ASUNTOS ENTRADOS
11. Señora Berta Fernández.- Solicita considerar en Sala el siguiente tema:
Maize crop was used to assess crop performance as it is sensitive to water availability and is also a staple food crop in Zimbabwe. The performance of the crop was assessed by monitoring crop growth and measuring biomass accumulation, grain and total yield. A
Figure 4-18: Soil moisture measurement locations used for spatial soil moisture analysis
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maize crop was planted in the plots between the contour ridges and managed by the farmers.
4.4.1
Soil sampling and measurement of physical and chemical
properties
Differentiating the effect of treatment from that of soil properties was made difficult by high spatial variability of soil conditions even at very small distances. Replication of treatments was used to increase the quantity of data and reduce uncertainty caused by the spatial variability in soil conditions. Replication of treatment considers the variation of environmental conditions such as soil conditions as random events that require crop yield or any associated data to be treated as a random outcome whose population characteristics are affected only by the treatment. Replication was achieved by establishing in each subplot, two crop yield measurement areas each named a check plot as shown in Figure 4-19.
Each check plot measured 4m by 4m. Since the experimental fields had two areas that were bound by contour ridge channels it means each treatment (DLC, GC and NC) had a total of twelve check plots and four subplots. This was considered large enough to ensure the results reflect the effect of the treatment and was able to minimize the effect of local soil variations.
Table 4-3 shows the soil properties from the experimental fields before the start of the experiments. Five samples were collected from each field in a diagonal pattern one at the centre of the field and the others 5m away from each other along the diagonal line towards the centre. At each sample location two samples were collected one from top soil at a depth of 150mm and the other from the sub soil at a depth of 450mm. The samples were then analysed and the average values reported.
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4-28 Field Textural class pH (CaCl2) N (ppm) P (ppm) K (me%) Clay content (me%) Silt Content (%) Sand content (%) Water holding capacity (WHC) (mm) Field A Silt Loam 5.9 7 4 0.43 10 12 78 13.43 Field B Sandy 5.3 12 6 0.39 3 2 95 4.85
In addition to the soil characteristics given in Table 4-3 other soil characteristic measurements that were carried out were field density and the soil moisture at saturation point, field capacity and at wilting point.
4.4.2
Procedure for crop growth data collection
Plant growth was measured using non-destructive methods carried out throughout the cropping season. These included measuring the crop height, counting number of leaves and crop leaf moisture content. Non-destructive methods of counting number of leaves and measuring plant height were used effectively by Memon et al. (2007) to assess the effect of sowing methods on growth of maize crop. Use of non-destructive methods was used to monitor plant growth so as to avoid destroying plants that would affect the yield. The research was farmer based and therefore the incentive for the farmers to participate was not only the long term knowledge transfer but also the grain that they would harvest at the end of the season. The method of monitoring crop growth through destructive methods such as above ground dry matter accumulation used by other researchers (Andrade, 1995) were considered inappropriate for a resource poor farmer based research.
At least 10 representative plants were selected at random from each check plot of a treatment. Crop heights were measured at least once every two weeks using a measuring tape. The height was taken as the distance between the ground and the highest point of the smallest (newest) leaf of the plant. During the same time the leaves on the selected plants were counted. Crop leaf moisture content was determined at the end of each of the dry spell periods. The dry spell selected for leaf moisture content determination was
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that which occurred when the crop was close to flowering stage as this is the stage when the crop has high crop water requirements. Sample leaves were collected from plants selected in the manner described above. The leaves were weighed before being sun dried and weighed again until no change in weight could be noticed to obtain the dry weight of the leaves.
4.4.3
Procedure for maize crop yield data collection
The second measurement was destructive measurement carried out at the end of the cropping season. It involved cutting down the maize plant at harvesting and measuring the grain, inner cob and stover yield. The procedure that was followed in assessing the crop yield at the end of the crop growing season was adapted from IDRC-AFNET Project as used by Chibulu (2007). This procedure is described below.
1. The dimensions of each check were recorded in the field book crop assessment form as shown in Table 4-4. The dimensions are the same for all the nine check plots.
2. The number of plants and cobs in each check plot were counted & recorded in the appropriate row/column.
3. The stover was cut down and the cobs removed and weighed together with their grain. The cobs could not be separated from the grain since the experimental field constituted the main grain source for the farmers. In order to determine the constituent grain and inner cob weight, average cobs with grain were taken as a sample for both the determination of moisture content and for determining the proportion of grain and inner cobs.
4. Three to four average cobs were taken as a sample for moisture content determination and determination of the proportion of grain and inner cob. The cobs were weighed and the grain separated from the inner cobs and again weighed separately. Both grain and inner cobs were oven dried and weighed again for moisture content determination. These were averaged and recorded as the same figure for all the nine check plots of the treatment in the maize crop assessment form of Table 4-4.
5. Two to three stalks of stover were randomly selected from each check plot and chopped into smaller pieces. The pieces were weighed and placed in a plastic bag with the label of the check plot. The pieces were later weighed after drying for
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moisture content determination averaged and recorded as same value for all the nine check plots.
