179
Village, located at 3°31′11″ S and 34°14′05″ E, for two consecutive cotton growing
seasons, season 1 (2015/16) and season 2 (2016/17).
2.2 Experimental Plot Initial Soil Properties
A composite soil sample was collected prior to our experiment at a depth of 0–20 cm,
air-dried and sieved through a 2-mm sieve and analysed to determine initial soil
properties. The composite sample was used to determine soil texture by the hydrometer method (Day 1965), and textural classes were determined using the USDA
textural triangle (Soil survey staff 2014). The soil pH and electrical conductivity
were determined by the potentiometric method (Okalebo et al. 2002). Organic carbon was determined by the Walkley and Black wet oxidation method (Nelson and
Sommers 1982), total nitrogen by the Kjeldahl wet digestion-distillation method,
extractable P by the Bray-1 method (Olsen and Sommers 1982), cation exchange
capacity for basic cations (Ca, Mg, K and Na) by the NH 4 OAc saturation method
(Thomas 1982) and micronutrients (Cu, Fe, Zn, Mn) by the diethylenetriaminepentaacetic acid (DTPA) method (Motsara and Roy 2008). Undisturbed soil samples
were also collected by using a core ring at the depth of 0–20 cm to determine soil
bulk density and porosity by the core method (Blake and Hartge 1986).
In summary, initial soil properties of the experimental field consisted of a sandy
clay texture (38% clay) and a soil pH of 9.0 and 7.2 in H 2 O and CaCl 2 , respectively;
organic carbon was 1.03%; total nitrogen was 0.14%; extractable phosphorus was
16.0 mg kg
−1
; and exchangeable bases in cmolc kg
−1
were 17.87, 3.47, 1.54 and
0.11 for Ca
2+
, Mg
2+
, K
+
and Na
+
, respectively. Micronutrient concentrations were
1.44, 1.11, 0.40 and 9.12 mg kg
−1
for Cu, Fe, Zn and Mn, respectively. The bulk
density was 1.36 g cm
−3
and the soil is rated marginally suitable for cotton production due to low soil fertility (Bwana 2019). The manure used had an organic carbon
content of 8%, total nitrogen of 1.03%, extractable phosphorus of 103 mg kg
−1
and
a C/N ratio of 7.8.
2.3 Weather Data
Weather data were recorded hourly using an automatic weather station (AWS)
installed at the experimental site at the beginning of the experiment. The AWS collected data on precipitation, measured with an ECRN-100 high-resolution rain gauge
(Decagon Devices Inc.). Air temperature and humidity were measured by a VP-4
sensor (Decagon Devices Inc.), solar radiation was measured by a PAR sensor, and
soil temperature and moisture were measured by a 5TM sensor (Decagon Devices
Inc.) at 20-cm depth. Hourly averages were logged in an Em50 data logger (Decagon
Devices Inc.). The soil water-filled pore space (WFPS) was calculated from the measured volumetric soil moisture (VWC) using the relation WFPS (%) = 100 ∗ VWC ∗
Yield and Profitability of Cotton Grown Under Smallholder Organic and Conventional…
Village, located at 3°31′11″ S and 34°14′05″ E, for two consecutive cotton growing
seasons, season 1 (2015/16) and season 2 (2016/17).
2.2 Experimental Plot Initial Soil Properties
A composite soil sample was collected prior to our experiment at a depth of 0–20 cm,
air-dried and sieved through a 2-mm sieve and analysed to determine initial soil
properties. The composite sample was used to determine soil texture by the hydrometer method (Day 1965), and textural classes were determined using the USDA
textural triangle (Soil survey staff 2014). The soil pH and electrical conductivity
were determined by the potentiometric method (Okalebo et al. 2002). Organic carbon was determined by the Walkley and Black wet oxidation method (Nelson and
Sommers 1982), total nitrogen by the Kjeldahl wet digestion-distillation method,
extractable P by the Bray-1 method (Olsen and Sommers 1982), cation exchange
capacity for basic cations (Ca, Mg, K and Na) by the NH 4 OAc saturation method
(Thomas 1982) and micronutrients (Cu, Fe, Zn, Mn) by the diethylenetriaminepentaacetic acid (DTPA) method (Motsara and Roy 2008). Undisturbed soil samples
were also collected by using a core ring at the depth of 0–20 cm to determine soil
bulk density and porosity by the core method (Blake and Hartge 1986).
In summary, initial soil properties of the experimental field consisted of a sandy
clay texture (38% clay) and a soil pH of 9.0 and 7.2 in H 2 O and CaCl 2 , respectively;
organic carbon was 1.03%; total nitrogen was 0.14%; extractable phosphorus was
16.0 mg kg
−1
; and exchangeable bases in cmolc kg
−1
were 17.87, 3.47, 1.54 and
0.11 for Ca
2+
, Mg
2+
, K
+
and Na
+
, respectively. Micronutrient concentrations were
1.44, 1.11, 0.40 and 9.12 mg kg
−1
for Cu, Fe, Zn and Mn, respectively. The bulk
density was 1.36 g cm
−3
and the soil is rated marginally suitable for cotton production due to low soil fertility (Bwana 2019). The manure used had an organic carbon
content of 8%, total nitrogen of 1.03%, extractable phosphorus of 103 mg kg
−1
and
a C/N ratio of 7.8.
2.3 Weather Data
Weather data were recorded hourly using an automatic weather station (AWS)
installed at the experimental site at the beginning of the experiment. The AWS collected data on precipitation, measured with an ECRN-100 high-resolution rain gauge
(Decagon Devices Inc.). Air temperature and humidity were measured by a VP-4
sensor (Decagon Devices Inc.), solar radiation was measured by a PAR sensor, and
soil temperature and moisture were measured by a 5TM sensor (Decagon Devices
Inc.) at 20-cm depth. Hourly averages were logged in an Em50 data logger (Decagon
Devices Inc.). The soil water-filled pore space (WFPS) was calculated from the measured volumetric soil moisture (VWC) using the relation WFPS (%) = 100 ∗ VWC ∗
Yield and Profitability of Cotton Grown Under Smallholder Organic and Conventional…