Do row spacing and plant density influence maize productivity under reduced tillage?

CEDRIC BALOYI, ARC-Grain Crops Institute

Maize remains the staple food for many household diets in South Africa, especially in rural communities. However, crop yields under smallholder farming practices are generally low. The inherent infertile soils and the fluctuating weather due to climate change could worsen the situation.

Large scale commercial farming had been the key contributor of maize production in the country. However, many of these groups are leaving the business; either due to reasons related to age or that they cannot keep up due to the vast yearly price hikes in production costs.

At present, numerous smallholder producers own large hectares of agricultural land benefited through LRAD programmes and many of them are often inexperienced in the field of agriculture. For that reason, a great number of them are forced to retire from farming and subsequently remain with loan burdens acquired that they cannot repay.

That results in decreased production of major crops. This could add huge pressure on the production of food per capita should the situation be left unattended for a few years longer. Conservation agricultural (CA) systems, such as minimal soil disturbance (reduced tillage), crop rotation and soil cover have been sought as an option to conventional tillage practices in order to reduce production costs and improve the soil fertility status.

Although some producers, especially in the maize production triangle, took advantage of the benefits that CA can offer, most are however still using old technology as if they are producing under deep ploughing (conventional tillage). That is, many are still fond of using a standard row spacing of 0,90 m and even 1,5 m in some cases, as well as the same plant population used under deep ploughing. Likewise, producers are still in search of the appropriate plant population that could maximise yields and bring net returns on investments under CA. This can be due to the fact that the best hybrids for CA are yet to be developed and released for commercial use.

Practicing a reduced tillage system typically has problems related to the forming of natural compaction, which is common when proper rotation is not followed. The situation could even worsen under smallholder farming activities where recommended plant density depends on the quantity of seed obtained due to cost. Plant breeders should therefore in a way fast-track breeding for improved maize varieties that will be suitable under CA and make it accessible to the whole range of farming enterprises. As part of the ARC-Grain Crops Institute’s (ARC-GCI) CA programmes, this study was initiated to evaluate maize performance at different row spacing and plant densities under minimal soil disturbance.

Evaluation information and method

On-farm, rainfed trials were conducted during 2012/2013 on commercial producer fields at Buffelsvallei (North West) and Viljoenskroon (Free State).

Three maize plant densities (20 000 plants/ha, 40 000 plants/ha and 60 000 plants/ha) and three row spacings
(0,52 m, 0,76 m and 0,90 m) were evaluated under two tillage practices (conventional tillage [Photo 1] and minimum soil disturbance [Photo 2]).

The same maize hybrids (PAN 6Q-445B at Buffelsvallei and DKC 78-35R at Viljoenskroon) that are used by producers at the respective sites, were chosen in order to make comparisons. If the results indicate better performance, producers might be convinced to adapt the new technology. Trials were planted by hand using jabbed planters.

The row spacing of 0,9 m was used as the control check since it represents the standard row spacing most commercial producers practice in South Africa. CA was practiced for approximately seven years at the Viljoenskroon field trial site, while no CA was previously done at the Buffelsvallei site. Each plot comprised of four rows, each 10 m long. The sites had a fairly reasonable content of NPK compared to average sandy loam soils in the maize production triangle, attributable to previous better field management.

The topsoil (0 cm - 20 cm) NPK values were 5,2 mg/kg, 28 mg/kg and 100 mg/kg for Buffelsvallei, while it was 6,33 mg/kg and 200 mg/kg at Viljoenskroon. Soil pH (H₂O) was within the norm for maize production at both sites. All plots received the same amount of fertiliser in the form of NPK.

All the other agronomic practices, such as crop management, were kept uniform during the cropping season. Rainfall during the planting season was 400 mm at Buffelsvallei and 270 mm at Viljoenskroon. Grain yield was measured at physiological maturity in the two middle rows at a length of 7 m each.

Results

Plant density
At Buffelsvallei, the one year data showed that planting maize at the lowest density of 20 000 and the highest of 60 000 plants/ha under deep ploughing (conventional tillage), resulted in a higher grain yield (approximately 30%) than with reduced tillage (Graph 1a). Comparable yields can however be obtained between the two tillage practices when maize is planted at 40 000 plants/ha.

In contrast, at the Viljoenskroon site, all plant densities under minimal soil disturbance resulted in higher yields compared to the conventionally tilled plots (Graph 1b). This yield increase ranged from 12% to 60% across plant density. Earlier reports show that there are no clear trends in the benefits of CA for only a few years of the system, but there is in the long term.

Results of this trial are in support of those findings as reported earlier, that the Viljoenskroon trial site was under CA for over five years and not at Buffelsvallei.

Row spacing
Using narrow row spacing did not compromise maize yields throughout the trials and for both tillage practices at Buffelsvallei, which is always the case when plants are planted closely (Graph 2a). For example, both tillage practices resulted in similar grain yield when rows are either narrowly (0,52 m) or widely (0,90 m) spaced. However, yields almost doubled in conventionally tilled plots when maize rows were spaced at 0,76 m (Graph 2a).

The poor performance from reduced tillage at Buffelsvallei can be attributed to damage by guinea fowls (Photo 3) as there were no stubble on the soil surface from the previous crop, thus it was easy for the birds to trace planting holes. The same was not observed at the Viljoenskroon trial site.

Planting maize with all spacing under minimal soil disturbance resulted in higher grain yield compared to the conventionally tilled plots (Graph 2b). However, superior yields were obtained when rows were narrow (0,52 m), with yield increases of about 34% compared to 21% (0,76 m) and 22% (0,90 m) relative to the conventionally tilled plots (Graph 2b).

Selecting row spacing and plant density
At Buffelsvallei, planting maize at narrower spacing (0,52 m) in both tillage systems gave comparable yields regardless of planting density (Graph 3a). However, when rows are spaced at 0,76 m, yields from conventionally tilled plots were superior to minimal soil disturbance across all plant densities. On the contrary, conventionally tilled plots gave higher yields only at the highest plant density of 60 000 plants/ha when rows are spaced at 0,90 m (Graph 3a).

At Viljoenskroon, planting maize under minimal soil disturbance resulted in superior yields regardless of the row spacing and plant density (Graph 3b). Grain yields were comparable only with maize planted at the narrower spaced rows (0,52 m) with a plant population of 60 000 plants/ha.

For more information on maize productivity as influenced by row spacing and plant population under CA, contact Cedric Baloyi at 018 299 6100.