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Maize crop yield assessment form (Individual farmers trials only)
Name of Farmer---- R. Nkala Village --- Mpumelelo Ward --- 1 Farming season --- 2009/10 District --- Insiza
Date of sampling --- Recorded by ---Lewis Ndlovu Treatment Graded contour late crop
12 April, 2010
Plot number as per
sketch 1 2 3 4 5 6 7 8 9 Total Average
Sub plot number GC1 GC2 GC3 GC4 GC5 GC6 GC7 GC8 GC9
Average width of 4 rows (m), (Average of at least 3
measurements)
4 4 4 4 4 4 4 4 4
Length of check plot
(m) 4 4 4 4 4 4 4 4 4
Area of check plot (ha) 0,0016 0,0016 0,0016 0,0016 0,0016 0,0016 0,0016 0,0016 0,0016 Number of plants in
check plot 43 39 39 45 32 22 41 24 18
Number of cobs 26 32 27 29 23 16 19 14 16
Weight of cobs and grain in check plot together (kgs)
2,3 3,0 2,0 2,0 2,2 1,2 1,0 0,6 0,7
Weight of sample cob and grain together (g)
183 183 183 183 183 183 183 183 183
Weight of grain only from sample cob (g) (air dried)
140 140 140 140 140 140 140 140 140
Moisture content of
grain (% by mass) 15 15 15 15 15 15 15 15 15
Initial weight of inner
cobs (g) 43 43 43 43 43 43 43 43 43
Moisture content of
inner cob (%) 7 0 7 7 7 7 7 7 7
Intial weight of stover (kgs), (at harvesting)
2,2 3,5 1,9 2 2,1 1,2 1,5 1 1
Intial weight of sample stover (g), (at harvesting) 72,8 72,8 72,8 72,8 72,8 72,8 72,8 72,8 72,8 Moisture content of stover (%) 9 9 9 9 9 9 9 9 9 Grain yield (12.5% MC) (kg/plot) 1,71 2,23 1,49 1,49 1,64 0,89 0,74 0,45 0,52 Population (Plants/ha) 26 875 24 375 24 375 28 125 20 000 13 750 25 625 15 000 11 250
Dry grain yield (kgs/ha) 1 069 1 395 930 930 1 023 558 465 279 325 6 973 775 Dry stover yield
(kgs/ha) 1 251 1 991 1 081 1 138 1 194 683 853 569 569 9 328 1 036
Dry inner cob yield
(kgs/ha) 312 437 271 271 298 163 136 81 95 2 064 229
Total biomass (kgs/ha) 2 632 3 822 2 281 2 338 2 515 1 403 1 454 929 989 18 364 2 040 Table 4-4: Maize Crop Assessment Form
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4.4.4
Characterization of rainfall seasons
The rainfall seasons were characterized as either a bad season, a fair season or a good season based on the criteria used by Chibulu (2007). The cropping season was described as being good, fair or bad based on the frequency of dry spells and the cumulative number of dry days experienced within 90 days after planting. The average growing period for a maize crop is considered as 90 days while the frequency and length of dry spells indicate water stress to the crop during the growing period. A dry day is defined as a day in which no rainfall or rainfall less than the interception amount is received. For the purpose of rainfall characterization interception was taken to be equal to the average evaporative demand of the study site which was found to be 4.3mm/day.
A bad season is a season in which at least 60 dry days out of 90 days after the planting date were experienced or three or more long dry spells lasting more than 21 days were experienced. A good season is a season in which less than 45 days of the 90 days were dry days and one or no long dry spell lasting 21 days were experienced. Any other season that does not fit the two criteria is a fair season.
4.4.5
Analysis of data for assessing effect of contour ridges on crop
yield
The leaf moisture content was calculated from Equation 4-6.
100 wdl wdl wwl lmc Where:
g leaves dry of weight is wdl g leaves wet of weight is wwl moisture leaf is lmc %The moisture content of grain, inner cob and stover were calculated using Equation 4-7 with leaf moisture content replaced by moisture content of grain, inner cob and stover as the case may be. The weight of wet leaves and dry leaves were also replaced by the weight at harvest and the weight after drying of grain, inner cob and stover as was necessary.
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The crop yield was considered to comprise of grain, inner cob and stover yield. While only grain is used for human consumption both inner cob and stover can be used for stock feed and therefore indirectly contribute to food security. Considering that the study area is a cattle rearing region it was considered necessary to include stock feed in the total yield of the crop. Grain yield, inner cob and stover yield were calculated separately and then added together to obtain the total yield. These separate yields were obtained using Equation 4-7. The total yield was obtained using Equation 4-8. The grain yield was calculated at 12% moisture content which is the moisture content at which harvesting of grain is recommended for good lasting storage. This is catered for by subtracting moisture content of grain from 112% instead of 100% moisture content in Equation 4-7(a). This means that mass of grain at storage is equal to 112% of mass of dry grain.
𝑌𝑔𝑐 = 𝑊𝑠𝑔 𝑊𝑠𝑐 × 𝑊𝑐𝑐(112 − 𝑚𝑐𝑔)% (𝑎) 𝑌𝑖𝑐 =𝑊𝑠𝑖𝑐 𝑊𝑠𝑐 × 𝑊𝑐𝑐(100 − 𝑚𝑐𝑖𝑐)% (𝑏) 𝑌𝑠𝑡𝑐 = 𝑊𝑠𝑡𝑐(100 − 𝑚𝑐𝑠𝑡)% (𝑐) Where:
Ygc is grain yield in check plot (kg/(check plot));
Yic is inner cob yield in check plot (kg/(check plot));
Ystc is stover yield in check plot (kg/(check plot));
Wcc is weight of cobs (inner cobs and grain together) in check plot (kg) at harvest;
Wsc is weight of sample cob (inner cob and grain together) (kg) at harvest;
Wsg is weight of sample grain (kg) at harvest;
Wsic is weight of sample inner cob (kg) at harvest;
Wstc is weight of sample stover at harvest;
mcg is moisture content of grain at harvest;
mcic is moisture content of inner cob at harvest;
mcst is moisture content of stover at harvest.
𝑌𝑡= (𝑌𝑔𝑐+ 𝑌𝑖𝑐+ 𝑌𝑠𝑡𝑐) ×10 000 𝐴𝑐 Where:
Yt is the total yield (kg/ha);
Ac is area of check plot (m2)
Equation 4-7
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