. In all four sites, rice husks combined with DAP and Urea was used as an alternative soil amendment.
In the lowland fields, sowing dates following farmer practice were set from the last week of December to mid-January (Table 4). Farmers mentioned that early sowing usually results in lower R. fistulosa infection. The combination of the local rice variety Supa India with inorganic fertilisers was selected as the conventional farmer practice. For improved R. fistulosa management strategy, lowland NERICA-L-12, -L-31 and -L-39 were selected as alternative varieties as they had a similar growth duration as NERICA-L-20 but were more resistant against R. fistulosa. This selection was also the result of a PVS conducted alongside the researcher-managed on farm trials in the same period (2012-2014). Alternative sowing times initially selected by the farmers were not much different from the conventional times and differed from 10 days earlier for the group planning to sow early January, to a five days delay for the group that planned to sow mid-December. Due to a delayed onset of the rains, the actual implemented sowing dates in the trials were however adjusted. Plots with farmers practice were sown soon after the first rains (early January) and plots with the alternative sowing date treatment were sown two weeks later.
Table 4. Proposed parasitic weed management strategies for the farmer-managed on-farm trials in upland (groups A, B, C and D) and lowland fields (groups E, F, G and H) in Kyela district, Tanzania. Results were obtained during individual group discussions in November 2014, shortly before instalment of the trials.
Upland (Striga asiatica)
Groups
Standard practice A B C D
Proposed sowing time 15 January 10 February 10 January 15 January
Variety Supa India Supa India Supa India Supa India
Soil amendment DAP + U DAP + U DAP + U DAP
Alternative practice
Sowing time -10 days 0 day +7 days +29 days
Variety NERICA-1,4, 10 NERICA-1,-4, -10 NERICA-1,-4, -10 NERICA-1,-4, -10 Soil amendment RH + ½ (DAP +U) RH + ½ (DAP +U) RH + ½ (DAP +U) RH + ½ (DAP +U)
Lowland (Rhamphicarpa fistulosa)
Standard practice E F G H
Proposed sowing time 5 January 1–15 January 23 December 15 December
Variety Supa India Supa India Supa India Supa India
Soil amendment DAP+U DAP+U DAP + U DAP
Alternative practice
Sowing time 0 day -10 days -3 days +5days
Variety NERICA-L-31 NERICA-L-39 NERICA-L-39 NERICA-L-12
Soil amendment DAP+U RH + ½ (DAP +U) RH + ½ (DAP +U) DAP+U
RH = Rice husks , DAP = Di-Ammonium Phosphate , NPK = Nitrogen, Phosphorus, and Potassium, U = Urea , Supa India = local rice cultivar also known as Kilombero
Table 5. Farmers’ outlook on the three components of a parasitic weed management strategy that were evaluated in famer-managed on-farm trials in upland and lowland fields in Kyela district – Tanzania, 2015. Results were obtained during individual farmer interviews (n = 40), shortly after the farmer group visits to the trials just before crop maturity. Answers per category are expressed in %.
Technology evaluation Upland Lowland
(S. asiatica) (R. fistulosa) (1) Sowing time
Are you going to modify sowing time? Yes, to an earlier time 0.0 80.0
No 5.0 17.5
Yes, to a later time 95.0 2.5
(2) Variety
Which variety do you prefer? Supa India 17.5 87.0
NERICA-10 82.5 -
NERICA-L-31 - 13.0
(3) Soil amendment
Which soil amendment do you prefer? DAP, Urea 0.0 35.0
Rice husks + ½ (DAP + U) 90.3 65.0
Including rice husks as soil amendment was decided on by two groups, while other groups preferred to use DAP + Urea.
The year 2015 was characterized with heavy S. asiatica-infections. Average rice grain yield was 1.4 ton ha-1. Late sown plots clearly showed lower infection levels than the earlier sown plots, and the plots with NERICA-varieties were less infected than the plots sown with Supa India. At the end of the season, the vast majority of farmers in the uplands selected late sowing (95%), preferably combined with NERICA-10 (83%), as the best way to combat S. asiatica (Table 5). Farmers characterized NERICA-10 as an early maturing variety with good grain appearance and S. asiatica resistance. The majority of the farmers (90%) selected rice husks + ½ (DAP + Urea) rates as the preferred soil amendment option. This selection was motivated by the realisation that application of the relatively cheap rice husks allowed farmers to reduce the rates of the relatively expensive inorganic fertilisers by 50%, without compromising productivity.
Only mild infestations of R. fistulosa were encountered in 2015 and average rice grain yield was just below 4 ton ha-1. A negative effect of a delayed sowing time on R. fistulosa infection level was noted, while differences between varieties were not observed. At the end of the season a majority of the farmers (80%) indicated a commitment not to delay sowing times in future (Table 5). Some farmers, however, expressed their concern that with early sowing, their local rice variety would be more affected by Rice Yellow Mottle Virus (RYMV). In the absence of differences in R. fistulosa infection level between varieties, most farmers (87%) preferred to stick to their local rice variety Supa India. Use of rice husks in combination with ½ (DAP and Urea) (65%) or DAP and urea only (35%) were the preferred soil fertility amendments among farmers in the lowlands. The substitution of part of the inorganic fertiliser by rice husks was motivated by financial reasons.
4. Discussion